Tetrahedron Letters,Vo1.28,No.48,pp 6013-6014,1987 0040-4039/87 $3.00 + .OO Printed in Great Britain Pergamon Journals Ltd. FURTHER STRUCTURAL STUDIES ON THE 2-METHYL-3(2H)-FURANONE DERIVED METABOLITES OF THE MARINE ALGA LAURENClA C/f/LENS/S Aurelio San-Martin’, and Juana Rovirosa Departamento de Quimica, Facultad de Ciencias, Universidad de Chile Casilla 653, Santiago, CHILE Changfu Xu, Helen S.M. Lu, and Jon Clardy’ Department of Chemistry - Baker Laboratory Cornell University, Ithaca, NY 14853-1301 SUIllllla~: Chilenone B was isolated from the red marine alga Laurencia chilensis, and its structure was determined by x-ray diffraction and spectroscopic techniques. Chilenone B is a trimer of 2-methyC3(2H)-furanone. Recently we reported the structure of chilenone A (1) from the red marine alga Laurencia chilenskl This naturally occurring racemate appeared to be a dimer of 2-methyl-3(2H)-furanone.1 A larger collection and re- examination of this alga has yielded the related metabolite chilenone B (2) which we report here. The alga (2.1 kg) was collected in Horcones Bay (Chile) in November 1985. The dried ground material was extracted with acetone at room temperature. The acetone extract (50.9 g) was chromatographed on silica gel with petroleum ether/ethyl acetate mixtures of increasing polarity. The chilenone containing fraction was rechro- matographed on a medium pressure silica gel column with petroleum ether/ethyl acetate to give, among other compounds, chilenones A (1,250 mg) and B (2, 25 mg). Chilenone B (2) had a m.p. of 1110 C and a formula of Cf5Hf806 from EIMS (m/z 294). Proton NMR and other spectral measurements suggested the two-dimensional structure shown as 2. but could not unambiguously define the stereochemical centers. A single crystal x-ray diffraction analysis was used to completely define the molecular structure. Chilenone B crystallized from ether/hexane in the monoclinic system with cell constants a=l0.0751(16), b=6.0502(14), c=23.5370(32) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE A, and 8=91.917(45)0. Systematic extinctions uniquely required space group PPl/n and density considerations (p=l.36 glcm3) indicated that one molecule of composition Cf5Hf 806 formed the asymmetric unit. All unique diffraction maxima with 28 -Z 1140 were collected on a computer controlled four-circle diffractometer using lo o-scans and Cu K& radiation (1.54178 A). After correction for 6013