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Keronopsamides, a New Class of Pigments from Marine Ciliates
Author(s) -
Guella Graziano,
Frassanito Rita,
Mancini Ines,
Sandron Tommaso,
Modeo Letizia,
Verni Franco,
Dini Fernando,
Petroni Giulio
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900905
Subject(s) - chemistry , conformational isomerism , amide , two dimensional nuclear magnetic resonance spectroscopy , moiety , density functional theory , stereochemistry , mass spectrometry , nuclear magnetic resonance spectroscopy , chemical structure , molecule , computational chemistry , organic chemistry , chromatography
New pigments with an unprecedented skeleton, named keronopsamides A–C, were isolated from the marine ciliate Pseudokeronopsis riccii . The structure of the most abundant secondary metabolite, keronopsamide A, was established through extended Nuclear Magnetic Resonance (NMR) analysis and mass spectrometric (MS) data obtained by using electrospray (ESI) and matrix assisted laser desorption (MALDI) ionizations. Structures of the minor analogues (keronopsamide B and C) were inferred from 1 H NMR, chemical correlation, and LC‐MS measurements. The analysis of NOE dipolar couplings and quantum chemical calculations, carried out by density functional theory (DFT) on the preferred rotamers of keronopsamide A, suggested a fully planar structure with amide bond in anti stereochemistry capable to break down the extended conjugation of the whole π electronic system. Although the presence of a 2‐substituted 3,4‐dibromo‐pyrrole moiety is reminiscent of previously isolated metabolites isolated from a cell extract of Pseudokeronopsis rubra (keronopsins) , keronopsamides show a new molecular skeleton formally derived from a peptide‐like condensation of a 3‐pyrrolepropenoic acid with an unsaturated bromotyramine.