Ascomycin (I) was protected as the C24,C32-bis(tert-butyldimethyl- silyl)ether (II), and then was selectively desilylated at the C32 position with p-toluenesulfonic acid in MeOH-CH2Cl2. The resulting monosilylated compound (III) was treated with allyl trichloroacetimidate (IV) and trifluoromethanesulfonic acid to provide the C32 allyl ether (V). Subsequent dihydroxylation of the allyl group of (V) using N-methylmorpholine-N-oxide in the presence of a catalytic amount of OsO4 afforded glycol (VI), and further oxidative cleavage of (VI) with sodium metaperiodate produced aldehyde (VII).

The aryl imidazole (IX) was then constructed by cyclization of (VII) with 3,5-dimethoxyphenylglyoxal (VIII) and ammonia in MeOH yielding (IX). Finally, the title compound was obtained by desilylation of (IX) with HF in pyridine-THF.

The aryl imidazole (IX) was then constructed by cyclization of (VII) with 3,5-dimethoxyphenylglyoxal (VIII) and ammonia in MeOH yielding (IX). Finally, the title compound was obtained by desilylation of (IX) with HF in pyridine-THF.

In a further procedure, 3,5-dimethoxybenzoic acid (X) was converted to the acetophenone (XI) using methyllithium. Treatment of (XI) with phenyltrimethylammonium tribromide provided the dibromoacetophenone (XII) which, upon reaction with morpholine at 55 C, followed by hydrolysis with aqueous HCl, gave the phenylglyoxal (VIII). Alternatively, (VIII) was prepared directly by treating acetophenone (XI) with DMSO and HBr or by oxidation with SeO2. Condensation of the phenylglyoxal (VIII) with methyl glyoxylate hemiacetal (XIII) and ammonium acetate produced the phenylimidazole (XIV), which was protected as the tetrahydrofuranyl derivative (XVI) with dihydrofuran and catalytic p-TsOH. Reduction of the protected imidazole ester (XVI) with LiBH4 provided alcohol (XVII), and then reaction of (XVII) with trichloroacetonitrile in the presence of DBU furnished the acetimidate (XVIII). Finally, the target compound was obtained by reaction of ascomycin (I) with trichloroacetimidate (XVIII) in the presence of fluoboric acid etherate, followed by hydrolytic deprotection.

The aryl imidazole (IX) was then constructed by cyclization of (VII) with 3,5-dimethoxyphenylglyoxal (VIII) and ammonia in MeOH yielding (IX). Finally, the title compound was obtained by desilylation of (IX) with HF in pyridine-THF.

The cyclization of 2-(3,5-dimethoxyphenyl)glyoxal monohydrate (I) with methyl glyoxylic acid (II) and ammonium acetate in acetonitrile gives the aryl imidazole (III), which is protected with dihydrofuran (IV) and Ts-OH, yielding compound (V). The regioselective lithiation of (V) with n-BuLi, followed by reaction with labeled 14CO2 provides the carboxylic acid (VI), which is esterified with MeI and CaO in DMSO to furnish the methyl ester (VII). The reduction of the ester group of (VII) with LiBH4 affords the carbinol (VIII), which is esterified with trichloroacetonitrile (IX) to provide the trichloroacetimidate (X).

The condensation of (X) with ascomycin (XI) by means of CF3SO3H in N,N-dimethylpivalamide gives the adduct (X), which is finally deprotected with hot aqueous CF3SO3H.

The cyclization of 2-(3,5-dimethoxyphenyl)glyoxal monohydrate (I) with methyl glyoxylate hemiacetal (II) and ammonium acetate in acetonitrile gives the imidazole derivative (III), which is protected with dihydrofuran (IV) and TsOH, yielding compound (V). The reduction of the ester group of (V) with LiBH4 affords the carbinol (VI), which is esterified with trichloroacetonitrile (VII) to provide the trichloroacetimidate (VIII). The condensation of (VIII) with ascomycin (IX) by means of CF3SO3H in N,N-dimethylpivalamide gives the adduct (X), which is finally deprotected with hot aqueous CF3SO3H.