Absolute Configuration and Conformational Study of Psammaplysins A and B from the Balinese Marine Sponge Aplysinella strongylata.

The absolute configuration of psammaplysin A (1) has been assigned as (6R,7R) using experimental and calculated electronic circular dichroism (ECD) data and NMR analysis of MPA esters prepared from the acetamide derivative of 1. Detailed conformational analyses of a truncated model compound of 1 with an in vacuo method and with the PCM solvent model for MeOH have identified the major conformers and factors governing the ECD spectrum of 1. The correlation of the ECD data with the stereochemistry of 1 allows configurational assignment of related psammaplysin analogues on the basis of their ECD spectra.