Sesquiterpenes, halogenated

In addition to hydrocarbons, Octocorallia contain several other examples of oxygenated sesquiterpenes, and, more rarely, halogenated sesquiterpenes or nitrogen- and sulfur-containing sesquiterpenes. Halogenated sesquiterpenes are not frequent and are still known only in gorgonians of the family Gorgoniidae Rumphella, Paramuriceidae... 

No crystalline halogen derivatives of cedrene have been prepared, only liquid compounds being obtained when the sesquiterpene is treated by the usual processes. 

Suzuki, M. and Kurosawa, E. 1978. Two new halogenated sesquiterpenes from the red alga Laurencia majuscula. Tetrahedron Lett. 4805-4808. 

Sims JJ, Lin GHY, Wing RM (1974) Marine natural products. X. Elatol, a halogenated sesquiterpene alcohol from the red alga Laurencia elata. Tetrahedron Lett 39 3487-3490 Singh S, Kate BN, Banerjee UC (2005) Bioactive compounds from cyanobacteria and microalgae an overview. Crit Rev Biotechnol 25 73-95... 

An array of new and unusual halogenated terpenes have been isolated and characterized from Laurencia red algae [14], This genus is well known as a source of halogenated sesquiterpenes. New chamigrane-type derivatives were isolated from Laurencia species, some from Laurencia... 

An examination of the digestive gland extracts from the South African sea hare Aplysia dactylomela has yielded new halogenated sesquiterpenes, e.g. algoane (216) and ibhayinol (217) [168]. 

In addition to the myriad natural marine halogenated sesquiterpenes (vide infra), the terrestrial plant kingdom is also a major source of halogenated (chlorinated) sesquiterpenes, most of which possess the guaianolide skeleton (498). 

The plant Achillea clusiana from the mountains of Bulgaria contains the new 2-epi-chIoroklotzchin (256), which is the first report of a halogenated sesquiterpene lactone from Achillea genus (512). Chloroform was used to process the plant. The Egyptian medicinal plant Ambrosia maritima, which is still used to treat renal colic and other aliments, has afforded 1 lp-hydroxy-13-chloro-l 1,13-dihydrohymenin (257) (513). Eupaglehnins E (258) and F (259) are novel germacranolides isolated... 

The new red algal species Laurencia mariannensis from the Great Barrier Reef provides the novel sesquiterpene 297, along with the known pacifenol and deoxy-prepacifenol, which are now fully characterized by NMR for the first time (539). The Philippine Laurencia majuscula has furnished 13 novel halogenated sesquiterpenes 298-310, of which the major components are the majapolenes A (298, 299) (two diastereomers), which are also found in Laurencia caraibica (540). Most of these compounds occur as inseparable diastereomers. A collection of Laurencia majuscula from the South China Sea has yielded the cedrene-type sesquiterpene majusin (311) (541). A new sesquiterpene dichloroimine, stylotellane A (312), was isolated from the sponge Stylotella aurantium (Fig. 3.3) (542). 

Nearly 40 halogenated eudesmanes and related halogenated sesquiterpenes were documented in the first survey (1), and terrestrial eudesmanes of all types are well represented with some 100 known examples (588). 

Brito I, Cueto M, Dorta E, Darias J (2002) Bromocyclococanol, a Halogenated Sesquiterpene with a Novel Carbon Skeleton from the Red Alga Laurencia obtusa. Tetrahedron Lett 43 2551... 

McPhail KL, Davies-Coleman MT, Copley RCB, Eggleston DS (1999) New Halogenated Sesquiterpenes from South African Specimens of the Circumtropical Sea Hare Aplysia dactylomela. J Nat Prod 62 1618... 

Brito I, Cueto M, Diaz-Marrero AR, Darias J, San Martin A (2002) Oxachamigrenes, New Halogenated Sesquiterpenes from Laurencia obtusa. J Nat Prod 65 946... 

Iliopoulou D, Roussis V, Pannecouque C, De Clercq E, Vagias C (2002) Halogenated Sesquiterpenes from the Red Alga Laurencia obtusa. Tetrahedron 58 6749... 

Participation of Br in marine terpene biosynthesis (Section II.C) is reflected in the impressive number (several hundred) of halogenated terpenes, some with useful biological activities, that have been identified. For example, the poly halogenated sesquiterpenes isoobtusol (14) and isoobtusol acetate (15), isolated from the red alga Laurencia obtussa, showed potent activity against HeLa 229 human carcinoma cells1011. 

The rhodium-cataiyzed intramoiecuiar [5+2] cycioaddition of an allene and vinylcyclopropane was the key step in the asymmetric total synthesis of the trinorguaiane sesquiterpene (+)-dictamnol by P.A. Wender and co-workers.The cyclization precursor allene-cyclopropane was assembled starting from commercially available cyclopropane-carbaldehyde. Using the HWE oiefination, the Weinreb s amide moiety was installed and subsequently reacted with a primary alkyllithium that was generated via lithium-halogen exchange. 

Allylic halogenation of aldehyde enol acetates, e.g. 23, derived from norbornadiene provided an elegant and efficient construction of the tricyclic structure 24 found in many sesquiterpenes such as cyclosativene, cyclocopacamphene, longicyclene, a-santalene and its derivatives. This rearrangement in fact arises from an electrophilic addition to a multiple bond with participation of the homoallylic bond. The tricyclic skeleton was also obtained successfully by treatment of 5-methylenenorborn-2-ene with A-bromosuccinimide in aqueous dimethyl sulfoxide which gave 5-bromo-2-hydroxymethyltricyclo[2.2.1.0 ]heptane (25) in high yield. 

Ohta, K. and Takagi, M., 1977. Halogenated sesquiterpenes from the marine red alga Marginisporum aberrans. Phytochemistry, 16 1062—1063. 

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