Diketopiperazines from Rhabdastrella globostellata

From the methanol extract of the Vietnamese marine sponge Rhabdastrella globostellata (Carter, 1883), four diketopiperazines (1-4) and one indol alkaloid (5) were isolated by various chromatographic methods. Their chemical structures were identified to be cyclo-(L-Pro-L-Ile) (1), cyclo-(L-Pro-L-Leu) (2), cyclo-(D-Pro-L-Ile) (3), cyclo-(L-Pro-L-Phe) (4), and tryptophol (5) by using a combination of ESI-MS, 1D and 2D NMR spectral data as well as by comparison with previous literature. This is the first report of these compounds from Rhabdastrella globostellata.