Determination of the absolute configuration of Anisotome irregular diterpenes: application of CD and NMR methods |
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Authors: | Van Klink John W Baek Seung-Hwa Barlow Anna J Ishii Hideki Nakanishi Koji Berova Nina Perry Nigel B Weavers Rex T |
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Institution: | Crop and Food Research, Department of Chemistry, Otago University, Dunedin, New Zealand. vanklinkj@crop.cri.nz |
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Abstract: | Several Anisotome diterpene derivatives were synthesized in an attempt to obtain a crystalline compound for X-ray analysis. Although we were unable to obtain a suitable crystal, the absolute configuration of the irregular diterpene skeleton was determined using two other techniques: a circular dichroism (CD) protocol based on a tetraarylporphyrin molecular tweezer that allowed prediction of the absolute stereochemistry on a microscale level, and a method employing differences in NMR shifts from derivatization of the naturally occurring acid 1 with enantiomers of a phenylglycine methyl ester (PGME) chiral anisotropic reagent. The excellent agreement between the CD and NMR methods led to the assignment of a 2S-absolute configuration for anisotomenoic acid 1. |
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Keywords: | irregular diterpene synthesis NMR circular dichroism exciton chirality porphyrin tweezer phenylglycine methyl ester PGME |
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