Resolution of the Confusion in the Assignments of Configuration for the Ciliatamides, Acylated Dipeptides from Marine Sponges.

Direct comparison of authentic ciliatamide A with four synthetic isomers (1-4) by means of NMR and chiral-phase HPLC revealed that ciliatamide A possesses the 12R (d-N-MePhe residue) and 22S (l-Lys residue) configurations, which were not identical with either our previous assignment or those proposed by others through total synthesis. The absolute configuration of the methionine sulfoxide residue in ciliatamide D was also revised to be d.