- Chemo-enzymatic enantio-convergent asymmetric synthesis of (R)-(+)-Marmin
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Asymmetric biohydrolysis of trisubstituted terpenoid oxiranes (rac-1a-rac-3a) was accomplished by employing the epoxide hydrolase activity Rhodococcus and Streptomyces spp. Depending on the biocatalyst, the biohydrolysis proceeded in an enantio-convergent fashion and gave the corresponding vic-diols in up to 97% ee at conversions beyond the 50%-threshold. In order to avoid a depletion of the ee of product by further oxidative metabolism, bioconversions had to be conducted in an inert atmosphere with exclusion of molecular oxygen. The synthetic applicability of this method was demonstrated by the asymmetric total synthesis of the monoterpenoid coumarin (R)-(+)-Marmin in 95% ee.
- Edegger, Klaus,Mayer, Sandra F.,Steinreiber, Andreas,Faber, Kurt
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p. 583 - 588
(2007/10/03)
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- MICROBIAL OXIDATION OF GERANYLACETONE AND GERANYLOXYCOUMARIN, AURAPTEN
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Geranylacetone and geranyloxycoumarin (aurapten) were investigated with 14 selected microorganisms for ω-hydroxylation and epoxydation of the subterminal double bond.Trichoderma koningii and Verticillium theobromae are in principal useable for both reactions of geranylacetone.Although the yields of these preferably intended reactions were low, while ω-1-, ω-3-, ω-4-hydroxylations partially combined with reductive side reactions take place, the results gave an insight in the different pathways of oxidations dependent on the microorganism used.In contrast aurapten is transformed in relatively high yield the E- or/and Z-configurated ω-alcohols (auraptenols) and to the aurapten-6,7-epoxide.The exclusively useable microorganisms for the oxidation of aurapten selected from the 237 strains tested were Nocardia alba and Bacillus cereus, which both formed enantioselectively the naturally configurated epoxyaurapten R-(+)--7-oxycoumarin in yields of 10,5percent respectively 21percent of excellent optical purity of 99percentee.
- Mueller, A.,Abraham, W.-R.,Kieslich, K.
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p. 405 - 424
(2007/10/02)
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