Tropical Marine Algae. III. New Sesquiterpenes From Laurencia majuscula (Rhodophyta, Rhodophyceae, Ceramiales, Rhodomelaceae)

Abstract

The isolation and structural elucidation of new sesquiterpenes from Laurencia majuscula, collected from Zoe Bay, Hinchinbrook Island, North Queensland, are reported. One collection contained the novel triquinane derivative: (1S*,2S*,3S*,5S*,8S*,9S*)- tricyclo [6.3.0.0^1.5] undecan-2-ol (3), and four halogenated chamigrene derivatives: the known 1(15)Z compound (4) and the new (1(15)E,2Z,4S,8R,9S)-8,15-dibromochamigra-1(15,2,1112-trien-9-ol (5), the known isoobtusadiene (6) and the new metabolite (1S,2S,4R,8R,9S)-1-chloro-2,8-dibromochamigr-11(12)-en-9-ol (7). A second collection afforded the same range of sesquiterpenes (3)-(7)and an additional tricyclic sesquiterpene related to ( Δ¹⁰)- rhodolaureol (16), namely ( Δ ¹¹⁽¹²⁾)-isorhodolaureol (8). The relationship was confirmed by oxidation of (8) to give the expected non-conjugated enone (15) which rearranged in slightly acidic chloroform to the conjugated enone (17), identical with the oxidation product from rhodolaureol (16).