Stereoselective Synthesis of Unnatural Stereoisomers of LL-P880[beta] and LL-P880[gamma], Pestalotin Analogues from Penicillium sp

A synthesis of unnatural stereoisomers of LL-P880β (2) and subsequent transformation of 2 into LL-P880γ (3) were achieved by starting from diacetoneglucose (4). A chiral building block, 5-deoxy-α-D-ribofuranose derivative 9, was derived from 4 by two synthetic routes. A chiral aldehyde (20) was prepared through a six-step sequence from 9, and treated with the dianion of methyl acetoacetate to complete the synthesis of (6S, 1'R, 2'R)-LL-P880β (2a) and its C6-epimer (2b). After converting 2a to its diacetate (23), this was transformed into (1'R, 2'R)-LL-P880γ (3a) via a 5-bromopyran derivative (24).