Chemical investigation of lipids of a marine sponge Spirastrella vagabunda

Abstract

Sponges are among the simplest of multicellular animals and are often described as the most primitive of all. Study of sponge lipids is as important as other secondary metabolites and has been well documented in a series of extensive reviews by Berge and Barnathan, Rod kina, etc. [1, 2]. Regular research into lipids of sponges began in the 1970s [3] and continues till today because they have the greatest diversity of fatty acids, sterols etc. Studies on fatty acids and sterols as lipid components of sponges and other organisms have been elaborately taken up by a number of investigators [4, 5]. There are only a few investigations on this species, Spirastrella vagabunda. The aqueous extract of this species has shown high phospholipase A2 catalytic activity [6]. The bacteria isolated from this sponge produced acetylcholinesterase, an essential enzyme [7], but no investigation on the chemistry of this species has been done so far. This paper presents a study of the fatty acid profile and sterol composition of the total lipid of S. vagabunda for the first time (Table 1). A significant number of fatty acids were identified by GC-MS. The fatty acids were characterized by linear saturated fatty acids, monobranched saturated fatty acids, polybranched saturated fatty acid, monounsaturated fatty acids, and polyunsaturated fatty acids. The percentage of straight-chain fatty acids was 28.22% of the total fatty acids. Generally, among the saturated fatty acids, C16:0 and C18:0 dominated in most of the sponges. In the present investigation, the main saturated fatty acids are also C16:0 (6.37%) and C18:0 (5.77%). It is interesting that long-chain saturated fatty acids like C23:0, C24:0, C25:0, and C28:0 are present in good quantity in S. vagabunda. S. vagabunda contains the highest percentage of monomethyl branched fatty acids, i.e., 45.5% of the total fatty acid content, as in the marine sponge species Geodia gibberosa, which also contains 40–50% of branched fatty acids [8]. Among these branched fatty acids the amount of 11-methyloctadecanoic acid was significantly high, i.e., 13.31% of the total FA. A long-chain branched fatty acid, i.e., br-24-methylhexacosanoic acid, is also present in good quantity (8.97%). The identification of 11-methyl-18:0 and 24-methyl-26:0 (ante-iso) acids was finally confirmed by comparing their key mass fragments (11-methyl-18:0: m/z 312 M+, 269, 213, 185, 143; 24-methyl-26:0: m/z 424 M+, 381, 339, 199, 266, 143) obtained by GC-MS analysis with their literature data. The presence of saturated isoand ante-iso acids (branched fatty acids) is known to have a bacterial origin [9, 10]. So, the presence of symbiotic bacteria cannot be excluded. 3,7,11-Trimethyldodecanoic acid, a very rarely found polymethyl branched fatty acid, which was earlier identified from the marine sponge Xestospongia muta [11], was reported to be present in S. vagabunda, which is an important finding. The identification of 3,7,11-trimethyldodecanoic acid was confirmed by the key mass fragments at m/z 101 and at m/z 171, which indicate the methyl branching at 3 and 7 position [11]. Generally in various sponge species, the percentage of monoenes varies from 2% to 50% of the total FA content. But in the present investigation, only one monoenic acid C18:1 (2.42%) is identified. C18:1 (9) and C18:1 (11) are the principal isomers of C18 monoenes in sponges [2]. The GC-MS spectrum of the C18:1 showed important mass fragments at m/z 296 (M+), 264, 221, 180, 123, 109, and 96, and by comparing with the literature data, the monoenic acid is identified as C18:1 (9). The polyunsaturated FA of this species is represented by one diene and one trienoic acids with total content of 17.91%.