Semisynthetic ∊-Isorhodomycins: Glycosylation and Modification Reactions1

The syntheses of 7-O-α-L-daunosaminyl-∊-isorhodomycinone (6) and 7-O-α-L-rhodosaminyl-∊-isorhodomycinone (7) are described. The glycosyl donors 1,4-di-O-p-nitrobenzoyl-3-N-trifluoroacetyl-α,β-L-daunosamine and 1,4-di-O-acetyl-α,β-L-rhodosamine have proven to be the most suitable for the glycosylation of ∊-isorhodomycinone (∊-iso RMN) (3), using the TMS triflate method. Deblocking (0.5 N NaOH) of the protected glycoside 4 led to the desired 7-O-glycosyl-∊-isorhodomycinones 5 and 6. The daunosaminyl glycoside 6 was methylated (CH2O, NaCNBH3) to provide the rhodosaminyl derivative 7. The photolytic demethylation of this product selectively provided the 7-O-(3′-N-methyl-α-L-daunosaminyl)-∊-isorhodomycinone (8).