Stereochemistry of Sagittamide A from Residual Dipolar Coupling Enhanced NMR

Abstract

Sagittamide A is a long-chain acyclic α,ω-dicarboxylic acid with eight stereocenters. The central hexahydroxyhexane moiety carries six of them. For this moiety, two different relative stereochemical assignments were published in 2006. In this communication, one relative configuration is clearly singled out based on NOEs, J- and residual dipolar couplings despite conformational averaging that is present in this moiety. The proposed NMR method relies on the measurement of dipolar couplings in recently introduced alignment media that are compatible with organic solvents, and cross validating the NMR determined ensemble of conformations against the residual dipolar couplings. The method is easily applicable to many other stereochemical problems.