Structural characterisation and absolute stereochemistry of some degraded carotenoids from New Zealand honeys
type: CreativeWork
description: The structures and absolute stereochemistries of some degraded carotenoids from New Zealand native honeys were elucidated. Determination of the absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was attempted by an enantioselective synthesis. A racemic synthesis was achieved starting from β-ionone. The key steps involved regioselective hydroboration of 3,4-dehydro-β-ionone, followed by molybdenum-mediated stereoselective epoxidation of the resulting homoallylic alcohol. Ring opening of the epoxide afforded the required trihydroxy-ionone. Synthesis of both enantiomers of 3,5,6-trihydroxy-β-ionone via enantio- and regioselective functionalisation of 3,4-dehydro-β-ionone was not achieved. Methods of enantioselective enzyme-mediated kinetic resolution of cyclic homoallylic alcohols were investigated. A satisfactory procedure was not developed. The absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was determined by analysis of the diastereoisomeric proton chemical shifts of (S)- and (R)-α-methoxyphenylacetate (MPA) derivatives using the extended Mosher-Trost configurational model. This analysis indicated a 3S,5R,6R absolute configuration, the same configuration as 3,5,6-trihydroxy carotenoids. The natural product was extracted from thyme (Thymus vulgaris) honey using established procedures. Diethyl ether extracts of kamahi (Weinmannia racemosa) honey were found to contain three diastereoisomers (kamahines) of an unusual degraded carotenoid with a 14 carbon skeleton. After acetylation, one of the isomers was fully characterised by multidimensional ¹H and ¹³C NMR spectroscopy, and single-crystal X-ray crystallography, indicating the parent alcohol was 4,5-dihydro-1',5-dihydroxy-2',4,8',8'-tetramethylspiro[furan-2(3)H,7'[6']oxabicylco[3.2.1]oct[2']ene]-4'-one. Comparison of NMR-derived NOE and coupling constant data of kamahine A and B acetates with kamahine C acetate indicated the parent kamahines were C-4, C-5 epimers. The absolute configurations of the kamahines w…
abstract: The structures and absolute stereochemistries of some degraded carotenoids from New Zealand native honeys were elucidated. Determination of the absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was attempted by an enantioselective synthesis. A racemic synthesis was achieved starting from β-ionone. The key steps involved regioselective hydroboration of 3,4-dehydro-β-ionone, followed by molybdenum-mediated stereoselective epoxidation of the resulting homoallylic alcohol. Ring opening of the epoxide afforded the required trihydroxy-ionone. Synthesis of both enantiomers of 3,5,6-trihydroxy-β-ionone via enantio- and regioselective functionalisation of 3,4-dehydro-β-ionone was not achieved. Methods of enantioselective enzyme-mediated kinetic resolution of cyclic homoallylic alcohols were investigated. A satisfactory procedure was not developed. The absolute stereochemistry of 3,5,6-trihydroxy-β-ionone was determined by analysis of the diastereoisomeric proton chemical shifts of (S)- and (R)-α-methoxyphenylacetate (MPA) derivatives using the extended Mosher-Trost configurational model. This analysis indicated a 3S,5R,6R absolute configuration, the same configuration as 3,5,6-trihydroxy carotenoids. The natural product was extracted from thyme (Thymus vulgaris) honey using established procedures. Diethyl ether extracts of kamahi (Weinmannia racemosa) honey were found to contain three diastereoisomers (kamahines) of an unusual degraded carotenoid with a 14 carbon skeleton. After acetylation, one of the isomers was fully characterised by multidimensional ¹H and ¹³C NMR spectroscopy, and single-crystal X-ray crystallography, indicating the parent alcohol was 4,5-dihydro-1',5-dihydroxy-2',4,8',8'-tetramethylspiro[furan-2(3)H,7'[6']oxabicylco[3.2.1]oct[2']ene]-4'-one. Comparison of NMR-derived NOE and coupling constant data of kamahine A and B acetates with kamahine C acetate indicated the parent kamahines were C-4, C-5 epimers. The absolute configurations of the kamahines w…
author: Broom, Susan J.
license: https://researchcommons.waikato.ac.nz/bitstreams/033ca188-eb17-4ae2-8db2-6ec777ae785f/download
date published: 1998
date modified: 2026-07-24T05:57:38Z
provider: University Waikato
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: The University of Waikato