Phytochemistry, Vol. 21, No. 2, pp. 46849, 1982 Printed in Great Britain. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0031-9422/X2/020468-02$03,00/O @ 1982 Pergamon Press Ltd. zyxwvu UDOTEAL, A LINEAR DITERPENOID FEEDING DETERRENT FROM THE TROPICAL GREEN ALGA UDOTEA FLABELLUM* VALERIE J. PAUL, HAO H. SUN and WILLIAM FENICAL institute of Marine Resources, Scripps Institution of Oceanography. La Jolla, CA 92093, U.S.A. zyxwvutsrqponm (Received 12 June 1981) Key zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Word Index-Udotea zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA f labellum; Codiaceae; Chlorophyta; marine diterpenoids; algal feeding deterrents. Abstract-The structure of a new linear diterpenoid, udoteal, has been determined by chemical and spectral methods. Udoteal induced feeding avoidance behavior in the herbivorous fish Eupomacentrus leucostictus. INTRODUCTION Tropical green seaweeds of the families Caulerpaceae and Codiaceae (phylum Chlorophyta) are found in conspicuous abundance in marine ecosystems of in- tense herbivore activity [l]. Several chemical studies of the genera Caulerpa [2,3], Chlorodesmus [4] and Rhipocephafus [5] have shown these algae to produce terpenoid 1,4-diacetoxybutadiene-containing metabolities which apparently function as chemical defense agents. In an attempt to define the biological properties of molecules of this latter type, we earlier showed that the metabolities of the related alga Rhipocephalus phoenix induce pronounced feeding avoidance in the herbivorous fish Eupomacentrus leucostictus [5]. In this short report we wish to des- cribe the structure of a related metabolite, udoteal (l), from the Caribbean alga Udotea flab&m (Ellis and Solander). Udoteal induced significant feeding avoi- dance in the herbivorous fish Pomacentrus coeru- leus, using a previously described bioassay [5,6]. RESULTS AND DISCUSSION Udoteal zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (1) was the major lipid component of freshly extracted U. flab&m, but could not be detected in extracts of isopropanol-preserved speci- mens. Once isolated, udoteal was moderately stable. A molecular formula of C,,H,.,Os was established for 1 by high resolution mass measurement of the M’-HOAc, -CHXO fragments taken in conjunction with 13C NMR features. IR absorptions at 1770 and 1740 cm-’ indicated the bis-enol-acetate functionality to be present, as already fully defined in several re- lated compounds [3-61. This assignment was supported by two 13C NMR ester carbonyl bands at 167.3 and 166Sppm, and by a ‘H NMR band at S 2.18 (in- tegrating for 6H) assigned to two acetate methyl groups. The ‘H NMR spectrum also illustrated the *Inshore Marine Shallow Water Ecosystem (IMSWE) contribution, No. 74. olefinic AB pattern at 6 7.43 (d, J = 13 Hz) and 5.95 (d, J = 13 Hz), and the olefinic singlet at 6 7.27 (C-16 proton), characteristic of the E,E-1,4-diacetoxy- butadiene functionality. The IR spectrum of 1 further indicated the presence of an &-unsaturated aldehyde group (-yco = 1680 cm-‘) in udoteal, and this assignment was confirmed by the expected ‘H NMR bands at 6 9.34 (s) and 6.45 (t, J=7Hz), and by a 13C NMR off- resonance doublet carbon at 193.9 ppm. The remain- ing “C NMR features illustrated two additional dou- ble bonds to be present in 1. Consideration of the molecular formula and the overall unsaturation del- ineated above showed udoteal to be a linear diter- penoid. Treatment of 1 with the dieneophile 4 - phenyl - 1,2,4 - triazoline - 3,5 - dione gave the adduct 2 in high yield. The ‘H NMR features of this compound were highly analogous to those from a similar adduct produced from rhipocephalin [6], thus reinforcing our initial snectral assignment of the E.E-diacetoxy- butadiene finctional gioup. What remained for the final assignment of udoteal was the location of the 468