LONG-CHAIN ALKENES OF THE HAPTOPHYTES ISOCHRYSIS-GALBANA AND EMILIANIA-HUXLEYI

The major alkenes of the haptophytes Isochrysis galbana (strain CCAP 9 27/14) and Emiliania huxleyi (strains CCAP 920/2 and VAN 556) have bee n identified by nuclear magnetic resonance spectroscopy and by mass sp ectrometric analysis of their dimethyl disulfide adducts. The dominant alkene in I, galbana is (22Z)-1,22-hentriacontadiene, with 1,24-hentr iacontadiene and 1,24-tritriacontadiene present in much lower abundanc e; (22Z)-1,22-hentriacontadiene also occurs in E. huxleyi (strain CCAP 920/2), together with (2Z,22Z)-2,22-hentriacontadiene (the major hydr ocarbon) and (3Z,22Z)-3,22-hentriacontadiene. Minor abundances oi 2,24 -hentriacontadiene and 2,24-tritriacontadiene are also present in this strain. In contrast, the dominant alkene in E. huxleyi (strain VAN 55 6) is (15 E,22 E)-1,16,23-heptatriacontatriene with the related alkatr iene 1,15,22-octatriacontatriene also present and (22Z)-1,22-hentriaco ntadiene occurring as a minor component. From structural relationships (15E,22 E)-1,15,22-heptatriacontatriene is proposed to derive from th e same biosynthetic pathway as that of the characteristic C-37 alkenon es which occur in both E. huxleyi and I. galbana. The C-31 and C-33 di enes likely derive from chain extension and decarboxylation of (Z)-9-o ctadecenoic acid or (Z)-7-hexadecenoic acid, using a pathway analogous to that elucidated previously in the chlorophyte Botryococcus braunii . Therefore, long-chain dienes and trienes, which can co-occur in hapt ophytes, may have distinct biosynthetic pathways.