Classifications

• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/55—Design of synthesis routes, e.g. reducing the use of auxiliary or protecting groups

Definitions

• the invention is directed to antibacterial compounds that expand the repertoire of erythromycin-like antibiotics. More particularly, the invention concerns macrolide antibiotics containing an erythronolide nucleus modified at least at the substituent at C-13.
• WO 98/09978 published 12 March 1998 and inco ⁇ orated herein by reference discloses modified forms of erythromycin which lack a cladinose residue at the 3-position and which are derivatized in various ways in positions 9-12 of the macrolide ring.
• U.S. Patent No. 5,750,510, issued 12 May 1998 and inco ⁇ orated herein by reference discloses modified erythromycin derivatives.
• the naturally occurring erythromycins have the structure
• R' can be H or OH and R" can be H or CH 3 .
• the invention is directed to erythronolide derivatives that contain modifications from the native structure. All of the compounds of the invention are modified at least at position 13.
• the invention is directed to compounds of the formula
• R a is H or OH, preferably OH;
• R b is H or halogen;
• R c is H or a protecting group;
• R d is methyl; unsubstituted alkyl (3-10C); substituted alkyl (1-lOC); substituted or unsubstituted alkenyl (2- IOC); substituted or unsubstituted alkynyl (2- IOC); substituted or unsubstituted aryl (4-14C); substituted or unsubstituted arylalkyl (5-20C); substituted or unsubstituted arylalkenyl (5-20C); substituted or unsubstituted arylalkynyl (5-20C); substituted or unsubstituted amidoarylalkyl (5-20C); substituted or unsubstituted amidoarylalkenyl (5-20C); or substituted or unsubstituted amidoarylalkynyl (5-20C);
• R e is H or a protecting group or is mono- or disubstituted amino carbonyl
• R f is H; substituted or unsubstituted alkyl (1-lOC); substituted or unsubstituted alkenyl (1-lOC); substituted or unsubstituted alkynyl (1-lOC); substituted or unsubstituted aryl (4-14C); substituted or unsubstituted arylalkyl (5-20C); or OR f may be replaced by H; one of Z and Y is H and the other is OH or protected OH, or is amino, mono- or dialkyl-amino, protected amino, or an aminoheterocycle or
• the invention is directed to pharmaceutical or preservative compositions containing the compounds of formulas (l)-(3) and to methods to treat infectious diseases by administering these compounds or to preserve materials by providing them.
• the compounds of the invention have antibiotic activity, but preferably are useful as semi-synthetic intermediates for forming 10, 11 anhydro forms of the compounds that are further converted to compounds having an erythronolide nucleus and having a ring between the CIO and Cl 1 positions of the erythronolide nucleus as described in U.S. provisional patent application Serial Nos. 60/140,175 filed 18 June 1999 and 60/172,159 filed 17
• Figure 1 shows a schematic of the synthesis of the compounds of the invention.
• Figure 2 shows the post-PKS biosynthesis of erythromycins. This pathway is employed in the present invention, as shown in Figure 1.
• Figure 3 shows the synthesis of compounds of formula (3) wherein R f is methyl.
• Figure 4 shows the synthesis of compounds of formula (1) and their corresponding 10,11 -anhydro forms.
• Figure 5 shows the synthesis of compounds of formula (3) wherein OR f is replaced by H.
• Figure 6 illustrates the conversion of 15-azidoerythromycin A into 15- amidoerythromycins .
• a microbial host preferably a host which does not itself produce a macrolide antibiotic
• a recombinant expression system for the production of modified 6-deoxyerythronolide B (6-dEB) which expression system in some instances will have been altered by a disruption in the catalytic domain of the ketosynthase moiety in the first module.
• 6-dEB modified 6-deoxyerythronolide B
• the polyketide resulting from expression of the modified PKS is then isolated and purified, if desired, from the recombinantly modified organism and fed to Saccharopolyspora erythraea, which contains the functionality for postpolyketide modifications, including glycosylation. Other modifications include hydroxylation at positions 6 and/or 12.
• Saccharopolyspora erythraea which contains the functionality for postpolyketide modifications, including glycosylation. Other modifications include hydroxylation at positions 6 and/or 12.
• the resulting modified erythromycin is then isolated and chemically modified to obtain the compounds of the invention. Synthetic methods for providing these modifications are described in WO 98/09978 and U.S. Patent No. 5,750,510, referenced hereinabove.
• the resulting antiinfective compound is active in vitro and in vivo for activity against a panel of representative microorganisms.
• the compounds of the invention thus exhibit a sufficient diversity in specificity to cover the spectrum of antibiotic activities desired.
• the compounds of the invention are formulated into suitable compositions which will include typical excipients, pharmaceutically acceptable counterions if the compound is a salt, further additives as desired, such as antioxidants, buffers, and the like, and administered to animals or humans.
• suitable compositions which will include typical excipients, pharmaceutically acceptable counterions if the compound is a salt, further additives as desired, such as antioxidants, buffers, and the like, and administered to animals or humans.
• the types of formulations that are appropriate for these compounds are similar to those for the macrolide antibiotics in general. Formulations may be found, for example, in Remington's Pharmaceutical Sciences, Mack Publishing Co., latest edition.
• the compounds can be administered by any desired route, including injection, oral administration, transdermal administration, transmucosal administration, or any combination.
• the compounds of the invention can also be administered with additional active ingredients if desired.
• the compounds of the invention are of formulas (l)-(3) as set forth above, as well as any stereoisomeric forms of these compounds as shown.
• the particular stereoisomers depicted are those resulting from the preferred method of synthesis set forth above and exemplified herein; however, by modifying the expression system for the PKS, or by altering the chirality of the diketide, or by synthetic chemical conversion, other stereoisomers may also be prepared. Additional chiral centers may be present in the substituents, such as R d and R f .
• the stereoisomers may be administered as mixtures, or individual stereoisomers may be separated and utilized as is known in the art.
• Halogen includes fluoro, chloro, bromo and iodo, and most preferably fluoro.
• Alkyl refers to a saturated straight-chain, branched chain or cyclic hydrocarbyl moiety containing a specified number of carbons and that may contain one or more suitable heteroatoms; similarly, alkenyl and alkynyl refer to straight or branched chain or cyclic hydrocarbon substituents containing one or more double bonds or one or more triple bonds, respectively, and containing one or more suitable heteroatoms.
• Aryl refers to an aromatic substituent that may contain one or more suitable heteroatoms such as phenyl, naphthyl, quinolyl, or phenanthryl.
• Arylalkyl refers to substituents wherein an aryl group is linked to the substituted moiety through an alkyl, alkenyl or alkynyl linkage, respectively. Again, the number of carbons in the arylalkyl, arylalkenyl or arylalkynyl groups will be specified.
• amidoarylalkyl refers to substituents wherein an aryl group is linked to the substituted moiety through an amido and an alkyl, alkenyl or alkynyl linkage, respectively. Again, the number of carbons in the amidoarylalkyl, amidoarylalkenyl or amidoarylalkynyl groups will be specified.
• heteroalkyl included among the defined substituents herein are “heteroalkyl,” “heteroalkenyl,” “heteroalkynyl,” “heteroaryl,” “heteroarylalkyl,” and the like.
• Suitable heteroatoms include N, O, and S.
• substituents may be unsubstituted or may be further substituted.
• Typical substituents include R, -OR, -SR, -NR 2 , -COR, -COOR, -CONR 2 , -OOCR, -NRCOR, -OCONR 2 , -CN, -CF 3 , -NO 2 , -SOR, -SO 2 R, halogen, wherein each R is independently H or is alkyl, alkenyl, alkynyl, aryl, arylalkyl, or the hetero forms of these as defined above.
• alkyl, alkenyl and alkynyl may be substituted by aryl or heteroaryl, which may, themselves, be further substituted.
• Aryl and heteroaryl may also be substituted by alkyl, alkenyl or alkynyl, or by additional aryl or heteroaryl moieties.
• a "protecting group" for a hydroxy includes acyl groups, silyl groups, and the like. Suitable protecting groups are described by Greene, T.W., et al, in Protecting Groups in Organic Synthesis, 2 nd Ed., John Wiley & Sons, Inc. (1991), inco ⁇ orated herein by reference.
• R d is preferably butyl, pentyl, methoxyethoxymethyl, isobutyl, methylcyclohexyl, phenyl, benzyl, ethylphenyl, 3 -(benzyloxy )propyl, 2-(pyrimidin-2-ylthio)ethyl, propyl, fluoroethyl, chloroethyl, vinyl, 3-butenyl, or azidoethyl and more preferably propyl, fluoroethyl, chloroethyl, vinyl, 3-butenyl, or azidoethyl.
• R f is H or lower C1-C3 alkyl, and more preferably methyl.
• R f is also preferably arylalkenyl or arylalkynyl such as 3-arylprop-2-enyl or 3- arylprop-2-ynyl.
• the aryl group in the preferred arylalkenyl or arylalkynyl embodiments are 3-quinolyl, 4-quinolyl, 5-quinolyl, phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-methoxyphenyl, 6-quinolyl, 6-quinoxalyl, 6-amino-3-quinolyl, or 4-isoquinolyl.
• the antibiotic starting materials for any further chemical synthesis to obtain the compounds of the invention are prepared, preferably, by feeding a suitable diketide to a microorganism modified to contain an expression system for the 6-dEB PKS containing a KS1 knockout, or by a host cell that provides a methyl at the 13-position, followed by feeding the resulting polyketide to a recombinant strain of Saccharopolyspora erythraea that has been altered to eliminate production of 6-dEB.
• a strain can be prepared that is able to hydroxylate either both the 6- and 12-positions or the 12-position only. In this case, -OR f is replaced by -H.
• a strain can be prepared that hydroxylates only the 6-position.
• the recombinant S. erythraea strain, K40-67 is obtained by transforming an S. erythraea strain that produces high levels of erythromycin A with a plasmid comprising a mutated eryAl sequence encoding an inactivated KS1 domain.
• the resulting transformants now are unable to produce 6-dEB as a competitor to the fed polyketide and, instead, hydroxylate the 6-position and 12-position and glycosylate the 3-position and 5-position of the modified polyketide that has been made in Streptomyces or other polyketide-producing transformant.
• an S. erythraea strain is constructed by disrupting the eryF hydroxylase gene in strain K40-67.
• the eryK gene can be disabled, wherein embodiments of compounds (l)-(3) wherein R. is H may readily be produced.
• glycosylation reactions for the production of the erythromycins result in the diglycosylated forms analogous to the naturally occurring erythromycins. If the compounds of formula (3) are to be prepared from the initial product, the hydroxyl group of the cladinose ring (attached to position 3) may then need to be protected for subsequent modification of the macrolide substituents.
• the modified erythromycins of the invention in addition to modification at C-13, may contain an -OH group at position 6, unless OR f is replaced by H as described above.
• the compound of formula (3) is provided with protecting groups which form one embodiment of R. and R-.. Such protection is effected using suitable protecting reagents such as acetic anhydride, benzoic anhydride, benzochloro formate, hexamethyldisilazane, or a trialkylsilyl chloride in an aprotic solvent.
• Aprotic solvents include, for example, dichloromethane, chloroform, tetrahydrofuran, N-methyl pyrrolidone, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and the like. Mixtures may also be used. Protection of both sugar hydroxyls in formula (3) may be done simultaneously or sequentially.
• the keto group at position 9 of the macrolide ring must also be protected. Typically, this is effected by converting the keto group to a derivatized oxime.
• Alkylating agents include alkyl halides and sulfonates.
• the alkylating agents may include methyl tosylate, 2-fluoroethyl bromide, cinnamyl bromide, crotonyl bromide, allyl bromide, propargyl bromide, and the like.
• the alkylation is conducted in the presence of base, such as potassium hydroxide, sodium hydride, potassium isopropoxide, potassium t-butoxide, and an aprotic solvent.
• R f Especially prefe ⁇ ed for R f are methyl, allyl and ethyl.
• the sugar residues and the macrolide ring may be deprotected.
• the oxime can then be removed and converted to a keto group by standard methods known in the art.
• Deoximating agents include inorganic sulfur oxide compounds such as sodium hydrogen sulfite, sodium pyrosulfate, sodium thiosulfate, and the like.
• protic solvents are used, such as water, methanol, ethanol, isopropanol, trimethyl silanol and mixtures of these.
• the deoximation reaction is conducted in the presence of an organic acid.
• the group introduced at the 6-hydroxyl can further be manipulated.
• the O-allyl derivative can also be oxidized with m-chloroperoxybenzoic acid in an aprotic solvent to provide the epoxy compound which can be opened with amines or N-containing heteroaryl compounds to provide compounds with N-containing side-chains, or can be oxidized under Wacker conditions to provide the substituent O-CH 2 -C(O)-CH 3 , or can be ozonized to provide the aldehyde.
• the aldehyde can then be converted to the oxime or reacted with a suitable amine and reduced in the presence of a borohydride reducing agent to provide an amine.
• the oxime can also be converted to a nitrile by reaction with a dehydration agent in an aprotic solvent.
• the O-allyl derivative can also be reacted with an aryl halide under Heck conditions (Pd(II) or Pd(O), phosphine and amine or inorganic base) to provide a 3 -aryl prop-2-enyl derivative.
• This derivative can then be reduced with hydrogen and palladium on carbon to provide a 3-arylpropyl derivative.
• R f is a 2-propyne
• similar reactions can be employed to provide alterations in the side-chain, including arylation.
• the compound of formula (3) is treated with mild aqueous acid or with a deglycosylating enzyme.
• Suitable acids include hydrochloric, sulfuric, chloroacetic, trifluoroacetic and the like, in the presence of alcohol. Reaction times are typically 0.5-24 hours at a temperature of -10-35°C. During this reaction, the 2' group of the remaining sugar is protected as set forth above and deprotected subsequent to the decladinizing reaction. The resulting hydroxyl group at the 3-position of the macrolide ring is then oxidized to the ketone using a modified Swern oxidation procedure.
• an oxidizing agent such as N-chlorosuccinimide-dimethyl sulfide or a carbodiamide- dimethylsulfoxide is used.
• a compound of formula (3) is added to pre-formed N-chlorosuccinimide and dimethyl sulfide complex in a chlorinated solvent such as methylene chloride at -10-25°C.
• a tertiary amine such as triethylamine is added to produce the co ⁇ esponding ketone and the 2' protecting group is then removed.
• the compound of formula (1) is treated with a base and an electrophilic halogenating reagent such as pyridinium perbromide or N-fluorobenzene sulfonic acid.
• the position 2 can be halogenated at any time after the 3 keto compound is prepared.
• the appropriate substituent such as vinyl, ethenyl, butenyl or azido at the C-13 position can be further manipulated.
• an amidoacetate salt of the compound of the invention can be derivatized using an arylacetyl chloride to yield an arylamino alkyl group on the C-13 position.
• the C13 derivatives of an azido group take place before the ketolide is formed.
• Derivations of an ethenyl group can take place either before or after the ketolide is formed.
• the compound resulting from the deglycosylation reaction of formula (1) is treated with a dehydrating agent such as carbonyl diimidazole and base.
• Novel methods of synthesis of the compounds of the invention are also provided.
• Table 1 illustrates compounds within the scope of the present invention which are: of formula (1) wherein R. is H or OH, R b is H, Cl, or F, and R c is H; of formula (2) wherein R. is H or OH and R c is H; and of formula (3) wherein R. is H or OH, R_ is H, and R-. is H, or a radical a, b, c, or d:
• a 6-deoxyerythronolide B (6-dEB) derivative compound is prepared by fermentation of a recombinant Streptomyces host cell.
• the fermentation to produce 15-methyl-6-deoxyerythronolide B and 14J5-dehydro-6- deoxyerythronolide B requires a synthetic diketide intermediate to be fed to the fermenting cells.
• the preparation of these synthetic diketides is described in Example 1.
• These synthetic diketides are substrates for a 6-deoxyerythronolide B synthase (DEBS) that is unable to act on its natural substrate (propionyl Co A) due to a mutation in the ketosynthase domain of module 1 of DEBS.
• This recombinant DEBS is provided by plasmid pJRJ2 in Streptomyces coelicolor CH999. S. coelicolor CH999 is described in U.S. Patent No.
• Plasmid pJRJ2 encodes the eryAI, eryAII, and eryAIII genes; the eryAI gene contained in the plasmid contains the KS1 null mutation.
• the KS1 null mutation prevents formation of the 6-deoxyerythronolide B produced by the wild-type gene unless exogenous substrate is provided.
• Plasmid pJRJ2 and a process for using the plasmid to prepare novel 13- substituted erythromycins are described in PCT publication Nos. 99/03986 and 97/02358 and in U.S. patent application Serial Nos.
• exogenous substrates can be prepared by the methods and include the compounds described in PCT patent application No. PCT/US00/02397 and U.S. patent application Serial No. 09/492,733, both filed 27 Jan. 2000, by inventors G. Ashley et al., and both of which claim priority to U.S. patent application Serial No. 60/117,384, filed 27 Jan. 1999, each of which is inco ⁇ orated herein by reference.
• PKS genes other than the ery genes can also be employed; suitable genes include the KS1 null mutation containing oleandolide and megalomicin PKS genes described in U.S. patent application Serial Nos. 60/158,305, filed 8 Oct. 1999 and 09/428,517, filed 28 Oct. 1999, and PCT application No. US99/24478, filed 22 Oct. 1999, each of which is inco ⁇ orated herein by reference.
• the fermentation to produce 14-nor-6-deoxyerythronolide B does not require diketide feeding, because the desired compound is produced by the recombinant host cell Streptomyces coelicolor CH999/pCK7. Plasmid pCK7 is described in U.S. Patent No.
• a derivative of plasmid pCK7, pKOSOl 1-26, can also be used.
• the host cell comprising pKOSOl 1-26 and a recombinant ptpA gene is S coelicolor 27-26/pKOS011-26. These host cells produce both 6-deoxyerythronolide B and 14-nor-6-deoxyerythronolide, due to the inco ⁇ oration of propionyl Co A and acetyl Co A, both of which serve as substrates for DEBS.
• Example 2 The fermentation of Streptomyces coelicolor CH999/pJRJ2 and S. coelicolor CH999/pCK7 is described in Example 2.
• the isolation of the 6-deoxyerythronolide products resulting from this fermentation can be achieved by separation.
• the isolated products are then added to the fermentation broth of Saccharopolyspora erythraea strains to make other useful intermediate compounds of the invention.
• the S erythraea strains catalyze the biosynthesis and attachment of sugar residues to the 3 and 5 positions of the 6-dEB derivative compounds. These strains also comprise a functional eryK gene product and so hydroxylate the 6-dEB derivative compounds at the 12 position. The strains differ in regard to whether a functional eryF gene product is produced. If so, then the compounds produced are hydroxylated at the 6 position as well. If not, then a 6- deoxyerythromycin A derivative is produced.
• S. erythraea fermentations are described in Example 3, together with the isolation of the erythromycin A derivative compounds from the fermentation broth.
• Examples 4-6 describe the process for alkylating the compounds to make the 6-O-alkyl intermediates of the invention and Example 11 describes the process for allylation to make 6-O-allyl intermediates which can be further derivatized as shown in Example 15 upon protection of the 2' and 4" hydroxyl groups and protection of the 9-position as shown in Example 14.
• the schematic for these reactions is shown in Figure 3.
• Examples 7-9 describe the conversion of the above-described compounds of formula (3) to compounds of formula (1), and co ⁇ esponding compounds that are the lOJ l-anhydro forms. This is shown schematically in Figure 4.
• Example 10 also sets forth the process for making the lOJ l-anhydro compounds of formula (3), but wherein OR f is replaced by H. The reaction scheme for these conversions is shown in Figure 5.
• Example 1 1 can be converted to compounds of formula (1) or (2) as shown in Examples 12 and 13, respectively.
• Example 16 illustrates the halogenation of the 2-position.
• Example 17 illustrates the conversion of 15-azidoerythromycin A into 15- amidoerythromycins, as shown in Figure 6.
• N-acetylcysteaminethioesters used to feed the recombinant Streptomyces host cells to make the 15-methyl and 14J5-dehydro-6- deoxyerythronolide B intermediate compounds are described in this Example.
• the synthesis protocols described below are also described in U.S. provisional patent application Serial No. 60/117,384, filed 27 Jan. 1999 and U.S. utility patent application Serial No. 09/492,733, filed 27 Jan. 2000, both of which are inco ⁇ orated herein by reference.
• (2S,3R)-2-methyl-3-hydroxyhexanoate NAcS (Preparation E), which is used to prepare the 15-methyl-6-deoxyerythronolide B intermediate, is prepared from reacting (4S)- N-[(2S,3R)-2-methyl-3-hydroxyhexanoyl]-4-benzyl-2-oxazolidinone (Preparation D) with N- acetylcysteamine (Preparation B).
• N-acetylcysteamine is, in turn, prepared from N,S- diacetylcysteamine (Preparation A).
• (2S,3R)-2-methyl-3-hydroxy-4-pentenoate NAcS (Preparation G), which is used to prepare the 14J5-dehydro-6-deoxyerythronolide B intermediate, is prepared from reacting (4S)-N-[(2S,3R)-2-methyl-3-hydroxy-4-pentenoyl]-4-benzyl-2-oxazolidinone (Preparation F) with N-acetylcysteamine (Preparation B).
• Acetic anhydride (125 mL) is placed in one addition funnel, and 8N KOH (350 mL) is placed in the other addition funnel.
• the acetic anhydride is added dropwise to the cysteamine solution, with 8 N KOH being added so as to keep the reaction pH at 8 +/- 1.
• the pH was adjusted to 7.0 using 1 N HCl and the mixture is allowed to stir for 75 min. on ice.
• Solid NaCl is added to saturation, and the solution is extracted 4 times using 400 mL portions of CH 2 C1 2 .
• the organic extracts are combined, dried over MgSO 4 , filtered, and concentrated under reduced pressure to yield 68.9 g (97% yield) of a pale yellow oil, which crystallizes upon standing at 4°C.
• N,S-diacetylcysteamine (42.64 g) is placed in a 2 L round bottom flask fitted with a magnetic sti ⁇ er, and dissolved in 1400 mL of water. The flask is purged with N 2 , and the mixture is chilled in an ice bath. Potassium hydroxide (49.42 g) is added, and the mixture is sti ⁇ ed for 2 hr. on ice under inert atmosphere. The pH is adjusted to 7 using 6 N HCl, and solid NaCl is added to saturation. The mixture is extracted 7 times with 500 mL portions of CH 2 C1 2 . The organic extracts are combined, dried over MgSO 4 , filtered, and concentrated under reduced pressure to yield 30.2 g (96% yield) of product. This material is distilled immediately prior to use, bp 138-140°C/7 mmHg.
• the addition funnel was charged with 78 mL of n-butyllithium (1.6 M in hexane) by cannula, which was added in a slow stream to the reaction.
• Distilled propionyl chloride (bp 77-79°C), 8.0 mL, was added rapidly via syringe. The reaction was allowed to stir for 30 min. in the dry ice/isopropanol bath.
• the reaction was removed from the cold bath, allowed to warm to >0°C, and quenched with 50 mL of saturated aqueous NH 4 C1.
• the mixture was concentrated to a slurry on a rotary evaporator.
• the slurry was extracted three times with 250 mL portions of ethyl ether.
• the organic extracts were combined and washed with 50 mL each of saturated aqueous NaHCO 3 and brine, dried with MgSO 4 , filtered, and concentrated to give a yellow oil.
• the material crystallized upon sitting. The crystals were triturated once with cold (-20°C) hexanes to give 21.0 g (80% yield) of white crystalline material, m.p. 41-43°C.
• the addition funnel was charged by cannula with 100 mL of dibutylboron triflate (1.0 M in dichloromethane), which was added in a slow stream to the reaction.
• Triethylamine (15.6 mL) was added dropwise by syringe, keeping the reaction temperature below -10°C.
• the reaction was then transfe ⁇ ed to an ice bath and allowed to stir at 0°C for 30 min. After that period, the reaction was placed back into the dry ice/isopropanol bath and allowed to cool to -65°C.
• Butyraldehyde (8.6 mL) was added rapidly by syringe, and the reaction was allowed to stir for 30 min.
• the reaction was transfe ⁇ ed to an ice bath and the addition funnel was charged with 100 mL of a 1 M aqueous phosphate solution, pH 7.0 (the phosphate solution is comprised of equal molar amounts of mono- and dibasic potassium phosphate).
• the phosphate solution was added as quickly as possible while keeping the reaction temperature below 10°C.
• the addition funnel was then charged with 300 mL methanol which was added as quickly as possible while keeping the reaction temperature below 10°C.
• the addition funnel was charged with 300 mL of 2:1 methanol:30% hydrogen peroxide. This was added dropwise to ensure that the temperature was kept below 10°C.
• the reaction was sti ⁇ ed for one hr. after completion of addition.
• N-acetylcysteamine thioester N- acetylcysteamine was distilled at 130°C/7 mm Hg to give a colorless liquid at room temperature.
• a dry, 1 L three-necked round bottomed flask equipped with a 500 mL addition funnel and a stir bar was capped with septa and flushed with nitrogen. The flask was then charged with 10.7 mL of N-acetylcysteamine by syringe and with 400 mL of anhydrous THF by cannula. The mixture was cooled with a MeOH/ice bath.
• Butyllithium 64 mL of 1.6 M in hexanes was added dropwise by syringe, resulting in formation of a white precipitate.
• trimethylaluminum 51 mL of 2.0 M in hexanes was added dropwise by syringe. The reaction became clear after addition of trimethylaluminum and was allowed to stir an additional 30 min.
• the reaction was treated with enough saturated oxalic acid to give a neutral reaction with pH paper (approximately 90 mL).
• the solvents were then removed on a rotary evaporator to give a white slurry.
• the slurry was extracted six times with 250 mL portions of ethyl ether.
• the organic extracts were combined and washed with brine, dried with MgSO 4 , filtered, and concentrated to give a slightly yellow oil.
• the thioester product was purified by flash chromatography on SiO 2 using 1 :1 hexanes:EtOAc until the elution of 4-benzyl-2- oxazolidinone.
• Dibutylboron triflate (100 mL of 1.0 M in dichloromethane) was added in a slow stream via the addition funnel at such a rate as to keep the reaction temperature below 3°C.
• Diisopropylethylamine (17.9 mL) was added dropwise by syringe, again keeping the internal temperature below 3°C.
• the reaction was then cooled to -65°C using a dry ice/isopropanol bath. Acrolein was added over 5 min. by syringe. The reaction was allowed to stir for 30 min. after completion of addition.
• the reaction was then transfe ⁇ ed to an ice bath and the addition funnel was charged with 120 mL (0J mol) of a 1 M aqueous phosphate solution, pH 7.0 (the phosphate solution is comprised of equal molar amounts of mono- and dibasic phosphate).
• the phosphate solution was added as quickly as possible while keeping the reaction temperature below 10°C.
• the addition funnel was then charged with 400 mL of methanol that were added as quickly as possible while keeping the reaction temperature below 10°C.
• the addition funnel was charged with 400 mL of 2:1 methanol:30% hydrogen peroxide by initial dropwise addition to keep the temperature below 10°C.
• the reaction was sti ⁇ ed for one hour.
• N-acetylcysteamine thioester N- acetylcysteamine was distilled at 130°C/7 mm Hg to give a colorless liquid at room temperature.
• a dry, 1 L three-necked round bottomed flask equipped with a 500 mL addition funnel and a stir bar was capped with septa and flushed with nitrogen. The flask was then charged with 7.5 mL of N-acetylcysteamine by syringe and with 500 mL of anhydrous THF by cannula. The reaction was then cooled with a MeOH/ice bath.
• Butyllithium 44 mL of 1.6 M in hexane was added dropwise by syringe. A white precipitate formed as the n-BuLi was added. After stirring for 30 min., 35.5 mL (0.071 mol) of trimethylaluminum (2.0 M in hexane) were added drop-wise by syringe. The reaction became clear after addition of trimethylaluminum and was allowed to stir an additional 30 min.
• Streptomyces coelicolor CH999/pJRJ2 is described in U.S. patent application Serial Nos. 08/896,323, filed 17 July 1997, and 08/675,817, filed 5 July 1996, each of which is inco ⁇ orated herein by reference.
• Plasmid pJRJ2 encodes a mutated form of DEBS in which the ketosynthase domain of module 1 (KS1) has been inactivated via mutagenesis (KS1°).
• coelicolor strains comprising this plasmid that are fed (2S, 3R)-2-methyl-3- hydroxyhexanoate-N-acetylcysteamine (Preparation E, propyl diketide) of Example 1 produce 15-methyl-6-deoxyerythronolide B.
• a 1 mL vial of the CH999/pJRJ2 working cell bank is thawed and the contents of the vial are added to 50 mL of Inoculum Medium 1 in a 250 mL baffled flask.
• the flask is placed in an incubator/shaker maintained at 30 ⁇ 1°C and 175 ⁇ 25 RPM for 48 ⁇ 10 hours.
• the 50 mL culture is then added to a 2.8 L baffled flask containing 500 mL of Inoculum Medium 1.
• This flask is incubated in an incubator/shaker at 30 ⁇ 1°C and 175 ⁇ 25 RPM for 48 ⁇ 10 hours.
• the 500 mL culture is divided equally among ten 2.8 L baffled flasks each containing 500 mL of Inoculum Medium 1. All flasks are then incubated as described previously.
• a 150 L fermenter is prepared by sterilizing 100 L of Production Medium 1 at 121°C for 45 minutes. After incubation, all 10 flasks are combined in a 5 L sterile inoculation bottle and aseptically added to a 150 L fermenter.
• the fermenter is controlled at 30°C, pH 6.5 by addition of 2.5 N H 2 SO 4 and 2.5 N NaOH, dissolved oxygen > 80% air saturation by agitation rate (500-700 RPM), air flow rate (10-50 LPM), and/or back pressure control (0.1-0.4 bar).
• Foam is controlled by the intermittent addition of a 50% solution of Antifoam B.
• the product is predominantly in the centrate; the centrifuged cell mass is discarded.
• This process has also been completed in a 1000 L fermenter (700 L working volume).
• the inoculum process is identical to the above process except that the 150 L fermenter is charged with Inoculum Medium 1 and the 1000 L fermenter is charged with Production Medium 1.
• the fermenter is controlled at 30°C, pH 6.5 by addition of 2.5-5 N H 2 SO 4 and 2.5- 5 N NaOH, dissolved oxygen >70% air saturation by agitation rate (140-205 RPM), air flow rate (100-200 LPM), and/or back pressure control (0.2-0.5 bar).
• Foam is controlled by the addition of a 50% solution of Antifoam B as needed.
• racemic 2-methyl-3- hydroxyhexanoyl-N-propionylcysteamine 300 grams is added to the 1000 L fermenter.
• the fermenter is harvested at 4.6 days by centrifugation as described above.
• the centrate is filtered.
• the filtrate (approximately 700 L) are passed through an Amicon Moduline column (20 x 350 cm) containing 20 L of HP20 resin (Mitsubishi).
• the flow rate during loading is 4 L/minute with a pressure drop below 8 psi.
• the resin is washed with 20 L of water and then 40 L of 30% methanol.
• 15- methyl-6dEB is eluted using 100% methanol.
• Four 12 L fractions were collected with fractions 2, 3 and 4 containing all of the detectable 15-methyl-6dEB.
• the 15-methyl-6dEB product pool is diluted with 36.7 L of water giving 75 L of a clear solution.
• the 6-dEB derivative compounds produced in Example 2 are converted to erythromycin derivatives using a recombinant strain of Saccharopolyspora erythraea.
• the S erythraea strain used was K40-67 or K39-14V. This strain was created by transforming an S. erythraea strain capable of producing high levels of erythromycin A with a pWHM3- derived plasmid comprising a mutated eryAI sequence encoding an inactivated KS1 domain. By homologous recombination, the resulting transformants were rendered incapable of producing 6-deoxyerythronolide B.
• the dEB analog fed is not subject to competition for hydroxylation at the 6-position.
• the S. erythraea strain used was K39-07. This strain was constructed from strain K40-67 by disruption of the eryF hydroxylase gene; this destroys ability to hydroxylate the analog at the 6-position. Both strains were fermented under substantially similar conditions, as described below.
• 15-methyl-erythromycin A is produced according to the following protocol: A 1 mL vial of the K39-14V working cell bank is thawed and the contents of the vial are added to 50 mL of Inoculum Medium 2 in a 250 mL baffled flask. The flask is placed in an incubator/shaker maintained at 3411°C and 175125 RPM for 48110 hours. The 50 mL culture is then added to a 2.8 L baffled flask containing 500 mL of Inoculum Medium 2. The flask is incubated in an incubator/shaker at 34il°C and 175125 RPM for 48110 hours. The 500 mL culture is divided equally among ten 2.8 L baffled flasks each containing 500 mL of Inoculum Medium 2. All flasks are then incubated as described previously.
• a 150 L fermenter is prepared by sterilizing 100 L of Production Medium 2 at 121°C for 45 minutes. After incubation, all 10 flasks are combined in a 5 L sterile inoculation bottle and aseptically added to a 150 L fermenter.
• the fermenter is controlled at 34°C, pH 7.0 by addition of 2.5 N H 2 SO 4 and 2.5 N NaOH, dissolved oxygen > 80% air saturation by agitation rate (500-700 RPM), air flow rate (15-50 LPM), andVor back pressure control (OJ-0.4 bar).
• Foam is controlled by the addition of a 50% solution of Antifoam B. At 2415 hours a 58-60 mL/hour 15% dextrin (w/v) feed is initiated.
• the dextrin solution is continuously mixed during the feed period.
• 25 grams of 15-methyl- 6dEB (Preparation A in Example 2) are added to the fermenter.
• the 15-methyl-6dEB is prepared by solubilizing 25 grams of 15-methyl-6dEB in 400-600 mL of 100% ethanol and filtering (0.2 ⁇ m, nylon filter). Conversion of 15-methyl-6dEB to 15-methyl-erythromycin A ceases after 60+10 hours and the fermenter is harvested.
• the fermentation broth is centrifuged at 20,500 g in an Alpha Laval AS-26 centrifuge. The product is predominantly in the centrate; the centrifuged cell mass is discarded.
• Centrifuged fermentation broth 127 L containing 34 g of the target molecule is passed through 18.3 L of HP20 sorbent packed into an Amicon P350 Moduline 2 chromatography column. At 4 L/min loading, backpressure is found to be less than 5 psi. Following loading, the resin is washed with 20 L deionized water and then 40 L of 30% methanol. 15-Methyl-Erythromycin A is eluted using 54 L of 100% methanol. The product pool is evaporated using a Buchi rotary evaporator (R-152). The solids were dissolved in a minimal amount of 100% methanol, filtered and the filtrate evaporated to dryness.
• R-152 Buchi rotary evaporator
• the methanol solution is loaded onto a HP20SS chromatography column (Kontes) previously washed and equilibrated with 50% methanol. Column dimensions were 4.8 x 115 cm. Column loading with respect to 15- Methyl-Erythromycin A is 11 g/L. The column is washed with 50% (0.8 L) and 60% (8 L) methanol in water. Elution of the target molecule is carried out using 70% (8L), 80% (16 L) and 85% (8 L) methanol in water. 1 L fractions were collected. Fractions 11-29 were combined, evaporated and dried in a vacuum oven giving 23 g of product with 93% purity.
• This material served as starting material for the chemical derivatization procedures described in the following examples.
• the erythromycin A derivatives were not separated from the erythromycin C derivatives; instead, mixtures of the erythromycin A and erythromycin C compounds were used as starting materials for chemical derivatization.
• fermentation broths are brought to pH 8.0 by addition of NaOH and ethanol is added (0.1 L/L broth).
• the broth is clarified by centrifugation and loaded onto an XAD-16 resin (Rohm and Haas) column (1 kg XAD/1 g erythromycin analogs) at a flow rate of 2-4 mL/cm 2 -min.
• the loaded resin is washed with 2 column volumes of 20% (v/v) ethanol in water and the erythromycin analogs are eluted from the resin with acetone and collected in 1/2 column volume fractions.
• the fractions containing erythromycin analogs are identified by thin-layer chromatography (ethyl acetate:hexanes 1:1) and HPLC/MS.
• the acetone fractions containing erythromycin analogs are pooled and the volatiles are removed under reduced pressure.
• the resulting aqueous mixture is extracted with ethyl acetate.
• the ethyl acetate extract is washed with saturated NaH 2 CO 3 and brine solutions, dried over sodium or magnesium sulfate, filtered, and concentrated to dryness under reduced pressure.
• Crude material is dissolved in dichloromethane and loaded onto a pad of silica gel and washed with dichloromethane methanol (96:4 v/v) until the eluent is no longer yellow.
• the desired material is with dichloromethane:methanol:triethylamine (94:4:2 v/v) and collected in fractions. Fractions containing erythromycin are identified by thin-layer chromatography, collected and concentrated under reduced pressure. This material is recrystalhzed from dichloromethane/hexanes.
• 14-Norerythromycin A 9-Oxime A solution of 14-norerythromycin A (0.621 g, 80% pure), hydroxylamine (0.5 ml of 50% aqueous solution) and acetic acid (0.2 ml) in isopropanol (2 ml) was kept at 50°C for 22 hours. It was extracted with chloroform/ethanol (3/2), washed with sodium bicarbonate, brine, and dried over MgSO 4 . Filtration and evaporation in vacuo yielded a crude product (0.65 g) as a white solid which was used directly for next transformation.
• 6-O-Methyl- 14-norerythromycin A 9-oxime A mixture of 6-O-methyl-2',4"- bis-O- trimethylsilyl- 14-norerythromycin A 9-[O-(l-isopropoxycyclohexyl)]oxime (0.29 g), acetic acid (3.6 ml), acetonitrile (6 ml) and water (3 ml) was sti ⁇ ed at ambient temperature for 4.5 hours. The mixture was driven to dryness using toluene to give a crude product as white solid (0.24 g), which was used directly for next step without further purification.
• the oxime from (A) (0.92 g) was dissolved in 6.2 mL of CH 2 C1 2 and treated with 1,1- diisopropoxycyclohexane (1.23 g) and pyridinium p-toluenesulfonate (0.464 gm) for 15 hours at ambient temperature.
• the mixture was diluted with 160 mL of CH 2 C1 2 , then washed sequentially with saturated NaHCO 3 , water, and brine.
• the organic phase was dried with MgSO 4 , filtered, and evaporated to yield a brown syrup. Chromatography on silica gel (gradient from toluene to 1:1 toluene/acetone + 1% Et 3 N) yielded 0.998 g of product.
• the reaction was monitored by thin-layer chromatography (silica gel, 10:1 toluene/acetone), and was judged complete after addition of 1.6 molar equivalents of base.
• the reaction was diluted with 200 mL of ethyl acetate and 70 mL of saturated NaHCO 3 .
• the mixture was transfe ⁇ ed to a separatory funnel, diluted with 850 mL of ethyl acetate and 280 mL of saturated NaHCO 3 , then washed sequentially with water and brine.
• 15-Methylerythromycin A 9-Oxime A suspension of 15-methylerythromycin A (20.0 g, 85%) purity, 22.6 mmol) in 40 mL of 2-propanol was treated with 20.5 mL of 50% aqueous hydroxylamine and sti ⁇ ed until dissolved. Acetic acid (6.41 mL) was added and the mixture was sti ⁇ ed for 15 hours at 50°C. Upon cooling to ambient temperature, saturated NaHCO 3 was added and the mixture was concentrated en vacuo to remove isopropanol. The resulting aqueous mixture was extracted three times with 250-mL portions of CHC1 3 .
• 6-O-Methyl- 15 -methylerythromycin A 9-oxime A solution of 6-O-methyl- 2',4"-bis-O-trimethylsilyl-15-methylerythromycin A 9-[O-(l-isopropoxycyclohexyl)]oxime (21.2 g) in 110 mL of acetonitrile was treated with 55 mL of water and 67 mL of acetic acid, and sti ⁇ ed for 8 hours at ambient temperature. The mixture was concentrated en vacuo, then repeatedly concentrated after addition of toluene to yield 19.7 g of 6-O-methyl- 15- methylerythromycin A 9-oxime.
• 6-O-Methyl- 15-methylerythromycin A A solution of 6-O-methyl- 15- methylerythromycin A 9-oxime (19.7 g) and sodium hydrosulfite (85%, 23J g) in 280 mL of 1:1 ethanol/water was placed under inert atmosphere. Formic acid (3.75 mL) was added dropwise, and the mixture was sti ⁇ ed at 80°C for 4.5 hours. After cooling to ambient temperature, the reaction was treated with saturated NaHCO 3 and extracted three times with 400-mL portions of ethyl acetate. The organic extracts were combined and washed sequentially with saturated NaHCO 3 , water, and brine. The organic phase was dried with MgSO 4 , filtered, and evaporated to yield 15J g of 6-O-methyl- 15 -methylerythromycin A suitable for further conversion.
• A. 5-O-Desosaminyl-6-O-methyl- 14-norerythronolide A A mixture of 6-O- methyl- 14-norerythromycin A (77 mg), 0.073 ml of 12 N HCl and water (2 ml) was sti ⁇ ed at ambient temperature for 3 hours. The mixture was brought to pH 8 with 8 N K ⁇ H, and extracted with ethyl acetate. The organic extract was washed with brine, dried with MgSO 4 , filtered, and evaporated. The residue was chromatographed on silica gel
• R- Benzoyl
• 2'-O-Benzoyl-6-O-methyl-14J 5-dehydroerythromycin A A solution of 6-O-methyl- 14J 5-dehydroerythromycin A (668 mg), benzoic anhydride (385 mg), and triethylamine (0.25 mL) in 3.6 mL of CH 2 C1 2 was sti ⁇ ed for 2 days. After addition of saturated NaHCO 3 , the mixture was extracted three times with CH 2 C1 2 .
• Methanesulfonylchloride (5.68 mL) was added dropwise to a solution of 2'-O-acetyl- 6-O-methyl-3-descladinosyl-3-oxo-15-methylerythromycin A (6.73 g) in 35 mL of pyridine at 0°C. The mixture was brought to ambient temperature and quenched by addition of 700 mL of ethyl acetate and 200 mL of saturated NaHCO 3 . The organic layer was collected and washed sequentially with saturated NaHCO 3 , water, and brine, then dried over MgSO 4 , filtered, and evaporated to yield 8.2 g of crude product.
• the 11, 4"-dimesylated form (190 mg, 0.21 mmol) was dissolved in acetone (7 mL) and DBU (63 L, 0.42 mmol) was added, and the reaction was sti ⁇ ed at room temperature over night.
• the mixture was poured on sodium hydroxide (1 N, 25 mL) and brine (25 mL) and the aqueous layer was extracted with ethyl acetate 6 times.
• the combined organic layers were dried with sodium sulfate, filtered, and the solvent removed in vacuo.
• the crude product, the 10,11-dehydro form of 6-deoxy- 15-methyl erythromycin was carried on to the next step.
• Step 2 A solution of 6-O-allyl-2',4"-bis-O-trimethylsilyl-15-methylerythromycin A 9-[O-(l-isopropoxycyclohexyl)]oxime (8.08 g) in 42 mL of acetonitrile was treated with 21 mL of water and 24 mL of acetic acid, and sti ⁇ ed for 18 hours at ambient temperature. The mixture was concentrated after addition of 2-propanol, then repeatedly after addition of toluene to yield 7.7 g of crude product. Chromatography on silica gel (gradient from 2:1 to 1 :1 hexanes/acetone + 1% Et 3 N) gave 3.75 g of 6-O-allyl-15-methylerythromycin A 9-oxime.
• Step 3 A solution of 6-O-allyl-15-methylerythromycin A 9-oxime (3.75 g) and sodium hydrosulfite (85%, 5.37 g) in 66 mL of 1 : 1 ethanol/water was placed under inert atmosphere.
• Formic acid (0.845 mL) was added dropwise, and the mixture was sti ⁇ ed at 80°C for 3.5 hours.
• the reaction was adjusted to pH 10 with 6 N NaOH and extracted three times with 150-mL portions of ethyl acetate.
• the organic extracts were combined and washed sequentially with saturated NaHCO 3 , water, and brine.
• the organic phase was dried with MgSO 4 , filtered, and evaporated to yield 3.42 g of 6-O- allyl- 15 -methylerythromycin A suitable for further conversion.
• Step 2 A solution of 6-O-allyl-2',4"-bis-O-trimethylsilyl-14-norerythromycin A 9- [O-(l-isopropoxycyclohexyl)]oxime (222 mg) in 4 mL of acetonitrile was treated with 2 mL of water and 2.4 mL of acetic acid, and sti ⁇ ed for 18 hours at ambient temperature. The mixture was concentrated after addition of 2-propanol, then repeatedly after addition of toluene to yield 220 mg of crude 6-O-allyl- 14-norerythromycin A 9-oxime.
• Step 3 A solution of 6-O-allyl- 14-norerythromycin A 9-oxime (220 mg) and sodium hydrosulfite (85%, 322 mg) in 4 mL of 1 J ethanol/water was placed under inert atmosphere. Formic acid (0.050 mL) was added dropwise, and the mixture was sti ⁇ ed at 80°C for 15 hours. After cooling to ambient temperature, the reaction was adjusted to pH 10 with 6 N NaOH and extracted three times with 150-mL portions of ethyl acetate. The organic extracts were combined and washed sequentially with saturated NaHCO 3 , water, and brine. The organic phase was dried with MgSO 4 , filtered, and evaporated to yield 156 mg of 6-O-allyl- 14-norerythromycin A suitable for further conversion.
• Step 1 A mixture of the compound prepared in Example 11, II (77 mg, crude), 0.073 ml of 12 N HCl and water (2 ml) was sti ⁇ ed at ambient temperature for 3 hours. The mixture was brought to pH 8 with 8 N KOH, and extracted with ethyl acetate. The organic extract was washed with brine, dried with MgSO 4 , filtered, and evaporated. The residue was chromatographed on silica gel (3:1 /hexanes: acetone, 1% triethylamine) to give pure product as a white solid (42 mg).
• Step 2 To protect the 2' OH, a mixture the above compound (73 mg), potassium carbonate(20 mg), acetic anhydride (14 ⁇ l) and acetone (1 ml) was sti ⁇ ed at ambient temperature for 18 hours. Ethyl acetate was added, washed with water and brine, dried over MgSO 4 , filtered, and evaporated. The residue was chromatographed on silica gel (3:1 /hexanes: acetone, 1% triethylamine) to yield the pure product (71 mg) as a white solid.
• Step 3 A solution of the compound resulting from step 2 (99 mg) and l-(3- dimethylaminopropyl)-3-ethylcarbodiidmide(EDC) hydrochloride (206 mg) in dichloromethane (2 ml) was treated with DMSO (0.21 ml) and cooled to 5°C. A solution of pyridinium trifluoroacetate (208 mg) in dichloromethane (2 ml) was added via a syringe pump in 4 hours. Ethyl acetate was then added, washed with saturated NaHCO 3 , water, brine, and dried over MgSO 4 , filtered, and evaporated.
• Step 4 To deprotect 2' OH, a solution of the compound resulting from step 3 (94 mg) in 5 mL methanol was sti ⁇ ed at room temperature for 24 hours. The solvent was removed in vacuo to give the desired compound of formula (1) (R a is OH, R c is H, R d is CH 3 , and R f is allyl).
• Example 13 Preparation of Compounds of Formula (2)
• the compound of formula (3) prepared as the 6-allyl derivative in Example 11, is protected at the 2' position, treated with acid and dehydrated, then deprotected to obtain the compound of formula (2), as shown in Figure 1, wherein R a is OH, R c is H, and R f is allyl.
• compounds of formula (1) wherein R d is propyl, butyl, benzyl, vinyl, or 3-hydroxybutyl are prepared as described above using as starting material the compounds of formula (I) wherein R d is as set forth above.
• Example 15 Conversions at -OR f
• reaction mixture is taken up in ethyl acetate and washed with aqueous 5% sodium carbonate, aqueous 2% tris(hydroxymethyl)aminomethane, and brine, dried over sodium sulfate, filtered, and concentrated in vacuo. Chromatography on silica gel (95:5:0.5 dichloromethane-methanol-ammonia) followed by a second chromatography (50:50:0.5 acetone-hexanes-triethylamine) gives the desired compound as a white foam.
• G. -CH 7 CHO ⁇ -CH Z CH 2 NHCH Z CH 2 -Phenyl: To a 0°C solution in methanol (10 mL) of the compound prepared in B (0.200 mmol) is added acetic acid (114 ⁇ L, 2.00 mmol) and phenethylamine (218 ⁇ L, 2.00 mmol) and the mixture sti ⁇ ed for 10 minutes. Sodium cyanoborohydride (24.8 mg, 0.400 mmol) is added and the reaction mixture sti ⁇ ed for 16 hours.
• reaction mixture is taken up in ethyl acetate and washed with aqueous 5% sodium carbonate, aqueous 2% tris(hydroxymethyl)aminomethane, and brine, dried over sodium sulfate, filtered, and concentrated in vacuo. Chromatography on silica gel (90:10:0.5 dichloromethane-methanol-ammonia) gives the desired compound.
• reaction mixture is taken up in ethyl acetate and washed with aqueous 5% sodium carbonate, aqueous 2% tris(hydroxymethyl)aminomethane, and brine, dried over sodium sulfate, filtered, and concentrated in vacuo. Chromatography on silica gel (95:5:0.5 dichloromethane-methanol-ammonia) gives the desired compound.
• reaction mixture is then warmed to 60°C for 0.5 hours and sti ⁇ ed at 80°C for 12 hours, taken up in ethyl acetate and washed twice with aqueous 5% sodium bicarbonate, once with aqueous 2% tris(hydroxymethyl)aminomethane, and once with brine, dried over sodium sulfate, filtered, and concentrated in vacuo. Chromatography on silica gel (95:5:0.5 dichloromethane-methanol-ammonia) gives the desired compound.
• Deprotection is accomplished by heating in methanol.
• -CH 2 CH CH-(7-benzimidazolyl).
• a solution of 15-azidoerythromycin A (7.75 g, 10 mmol) in 50 mL of methanol is treated with acetic acid (2.0 mL) and 10% palladium on carbon (0J g) and sti ⁇ ed under 1 atm of hydrogen gas until thin-layer chromatographic analysis reveals complete reduction of the starting material.
• the suspension is filtered through Celite to remove the catalyst, then evaporated to dryness to yield the product, which is used as a starting material for the following derivatizations.

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