Secondary Metabolites of the Marine Sponge Penares cf. schulzei, Fluorescence Properties of 24-Methylenecholesta-4,6,8(14)-Trien-3-One

Abstract

Marine sponges of the genus Penares are known as sources of various low-molecular-weight secondary metabolites including bioactive indoles, azetidine alkaloids [1], unusual triterpenoids [2, 3], proline-containing macrolides [4], and sphingolipids [5]. In continuation of our research on natural compounds from sponges of this genus inhabiting the littoral waters of Vietnam [6,7], we communicate about slightly polar components of the EtOH extract of P. cf. schulzei (dry weight 22.1 g) collected during an expedition of the RV Akademik Oparin near the shores of Vietnam. We isolated and elucidated the structures of five ketosteroids. The composition of the low-molecular-weight metabolites of the sponge was studied for the first time.Compounds 1, 2, and 3 (6.7, 2.1, and 6.4 mg) were isolated by combined column chromatography over Sephadex LH-20 (CHCl 3 -MeOH, 1:1) and silica gel (n-hexane-EtOAc, 4:1) followed by reversed-phase HPLC over a YMC-Pack ODS-A column (9.4 u 250 mm, EtOH-H 2 O, 98:2). Ketones 4 and 5 (1.3 and 2.3 mg) were also obtained pure after rechromatography of the respective fractions over a normal-phase Ultrasphere TM Si column (9.4 u 250 mm; hexane-EtOAc, 5:1 for 4 and CHCl 3 -EtOH, 300:1 for 5).The structures of compounds 1-4 were elucidated using NMR spectroscopy and GC-MS as 24-methylenecholest-4-ene-3,6-dione (1) and cholest-4-ene-3,6-dione (2) [8], ergosta-4,24(28)-dien-3-one (3) and cholest-4-en-3-one (4) [9, 10]. Compounds 1, 2, and 4 were not observed earlier in sponges of the genus Penares. We isolated compound 3 from a Penares sp. of sponge [7].The PMR spectrum of 5 exhibited a series of methyl resonances at 0.96 contained a peak for the molecular ion [M + H] + (m/z 393.3154) that corresponded to the formula C 28 H 40 O. A comparison of the experimental results and the literature on 5 identified it as 24-methylenecholesta-4,6,8(14)-trien-3-one. At present, only anecdotal instances of the isolation of ketosteroids with a similar unusual core are known from natural specimens [11][12][13]. 24-Methylenecholesta-

Oxysterols from a Marine Sponge Inflatella sp. and Their Action in 6-Hydroxydopamine-Induced Cell Model of Parkinson’s Disease

“…The search for new oxysterols in marine organisms and the studies on their action in model cell systems could be also considered as an approach to the creation of new pharmaceutical leads against neurodegenerative diseases. As a part of our chemical investigations of steroidal compounds from marine sponges [ 9 , 10 , 11 ], we have studied oxysterols of a cold-water marine sponge Inflatella sp. The sponges belonging to the genus Inflatella are insufficiently studied for their secondary metabolites, though some bioactivities of their extracts were noted [ 12 ].…”