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On the unusual propensity by the red seaweed Laurencia microcladia of II Rogiolo to form C 15 oxepanes: Isolation of rogioloxepane A, B, C, and their likely biogenetic acyclic precursor, prerogioloxepane
Author(s) -
Guella Graziano,
Mancini Ines,
Chiasera Giuseppe,
Pietra Francesco
Publication year - 1992
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19920750128
Subject(s) - acetogenin , chemistry , stereochemistry , laurencia , intramolecular force , ring (chemistry) , epoxide , derivative (finance) , absolute configuration , nuclear magnetic resonance spectroscopy , chemical shift , algae , organic chemistry , annonaceae , medicine , economics , financial economics , catalysis , traditional medicine , ecology , biology
It is shown here that the red seaweed Laurencia microcladia KÜTZNING, collected in the Mediterranean off the torrent Il rogiolo, contains the C 15 acetogenin rogioloxepane A ( = (+)‐ (2 R, 7 R )‐2‐(1‐bromopropyl)‐7‐[( Z )‐1‐chlorohex‐3‐en‐5‐ynyl]‐2,3,6,7‐tetrahydrooxepin ; (+)‐ 3 ) besides its epoxy derivative rogioloxepane B ((+)‐ 4 ) and the rogioloxepane C ((+)‐ 5 ) derived from (+)‐ 4 by epoxide opening. Co‐occurring is an acyclic C 15 acetogenin, perrogioloxepane ( = (7 R ,4 Z ,9 Z ,12 Z )‐6‐chloropentadeca‐3,9,12‐trien‐1‐yn‐7‐ol; 9 ), which exists preferentially in a folded conformation as required to give, by intramolecular cyclization, rogioloxepane A ( 3TC ) in its favored twist‐chair form. Molecular‐mechanics calculations support this view and help also to assign the relative configurations at the side chains, whereas the configurations at the seven‐membered ring are established via NMR spectroscopy and chemical correlations. The absolute configuration is established by Mosher 's NMR method applied to the MTPA esters of (+)‐ 5 or 9 .