Chemotaxonomical evaluation of the red alga Laurencia Nangii Masuda (Rhodomelaceae, Ceramiales) in the coastal waters of Sabah

• Main Author: Tan, Kai Lee
• Format: Thesis
• Language: English; English
• Published: 2009
• Subjects: QK504-(638) Cryptogams
• Online Access: https://eprints.ums.edu.my/id/eprint/10082/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/10082/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/10082/
• Institution: Universiti Malaysia Sabah

Species discrimination in the red alga genus Laurencia is difficult due to a high degree of morphological variation within individual species. Chemical studies on a worldwide basis revealed that most species of Laurencia can be characterized by a specific set of halogenated secondary metabolites. Some species, however, produce unrelated sets of metabolites depending on geographical distribution. The morphologically similar but chemical distinct populations can be referred to as sibling species or chemical races. This study was carried out to identify the halogenated secondary metabolites that can be utilized as taxonomic markers for Laurencia nangii Masuda. Samples of L. nangii from three localities: Pulau Sulug, Kota Kinabalu; Pantai Bak-Bak, Kudat; and Dogoton, Pulau Banggi, Kudat were investigated. Voucher herbarium specimens of each population (BORH 37572- 37577, 37587-37588) were deposited in the Borneensis Collection in the Institute for Tropical Biology and Conservation. Plants are purplish-green in colour and attain height of 3 - 6.5 cm, with several upright axes arise from discoid holdfast and stolon-like branches. Microscopy study showed that superficial cortical cells contain two to three corps en cerise, while trichoblast cells contain one or two corps en cerise. Tetrasporangia are formed on all four orders of branches and measure 100 - 120 µm in diameter. Ovoid cystocarps are formed on first- to fourth-order branches, measure 550 - 800 µm in height by 500 - 750 µm in diameter. Male trichoblasts are formed in the cup-shaped apical depression of first- to fourth-order branches. Samples were extracted and the crude extracts from these three populations showed different chemical profiles on TLC and RP-HPLC. Crude extracts were fractionated by column chromatography and isolation of secondary metabolites was carried out via RP-HPLC. The structures of the isolated compounds were deduced from ¹H-NMR, ¹³C-NMR, and 2D NMR (COSY, HSQC, HMBC and NOESY) spectra. Three C₁₅ -acetogenins (C1 - C3) were isolated from Pulau Sulug's sample. C1 present in 2.4% of crude extract, C2, 2.0% and C3, 1.0%. Five C₁₅ -acetogenins (C4 - C8) were isolated from Pantai Bak-Bak samples. C4 present in 1.8%, C5, 1.3%, C6, 2.6%, C7, 1.1% and C8, 1.9%. And, one C₁₅ -acetogenins, C9 (15.0%) was isolated from Dogoton's sample. Thus it is conclusive that L. nangii is characterized by Cwacetogenins and they could serve as chemotaxonomic markers for the species. Since these compounds are derived from Similar metabolic pathway, sibling species or chemical races may not be present in this species