32 光学活性グリシンの合成とランカシジンの生合成研究

抄録

A chirality transfer approach was developed for the preparation of chiral glycine which was supposed to be a key substrate for the stereochemical studies of the biosynthesis of unique 17-membered carbocyclic antibiotics lankacidins. This approach is comprised from conversion of acetylene (HC≡CH) into chiral glycine (H_2N-H-C-^2H-COOH) via: 1) addition of acetylene to a chiral ketone 2; 2) stereospecific ^2H introduction during the reduction of the acetylene 3 to olefins (e.g. 5); 3) epoxidation followed by introduction of a nitrogen functionality; and 4) oxidative cleavage of the resulting glycol (e.g. 8) and further oxidation to the desired chiral glycine derivatives (e.g. 10). Also described was a new access to chiral acetic acid from the above-mentioned epoxides (e.g. 6 and 7) by the use of stereospecific reduction with tritiated LiAlH_4 and oxidation. Simultaneous feeding of [1-^<13>C]- and [^2H_5]glycine to the fermentation of a lankacidin producing Streptomyces strain was undertaken to clarify the behavior of hydrogen atoms of glycine during the formation of its 17-membered carbocyclic system and no deuterium incorporation was observed into the H-3 position in contrast to apparent ^<13>C enrichment at the C-4 position. A mechanism suggested is the formation of an 18-membered carbocyclic intermediate prior to the ring contraction to the 17-membered ring probably via a Favorskii-type rearrangement analogous to the biosynthetic mechanism of polyketide δ-lactones such as an Aspergillus pyrone (aspyrone) and vulgamycin.