Racemosin C, a novel minor bisindole alkaloid with protein tyrosine phosphatase-1B inhibitory activity from the green alga Caulerpa racemosa

Abstract

A novel minor bisindole alkaloid, racemosin C (1), characterized by a naturally unprecedented 8-hydroxy-2,4,6-cyclooctatrienone ring fused with two indole systems, was isolated from the green alga Caulerpa racemosa, together with one known related metabolite, caulersin (2). The structure of 1 was elucidated on the basis of extensive spectroscopic analysis, and by comparison with the data of related known compounds. A plausible biosynthetic pathway of 1 was proposed. Compounds 1 and 2 exhibited significant PTP1B inhibitory activity with IC₅₀ values of 5.86 ± 0.57 and 7.14 ± 1.00 μM, respectively, compared with the positive control oleanolic acid (IC₅₀ = 3.03 ± 0.20 μM). On the basis of the data obtained, the Caulerpa bisindole alkaloids may be considered as a new class of PTP1B inhibitors.

Keywords::

• green alga
• Caulerpa racemosa
• bisindole alkaloid
• racemosin C
• PTP1B inhibitory activity

Acknowledgments

This research work was financially supported by the National Natural Science Foundation of China (Nos 81001397, 21162016, and 21362024), the Young Scientists Training Program of Jiangxi Province (No. 20133BCB23004), and the Natural Science Foundation of Jiangxi Province (No. 20114BAB205034). We are also grateful to Dr Yan Luo (Ocean University of China) for identification of the alga.

Notes

^1. These authors contributed equally to the work.