NZ789592A - Synthesis of (s)-2-amino-4-methyl-1-((r)-2-methyloxirane-2-yl)- pentan-1-one and pharmaceutically acceptable salts thereof - Google Patents

Abstract

The present invention provides new methods for preparing compound (5), and pharmaceutically acceptable salts thereof, of structure. Compound (5), or a pharmaceutically acceptable salt thereof, is an important intermediate in the synthesis of carfilzomib. The invention further provides methods of making a useful manganese catalyst that may be used in the epoxidation step of the present invention. ing a useful manganese catalyst that may be used in the epoxidation step of the present invention.

Description

SYNTHESIS OF AMINOMETHYL((R)METHYLOXIRANEYL)- PENTANONE AND PHARMACEUTICALLY ACCEPTABLE SALTS THEREOF RELATED APPLICATIONS The present application is a divisional application of New Zealand Application No. 750354, which is incorporated in its entirety herein by nce.

This application claims the benefit of U.S. Provisional patent ation 62/371,686 filed on August 05, 2016 and the benefit of U. S. Provisional patent ation 62/536,862 filed on July 25, 2017, both ications of which are hereby incorporated herein by reference in their entireties.

FIELD OF THE INVENTION The present invention relates to an improved, efficient, scalable process to prepare an intermediate, (S)aminomethyl((R)methyloxiraneyl)pentanone, useful for the synthesis of carfilzomib.

BACKGROUND OF THE ION Carfilzomib, also known as Kyprolis®, is a tetrapeptide epoxy ketone some inhibitor that binds selectively and irreversibly to the constitutive proteosome and proteosome. More specifically, the electrophilic etone warhead binds to the catalytic threonine residue of the β5 subunit of the proteasome protein. Carfilzomib is approved for human use, for the treatment of multiple myeloma. Carfilzomib and various methods of making carfilzomib are described in US patent publications US20050245435, US20140105921 and in PCT published patent applications 017842, WO2009045497, WO2014169897, WO2013169282, WO2014011695, WO2006063154, WO2014015016, and WO2010048298, each specification of which is hereby incorporated herein by reference in its entirety.

One intermediate that may be used in the synthesis of carfilzomib is a compound 5, or a pharmaceutically acceptable salt thereof where X- is present, of the formula: X O . nd 5 having a chemical name of (S)aminomethyl((R)-(2-methyloxirane- 2-yl)pentanone (as named by ChemBioDraw Ultra software, version 12.0). Sin and colleagues at Yale used this intermediate in the synthesis of epoxomicin (N. Sin et al., Bioorg. Med Chem. Letters, 9 2283-2288, 1999). They synthesized this intermediate beginning with Boc-leucine-weinreb amide 9 and proceeded through a step synthesis generating the corresponding (LB-unsaturated ketone 10, and finally epoxidation of the double bond using hydrogen peroxide as the oxidant to afford a mixture of 11a and 11b in a 1.721 ratio, as shown schematically below (also see Sin, page 2285, scheme 1). 2-bromopropene t-BuLi,Et20 N\ -78°C BocHN OMeWBocHN O O "12021120 benzonitrile, i-Pr2EtN 76% yield + 0&‘0 BocHN BocHN O 0 (1.7: 1.0) 11a 11b The compounds 11a and 11b can be separated by column chromatography, and the Boc protecting group of compound 11a is removed with acid, such as roacetic acid (TFA), to provide the desired epoxide intermediate (S)aminomethyl((R) methyloxiraneyl)pentanone as a TFA salt.

Patent publication 045497 describes the synthesis of Boc or other protected epoxyketone ediate 11a (Boc protected amine shown above) using aqueous calcium hypochlorite or aqueous sodium hypochlorite (bleach), as the oxidizing agent, in the presence of a co-solvent such as pyridine, acetonitrile, DMF, DMSO, N- pyrrolidinone (NMP), DMA, THF and nitromethane, to convert compound 10 (above) to a 1:1 mixture of product 11a and 11b.

US patent publication US2005 0256324 describes the synthesis of amino acid epoxyketones, and ularly the synthesis of intermediate 5. This publication teaches that intermediate 5 may be prepared from the carboxybenzyl (cbz) ted amino-afi- unsaturated ketone 20 (see scheme below) to the corresponding carboxybenzyl protected amino epoxyketone 23a, as illustrated: NaBH4 CeCI3-7H20 M, + CszN CszN CszN o OH (9: 1) 5H - 48 21a - (4S)(3R) 21 b - (4S)(38) VO(acac)2 t—BuOOH, DCM 76% yield + 9&0 CszN CszN CICOCOCI, DMSO - EtsN, DCM 22a - (4S)(3S)(2R) 22b - (4S)(3R)(28) + 9&0 CszN CszN 0 0 (9 : 1) 23a - (4S)(2R) 23b — (4S)(28) Compounds 23a and 23b can be ted from the e using column chromatography (assumes the 9 : 1 e of 21a : 21b was carried through without separation), and the amine protecting carboxybenzyl group of compound 23a is removed using known, conventional methods such as hydrogenation with a suitable metal catalyst, such as palladium on carbon, to provide the desired epoxide ediate (S)amino methyl-l-((R)methyloxiraneyl)pentan-l-one (23a) as a free base.

US patent publication US20050256324 also discloses a process where intermediate 23a may alternatively be prepared using metachloroperbenzoic acid (mCPBA) in dichloromethane (DCM), or Dess-Martin Periodinane in dimethylsulfoxide (DMSO) or tetrapropylammonium perruthenate (TPAP) with 4-methylmorpholine-N- Oxide (NMO) in DCM, as the oxidizing agents, tively. The mCPBA method was described to replace the previously taught VO(acac)2 oxidizing agent (shown above) with these as .

A more recent publication (Wang, B et al, Chemistry European Journal, 3, 6750-6753, 2012) discloses the use of a manganese catalyst to enantioselectively convert an olefin to an epoxide. It further mentions the application of this technique to preparing the epoxide intermediates of epoxomicin and of zomib. More specifically, ng with Boc-L-Leu-OH, this reference teaches that the corresponding epoxyketone intermediate may be prepared in a 7:1 diastereomeric ratio in favor of the undesired (SS) epoxide ediate diastereomer using en peroxide as the oxidizing agent (see Wang scheme 2).

While these procedures to prepare intermediate compound 5 are methods that afford intermediate 5 (shown , they are not very practical, not very ent from a time, effort and cost perspective, and not very effective. Thus, these methods are not optimal for the manufacture of intermediate 5 for the global manufacture and sale of the commercial drug product carfilzomib. For instance, the process taught in Sin utilizes highly pyrophoric reagents (t-BuLi) and cryogenic reaction conditions (-78°C) and results in a less than optimal overall yield of intermediate 11a. The final epoxidation step provides an overall 76% product yield ning a mixture of diastereomers (1.7 : 1) thus requiring time consuming, and costly column chromatographic separation to isolate the d product. On a large manufacturing scale, such column tography will generate huge solvent waste which is nmentally unfriendly. Thus, the undesired and unusable 35-40% reaction product with the wrong, undesired stereochmistry from the method taugh in Sin increases overall costs and contributes chemical waste that adds disposal expense and potential harm to the environment.

The process taught in US20050256324 consists of more steps than those taught in Sin and utilizes expensive reagents. This process goes through the additional step of reducing the ketone using environmentally ndly and costly borane and cerium catalysts to provide the corresponding alcohol. Despite the 9:1 ratio of the desired reomer 22a to the undesired diastereomer 22b, one must then m another reaction to oxidize the hydroxyl group of the diastereomeric mixture up to the corresponding ketone. This process effectively reduces the ketone then re-oxidizes the same ketone. Thus, while the diastereoselectivity may be improved relative to Sin, this process is synthetically inefficient thereby increasing associated costs, time, waste generation and labor of production.

The process taught in 045497 ed bleach to accomplish the epoxidation on avoiding the inefficient reduction/oxidation cycle of the adjacent ketone. However, this epoxidation reaction results in about a 1:1 ratio of (R) and the (S) stereoisomers at the epoxide carbon. In addition, the oxidation reaction with bleach is an exothermic reaction to the extent of being a potential safety hazard, particularly when conducted on a , manufacturing scale. To this end, this process requires costly and time consuming chromatographic separation and re-crystallizations to isolate the desired stereoisomeric product, resulting in significant waste.

The process taught in Wang provides diastereoselective epoxidation reaction favoring the undesired epoxide stereochemistry. The desired epoxide diastereomer only accounts for 12% of the crude reaction mixture. Therefore, use of this process is overall low yielding, and would require a laborious column chromatography setp resulting in increased time and expense, as well as to the potential of having to e of additional chemical waste. To this end, the ture teaches epoxidation processes that are simply not very efficient and/or timal for large scale production of the cial drug product carfilzomib. Therefore, there is a need to identify alternative synthetic methods, of increased efficiency and effectiveness, to prepare key ediate 5 for the manufacture of carfilzomib.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a new method for the synthesis of keto-epoxide intermediate compound 5 or a pharmaceutically acceptable salt thereof where X' is present, the method comprising steps 1-5 according to scheme 1 _ 6 _ A amide rd step 1 fl?= step 2 PG - OH-H20 _. PG - N —» \N \N \R2 H H PG-D-Leu-OH-H2O 1 2 epoxidation E)\ epimerization ' E o O deprotectlon step 3 _ 0 PG\ /fi‘k step 4 pg\ step 5 X 0 O O 3 4 5 Scheme I wherein PG is a protecting group selected from t-butoxycarbonyl (Boc) and ybenzyl (cbz); R1 is CH3 and R2 is —OCH3 or R1 and R2 taken together with the nitrogen atom to which they are attached form a morpholine ring; X' is absent or X' is an addition salt anion selected from TFA; Cl; Br; I and mesylate; the amide step 1 comprises use of an acid activating agent and a basic amine selected from (CH3)NH(OCH3) and morpholine; the rd step 2 ses use of isopropyl magnesiumchloride; Mg and 2- bromopropene or isopropenylmagnesium bromide; the epoxidation step 3 comprises use of an oxidizing agent and a manganese catalyst; the epimerization step 4 comprises the use of a base; and the deprotection step 5 ses use of a catalyst or an acid.

The invention r provides various reaction conditions and reagents that may be used to prepare compound 5; as discussed further herein. The method of the present invention is efficient from a bond uction perspective. For example; it involves an amine protected (LB-unsaturated ketone compound 2 and converts the double bond directly to the corresponding epoxide group with a strong preference for the desired 2R epoxide isomer; such as that shown in compound 3 (above). The process is advantageously diastereoselective in its epoxidation step 3. The method results in high overall yields of compound 5 and enables the process to be scaled up to large, manufacturing grade . The present invention provides fewer synthetic steps, requires no column chromatography to separate reomeric es and/or produces less chemical and environmentally harmful waste materials than the s different methods taught in the art. To this end, the present invention results in surprising and unexpected advantages including, without limitation, reduced time, reduced expense, and reduced waste, when compared to those methods for making the keto-epoxide intermediate compound 5 described in the art.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides novel methods of preparing a keto-epoxide ediate compound 5, as either a free base or a pharmaceutically acceptable salt f, for the synthesis of carfilzomib.

The terms “aspect” and embodiment” are used interchangeably herein.

In aspect I of the invention, the invention provides a method of making compound 5 or a pharmaceutically acceptable salt thereof where X' is present, the method comprising steps 1-5 according to scheme 1 A amide E)\R1 rd } g step 1 E I step 2 5 PG\N OH-HZO —» PG\ - H/Y N\ —> NH/\lr R2 PG\N O O O PG—D—Leu—OH-HZO 1 2 epoxidation } epimerization de ' 0 0 protectlon step 3 E 0 PG = step 4 PG step 5 X_ —’ \N —’ \N —’ H2N H H O O O 3 4 5 Scheme I wherein PG is a protecting group selected from t-butoxycarbonyl and carboxybenzyl; R1 is CH3 and R2 is —OCH3 or R1 and R2 taken together with the nitrogen atom to which they are attached form a line ring; X' is absent or X' is an addition salt anion selected from TFA; Cl; Br; I and mesylate; the amide step 1 comprises use of an acid activating agent and a basic amine selected from (CH3)NH(OCH3) and morpholine; the Grignard step 2 comprises use of isopropyl magnesiumchloride; Mg and 2- ropene or isopropenylmagnesium bromide; the epoxidation step 3 ses use of an oxidizing agent and a manganese catalyst; the epimerization step 4 ses the use of a base; and the deprotection step 5 ses use of a catalyst or an acid.

In aspect 2 of the invention; the invention provides the method of aspect I wherein PG is Boc.

In aspect 3 of the invention; the invention provides the method of aspect I wherein PG is carboxybenzyl.

In aspect 4; the invention provides product compound 1 of the amide step 1 wherein R1 is CH3 and R2 is —OCH3.

In aspect 4a; the invention provides product compound 1 of the amide step 1 wherein R1 and R2 taken together with the nitrogen atom to which they are attached form a morpholine ring.

In aspect 5 of the invention; the invention provides the method of any one of aspects 1; 2; 3; 4 and 4a wherein the amide step 1 comprises the use of an acid activating agent.

In aspect 5a of the invention; the invention provides the method of any one of aspects 1; 2; 3; 4 and 4a n the acid activating agent used in the amide step 1 is an acid chloride; an anhydride; a carbodiimide; a CD1, a phosphonium salt or a inium or uranium salt.

In aspect 5b of the invention; the invention provides the method of aspects 5a and 4b wherein acid ting agent is a carbodiimide selected from DCC, DIC and EDC.

In aspect 5c of the invention, the invention provides the method of aspects 5a and 4b wherein acid activating agent is a pohosphonium salt selected from BOP and PyBOP.

In aspect 5d of the invention, the invention provides the method of aspects 5a and 4b wherein acid activating agent is (a) an acid chloride made using an agent selected from thionyl chloride, oxalyl de and phosphorus oxychloride, or (b) an anhydride using an agent seleted from ethylchloroformate (ECF), isobutylchloroformate (IBCF), boc anhydride, EEDQ, acetic anhydride and pivaloyl chloride.

In aspect 5e of the invention, the invention provides the method of any one of s 1, 2, 3, 4 and 4a n the acid ting agent used in the amide step 1 is CDI.

In aspect 5f of the invention, the invention provides the method of any one of s 1, 2, 3, 4, 4a and 5 wherein the acid activating agent used in the amide step 1 is CD1 and the amide step 1 reaction is ted at a ature of at or below 20°C.

In aspect 5f—l of the invention, the invention provides the method of any one of aspects 1, 2, 3, 4, 4a and 5 wherein the acid activating agent used in the amide step 1 is I5 CD1 and the amide step 1 reaction is conducted at a temperature of at or below 10°C.

In aspect 5g of the invention, the invention provides the method of any one of aspects 1, 2, 3, 4, 4a, 5e and 5f wherein the acid activating agent used in the amide step 1 is CD1 and wherein the CDI is added at a temperature of 5°C or less and the morpholine is added at a temperature of 10°C or less.

In aspect 6 of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5 and 5a-5 g wherein the Grignard step 2 comprises use of isopropyl magnesiumchloride, Mg and 2-bromopropene.

In aspect 6a of the invention, the invention es the method of any one of aspects 1 — 4, 4a, 5 and 5a-5g wherein the Grignard step 2 ses use of isopropenylmagnesium e.

In aspect 7 of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g and 6 wherein the oxidizing agent used in the epoxidation step 3 is hydrogen peroxide, peracetic acid, t-BuOOH and PhIO.

In aspect 7a of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g and 6 wherein the oxidizing agent used in the epoxidation step 3 is hydrogen peroxide.

In aspect 7b of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g and 6 wherein the oxidizing agent used in the epoxidation step 3 is t-BuOOH and PhIO.

In aspect 8 of the invention, the invention provides the method of any one of s 1 — 4, 4a, 5, 5a-5 g, 6, 6a, 7 and 7a-7b wherein manganese catalyst used in the ation step 3 has a structure of wherein each R3, independently, is C1-6alkyl.

In aspect 8a, the invention provides a method of aspect 8 wherein each R3, independently, is methyl or ethyl.

In aspect 8b of the invention, the ion provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7 and 7a-7b n manganese catalyst used in the epoxidation step 3 has a structure of 3N NN/\7IQ\N 3 \ / N’R TfO OTf® wherein each R3, independently, is methyl or ethyl.

In aspect 8c of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7 and 7a-7b wherein manganese catalyst used in the I5 epoxidation step 3 has a structure of leO/ \OTf\\/ WO 27021 In aspect 9 of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b and 8 wherein manganese catalyst used in the epoxidation step 3 has a structure of In aspect 10 of the ion, the invention es the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c and 9 wherein the base used in the epimerization step 4 is selected from DBU, triazabicyclodecene (TBD), pyrrolidine, potassium carbonate and sodium hydroxide.

In aspect 11 of the invention, the ion provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5 g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9 and 10 wherein the base used in the epimerization step is DBU.

In aspect 11a of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9 and 10 wherein the base used in the epimerization step is TBD.

In aspect 11b of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5 g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9 and 10 wherein the base used in the epimerization step is TBD in an amount ranging from about 0.01 to about 0.1 equivalents.

In aspect 12 of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10 and 11further comprising a solvent swap involving a switch to an alcohol solvent or a basic solvent.

In aspect 13 of the invention, the ion es the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10 and her comprising a solvent swap involving a switch to methanol, isopropanol or N—methylpyrrolidinone.

In aspect 13a of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10 and 11further comprising a solvent swap involving a switch to methanol.

In aspect 14a, the invention provides a method of making compound 4a the method sing steps 1-4 according to scheme l-a "m? a)CD| )\ i- rM CI M R1 p g ' g b)morpholine 2-br-propene | Boc OH-H o 3 2 —» Boc N —>800 \N \N \R2 \ H H o 0 Boc—D-Leu-OH-HZO H O L, Boc\ manganese catalyst Scheme l-a wherein R1 is CH3 and R2 is —OCH3 or R1 and R2 taken together with the nitrogen atom to which they are attached form a morpholme ring, and manganese catalyst has a structure N H R: I \M/N) J” N \N//\\N/ N TfO OTf wherein each R3, independently, is methyl or ethyl.

In aspect 14a, the invention provides a method of making compound 4a the method sing steps 1-4 according to scheme l-a m"? a) CDI )\ b) morpholine _ ropene _ (\0 i-pngCl Mg Boc\N = OH-HZO _, Boc\N = Nu —> H/Y H/Y B°°\ O 0 Boc—D-Leu-OH-HZO %Boc\ DBU Boc\ manganese N catalyst 3a 4a Scheme l-a wherein the manganese catalyst has a structure of N H‘“ N wherein each R3, independently, is methyl or ethyl.

In aspect 14b, the invention provides a method of making compound 4a 4a the method comprising steps 1-4 according to scheme l-a M"? a)CD| )\ i-pngCl Mg b) morpholine . _ (\0 2-br-propene Boc\N = ’ Nu H/YOH-H20 —> /Y _,Boc\ O 0 Boc—D-Leu-OH-HZO &, Boc\ DBU Boc\ manganese N 3a 4a Scheme l-a wherein CD1 is used in an amount ranging from about 1.0 equivalents to about 2.5 equivalents; line is used in an amount ranging from about 1.2 equivalents to about 2.0 equivalents; 2-bromopropene is used in an amount ranging from about 1.5 equivalents to about 3.5 equivalents; hydrogen peroxide is used in an amount ranging from about 1.5 equivalents to about 3.0 equivalents; the manganese catalyst has a structure of N H§ N R3\ \Mn/ 1 /R3 N \N//\\N/ N TfO OTf wherein each R3, independently, is methyl or ethyl, and used in an amount 1 5 ranging from about 0.0002 equivalents to about 0.001 equivalents; and DBU is used in an amount ranging from about 0.1 to about 0.5 equivalents. 1n aspect 14c; the ion provides a method of making compound 4a the method comprising steps 1-4 according to scheme 1 a a) CDI )\ i-pngCl Mg b) morpholine _ (\0 2—br—propene Boc\N OH'Hzo _. BOC\N : Nu HW H/Y ' Boc\ O O Boc—D-Leu-OH-HZO H202 Boc\ manganese N Scheme l-a wherein CDI is used in an amount of about 2.0 equivalents morpholine is used in an amount of about 1.5 equivalents -bromopropene is used in an amount of about 3.0 lents l 0 hydrogen peroxide is used in an amount of about 2.0 equivalents the manganese catalyst has a structure of [*0\‘ .4.1/1“ TfO/ \OTf wherein each R3, independently, is ethyl, and used in an amount of about 0 001 equivalents; and TBD is used in an amount of about 0.1 equivalents WO 27021 In aspect 15 of the ion, the invention provides the method of any one of aspects 14 and 14a wherein manganese catalyst has a structure of In aspect 15a of the invention, the invention provides the method of any one of s 14, 14a and 15 n manganese st used in the epoxidation step 3 has a structure of In aspect 16 of the invention, the invention provides the method of any one of aspects 1— 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 12, 13, 14, 14a, 15 and 15a wherein the ese catalyst is used in a amount ranging from about 0.0001 to about 0.002 molar equivalents to the moles of the starting material compound 2a.

In aspect 16a of the invention, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 12, 13, 14, 14a, 15 and 15a wherein the manganese catalyst is used in a amount ranging from about 0.0002 to about 0.0006 molar equivalents to the moles of the starting material compound 2a.

In aspect 17 of the invention, the invention provides the method of any one of aspects 1 —4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 12, 13, 14, 14a, 15, 15a, 16 and 16a wherein the manganese catalyst is used in an amount of about 0.0004 molar equivalents to the moles of the starting material 2 or 2a.

In aspect 17a of the invention, the invention provides the method of any one of aspects 1 —4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 12, 13, 14, 14a, 15, 15a, 16 and 16a wherein the manganese catalyst is used in an amount of about 0.001 molar equivalents to the moles of the starting material 2 or 2a.

In aspect 18 of the invention, the invention provides the method of any one of aspects 12-13 and 17 wherein the solvent swap comprises a switch from ACN to isopropanol between the Grignard step and the epoxidation step.

In aspect 19 of the ion, the invention provides the method of any one of aspects 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 14, 14a-14c, 15, 15a and 16-18 further sing a solvent swap involving a switch to methanol, isopropanol or N—methylpyrrolidinone.

In aspect 19a of the invention, the invention provides the method of any one of s 1 — 4, 4a, 5, 5a-5g, 6, 6a, 7, 7a-7b, 8, 8a-8c, 9, 10, 11, 14, 14a-14c, 15, 15a and 16-18 r comprising a solvent swap involving a switch to methanol.

In aspect 20, the invention provides a compound of structure 5 or a pharmaceutically acceptable salt thereof where X' is present, prepared by the process according to scheme 1 grignard . § I step 2 \NWOH-HZO —> PG\ ' PG N _.

H HN/\”/ \N/W‘JKH o o o PG-D-Leu-OH-HZO 2 epoxidation g 0 epimerization O deprotection Step 3 _ 0 PG\ = step 4 PG\ Step 5 X 0 0 o 3 4 5 Scheme I wherein PG is a ting group selected from t-butoxycarbonyl and carboxybenzyl, R1 is CH3 and R2 is —OCH3 or R1 and R2 taken er with the nitrogen atom to which they are attached form a morpholine ring; X' is absent or X' is an addition salt anion selected from TFA, Cl, Br, I and mesylate; the amide step 1 ses use of an acid activating agent selected from CDI, DCC, TBTU, HATU, PyBOP, TCTU, EDCI, pivaloyl chloride, isobutylchloroformate, propylphosphonic anhydride and N,N—diisopropylcarbodiimide (DIC) and a basic amine selected from (CH3)NH(OCH3) and morpholine; the Grignard step 2 ses use of isopropyl magnesiumchloride, Mg and 2- ropene or isopropenylmagnesium e, the epoxidation step 3 comprises use of an oxidizing agent and a manganese catalyst wherein the manganese catalyst has a structure of wherein each R3, independently, is methyl or ethyl, the epimerization step 4 comprises the use of a base; and the deprotection step 5 comprises use of a catalyst or an acid.

In aspect 20a of the invention, the invention provides the method of aspect 20 wherein manganese st has a structure of In aspect 21, the invention provides a compound 4a prepared by the s according to scheme l-a m"? a) CDI )\ b) morpholine _ 2—br-propene _ (\0 i-pngCl Mg Boc\N : OH-HZO _, Boc\N : Nu H/Y H/Y O 0 Boc—D-Leu-OH-HZO %> i» BM catalyst Scheme l-a wherein the manganese catalyst has a structure of wherein each R3, independently, is methyl or ethyl.

In aspect 21a of the invention, the invention provides the method of aspect 21 wherein manganese catalyst has a structure of In aspect 21b, the invention provides compound 4a prepared by the the process ing to scheme l-a M"? a) CDI )\ i-pngCl Mg b) morpholine . _ (\0 2-br—propene Boc\N = OH'Hzo _. BOC\N : Nu HW H/Y _.Boc\ O 0 Boc—D-Leu-OH-HZO H O %Boc\ manganese catalyst Scheme l-a wherein CD1 is used in an amount ranging from about 1.0 lents to about 2.5 equivalents; morpholine is used in an amount ranging from about 1.2 equivalents to about 2.0 l 0 equivalents; 2-bromopropene is used in an amount ranging from about 1.5 equivalents to about 3.5 equivalents; hydrogen peroxide is used in an amount ranging from about 1.5 equivalents to about 3.0 equivalents; the manganese st has a structure of _ 21 _ wherein each R3, independently, is methyl or ethyl, and used in an amount ranging from about 00002 equivalents to about 0.001 equivalents; and TBD is used in an amount ranging from about 0.01 to about 0.1 equivalents.

In aspect 21c, the invention provides compound 4a prepared by the the process according to scheme l-a V a) CDI )\ b) line (\O i-pngCl, Mg _ 2—br-propene Boc\N : OH-HZO ‘ H/Y —> , Boc\N Nu H/Y BOC\ O 0 Boc—D-Leu-OH-HZO %Boc\ DBU manganese N catalyst 3a 4a Scheme l-a wherein CDI is used in an amount of about 2.0 equivalents; morpholine is used in an amount of about 1.5 equivalents; 2-bromopropene is used in an amount of about 3.0 equivalents; hydrogen de is used in an amount of about 2.0 equivalents; the manganese catalyst has a structure of wherein each R3, independently, is ethyl, and used in an amount of about 0.001molar equivalents; and TBD is used in an amount of about 0.1 equivalents.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ry skill in the art to which this disclosure belongs. s and materials are bed herein for use in the present disclosure, other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All ations, patent ations, patents, sequences, database entries, and other references mentioned in the brief description of the invention and later sections herein are incorporated by reference herein in their entirety. In case of conflict, the present specification, including definitions, will l. Other es and advantages of the disclosure will be apparent from the ing additional description, examples and from the claims set forth hereinbelow.

DEFINITIONS The following definitions should further assist in understanding the terms as used herein and the scope of the invention described herein.

The term “Cx.yalkyl” refers to substituted or unsubstituted saturated hydrocarbon groups, including straight-chain alkyl and branched-chain alkyl groups that contain from x to y carbons in the chain. The term “haloalkyl” refers to alkyl groups in which at least one hydrogen atom is replace by a halo (e.g., fluoro, chloro, bromo, iodo), e. g., CH2F, CHF2, romethyl and 2,2,2-trifluoroethyl.

The term ising" is meant to be open ended, including the indicated component(s) but not excluding other elements.

The term “equivalents’ is intended to mean molar equivalents, as ly understodd by persons of ordinary skill in the art.

The term “pharmaceutically acceptable salt” refers to the vely non-toxic, inorganic and organic acid addition salts of the compound 5 of the invention. The nature of the salt is not critical, provided that it is pharmaceutically-acceptable. These salts can be prepared in situ during the final isolation and purification of the compound(s), or by separately reacting a purified compound in its free base form with a le organic or inorganic acid, and isolating the salt thus formed. Suitable pharmaceutically -acceptable acid addition salts of the compound may be prepared from an inorganic acid or from an c acid. Examples of such nic acids include, without tion, hydrochloric, hydrobromic, hydroiodic, nitric, carbonic, sulfuric and phosphoric acid. Examples of organic acids include, without limitation, aliphatic, cycloaliphatic, aromatic, arylaliphatic, cyclic, carboxylic and sulfonic classes of organic acids, es of which are formic, acetic, adipic, butyric, propionic, ic, glycolic, gluconic, lactic, malic, tartaric, citric, ascorbic, glucuronic, maleic, fumaric, pyruvic, aspartic, glutamic, benzoic, anthranilic, mesylic, 4-hydroxybenzoic, phenylacetic, mandelic, embonic (pamoic), methanesulfonic, ethanesulfonic, ethanedisulfonic, benzenesulfonic, pantothenic, 2- hydroxyethanesulfonic, toluenesulfonic, sulfanilic, exylaminosulfonic, camphoric, camphorsulfonic, digluconic, cyclopentanepropionic, dodecylsulfonic, glucoheptanoic, glycerophosphonic, oic, hexanoic, 2-hydroxy-ethanesulfonic, nicotinic, 2- naphthalenesulfonic, oxalic, palmoic, pectinic, persulfuric, 2-phenylpropionic, picric, pivalic propionic, succinic, tartaric, thiocyanic, mesylic, undecanoic, stearic, algenic, B- hydroxybutyric, salicylic, galactaric and galacturonic acid (See, for example, Berge et al. (1977) “Pharmaceutical Salts”, J. Pharm. Sci. 66: 1-19.).

The term “substituted” refers to moieties having substituents replacing a hydrogen on one or more non-hydrogen atoms of the molecule. It will be understood that “substitution” or “substituted with” includes the implicit o that such substitution is in accordance with permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound, e.g., which does not spontaneously undergo transformation such as by rearrangement, cyclization, elimination, etc. As used herein, the term “substituted” is contemplated to include all permissible substituents of organic compounds. In a broad aspect, the permissible substituents e acyclic and cyclic, branched and ched, yclic and heterocyclic, aromatic and non-aromatic substituents of organic compounds. The permissible substituents can be one or more and the same or different for appropriate organic nds. For purposes of this disclosure, the heteroatoms such as nitrogen may have hydrogen substituents and/or any permissible substituents of organic compounds described herein which satisfy the valences of the heteroatoms. Substituents can include, for example, a n, a hydroxyl, a carbonyl (such as a carboxyl, an alkoxycarbonyl, a formyl, or an acyl), a thiocarbonyl (such as a ter, a thioacetate, or a thioformate), an l, a phosphoryl, a phosphate, a phosphonate, a phosphinate, an amino, an amido, an amidine, an imine, a cyano, a nitro, an azido, a sulfhydryl, an alkylthio, a e, a sulfonate, a sulfamoyl, a sulfonamido, a sulfonyl, a cyclyl, an aralkyl, or an aromatic or heteroaromatic moiety. It will be understood by those skilled in the art that the moieties substituted on the hydrocarbon chain can themselves be substituted, if appropriate and if d by valence.

General Synthesis and Representative Examples of the Invention The following abbreviations used hout the description, including the l schemes and the examples, mean the ing: ACN acetonitrile Boc t-butoxycarbonyl cbz carboxybenzyl CD1 carbonyldiimidazole (acid ting agent) DBU azabicyclo[5.4.0]undecene DCM dichloromethane, methylene dichloride DMF dimethylformamide DMSO dimethyl sulfoxide l5 eq, equiv equivalent (molar) EtOAc ethyl acetate g. gm gram HOAc acetic acid IPAc ispropyl acetate MeOH methanol mL, ml milliliter Mg magnesium Mn manganese mpk, mg/kg milligram per kilogram RT, rt room temperature NaCl sodium chloride NaOH sodium hydroxide tBuOH t-butanol; t-butyl alcohol THF tetrahydrofuran Representative Examples of the invention The following carfilzomib prodrug compounds are representative es of the invention and are not intended to be construed as limiting the scope of the present invention.

Example 1: Scheme 2 i. PivCI (1.0 equiv) N-methylmorpholine (1.0 equiv) IPAc (8 V) (\o OH-H 02 BocHN ii. morpholine (1.1 equiv) BocHN Nu —5 to 20 °C 0 iii. wash with 1M H2804, O 1.0 equrv- 1M NaOH and water - - . morpholine amide IV. solvent swap to THF/heptane Boc—L-Leu-OH-HZO in ptane (3:1 WV, 8 V) i. Mg turnings (2.2 equiv) ii. iPngCI (2.0 M in THF, 1.0 equiv), 0 °C iii. 2-bromopropene (1.8 equiv) BocHN portionwise at 35 °C iv. quench with aq. citric acid 0 and heptane Intermediate 1 v. wash with water 75% yield (two steps) vi. silica pad vii. concentrate to an oil S s of -tert-bu l 2 6-dimeth loxohe ten l carbamate ediate 1 Ste 1: -tert-bu l 4-meth lmor holino-l-oxo entan l carbamate The starting material (S)(tert-butoxycarbony)amino)methylpentanoic acid monohydrate (Boc-Leu-OH.H20; 1.0 equivalent) was charged to a reaction vessel.

Isopropyl acetate (8 ml per gm of Boc-Leu-OH.H20) was added to the vessel and the mixture was stirred at 15°C to 25°C to dissolve u-OH.H20. The solution was then cooled to -10°C to -5°C. Pivalic acid (1.0 eq) was added to the solution over 5-30 minutes while maintaining the solution temperature n -10°C and 0°C. The mixture was stirred for 20-40 minutes. The mixture was cooled to -10°C to -5°C and morpholine (1.1 eqs) was added over 10-30 minutes while maintaining the reaction temperature between -10°C and 0°C. The mixture was stirred at -5°C to 0°C for 30-60 minutes then warmed to -25°C. A 1 molar solution of H2SO4 (0.8ml per gm boc-Leu-OH, H20; 02 eq) was then added over 5-30 minutes while maintaining the temperature between 15-30°C. The e was stirred for 15-30 minutes, then the aqueous layer is removed. A 1 molar on ofNaOH (4.4ml per gm u-OH.H20; 1.1 eq) was added over 5-30 minutes while maintaining the temperature between 15-3 0°C. The mixture was stirred for 15-30 minutes, then the aqueous layer is removed. Water (5ml per gm u-OH.H20) was added over 5-30 minutes while maintaining the temperature between 15-30°C. The mixture was stirred for 15-30 minutes, then the aqueous layer is removed. The isopropylacetate solution was concentrated under vacuum to 3 to 4 volumes, then heptane (4 mL per gm) was added over 5-15 minutes. The mixture was concentrated under vacuum to 3 to 4 volumes, then heptane (4 mL per gm) was added over 5-15 minutes. The mixture was again concentrated under vacuum to 3 to 4 volumes, then heptane (4 mL per gm) was added over 5-15 minutes.This azeotropic step was repeated until <1% isopropyl acetate remains (by GC analysis). The contents were then distilled to about 1 volume of heptane, then charged with THF (3mL per gm) and stored at 15-25°C or used in step 2.

Yield: 90% (based on HPLC assay) Ste 2: bu l 2 6-dimeth loxohe ten l carbamate ediate 1 (S)-tert-butyl (4-methylmorpholino-oxopentanyl)carbamate (1.0 eq) dissolved in THF (3 mL per gm) and heptane (1 mL per gm) was charged to a reaction vessel that was flushed with nitrogen gas. THF (3 mL per gm) and es (1 mL per gm) were added to bring the solution to a total of 8 mL per gm morpholino starting material. Magnesium powder (2.2 eqs, Sigma Aldrich or Alfa Aesar) was added and the solution was cooled -10°C to -5°C. i-PngCl (2.0M solution in THF, 1.0 eq) was added to the reaction while maintaining the temperature between -10°C and 0°C. The solution was then warmed to 35°C and 2-bromopropene (0.15 eq) was added. The ature was red to observe initiation of the Grignard reaction which results in about a 5-10°c exotherm. Once the termperature dropped to <40°C, the ing 2-bromopropene (1.56 eq, 1.8 eq in total) was added at a rate to maintain the temperature below 42°C. After te addition of bromide, the solution was stirred at 30-35°C for 3 hours, or until >99% conversion was observed by HPLC. The solution was cooled to ambient temperature, then added to a reaction vessel containing citric acid (8 mL per gm of morpholino starting material, 30% w/w in H20) and heptane (2 mL per gm) cooled to -10°C to -5°C, while maintaining the temperature between -10°C to -5°C. During the quench it was important to keep the unquenched reaction solution stirring, as the stagnant solution could solidify and cause clogging of the pump. The quenched solution was warmed to ambient temperature and stirred for 15-30 minutes and the aqueous layer was removed. Water (5 mL per gm) was added over 5-30 minutes while ining the ature at 15-30°C. The e was stirred for 15-30 minutes and the aqueous layer was removed. Si02 (2 gm/gm, 60um 70-230 mesh) was added to the solution and the slurry was stirred for 15-30 minutes. The slurry was then filtered through a wet pad of Si02 (2 gm $102/g111 of morpholino starting material), washed with 2% IPAc in heptanes (10 mL per gm). The solution was concentrated to afford ediate 1, which was either stored for later use or immediately used in the next step. Yield: 83% (based on HPLC assay). This method of generating the morpholino intermediate above is efficient as it reduced the volume of us methods from 50 V to 25 V and tedious and time consuming column tography for purification was replaced with a silica gel plug filtration. The product of example 1 was isolated from Boc-L-Leu-monohydrate with an assay yield of 75% over two steps.

Exam le 2: Scheme 3 Step1 x0ifl/YY tep2 BocHN/\n/OH-H20_> in? o fix Boc—D—Leu—OH-HZO Step3 *0iN/WKEm—p Step4 >k0iN 0 3a 4a S nthesis of tert-bu l meth l R meth loxiran loxo entan l carbamate also referred to as Com ound A herein Ste 1: S nthesis of R -tert-bu l 4-meth r holinooxo entan lcarbamate A solution of (R)((tert—butoxycarbonyl)amino)methylpentanoic acid monohydrate (1.0 equiv) in THF (2.5 mL/gm) was concentrated under vacuum to remove residual water. Methyl tert—butyl ether (5 mL/gm) was added and the solution was cooled to 0 °C. A slurry of 1,1’-carbonyldiimidazole (1.2 equiv) in methyl tert—butyl ether (3 mL/gm) was added to the reaction at a rate to maintain the reaction temperature :5 °C and the reaction mixture was stirred at 0 °C for 1 h. To the cooled reaction mixture was added morpholine (1.5 equiv) at a rate to maintain reaction temperature :10 °C and the on mixture was d for 1 h at 0 °C. A 1 M aqueous solution of hydrogen chloride (3.5 mL/gm) was added and the biphasic mixture was warmed to 20 °C and stirred for 15 min. The layers were allowed to separate and the bottom aqueous layer was removed. The organic layer was washed sequentially with a 1 M aqueous solution of hydrogen chloride (1.5 , an 8 wt% aqueous solution of sodium bicarbonate (1 mL/gm), and a saturated aqueous solution of sodium de (3 mL/gm). The organic solution containing rt—butyl (4-methylmorpholinooxopentanyl)carbamate was concentrated under vacuum to remove al water, reconstituted with methyl tert- butyl ether (5 mL/gm), to provide compound 1a and used in the following step without additional purificationYield: 99% (based on HPLC assay) 1H NMR (400 MHz : 5.26 (d, J: 8.9 Hz, 1H), 4.62 (m, 1H), 3.45—3.72 (m, 8H), 1.71 (m, 1H), 1.42 (m, 11 H), 0.96 (d, J: 6.7 Hz, 3H), 0.92 (d,J= 6.5 Hz, 3H) HRMS (ESI-TOF) m / z calcd for C15H29N204 (M + H)+ 301.2127, found 301.2126.

Ste 2: S nthesis of R -tert-bu l 2 6-dimeth ohe ten l carbamate 2a To a reactor flushed with nitrogen gas was charged Mg turnings (2.1 equiv), the solution from step 1 containing (R)-tert—butyl (4-methylmorpholinooxopentan yl)carbamate, and THF (3 mL/gm). The slurry was cooled to 0 °C and isopropenyl magnesium chloride (1.9 M solution in THF, 0.9 eq) was added at a rate to maintain the on ature :10 °C. The reaction mixture was then warmed to 40 °C and 2- bromopropene (0.2 eq) was added to initiate the Grignard formation. Once the initial exotherm (~5—10 °C) had subsided, 2-bromopropene (1.8 equiv) was added portionwise (0.3 eq portions) to maintain the reaction temperature :50 °C. The reaction mixture was stirred for >2 h at 40 °C, cooled to 20 °C, and then added to a separate pre-cooled (0 °C) vessel containing a 25 wt% aqueous solution of citric acid (9 mL/gm) and methyl tert- butyl ether (5 mL/gm) at a rate to maintain the reaction temperature :5 °C. The biphasic mixture was warmed to 20 °C, the layers allowed to separate, and the lower aqueous layer removed. The c layer was washed sequentially with water (5 mL/gm), an 8 wt% s solution of sodium bicarbonate (5 mL/gm), and a saturated aqueous solution of sodium de (5 mL/gm). The organic solution containing rt—butyl (2,6- dimethyloxoheptenyl)carbamate was concentrated under vacuum, reconstituted with acetonitrile (10 mL/gm) to provide compound 2a, which was used in the next step t additional cation. Yield: 85% (based on HPLC assay) 1H NMR (400 MHz CDCl3): 1H NMR (400 MHz, CDCl3) 6.09 (s, 1H), 5.89 (s, 1H), 5.10 (m, 2H), 1.91 (s, 3H), 1.74 (m, 1H), 1.49 (m, 1H), 1.44 (s, 9H), 1.34 (m, 1H), 1.01 (d,J= 6.5 Hz, 3H), 0.92 (d, J: 6.6 Hz, 3H) HRMS (ESI-TOF) m / z calcd for C14H25NNaO3 (M + Na)+ 278.1732, found 278.1731.

Ste 3: S nthesis of tert-bu l R meth l R meth loxiran l oxo entan yl)carbamate 13a) To a reactor containing the on of (R)-tert—butyl (2,6-dimethyl-3 pt enyl)carbamate (1.0 eq) in ACN (10 mL/gm) from Step 2 was added the mangenese catalyst (0.0004 eq) and HOAc (5.0 eq). The reaction mixture was cooled to —20 °C and a 50 wt% aqueous solution of hydrogen peroxide (2.0 eq) was added at a rate to maintain reaction temperature 5—10 °C. The on mixture was d at —20 °C for 2 h, warmed to 5 °C, and quenched with a 25 wt% aqueous solution of sodium bisulfite (3.7 . The ic mixture was warmed to 20 °C, the layers allowed to separate, and the lower aqueous layer removed. The organic solution was concentrated under vacuum and reconstituted with panol (4 mL/gm). Water (6 mL/gm) was added over 2 h and the resultant white slurry was cooled to 5 °C and filtered to provide utyl ((R) methyl((R)methyloxiranyl)oxopentanyl)carbamate (compound 3a) as a white crystalline solid (77% yield). 1H NMR (400 MHz CDCl3): 4.88 (m, 1H), 4.58 (m, 1H), 3.04 (d,J= 5.1 Hz, 1H), 2.86 (d, J: 5.1Hz, 1H), 1.71 (m, 1H), 1.56 (s, 3H), 1.44 (s, 9H), 1.36 (m, 2H), 0.98 (d, J: 6.4 Hz, 3H), 0.93 (d, J: 6.6 Hz, 3H) HRMS (ESI-TOF) m / z calcd for C14H25NNaO4 (M + Na)+ 294.1681, found 294.1680.

Ste 4: S nthesis of tert-bu l S meth l R meth loxiran l oxo entan yl)carbamate 14a) To a 20 oC solution of tert-butyl ((R)methyl((R)methyloxiranyl) oxopentanyl)carbamate (1.0 eq) in methyl tert—butyl ether (10 mL/gm) was charged 1,8-diazabicyclo[5.4.0]undecene (0.20 eq). The reaction mixture was allowed to stir at °C for 12 h and then washed with a 5 wt% aqueous solution of sodium bisulfate (0.50 eq). The layers were allowed to separate and the bottom aqueous layer removed. The organic layer was washed with water (5 , concentrated under vacuum, and reconstituted with N-methylpyrrolidinone (5 mL/gm). Simultaneous addition of the organic solution and water (5 mL/gm) to a pre-cooled (5 °C) slurry of tert—butyl ((S) methyl((R)methyloxiranyl)oxopentanyl)carbamate (0.05 equiv) in N- methylpyrrolidinone/water (1:1 v/v, 5 mL/gm) generated a slurry, which was filtered to provide compound 4a, tert—butyl ((S)methyl((R)methyloxiranyl) oxopentanyl)carbamate, as a white crystalline solid (84% yield). 1H NMR (400 MHz CDCl3): 4.86 (d, J: 8.5 Hz, 1H), 4.31 (m, 1H), 3.29 (d, J: 4.9 Hz, 1H), 2.88 (d,J= 5.0 Hz, 1H), 1.72 (m, 1H), 1.51 (s, 3H), 1.48 (m, 1H), 1.41 (s, 9H), 1.17 (m, 1H), 0.96 (d, J: 6.5 Hz, 3H), 0.93 (d, J: 6.6 Hz, 3H) HRMS OF) m / z calcd for C14H25NNaO4 (M + Na)+ 294.1681, found 294.1681.

The morpholine amide step 1 may be accomplished using a variety of acid coupling reagents, each of which is referred to herein an “acid activating agent.” The term “acid activating agent” is ed to refer to an agent that is capable of converting the hydroxyl group of a carboxylic acid functional group to a labile moiety susceptible to displacement upon nucleophilic attack. For instance, an acid activating group that can convert the hydroxyl group of the carboxylic acid moiety of Boc-D-leucine-OH to a group that is easily displaced by the nucleophilic morpholine nitrogen, thereby affording the step 1 morpholine amide product. Similarly, the “activated” carboxylic acid functional group can be displaced by CH3NHOCH3 to form the corresponding b amide (See compound 9 herein). es of classes and types of acid activating reagents include, without tion, (a) formation of an acid chloride by use of thionyl chloride, oxalyl chloride, phosphorus oxychloride, or a vilsmeier reagent; (b) formation of an anhydride by use of carboxylix/carbonic acid anhydrides, a sulfonate mixed anhydrides such as methane sulfonyl chloride (MsCl) or p-toluene sulfonyl chloride (TsCl); a orus based mixed anhydride such as n-propanephosphonic acid ide (T3P) or ethyhnethylphosphonic anhydride; (c) formation of an activated ester moiety by use of a carbodiimide such as dicyclohexylcarbodiimide (DCC), N,N-diisopropylcarbodiimide (DIC) or 1-ethyl—3 -(3’-dimethylaminopropyl)carbodiimide (ECD), or HOBt (1- hydroxybenzotriazole), HOAt (1-hydroxy-7—azabenzotriazole); (d) formation of a inium or uronium salts such as with N,N,N’,N ’-tetramethyl-O-(1H-benzotriazol yl)uronium hexafluorophosphate (HBTU), N-[(dimethylamino)-1H-1,2,3 olo[4,5- b]pyridineyl-methylene]-N-methylmethanaminium hexafluorophosphate (HATU), N- [(1H-benzotriazol-1 -y l)(dimethylamino)methylene] -N-methylmethanaminium tetrafluoroborate-N—oxide (TBTU), 2-(2-oxo-1(2H)-pyridyl-1 1,3 ,3-tetramethyluronium tetrafluoroborate (TPTU) and ano(ehtoxycarbony)-methyleneamino]-N,N,N ’,N ’- tetramethyluronium terafluoroborate (TOTU); (e) formation of an ide using 1,1’- carbonyldiimidazole (CD1); or (f) formation of a phosphonium salt using an agent such as riazol-l-yloxy)tris-(dimethylamino)phosphonium hexafluorophosphate (Castro’s reagent or BOP) or triazolyloxy)tris(pyrrolidine)-phosphonium hexafluorophosphate (PyBOP). These and other acid activating agents are described in more detail in Org Process Res. Dev., Q, 140-177, 2016.

The method of Example 2 is novel as it begins with protected-D-leucine as the starting material. Example 2 also presents the advantage of reducing the volume of the Grignard step from 50 V to 25 V. This significantly improves scalability and throughput, and protects the environment by reducing generated solvent waste. Example 2 also completely eliminates tedious and time consuming column chromatography operation in both steps 2 and 3. The ties that would have been removed via chromatography can now be d via crystallization of the step 3 and step 4 products. Finally, example 2 utilizes mild reaction conditions thereby mitigating risks of epimerization.

Note that excess water may be removed from the Boc-D-Leu-OHomonohydrate by azeotropic distillation in THF (2 x 2.5 vol). However, where the CDI molar equivalents is higher, azeotropic distillation of the water may not be needed. The final water level of <1000 ppm was ed for the acid activation step. Various acid activating agents for Boc-D-Leu-OH were used (Piv-Cl, CDI, T3P, yma, cyanuric chloride and diphenylphosphonic chloride). Use of T3P resulted in an emulsion in the s work-up contributing to onal time for seperation. Use of diphenyl phosphonic chloride resulted in a high yielding reaction, but containing a lt to remove by-product. Use of DIC resulted in a 88% yield for step 1 after column chromatography, by also was found to contain a by-product which needed to be separated.

Use of Piv-chloride, run at about 0°C also resulted in high yields (about 95%) and contained a piv-amide impurity necessitating additional purification. CDI was elected as I5 the ting agent of choice as it provided a clean reaction profile with a high yield in the shortest reaction time. It was found that the temperature of the reaction when using CDI was important and meaningfully affected the product yield. For ce, it was discovered that the best results were obtained when the reaction was ted at a temperature of at or below 20°C. In one aspect of the invention, the invention es the morpholine amide step 1 to be conducted at a temperature of at or below 20°C. In another aspect of the invention, the invention provides the morpholine amide step 1 to be conducted at a temperature of at or below 10°C. In another aspect, the invention provides the methods described herein wherein the morpholine amide step 1 comprises formation of the activated acid with CD1 at a ature of at or below 5°C, and the morpholine amide formation portion of the reaction to be conducted at or below 10°C. The reaction step 1 to form the morpholine-amide was performed in a y of solvents including THF, Me-THF, toluene and MTBE. In one aspect of the invention, the solvent MTBE (10 V) was ed for this step. IN another aspect of the invention, the solvent MeTHF was used. Among the solvents that were evaluated using dynochem modelling re for a straightfoward solvent swap, methyl tert—butyl ether (MTBE) was identified as a choice solvent for exchange to ACN due to the minimal distillation operations required.

Therefore, optimization of the two-step sequence was carried out using MTBE or a combination of MTBE and THF to improve solubility. Additionally, while solvents other than ACN may be used in the epoxidation step 3, ACN was found to be the solvent of choice for the given conditions and providing an optimal yield.

Though the CD1 may be used in an amount ranging from about 1.0 equivalent to about 2.5 eq, the l amount of CD1 used for activation in step 1 was found to be about 2.0 lents. If one were to use less CD1 equivalents, such as only about 1.2 equivalents of CD1, then one would likely need to azeotropically remove water from the reaction. The optimal activation time was found to be about 3.0 hours. The time may vary depending upon the apparatus set-up used. n apparatus set-ups, such as continuous manufacturing set-up may take less time, such as little as 2 minutes. These conditions resulted in a product yield of about 98% (Table 2, entry 1). With a slight excess of CD1, 1.5 equivalents of morpholine was found to be optimal for the coupling reaction. The line-amide adduct was isolated as a crystalline solid and may be used as an MTBE solution as both the yield and purity after work-up were superior (99.0% assay yield, >995 LCAP) without any racemization ed under standard conditions. Therefore, the product was telescoped as an MTBE solution and subjected to opic distillation to remove residual water (target <5 00 ppm).

The Grignard on step 2 was found to be optimal when conducted using the morpholine-amide solution in MTBE (5 V). An important nge in this step from both a product-quality and safety perspective was confirmation of the activation process to form the rd reagent in situ and control of this exothermic process. A potential safety issue was the accumulation of 2-bromopropene and delay in initiation/activation of Mg(0) turnings. The latent exotherm generated due to delayed activation could have lead to uncontrolled excursion of temperature that may have been difficult to handle in a large- scale manufacturing environment.

THF (3 V) was found to be a suitable co-solvent in this step as it was found to alleviate the generation of solids during the reaction, which solids would have resulted in poor agitation of the reaction mixture. Isopropylmagnesium chloride on (2M in THF, 0.9 equiv) was used as a sacrificial base to deprotonate the amide and for activation of the Mg tumings (2.1 equiv) prior to addition of 2-bromopropene. The stoichiometry of isopropylmagnesium chloride was important to reduce or eliminate the potential impurity from pylmagnesium chloride addition to the morpholine amide. Again, depending upon the tus used, one may not need to use isopropylmagnesium chloride at all.

This was the case where a continuous manufacturing set-up was used. Both the formation of Grignard (isopropenylmagnesium bromide) and its reaction with morpholine-amide were found to be rapid and efficient by UPLC and react-IR. The bromide was consumed in about 20—30 minutes after each charge of 2-bromopropene and the corresponding product formation was observed by UPLC. IR results demonstrated that there was no accumulation of 2-bromopropene and the reaction remained safe throughout the dose- controlled addition process. Based on the data collected during the use-test and scale-up runs, the process achieved conversion ranging from >97% to about 99.7% or practically complete conversion with only about 1.2 — 2.0 equivalents of 2-bromopropene. About 1.4 — 1.5 equivalents of 2-bromopropene was discovered to be optimal, resulting in about a 99% conversion for step 2. The impurity profile of the step 2 Grignard was ent in part ojn the quality of the 2-bromopropene. These impurities were important to monitor to ensure column chromatography could be avoided. The potential impurity in 2- bromopropene is estimated to be polymeric in nature and ed in stalling of the downstream epoxidation process. Using re-distilled 2-bromopropene (93.3 wt% by qNMR), the ant Grignard prouct of step 2 was found to perform well in the following epoxidation step 3.

Appropriate quenching of the Grignard process is important to ensure product quality and to eliminate racemization. A rd adduct impurity resulting from double- addition of the Grignard reagent was detected by LCMS at ~2 LCAP during inverse on of the reaction mixture to a mixture of MTBE (5 V) and 25% citric acid aqueous solution (10 V). An increase in the level of the double-addition duct (up to 11 LCAP) was observed when quenching the reaction mixture into citric acid solution (in the absence of MTBE) with an ated decrease in product yield by 235%. The excess Grignard could react with product of step 2 that was hydrolyzed after work-up leading to the formation of the ty. Of note, the impurities of double-addition, morpholine- adduct and dimers could not be detected by HPLC due to their relatively low response factors, but could be ed by LCMS and TLC /heptane 1:4, Nihydrin). Thus, it is important to carefully control the amount of rd reagents used and to carefully quench the reaction upon completion. Racemization of step 2 product was not observed during the course of optimization of the rd process or during the inverse quenching step. The concentrated product with BHT was stable at ambient temperature for one month; BHT in this sample originated from the solvent (250 ppm in stabilized THF) used in the Grignard process. The solution ning the product of step 2 in 2—10 V of ACN or MTBE was stable at room ature or 5 °C for at least 4 days or 18 hours at 35 °C, which was required to optimize the solvent switch to ACN for the step 3 epoxidation.

The improved s of steps 1 and 2 described herein was demonstrated starting from about 1.93 kg boc-D-leucine hydrate and found to be successfully scalable and robust with good solution assay yield (83%) and acceptable product quality (96.7% LCAP and 100% chiral purity) for the subsequent epoxidation step. The Grignard reaction of step 2 can be controlled by addition rate of 2-bromopropene and the total reaction volumes maintained below 25 V, while eliminating the need for column chromatography purification and mitigating racemization risk of the resulting products.

Exam le 3: S nthesis of meth l R meth loxiran loxo entan m 2 2 2-trifluoroacetate FstLOe o To a cooled (0 °C) solution of tert—butyl ((S)methyl((R)methyloxiran oxopentanyl)carbamate (1.0 equiv) in DCM (3 ml/g) was added TFA (5.0 equiv).

The reaction mixture was allowed to warm to 20 °C and aged for 4 h. To the solution was added methyl tert—butyl ether (6.6 ml/g) and then n-heptane (13.3 ml/g). The ant slurry was cooled to 0 °C and then filtered to afford (S)methyl((R)methyloxiran- 2-yl)oxopentanaminium trifluoroacetate as a white crystalline solid (88% yield) 1H NMR (400 MHz, CDCl3) 8.20 (bs, 3H), 4.05 (dd, J: 9.7, 3.2 Hz, 1H), 3.13 (d, J: 4.4 Hz, 1H), 2.95 (4.5 Hz, 1H), 1.85 (m, 1H), 1.71 (m, 1H), 1.57 (m, 4H), 1.00 (dd,J= 6.5, 2.4 Hz, 6H) HRMS (ESI-TOF) m / z calcd for C9H13N02 (M + H)+ 172.1338, found 172.1333.

The present invention provides s of making an important intermediate, compound 5, useful for the manufacture of carfilzomib. For example, the invention provides a cost of goods (COG) for synthesis of compound 5 as a TFA salt, by s of the invention, of about USD /kg of the TFA salt of compound 5 with an overall yield of about 50% and an E-factor of 304. In contrast, the method taught in PCT publication W02009045497 s in a COG of about USD$53, 124 per kg of the TFA slat of compound 5 with an overall yield of about 14% and an E-factor of 2639. Further, the process of W02009045497 requires laborious and costly column chromatography, thereby resulting in the poor throughput efficiency and high COG exhibited.

Exam le 4: S nthesis of Man anese Catal st used in the Invention Scheme 4 fV—(j @1340(MW) M ' l n(OTf) (1. 0 2 equw) _> I \Mn/\1N« H3 H20H TBAB(10moI%) /‘N \N N N’\ MeCN (10V) 0°C ”N N/\ N Na2C03 (8.0 equiv) TfO OTf -tartrate MeCN (20 V), 60 °C Step 2 Step 1 (R,R)-CZ White crystalline solid Ste 1: S nthesis of 2R 2'R -1 1'-bis 1-eth l-1H-benzo d imidazol lmeth l -2 2'- bi rrolidine catal st 1i and To a solution (20 °C) of R)-2,2'-bipyrrolidine L-tartrate trihydrate (1.0 equiv, commercially ble) in ACN (15 ml/g) was added 2-(chloromethyl)ethyl- 1H-benzo[d]imidazole (2.0 equiv), utylammonium bromide (0.10 equiv) and sodium carbonate (8.0 equiv) and then the reaction mixture was heated to 55 °C. After aging for 20 h at 55 °C, the reaction mixture was cooled to 20 °C, filtered through a pad of celite and concentrated under vacuum. The ing oil was reconstituted with DCM (20 ml/g) and washed with a 1 M aqueous solution ofNaOH (20 ml/g). The aqueous layer was extracted with DCM (2 x 10 ml/g) and the combined organic layers were washed with a saturated aqueous solution of sodium bicarbonate (10 ml/g), and a saturated aqueous solution of NaCl (10 mL/g). The organic layer was dried over sodium sulfate and concentrated under vacuum to provide (2R,2'R)-1,1'-bis((1-ethyl-1H- benzo[d]imidazolyl)methyl)-2,2'-bipyrrolidme as an oil with >95% mass recovery.

The crude oil was used in the following step without additional purification. 1H NMR (400 MHz, (CD3)2SO)) 7.54 (m, 4H), 7.18 (m, 4H), 4.32 (m, 6H), 3.53 (m, 2H), 2.86 (m, 2H), 2.63 (m, 2H), 2.21 (m, 2H), 1.86—1.45 (m, 8H), 1.33 (t, J: 7.1 Hz, 6H) HRMS (ESI-TOF) m / z calcd for C23H37N6 (M + H)+ 457.3080, found 457.3086.

Step_ 2: sis of C2 Manganese catalyst To a solution (20 °C) of R)-1,1'-bis((1-ethyl-1H-benzo[d]imidazol yl)methyl)-2,2'-bipyrrolidine (1.0 equiv) in ACN (5 ml/g) was added a pre-made solution of ese bis(trifluoromethanesulfonate) (1.0 equiv) in ACN (5 ml/g). The resultant slurry was allowed to age for 20 h at 20 °C, cooled to 0 °C, and then filtered. The filter cake was washed with ACN (2 x 2 ml/g) to generate the Mn-complex as a white crystalline solid (35% yield).

HRMS OF) m / z calcd for C29H36F3MnN603S (M - OTf)+ 660.1902, found 660. 19 13.

Multi-gram quantities of the ligand were prepared in-house, complexation with Mn(OTf)2 provided a crystalline, air-stable Mn-catalyst complex that could be isolated from ACN. The process to prepare this catalyst works on a manufacture grade scale and successfully provided 44 g of the Mn-catalyst, which was an amount sufficient to e about 20 kg of compound 4a using the methods of the present invention.

Discoveg of Mn-Catalyst for the Asymmetric Epoxidation (Step 3 of Example 2) The published literature epoxidation methods to prepare nd 2a of Example 2 used protocols that lacked compatibility with the enone substitution pattern of compound 2a. First, the electron-deficient nature of the olefin in 2a requires a philic ation method. This precludes the more commonly chosen asymmetric epoxidation methods such as, Jacobsen, Sharpless and Shi epoxidation. In addition, the steric bulk surrounding the ketone of compound 2a presents a challenge to iminium ion catalysis, which has proven to be a promising approach for the asymmetric epoxidation of enals (See for example , B.P et al, Org Lett. 2010, g, 5434-5437). Lewis-acid catalysis (See Hinch, M. et al. .1. M01. Catal. 2006, £1, 8; Nemoto, T. et al. J. Am.

Chem. Soc. 2001, L3, 732) and thiourea-based activation methods also proved challenging for this reason. Phase-transfer catalysis protocols (See, for example: Lifchits, O. et al. J. Am. Chem. Soc. 2013, L5, 6677—6693) suffered from poor sions or epimerization of the labile amino-acid side chain.

A manganese-catalyzed asymmetric epoxidation was described in the literature (See Wang, B.; et al. Chem. Eur. J. 2012, 1_8._ 6750—6753). The method in Wang utilizes a mmercial Mn-catalyst (C1) in the ce of H202 and AcOH. When the Wang method was applied to intermediate compound 1 (See Example 1, also shown below in Scheme 5 , to prepare compound 4a (Example 2), it resulted in providing the epoxide in good yield with good diastereoselectivity favoring the undesired product.

ADAM0 C1 (0.2 mol %) o o A OH (.5 O equnv)_ E >LOA H c H O O H 2. - O Intermediate 1 intermediate 4a intermediate 4b Me283 (_2%ec(13w;)h Din]: C1: 99% assay yield, 1 : 7.3 dr (4a/4b) AN/{N\Mn\N /\Compound 2a + C1: 85% assay yield, 1 : 2.5 dr (4a/4b) O OTf ©A Use of the Wang manganese catalyst (Cl) on the D-enantiomer (compound 2a of Example 2) resulted in a diminished yield and decreased selectivity still ng the undesired epoxide diasteromer 4b. This data indicated that the Wang manganese catalyst Cl and the enone derived from Boc-L-Leucine could not be used to form the desired epoxide t 4a in high yields. Instead, an improved manganese catalyst and the enone derived from the unnatural Boc-D-Leucine was required for a scalable s. To this end, the Applicants’ invention r provides herein a managanese catalyst capable of supporting the efficient, improved epoxidation yields of compound 2a and amenable to larger, manufacture level scale. ive optimization of the ligand, metal, acid, additive, oxidant, temperature, and solvent were not succesful in identifying reaction conditions suitable for reversing the reoselectivity of the epoxidation reaction. l experiments trated the unpredictable nature of each reagent in the reaction system, i.e., each reagent was important for the desired conversion and stereoselectivity. Of the various manganese catalysts discovered and tested, C2 (see scheme 4) was found to be the most efficient catalyst for the transformation of compound 2a to nd 3a (in scheme 3) in terms of catalyst loading (0.04 mol %), reaction conversion (>99.5%), and diastereoselectivity (affording about a 10:1 stereoisomeric ratio favoring the d product 3a). More ically, the Mn catalyst of the present invention is capable of converting compound 2a to nd 3a in a diastereoselectivity of about 90-95% favoring the desired product (3a). The manganese catalyst structure, and in particular, the precise ligand structure was found to have a significant impact on the diastereoselectivity of the epoxidation step.

Despite the preference for this Mn-catalyzed epoxidation process to produce the undesired epoxide diastereomer, efforts on epimerization of the amino-acid side chain surprisingly revealed a thermodynamic preference for the desired stereochemistry of nd 4a (Example 2). Thus, it was unexpectedly found that the selective synthesis of compound 3a from the D-enantiomer of compound 2a with the Mn-catalyzed epoxidation, followed by a thermodynamically-favored epimerization step, provided an expedient route to the desired product 4a. To this end, the present ion addresses some of the major challenges associated with the commercial manufacture of compound 4a including without limitation, safety, throughput efficiency, overall yield, and cost of goods. antly, the intermediate synthesis of compound 3a allowed for the development of a crystallization process capable of purging upstream impurities and eliminating the requirement for column chromatography at step 1 or 2. The crystallization of compound 4a as a method of purifying compound 4a presented challenges due to its low-melting point (41 °C) and high solubility in most all organic solvents. For example, it was found that the solubility of compound 4a in n-hexane at —20 °C is about 34 mg/mL. Conversely, compound 3a melts at 78 °C and has demonstrated an improved solubility profile allowing for greater flexibility in developing isolation conditions. Heptane and IPA/water were found to be two potential t systems for the isolation of nd 3a. Alterntively, a ternary system of three (3) ts, such as acetonitrile/water/acetic acid will also work to e compound 3a. Further, the epoxidation step 3 in scheme 3 using the Mn-y76t catalyst of the present invention followed by crystallization with IPA/water worked well to not only to purge the diasteromer impurity but also to purge upstream process impurities. Finally, the epoxidation chemistry of step 3 in scheme 3 unexpectedly demonstrated excellent consistency across a wide range of compound 2a of varied quality and purity thus demonstrating a robust s.

The foregoing is merely illustrative of the invention and is not intended to limit the invention to the sed uses. Variations and changes, which are routine to one d in the art, are intended to be within the scope and nature of the invention, which are d in the ed claims. All mentioned references, s, applications and publications, are hereby incorporated by reference in their entirety, as if here written.

Claims (1)

What is claimed is:

1. A method of making compound A 5 O or a ceutically acceptable salt thereof, the method comprising steps 1-5 according to scheme 1 x morpholine )