Marine natural products-XV. Polyhalogenated cyclic monoterpenes from the red alga plocamium cartilagineum of antarctica

Examination of the red alga Plocamium cartilagineum (L.) Dixon collected along the Antarctic Peninsula yielded several new cyclic halogenated monoterpenes. The structures of a 2,4-dichloro-trans-1-chloro-vinyl-1-methyl-5-methylene-cyclohexane, a 2-chloro-4-bromo-trans-1-chlorovinyl-1-methyl-5-methylene-cyclohexane, a 2-chloro-trans-1-chlorovinyl-1-methyl-5-chloromethyl-4-cyclohexene, and a 2,5-dichloro-4-bromo-trans-1-chlorovinyl-1-methyl-5-bromomethyl-cyclohexane are described. The structures were determined by spectroscopic methods and chemically related to the halogenated monoterpene violacene.