Absolute stereochemistry of the (+)-enantiomer of keramaphidin B (1) was established to be 1R, 4S, 4aR, and 8aS on the basis of H-1 NMR data of the MTPA esters of 9,10-dihydroxy-15,16,23,24-tetrahydrokeramaphidin B (3). Copyright (C) 1996 Elsevier Science Ltd