PHYCOCHEMICAL STUDIES ON TWELVE COMMON SPECIES OF GREEN SEAWEEDS FROM THE COAST OF KARACHI

Twelve commonly occurring coenocyte and saponaceous species of marine benthic algae i.e. Bryopsis pennata Lamouroux, Caulerpa chemnitzia (Esper) Lamouroux, Ca. faridii Nizamuddin, Ca. manorensis Nizamuddin, Ca. racemosa (Forsskal) 1. Agardh, Ca. taxifolia (Vahl) C. Agardh, Chaetomorpha antennina (Bory de Saint-Vincent) Kutzing, Cladophora uncinella Harvey, Codium decorticatum (Woodward) Howe, Co. flabellatum Nizamuddin, Co. iyengarii Borgesen and Valoniopsis pachynema (Martens) Borgesen, belonging to four different orders of the class Bryopsidophyceae of the division Chlorophyta, have been collected from the intertidal region at different coastal areas near Karachi (Pakistan) and investigated taxonomically as well as phycochemically. Although, all of them are taxonomically known species, but they have been studied phycochemically for the first time. Codium decorticatum is a new report from this region and Co.decorticatum, Co.flabellatum and Co. iyengarii have been described for the first time from the coast of Pakistan.Altogether 50 different fatty acids were detected in the methanolic or etlanolic extracts of these algal species and analysed as methyl esters qualitatively as well as quantitatively through GLC and GC-MS techniques. Twenty-two saturated fatty acids including one dicarboxylic (malonic) acid and 28 unsaturated fatty acids including 16 monoenoic, five dienoic, five trienoic and two monoynoic acids were identified. They included one saturated hydroxy (2,3-hydroxy propanoic) and four substituted unsaturated fatty acids. Unsaturated fatty acids were found to be present in larger proportion (46.65-74.31%) than the saturated ones (25.64-53.32%). The acids detected were mostly with 9-29 C atoms. Their compositions varied not only from genus to genus but also from species to species, the predominant acids also varied from species to species. Valoniopsis pachynema exhibited the greatest diversity with 30 acids, while Chaetomorpha antennina appeared to be the least diverse specie, with 10 fatty acids only.Although, no fatty acid could be detected in all the investigated species, myristoleic, palmitic and stearic acids were present in 11 species and heptadecylenic, oleic, nonadecylenic and liguoceric acids in nine species. No characteristic difference was observed between members of the four investigated orders. In general, Bryopsidophyceaeappeared to be characterized by a wide variety of saturated and unsaturated fatty acids of all chain lengths and all degrees of unsaturation. The C3:0, C7:0, C8:0, C9:0, C9:2, C10:0, C11:0, C11:3, CI2:0, C13:I, CI3:2, CI6:1, C27:0, C29:0, C29:l and C29:3 acids were present in one to three species only, they are highly uncommon and of poor occurrence in Bryopsidophyceae, which differ from the general pattern of green seaweeds (Chlorophyta).Apart from that 13 sterols, two sterol derivatives and six acyclic diterpenes have been isolated from these green seaweeds, purified and their structures elucidated chemically through standard spectroscopic methods e.g. IR & UV, EI-, FAD-, FD- & HR-MS, 1H- & l3C-NMR and COSY-45 & 20 1H-l3C chemical shift experiments. Different C27 sterols including nine with cholesta skeleton a11 d six with stigmasta skeleton have been extracted and identified. They also included two sterol derivatives, out of which one was a glycoside (clerosterol galactoside). The sterols with cholesta skeleton included six 24-derivatives, a 4,4, 14-trimethyl sterol (cycloartanol) and an acetate derivative (cholestryl acetate). Cholesterol was the most common sterol in all the investigated species, it was found in eight species. Clerosterol appeared to be the characteristic sterol of the genus Codium, all the three species contained this sterol as well as its galactoside.Codium decorticatum was found to be very rich in sterol contents, seven different sterols were detected in this species.Six different acyclic diterpene alcohols including phytol have also been obtained and chemically elucidated. Codium decorticatum appeared to be very rich in diterpenoids as it contained four such compounds, while rest of the seaweed species did not contain more than two. Trans-phytol is tile most common diterpenoid and was detected in five different species, while others were present either in two or only one species.Certain new and novel compounds have been isolated and identified from these algae: e.g. malonic, l2-tridecynoic and 12-metlloxy-4-hexadecynoic acids from Codium iyengarii 2,3-dimethoxy-12-propanoic acid from Caulerpa chemnitzia, Codium decorticatum and Co. flabellatum; heptylic acid from Chaetol1lorpha antennina, Codiul1I flabellatum and Co. iyellgarii; 3,8-dimethyl-2,7-nonadienoic acid from Codium flabellatum and Valoniopsis pachynema; 24-metllyl-cholesta-7,22-diene-3β-01 and 4,24dimetllyl-cholesta-5,22-diene-3β-01 from Caulerpa faridii decortinone, decortinol, isodecortinol and 3,7,1l,15-tetramethyl-hexadecan-l,2-diol from Codium decorticatum;3,7,11,15-tetramethyl-hexadec-3-en-1,2-diol from Caulerpa chemnizia and Codium decorticatum; [2,3]-epoxide-3,7,11,15-tetramethyl-hexadecan-I-ol from Valoniopsis pachynema and clerosterol galactoside from Codium decorticaum, Co. flabellatum and Co. iyellgarii. CodiulII decorticaum appeared to be a unique alga, it revealed the presence of seven novel natural products, out of which four chemical constituents were not found in any other species and six were the new compounds.All the natural products isolated have been reported for the first time from the corresponding algal species. The decortinone, decortinol and isodecortinol among sterols, 3,7, 11, 15-tetrametyl-hexadecan-I,2-diol, 3,7,11,15-tetrametyl-hexadec-3-en1,2-diol and [2,3]-epoxide-3,7,1l,15-tetramethyl-hexadecan-1-ol among diterpenes and clerosterol galactoside among glycosides Were the new compounds, isolated for tile first time /Tom a natural source. The phycochemistry of Bryopsidophyceae appeared to be quite promising, several new as well as novel and unique secondary metabolites and chemical constituents have been isolated from them. It appears that the siphonaceous and coenocytic thallus has a peculiarity of some kind in its metabolism, which results in the biosynhesis of specialized natural products.