Leucomycin A7 (I) was selectively esterified at the 2'-hydroxyl group with acetic acid in acetonitrile at room temperature to afford acetate (II). Subsequent reaction with tert-butyldimethylsilylchloride (TBDMS-Cl) and imidazole effected cyclization to the hemiacetal between aldehyde and the 3-hydroxyl group, and simultaneously protected as silyl ethers the hemiacetalic and the 9-hydroxyl groups. From this compound (III), propionic ester of 4''-position was selectively hydrolyzed on treatment with NaOH under phase-transfer conditions, and the resulting alcohol was esterified again with n-valeryl chloride in pyridine to the 4''-valeryl ester (IV). Further treatment with acetic anhydride in dimethyl sulfoxide introduced a methylthiomethyl group into tertiary hydroxyl group at 3''-position yielding (V).

Then, the 2'-acetyl group of (V) was cleaved on treatment with MeOH at 40 C to afford VI, and the methylthiomethyl ether was reduced to the 3''-methoxy compound (VII) with an excess of Raney Nickel in ethanol. Finally, treatment with tetrabutylammonium fluoride (TBAF) in tetrahydrofuran effected hydrolysis of the silyl ethers and opened the cyclic hemiacetal to afford the title compund, which was purified by preparative TLC.