Described is a process for producing a new immunosuppressant, a C-31 desmethyl, C-19/C-22 cyclic hemiketal biotransformation analog (Compound I) of FR-900520, under novel fermentation conditions utilizing the novel microorganism, Streptomyces, lavendulae ATCC No. 55209. Also disclosed is the C-31 methylated derivative (Compound II) of Compound I produced by enzymatic methylation using 31-O-desmethylimmunomycin O-methyl transferase, (DIMT), a methyl transferase enzyme. The macrolide immunosuppressants are useful in preventing human host rejection of foreign organ transplants, e.g. bone marrow, liver, lung, kidney and heart transplants.