Isomalabaricane triterpenes with potent protein-tyrosine phosphatase 1B (PTP1B) inhibition from the Hainan sponge Stelletta sp.

A new isomalabaricane triterpene, stellettin N (1), has been isolated together with five known analogues, stellettin H (2), rhabdastrellic acid A (3), stellettin G (4), stellettin D (5), and 22,23-dihydrostellettin D (6), from the Hainan sponge Stelletta sp. The structure of 1 was elucidated on the basis of detailed spectroscopic analysis of its methyl ester (7) and by comparison of NMR data of 7 with those of related known compounds. Compounds 3-8 were evaluated for their inhibitory activity against hPTP1B and the result showed compound 4 had a strong hPTP1B inhibitory activity with IC50 value of 4.1 +/- 0.9 mu M. Compound 4 also exhibited weak cytotoxicity against A549 and HL-60 cells at a concentration of 10 mu M. Furthermore, the chemotaxonomic significance of these compounds was also summarized. (c) 2013 Elsevier Ltd. All rights reserved.