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1 H and 13 C NMR spectra of the methanolic allomerization products of 13 2 ( R )‐chlorophyll a
Author(s) -
Hyvärinen Kristiina,
Helaja Juho,
Kuronen Pirjo,
Kilpeläinen Ilkka,
Hynninen Paavo H.
Publication year - 1995
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260330806
Subject(s) - chemistry , steric effects , nmr spectra database , proton , epimer , carbon 13 nmr , proton nmr , spectral line , stereochemistry , analytical chemistry (journal) , crystallography , organic chemistry , physics , quantum mechanics , astronomy
The spontaneous autoxidation (allomerization) of 13 2 ( R )‐chlorophyll a in methanol produces seven main products containing three epimer pairs. The 1 H and 13 C NMR spectra of these products in acetone‐ d 6 were recorded on a 500 MHz spectrometer and fully assigned using two‐dimensional HMQC and HMBC techniques. The absolute configurations of the oxidized carbons, originally C‐13 2 , were determined using the ROESY technique. In comparison with 13 2 ( R )‐chlorophyll a , the steric repulsion between the C‐17 side‐chain and the bulky substituents of the oxidized C‐13 2 causes steric strain in the chiral part of an allomer, relieved by conformational changes in rings D and E and to a lesser extent also in the whole macrocycle. These changes were estimated for each allomer from the Δδ values of the carbon and proton resonances and from proton‐proton coupling constants. Information about the orientation of the front part of the phytyl chain in 13 2 ( R )‐chlorophyll a and its methanolic allomers was obtained by analysing the variation in the form of the P1‐C H 2 signal.