Gas Chromatography-Mass Spectrometry (GC-MS) Combined with Retention Index Prediction for the Rapid Identification of Halogenated monoterpenes from a Namibian Plocamium species

Plocamium species collected from the Namibian coast display morphological features similar to those of both P. rigidum and P. suhrii which makes identification of these species a difficult task. It has been reported that the major secondary metabolites found in various Plocamium species are unique to each species [1]. In this study GC-MS combined with a retention index (RI) prediction strategy was used for the rapid identification of halogenated monoterpenes characteristic of a particular Namibian Plocamium species. The RIs of the metabolites were matched with the predicted RIs of halogenated monoterpenes for which similar MS data have been reported for the same species of Plocamium. Based on the identification of the major secondary metabolite, 1E,3R,4S,5E,7Z-1-bromo-3,4,8- trichloro-7-(dichloromethyl)-3-methylocta-1,5,7-triene [2], it was proposed that these Namibian samples are closely related to that of P. suhrii. From this, it was determined that the proposed P. suhrii specimens collected in Namibia contain four additional metabolites (with molecular formulae C₁₀H₁₆Br₂Cl₂, C₁₀H₁₁BrCl₄, C₁₀H₉BrCl₆ and an unknown compound) previously not reported in P. suhrii species. In addition, a compound previously identified in South African P. suhrii was not present in the Namibian Plocamium specimens.