AU2008201157A1

AU2008201157A1 - Improved oxidation process with enhanced safety and use thereof

Info

Publication number: AU2008201157A1
Application number: AU2008201157A
Authority: AU
Inventors: Marco Caraco; Pasquale Massara; Giuseppe Miraglia; Jignesh Patel; Stefania Sapienza
Original assignee: Wyeth LLC
Current assignee: Wyeth LLC
Priority date: 2006-06-22
Filing date: 2008-03-12
Publication date: 2008-04-03

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Improved oxidation process with enhanced safety and use thereof The following statement is a full description of this invention, including the best method of performing it known to us: 004853674 00 0 2 IMPROVED OXIDATION PROCESS WITH ENHANCED SAFETY AND USE t THEREOF Background of the invention Moxidectin (23-methoxime-LL-F-28249-a) is a potent endectocidal agent. An important step in the manufacture of moxidectin is the oxidation of the 5-O-protected-LL-F-28249a intermediate compound. Oxidizing agents which may be used in this manufacturing 00 step are disclosed in US 4,988,824 and US 6,762,327. In many instances, on a manufacturing scale, these oxidizing agents require large amounts of pyridine and a corrosive catalyst, such as dichloroacetic acid, or involve oxidizing agents, which on a manufacturing scale, may introduce unwanted risks. Further, as with all manufacturing processes, improvements in energy efficiency, in product yield and product purity are highly desirable.

This invention seeks to provide an improved oxidation process for the production of moxidectin, preferably which affords mild reaction conditions and high product yields.

The oxidation process of this invention may preferably utilize an oxidizing agent with enhanced safety.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

Summary of the invention The present invention provides an improved process for the selective oxidation of a O-protected-LL-F-28249-a compound of formula II 004853674 wherein R is a protecting group to the corresponding 23-keto compound of formula I

(I)

wherein R is as described for formula II which process comprises reacting said formula II compound with stabilised o-iodoxybenzoic acid, optionally in the presence of a solvent.

Also provided is the use of this oxidation process in the manufacture of moxidectin.

As used herein, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or steps.

004853674 00 00 4 Detailed description of the invention Moxidectin is a potent broad-spectrum endectocide of the macrocyclic lactone antimicrobial class. The unique activity of moxidectin against endo- and ectoparasites in both humans and animals, along with its high margin of safety, has had a tremendous impact on the control of internal and external parasites in companion animals and livestock. Therefore, availability of this compound is highly desired. Moxidectin is the N 23-oxime derivative of LL-F28249-a. A process for the manufacture of moxidectin from 00 0 LL-F28249-a is disclosed in US 4,988,824. Said process includes an oxidation step CN wherein the oxidizing agents disclosed are conventional agents such as pyridinium dichromate, aluminum t-butoxide, o-benzoquinone, phophorous pentoxide, dicyclohexylcarbodiimide, manganese dioxide, acetic anhydride, dimethyl sulfoxide and the like or mixtures thereof. Another process, disclosed in US 6,762,327, uses a periodinane derivative. Some common difficulties encountered in using these reagents, such as long reaction times, difficult workup procedures, possible use of a large excess of the oxidizing agent, potential instability of oxidizing agent and the like, can be problematic on a commercial manufacturing scale.

Surprisingly, it has now been found that stabilised o-iodoxybenzoic acid may be used to selectively oxidize a 5-O-protected-LL-F28249-a compound to the corresponding 5-O-protected-23-ketone compound under mild reaction conditions, with high product yield and without the hazardous chemical properties generally associated with conventional oxidizing agents.

Accordingly, the present invention provides an improved process for the selective oxidation of a 5-O-protected-LL-F28249-a compound of formula II 004853674 (I0 wherein R is a protecting group to the corresponding 23-keto compound of formula I

(I)

wherein R is as described for formula II which process comprises reacting said formula II compound with stabilised o-iodoxybenzoic acid, optionally in the presence of a solvent. The reaction is shown in flow diagram I wherein R represents a protecting group.

004853674 00 0 6 FLOW DIAGRAM I C23

_OH

_CH3 230 CH, c32 H H H-HH 3 C

CH

3 H- H H H 2"'H SI Vol l I OH A H 0 0 stabilised o-iodoxybenzoic acid OH 00 =HK I H- CC OR

H

R

(II) (i) As used in the specification and claims the term "stabilised o-iodoxybenzoic acid" designates a mixture comprising about 48-50%, preferably 49%, of o-iodoxybenzoic acid, about 28-30%, preferably 29%, of isophthalic acid and about 21-23%, preferably 22% of benzoic acid.

Solvents suitable for use in the inventive process include toluene, dimethyl sulfoxide, N-methylpyrrolidinone, or the like, or a mixture thereof, preferably toluene.

As used in the specification and claims, the term protecting group designates pnitrobenzoyl, acetyl, benzyl, methyl, methoxymethyl, methylthiomethyl, (phenyldimethylsilyl)methoxymethyl, p-methoxybenzyloxymethyl, o-nitrobenzylmethyl, o-nitrobenzyl- oxymethyl, 4-methoxyphenoxymethyl, guaiacolmethyl, t-butoxymethyl, 4-pentenyloxymethyl, siloxymethyl, 2-ethoxyethoxymethyl, 2,2,2-trichloroethxymethyl, 2-(trimethylsilyl)ethoxymethyl, trimethylsilyl, t-butyldimethylsilyl, phenyldimethylsilyl, or any protecting group known to protect an hydroxy group in organic synthesis, preferably p-nitrobenzoyl.

The stabilised o-iodoxybenzoic acid agent may be admixed with a compound of formula II in a ratio of about 1.1 to 1.5 wt/wt, o-iodoxybenzoic acid to the compound of formula II, optionally in the presence of a solvent, at a temperature range of about 20°C to until oxidation is complete. Reaction times for the process of the invention may vary 004853674 00 7 according to the amount of stabilised o-iodoxybenzoic acid agent used, the concentration of the formula II compound, the reaction temperature, or the like, in c- general reaction times of one to two hours are sufficient. For optimum product yield, a ratio of about 1.1 to 1.5 wt/wt of o-iodoxybenzoic acid to the compound of formula II is suitable for use in the inventive process.

In Advantageously, the process of the invention may be used in the manufacture of 00 moxidectin. Accordingly, the present invention provides an improved process for the manufacture of moxidectin which comprises the following steps: 1) protecting the 5-hydroxy group of LL-F28249-a to give the compound of 0 formula II; 2) reacting said formula II compound with stabilised o-iodoxybenzoic acid optionally in the presence of a solvent to give the ketone of formula I; 3) reacting said formula I ketone with methoxylamine or a salt thereof to give the compound of formula III; and 4) deprotecting said formula III compound in the presence of a base to yield the moxidectin product.

Alternatively, the compound of formula I may be deprotected to give the compound of formula IV and the formula IV compound may be reacted with methoxylamine or a salt thereof to give the desired moxidectin product. Accordingly, the invention also provides a process for the manufacture of moxidectin which comprises the following steps: 1) protecting the 5-hydroxy group of LL-F28249-a to give the compound of formula II; 2) reacting said formula II compound with stabilised o-iodoxybenzoic acid optionally in the presence of a solvent to give the ketone of formula I; 004853674 00 O 8 3) deprotecting said formula I ketone in the presence of a base to give the G compound of formula IV; and 4) reacting said formula IV compound with methoxylamine or a salt thereof to yield the moxidectin product.

The processes of the invention are shown in flow diagram II wherein R is a protecting oo group as described hereinabove.

0 004853674 9 Flow Diagram 11 Protection (LL-F28249-alpha) (11) VOCH stabilised o-iodoxybenzoic acidl

OC

3

CH

3

ONH

2 -HCI H (111) Basj Deprotection

(I)

Base IDeprotection

CH

3

ONH-

2

-HCI

(Moxidectin) Protection of the 5-hydroxy group of LL-F28249-a may be achieved by the reaction of LL-F28249-a with a halide precursor of a protecting group as described hereinabove, 004853674 00 00 for example p-nitrobenzoyl chloride, trimethylsilyl chloride, methoxymethylbromide, or the like, preferably p-nitrobenzoyl chloride, in the presence of an orgainc solvent such as toluene, methylene chloride, ethyl acetate, acetonitrile, or the like, preferably toluene, and an organic base such as pyridine, triethylamine, N-methylpyrrolidinone, or the like, preferably triethylamine. Oxidation of the protected LL-F28249-a compound of formula II is successfully achieved using the improved 0 oxidation process described hereinabove, i.e. reacting said formula II compound with 00 stabilised o-iodoxybenzoic acid optionally in the presence of a solvent to give the ketone of formula I. The formula I compound (either isolated and purified or as a solution of the crude reaction product in an organic solvent, such as toluene) is reacted with an aqueous solution of methoxylamine or a salt thereof and sodium acetate to give the protected moxidectin compound of formula III. Deprotection is achieved by reacting a solution of said formula III compound in an organic solvent such as toluene, dioxane, n-butanol or the like, preferably dioxane, with an aqueous solution of sodium hydroxide at 00-250 C and isolating the desired moxidectin product from the organic phase using standard procedures such as concentration and filtration or removal of the solvent.

In order to facilitate a further understanding of the invention, the following examples are presented primarily for the purpose of illustrating more specific details thereof. The invention is not to be limited thereby except as defined in the claims.

Unless otherwise noted, all parts are parts by weight. Stabilized o-iodoxybenzoic acid (SIBX) was supplied by Simafex Company, France. The composition of the SIBX used was: 49% o-iodoxybenzoic acid; 29% isophthalic acid; and 22% benzoic acid. The terms HPLC and DMSO designate high performance liquid chromatography and dimethyl sulfoxide, respectively. In the chemical drawings, the term PNB designates p-nitrobenzoyl.

004853674 I1I EXAMPLE I Preparation 5-O-(P-N itrobenzovl)-23-keto-LL-F28249-a stabilised o-iodoxybenzoic acid A solution of 5-O-(p-nitrobenzoyl)-LL-F28249-a (8.68 grams) in toluene was treated with a 20% w/w solution of SIBX (12 grams SIBX) in DMSO. The reaction mixture was stirred vigorously and maintained at 25 0 C for 2 hours 30 minutes (92.7% conversion was obtained). The mixture was quenched with aqueous sodium sulfite solution (24% w/w concentration). The phases were separated and the toluene phase was analyzed by HPLC to give the title product in 88.4% yield.

EXAMPLE 2 Preparation 5-O-(p-N itrobenzovl)-23-keto-LL-F28249-ct I 0] stabilised &-iodoxybenzoic acid 004853674 00 12

O

A solution of 5-O-(p-nitrobenzoyl)-LL-F28249-a (7.44grams) in toluene was treated with a 30% w/w solution of SIBX (10.3 grams SIBX) in DMSO. The reaction mixture was c-i stirred vigorously and maintained at 59 oC for 30 minutes (99.5% conversion was obtained). The mixture was quenched with aqueous sodium sulfite solution (24% w/w concentration). The phases were separated and the toluene phase was analyzed by HPLC to give the title product in 94.5% yield.

N EXAMPLE 3 0 0 Preparation 5-O-(p-Nitrobenzovl)-23-keto-LL-F28249-a

OH

cH. r e JkfH HC H CH, 23 0 o stabilised o-iodoxybcnzoic acid OH H

K

C AH OPNB A N 'B 0 A solution of 5-O-(p-nitrobenzoyl)-LL-F28249-a (7.44grams) in toluene was treated with a 30% w/w solution of SIBX (8.1 grams SIBX) in DMSO. The reaction mixture was stirred vigorously and maintained at 60 oC for 30 minutes (98.9% conversion was obtained). The mixture was quenched with aqueous sodium sulfite solution (24% w/w concentration). The phases were separated and the toluene phase was analyzed by HPLC to give the title product in 93.9% yield.

004853674 00 0 13 EXAMPLE4 Preparation 5-O-(p-Nitrobenzoyl)-23-keto-LL-F28249-a

OH

CHH

c H 3 CH, 2 ,I CH3 S HH 2CH H§OH OH H01 H stabilised o-iodoxybenzoic acid OH H CH, C H

H

OPNB

H

PNB

A solution of 5-O-(p-nitrobenzoyl)-LL-F28249-a (19.84 grams) in toluene was treated with 40.48 grams of DMSO, followed by treatment with solid SIBX (27.04 grams). The reaction mixture was stirred vigorously and maintained at 50 °C for 1 hour (98.5% conversion was obtained). The mixture was quenched with aqueous sodium sulfite solution (22% w/w concentration). The phases were separated and the toluene phase was analyzed by HPLC to give the title product in 88.1% yield.

0 EXAMPLE Preparation of 23-Methoxime-LL-F28249-a A stirred solution of LL-F28249a (6.36 g, 10.4 mmole) in methylene chloride was treated with pyridine (1.98 g, 25.0 mmole) and p-nitrobenzoyl chloride (2.45 g, 13.2 mmole) at 0 -25°C. After 4 hours at 20 0 -25°C, the reaction mixture was treated with saturated sodium bicarbonate and methylene chloride and stirred until reaction is complete. The phases were separated, the organic phase was washed sequentially with saturated sodium bicarbonate, 5% hydrochloric acid, and saturated sodium chloride and concentrated in vacuo to give 5-O-(p-nitrobenzoyl)-LL-F28249a. A solution of the resultant 5-O-(p-nitrobenzoyl)-LL-F28249-a in toluene was treated with a 20% w/w solution of SIBX in DMSO. The reaction mixture was stirred vigorously and maintained at 25 °C for 2 hours 30 minutes. The mixture was quenched with aqueous sodium 004853674 00 14 00 N14 sulfite solution (24% w/w concentration). The phases were separated. The organic S phase containing 23-keto-5-O-(p-nitrobenzoyl)-LL-F28249a was treated with 4% N sodium hydroxide (1.65 molar equivalents NaOH), stirred for 2 hours at 23 0 C, treated with toluene and water, and shaken. The phases were separated and the organic phase r- 5 was washed with water. The organic phase containing 3-keto-LL-F28249a (determined by HPLC analysis) was treated with a solution of methoxylamine hydrochloride 0 molar equivalents) and sodium acetate (1.5 molar equivalents) in water and stirred at 00 20-25 0 C for 10 hours, diluted with toluene and water and stirred for 30 minutes. The O phases were separated and the organic phase was evaporated to dryness. The resultant residue is dispersed in methanol, diluted with water and filtered. The filtercake is dried to give the title compound as a white solid, identified by HPLC analysis.

Claims

1. of formula II A process for the selective oxidation of a 5-O-protected-LLF-28249-a compound (II) wherein R is a protecting group to the corresponding 23-keto compound of formula I wherein R is as described for formula II which process comprises: reacting said formula II compound with stabilised o-iodoxybenzoic acid in the presence of at least one organic solvent and at a temperature range of about 200 C to 70° C to give the compound of formula I, wherein said stabilized o-iodoxybenzoic acid is present in a wt/wt ratio of about 1.1 to 1.5 of o-iodoxybenzoic acid to said compound of formula II. 005100100 16 00 O

2. A process according to claim 1 wherein R is p-nitrobenzoyl.

S3. A process according to claim 1 or claim 2 wherein said stabilised o- G iodoxybenzoic acid is a mixture of o-iodoxybenzoic acid, isophthalic acid and benzoic acid.

4. A process according to any one of claims 1 to 3 wherein the organic solvent is toluene.

In A process according to any one of claims 1 to 3 wherein the organic solvent is a CN mixture of toluene and dimethyl sulfoxide. 00 C

6. A process according to claim 3 wherein said mixture comprises about 48-50% of o-iodoxybenzoic acid, about 28-30% of isophthalic acid and about 21-23% benzoic acid.

7. A process according to claim 6 wherein said mixture comprises about 49% of o- iodoxybenzoic acid, about 29% of isophthalic acid and about 22% of benzoic acid.

8. A process for the manufacture of moxidectin which comprises the following steps: 1) providing a 5-O-protected-LLF-28249-a compound of formula II OH CH C CH3 H 2 3 H H IH, H H 0 OH AH S CH 3 R (II) wherein R is a protecting group; 2) reacting said formula II compound with stabilised o-iodoxybenzoic in the presence of at least one organic solvent and at a temperature range of about 200 C to 70° C to give the ketone of 005100100 00 00 0C rs-l 17 formula I, wherein said stabilized o-iodoxybenzoic acid is present in a wt/wt ratio of about 1.1 to of o-iodoxybenzoic acid to said compound of formula II wherein R is as described for formula II; 3) reacting said formula I ketone with methoxylamine or a salt thereof to give the compound of formula III (III) wherein R is as described for formula II; and 4) deprotecting said formula III compound in the presence of a base to yield the moxidectin product. 005100100 18

9. A process according to claim 8 wherein said stabilised o-iodoxybenzoic acid is a mixture of o-iodoxybenzoic acid, isophthalic acid and benzoic acid.

A process according to claim 9 wherein said mixture comprises about 48-50% of o-iodoxybenzoic acid, about 28-30% of isophthalic acid and about 21-23% benzoic acid.

11. A process according to claim 10 wherein said mixture comprises about 49% of o- iodoxy- benzoic acid, about 29% of isophthalic acid and about 22% of benzoic acid.

12. A process according to any one of claims 8 to 11 wherein the organic solvent is a mixture of toluene and dimethyl sulfoxide.

13. A process for the manufacture of moxidectin which comprises the following steps: 1) providing a 5-O-protected-LLF-28249-a compound of formula II wherein R is a protecting group 2) reacting said formula II compound with stabilised o-iodoxybenzoic in the presence of at least one organic solvent and at a temperature range of about 20* C to 70° C to give the ketone of formula I, wherein said stabilized o-iodoxybenzoic acid is present in a wt/wt ratio of about 1.1 to of o-iodoxybenzoic acid to said compound of formula II 005100100 wherein R is as described for formula II; 3) deprotecting said formula I ketone in the presence of a base to give the compound of formula IV (IV) and 4) reacting said formula IV compound with methoxylamine or a salt thereof to yield the moxidectin product.

14. A process according to claim 13 wherein said stabilised o-iodoxybenzoic acid is a mixture of o-iodoxybenzoic acid, isophthalic acid and benzoic acid.

A process according to claim 14 wherein said mixture comprises about 48-50% of o-iodoxybenzoic acid, about 28-30% of isophthalic acid and about 21-23% benzoic acid. 005100100

16. A process according to claim 15 wherein said mixture comprises about 49% of o- iodoxy- benzoic acid, about 29% of isophthalic acid and about 22% of benzoic acid.

17. A process according to any one of claims 13 to 16 wherein the solvent is a mixture of toluene and dimethyl sulfoxide.

18. A moxidectin product whenever produced by a process according to any one of claims 8 to 17.