A new anthraquinone and a new naphthoquinone from the whole plant of Spermacoce latifolia

Abstract

A phytochemical study on the whole plant of Spermacoce latifolia led to the isolation of a new anthraquinone, 1,2,6-trihydroxy-5-methoxy-9,10-anthraquinone (1), and a new naphthoquinone, (2R)-6-hydroxy-7-methoxy-dehydroiso-α-lapachone (2), together with three known anthraquinones (3-5). Their structures were established on the basis of detailed spectroscopic analysis, including one- and two-dimensional NMR, ESI-MS, and HR-ESI-MS techniques. All the compounds were isolated from S. latifolia for the first time. Compounds 1, 2, 4, and 5 showed significant antibacterial activity toward Bacillus subtilis with MIC values ranging from 0.9 to 31.2 μg/ml, and compound 4 aslo exhibited antibacterial activity against Bacillus cereus with a MIC value 62.5 μg/ml. Compound 1 was further revealed to show significant in vitro α-glucosidase inhibitory activity with IC₅₀ value of 0.653 mM.

Keywords: Rubiaceae; Spermacoce latifolia; anthraquinone; antibacterial activity; naphthoquinone; α-glucosidase inhibitor.