Abstract
Fractionation and purification of the ethyl acetate extract of the culture of a sponge-derived actinomycete,
species Call-36, resulted in the isolation and identification of a new diketopiperazine, actinozine A (
), cyclo(2-OH-d-Pro-l-Leu) (
), two new nucleosides, thymidine-3-mercaptocarbamic acid (
) and thymidine-3-thioamine (
), together with cyclo(d-Pro-l-Phe) (
) and cyclo(l-Pro-l-Phe) (
). The structure assignments of the compounds were carried out by interpretation of 1D and 2D NMR data and mass spectral determinations. The absolute configurations of
and
were determined by Marfey's method and by comparison of the experimental and TDDFT-calculated ECD spectra. Actinozine A possesses an unprecedented hydroperoxy moiety at C-2 of the proline moiety, while
and
possess unusual mercaptocarbamic acid and thiohydroxylamine functionalities at
-3 of the thymine moiety. The isolated compounds displayed variable cytotoxic and antimicrobial activities.