NOVEL SPONGE-DERIVED AMINO-ACIDS .11. THE ENTIRE ABSOLUTE STEREOCHEMISTRY OF THE BENGAMIDES

The complete stereochemistry of bengamides A (1) and B (2) can be assigned as 5i?,6S,7/?,8i?,10S,13S, and this absolute stereochemistry can also be extended to other bengamide derivatives C, D, E, and F (3–6) and isobengamide E (7). The absolute stereochemical results were obtained by isolating a monohydroxy lactone 12, which was then converted to dihydroxy lactone 11. The relative stereochemistry of 11 had been previously shown to be the same as that of the 2-methoxy-3,4,5-trihydroxy-8-methylnon-6tE)-enoyl side chain (A) in the bengamides. The absolute stereochemistry of lactone 12, deduced by esterifying with O-methylmandelic acids followed by an analysis of their different 1H NMR chemical shifts, gave the absolute configuration of the stereocenters in A. Combining the new assignments with those obtained previously for the δ-hydroxycaprolactam moiety of the bengamides completed assignment of the absolute configuration at all chiral sites. © 1990, American Chemical Society. All rights reserved.