Algal carotenoids 47–NMR study of all‐trans‐peridinin, including complete 1H and 13C NMR assignments

Abstract

AbstractThe allenic C37 skeletal carotenoid all‐trans‐(3S, 5R, 6R, 3′S, 5′R, 6′S)‐peridinin, isolated from Amphidinium carterae by an improved isolation procedure, was subjected to a detailed 1H and 13C NMR spectroscopic analysis. Complete assignments of the 500.13 MHz 1H and 125.76 MHz 13C spectra, including determination of coupling constants and relative stereochemistry, were obtained by ID and 2D techniques. These included 1H1H chemical shift correlated spectroscopy (2D COSY), phase‐sensitive double‐quantum COSY, difference 1D NOE experiments, 1D and 2D total correlation spectroscopy (HOHAHA, TOCSY) and 1D and 2D rotating frame nuclear Overhauser spectroscopy (ROESY, CAMELSPIN). The 13C NMR assignments were obtained through editing sequences (DEPT) and heterocorrelated 2D experiments. In particular, the 1H detected multiple bond 1H13C correlated 2D experiment proved valuable for assignments of all 13 quatenary carbons together with 13 methine carbons in peridinin [C37H47O6(COCH3)]. Detailed analysis of the proton coupling constants supported the conformations and relative stereochemistry of the two end‐groups. Spectral simulation of protons in the conjugated chain was necessary in order to ascertain more accurate chemical shifts for some protons in the strongly overlapping olefinic region. Variation in the trans double bond 3J(H, H) coupling was noted along the conjugated chain.