Determination of the Absolute Configurations of Microtermolides A and B

Absolute configurations of the three consecutive chiral centers in the cyclic depsipeptide microtermolide A have been tentatively assigned as 2'''R, 3'''R, and 4'R. However, on the basis of a structural comparison with vinylamycin, another depsipeptide with a unique 4-amino-2,4-pentadienolate structure, the chiral centers could also be assigned as 2'''R, 3'R, and 4'S. Here, the first total synthesis of microtermolide A is reported and the configurations of the three consecutive chiral centers were confirmed to be 2'R, 3'R, and 4'S. A similar approach was used to determine the analogous centers in microtermolide B as 2'R, 3'R, and 4'S.