“…11 The relative configuration of psammaplysin A (1) was first determined as (6S*,7S*) in 1985 by single-crystal X-ray crystallographic analysis of its diacetyl derivative (2). 3 Subsequent reports on the relative configuration of psammaplysins C−H were made by comparing their specific rotation values with those of psammaplysin A, 4,8,9,11,12 by chemical shift comparisons, [5][6][7]11 or by ROESY/NOESY correlation data. 8−10 The potent biological activities of the psammaplysins, together with their unusual 1,6-dioxa-2-azaspiro [4.6]undeca-2,7,9-triene motif, clearly justify efforts to resolve their absolute configuration, an aspect of their structure elucidation that could not be pursued in the original X-ray crystallographic work due to inferior crystal quality.…”