Clerodane Diterpenes from the Marine Sponge Collected in South Brazil.

The marine sponge , collected in South Brazil, was selected for detailed investigation considering the results of a screening that pointed to an in vitro antiproliferative effect against non-small cells of human lung cancer (A549) and anti-herpes activity against type 1 (KOS and 29R strains) of ethanolic extracts. The fractionation and chemical investigation of the sponge's hexanic fraction led to the isolation and structural elucidation of six clerodane diterpenes. The main component was identified as the already-reported raspailol (), isolated from a sponge of the same genus collected in New Zealand. The structure of a new diterpene () with a rearranged skeleton was established by high-resolution mass spectrometry (HRMS) and 1D and 2D Nuclear magnetic resonance spectroscopy (NMR) experiments, and named here as raspadiene. Furthermore, four diterpenes were elucidated as isomers of clerodane diterpenes previously obtained from plants, namely kerlinic acid (), kerlinic acid methyl ester (), annonene (), and 6-hydroxyannonene (). They differ in their stereochemistry, since these diterpenes are characterized by a ring fusion at the decalin moiety and the relative configuration of the two methyl groups at C-8 and C-9 in a relationship (type ). The diterpenes have a ring fusion at the decalin moiety, and the two methyl groups at C-8 and C-9 are in a relationship (type /). The isolated compounds were evaluated for their potential antiproliferative effects on human cancer cell line A549, and it was observed that the diterpenes bearing a hydroxyl group at C-6 exhibited moderate cytotoxic activity, with 50% inhibitory concentration (IC) values lower than 25 μM. The evaluation of the potential anti-herpes activity against type 1 (HSV-1, KOS and 29R strains) showed that the more promising results were observed for the new compound , since it inhibited HSV-1 (KOS and 29R strains) replication by 83% and 74%, respectively.