The first systematic study of the cis and trans stereoselectivity in the m-CPBA epoxidation of N-protected cyclic allylic amines has been completed. Mono-N-protected systems gave epoxides with cis stereochemistry (amides are better cis directors than sulfonamides or carbamates) whereas di-N-protected systems gave trans-epoxides (TsNBoc protection gave complete trans stereoselectivity). [structure: see text]

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The enzyme 6-oxocamphor hydrolase (OCH) from Rhodococcus sp. NCIMB 9784 catalyses the cleavage of a carbon-carbon bond between two carbonyl groups in both mono-and bicyclic non-enolisable b-diketone substrates. In this mode OCH has been shown to effect the desymmetrisation of both bridged symmetrical bicyclic [2.2.1] and [2.2.2] systems and a series of 1-alkylbicycloA C H T U N G T R E N N U N G [3.3.0]octane-2,8-diones, yielding chiral substituted cyclopentanone and cyclohexanone products in high optical purity. In the present study, OCH has been challenged with a series of heteroannular substrates including 1-methylbicycloA C H T U N G T R E N N U N G [4.3.0]nonane-2,9-dione (7a-methylhexahydroindene-1,7-dione) in an effort to assess the competence of the enzyme for kinetic resolutions of asymmetric, racemic substrates. OCH was shown to catalyse the resolution of 1-methylbicyclo-A C H T U N G T R E N N U N G [4.3.0]nonane-2,9-dione with an E value of 2.9. The effect of increasing the length of the alkyl chain in the 1-position, or enlarging one of the rings, was to increase the enantioselectivity of the enzyme to 5.7 and 3.1 for the substrates 1-allylbicyclo-(9a-methyloctahydrobenzocycloheptene-1,9-dione) was not a substrate for OCH. These experiments constitute the first description of the resolution behaviour of such a retro-Claisenase enzyme, and suggest a maximum steric limit for substrate recognition by OCH.

Previously, we reported a general method for the chemo-enzymatic deracemization of primary, 1 secondary 2 and tertiary 3 amines in high yield and enantiomeric excess. The deracemization process involves a two-step, one-pot reaction and employs an enantioselective amine oxidase (MAO-N) in combination with a nonselective chemical reducing agent (Figure 11.1). We have further demonstrated the utility of this variant enzyme by way of the asymmetric synthesis of the natural product (þ)-crispine A in 97 % ee. 4 The previously reported MAO-N-D5 variant, which contains five important mutations (Ile246Met/Asn336Ser/Met348Lys/ Thr384Asn/Asp385Ser) was used; its preparation has been described previously. 5,6 R 3 R 4 N R 3 R 4 N R 3 R 4 N + NH 3 :BH 3 enantio selective amine oxidase R 1 R 2 R 1 R 2 R 1 R 2 (S) (R) Figure 11.1 Enzymatic deracemization of racemic amines via a two-step, one-pot process utilizing an enantioselective amine oxidase in combination with ammonia-borane. Practical Methods for Biocatalysis and BiotransformationsEdited

A generic and reproducible method for the preparation of homo-and heteroannular bicyclic b-diketones is reported. The method employs the copper acetate mediated 1,4-conjugate addition of organozinc derivatives of iodopropionate and iodobutanoate esters to a,b-unsaturated cycloalkenones, followed by intramolecular Dieckmann condensation.