NOTE Two new indole derivatives from a marine sponge Ircinia sp. collected at Iriomote Island Delfly B. Abdjul • Hiroyuki Yamazaki • Kazuyo Ukai • Michio Namikoshi Received: 26 October 2014 / Accepted: 5 February 2015 Ó The Japanese Society of Pharmacognosy and Springer Japan 2015 Abstract Two new indole derivatives, 5-hydroxy-1H- indole-3-carboxylic acid ethyl ester (1) and 5-hydroxy-1H- indole-3-glyoxylate ethyl ester (2), and seven known indole alkaloids, dragmacidonamine B (3), gesashidine A (4), hyrtiosulawesine (5), hyrtiomanzamine (6), hyrtimomine D (7), hyrtiosine A (8), and 5-hydroxy-1H-indole-3-car- baldehyde (9), were isolated from a marine sponge Ircinia sp., Irciniidae, collected at Iriomote Island. The structures of 1 and 2 were elucidated on the basis of their spectro- scopic data. Compound 1 has previously been reported as a synthetic intermediate and this is the first time that it has been obtained from a natural source. Keywords Marine natural product Á Indole alkaloid Á Marine sponge Á Ircinia sp. Introduction The ocean covers two-thirds of the earth’s surface and it is estimated that approximately 80 % of the living organisms on earth live in the sea. Marine environments have a high concentration of salt, high pressure, a low concentration of oxygen, and dark conditions, which are quite different from terrestrial environments. Therefore, marine organisms, such as invertebrates, microorganisms, and algae have ac- quired unique metabolic pathways enabling them to pro- duce a wide variety of metabolites, which have possibilities of potential therapeutic applications [1–3]. A number of useful substances possessing diverse biological activities and unique structures have been reported, especially from marine sponges [1–4]. In the course of our screening program searching for antimycobacterial substances from marine invertebrates and microorganisms, we found that the ethanol (EtOH) extract of a marine sponge Ircinia sp. inhibited the growth of Mycobacterium smegmatis. The chemical study on the EtOH extract led to the isolation of two new indole derivatives, 5-hydroxy-1H-indole-3-carboxylic acid ethyl ester (1) and 5-hydroxy-1H-indole-3-glyoxylate ethyl ester (2), along with seven known indole alkaloids, dragmaci- donamine B (3), gesashidine A (4), hyrtiosulawesine (5), hyrtiomanzamine (6), hyrtimomine D (7), hyrtiosine A (8), and 5-hydroxy-1H-indole-3-carbaldehyde (9) [5–10] (Fig. 1). We report here the isolation and structure eluci- dation of two new compounds 1 and 2. Results and discussion The EtOH extract of the marine sponge inhibited the growth of M. smegmatis with an inhibition zone of 9 mm at 50 lg/disc and was separated into seven fractions by an ODS column. Compounds 1 (1.62 mg), 2 (0.72 mg), 3 (21.51 mg), 4 (4.08 mg), 5 (2.22 mg), 6 (2.13 mg), 7 (4.05 mg), 8 (5.85 mg), and 9 (7.99 mg) were isolated from the ODS fractions by preparative HPLC as described in materials and methods. Compounds 3–9 were identified as dragmacidonamine B (3), gesashidine A (4), hyrtiosulawesine (5), hyrtiomanza- mine (6), hyrtimomine D (7), hyrtiosine A (8), and 5-hy- droxy-1H-indole-3-carbaldehyde (9) by comparing the spectroscopic data with the reported values [5–10]. These known compounds have been reported to exhibited antimi- crobial (4 and 7), PLA2 inhibitory (5), immunosuppressive D. B. Abdjul Á H. Yamazaki (&) Á K. Ukai Á M. Namikoshi Faculty of Pharmaceutical Sciences, Tohoku Pharmaceutical University, Sendai 981-8558, Japan e-mail: yamazaki@tohoku-pharm.ac.jp 123 J Nat Med DOI 10.1007/s11418-015-0891-y