合成路线1

Treatment of cis-oxazolidine derivative (I) with isobutyraldehyde (II), LDA and LiBr in THF yields aldol product (III), which is then converted into (IV) by first aminal cleavage by means of MeOH and TfOH, followed by silylation with Tbdms-Cl and imidazole in DMF. Reaction of (IV) with formaldehyde and TsOH in benzene gives oxazolidine system (V), which is then first reduced with LiBH4 in THF/MeOH and then oxidized by means of DMSO, oxalyl chloride and Et3N in CH2Cl2 to provide aldehyde (VI). Mukaiyama aldol coupling of (VI) and (VII) in CH2Cl2 with MgI2 as catalyst, followed by treatment with K2CO3 in MeOH, yields aldol product (VIII), which is then converted into hydroxy lactam (IX) by the sequence: i) N-benzyl cleavage by hydrogenolysis over Pd/C in EtOH in the presence of DIEA; ii) ring closure by heating in MeOH; and iii) desilylation by treatment with HF in acetonitrile. Conversion of alcohol (IX) into dihydroxy acid (X) is achieved by a first oxidation with DMSO, oxalyl chloride and Et3N in CH2Cl2, followed by reaction with NaClO2, NaH2PO4 in t-BuOH and 2-Me-butene and final N/O methylene bridge removal with 1,3-propanedithiol (A) catalyzed by HCl and TFA. Compound (X) undergoes beta-lactonization to omuralide (XI) by means of BOPCl and Et3N in CH2Cl2 and finally (XI) is coupled to N-acetyl-L-cysteine (XII) in CH2Cl2 in the presence of Et3N.