Obtusallene I, a new halogenated allene from Laurencia Obtusa

✍ Scribed by Philip J. Cox; Sedat Imre; Sezen Islimyeli; Ronald H. Thomson

• Publisher: Elsevier Science
• Year: 1982
• Tongue: French
• Weight: 125 KB
• Volume: 23
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)86895-1

✦ Synopsis

Obtusallene, a new halogenated bicyclic ether with an allenic side chain, has been isolated from the red form of the alga Laurencia obtusa, and identified by spectroscopic methods and X-ray crystallography.

The numerous secondary metabolites elaborated by the red algal genus Lumen&a include a group of ~1s acetylenic cyclic ethers which show remarkable structural variation.' Usually they contain a terminal enyne system as in obtusenyne and cis-isodihydrorhodophytin which we found's3 in the yellowish green colour form of L. obtusa, and in laurenyne which occurs in the red form.

In continuing our work on the red colour form, collected at GBkceada in the Aegean Sea, we have isolated two further members of the group in which the terminal enyne function is replaced by an allenic side chain. They were obtained by further chromatography of the ether extract4 on silica gel in benzene. Obtusallene I, m.p. 165-167" (from ether-petrol), [c~1,!,~-257.6" (c 0.53, ClfCR3), ClsHr7BrzC1102 (Found: M"-CL, 386.9593, ClsHr77gBrz02 requires 386.9594; M+-Br, 343.0100, CrsH177gBr35CR0z requires 343.0099; M' too weak to measure). In the IR spectrum5 a band at 1953 cm-' first suggested the presence of an allene function, which was supported by a 13C HMR peak6 at 202.2 ppm attributable to the central carbon atom, and allenic proton coupling in the 'H HMR spectrum7 corresponding to the part structure below.