Studies Towards the Stereoselective α-Hydroxylation of Flavanones. Biosynthetic Significance

Zola-Michéle Border; Charlene Marais; Barend C. B. Bezuidenhoudt; Jacobus A. Steenkamp

doi:10.1071/CH07325

RESEARCH ARTICLE

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Studies Towards the Stereoselective α-Hydroxylation of Flavanones. Biosynthetic Significance

Zola-Michéle Border ^A ^B , Charlene Marais ^A , Barend C. B. Bezuidenhoudt ^A ^C and Jacobus A. Steenkamp ^A

+ Author Affiliations

- Author Affiliations

^A Department of Chemistry, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.

^B Dedicated to the husband and close family of Z.-M. Border who passed away tragically at the age of 31 before she could fully complete this project and her PhD.

^C Corresponding author. Email: bezuidbc.sci@ufs.ac.za

Australian Journal of Chemistry 61(2) 122-130 https://doi.org/10.1071/CH07325
Submitted: 12 September 2007 Accepted: 11 January 2008 Published: 11 February 2008

Abstract

The enolates of various propiophenones, chromanones, and also analogues of naturally occurring flavanones were stereoselectively hydroxylated at the α-position, by employing commercially available enantiopure oxaziridines, to afford the desired α-hydroxylated target molecules in good to exceptional stereoselectivities and in moderate to good chemical yields. A mechanistic rationale is presented to account for the stereoselectivities achieved. These in vitro results were tentatively related to the stereoselective biosynthesis of enantio-enriched dihydroflavonols while questions were raised about the authenticity of certain natural compounds.

Acknowledgements

Support from the Sentrale Navorsingsfonds, of this University, and the Foundation for Research and Development, Pretoria, is acknowledged. We are also grateful to Professor D. Ferreira, formerly from this University, for financial support to Z.-M.B. and fruitful discussions during the execution of the work leading to the present manuscript.

References

^* As both alcohol isomers are present in the reaction mixture, both of them are esterified with the (R)-(+)-Mosher acid chloride, which enables comparison of the chemical shifts of corresponding protons of these isomers and thus allocation of the absolute configuration according to the established model. By the same token, the %ee is conveniently calculated by the comparison of the integration values of the relevant protons (A. F. Hundt, J. F. W. Burger, J. P. Steynberg, J. A. Steenkamp, D. Ferreira, Tetrahedron Lett. 1990, 31, 5073).

Studies Towards the Stereoselective α-Hydroxylation of Flavanones. Biosynthetic Significance

Abstract

Acknowledgements

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