It doesn′t take much to oxidize cycloalkanes directly to the corresponding cyclic ketones: molecular oxygen as the oxidant, water as the solvent, the cofactor NADP+ (and a little 2‐propanol to reduce it), as well as two catalytic enzymes—a hydroxylating P450 monooxygenase and an alcohol dehydrogenase (see scheme).
A novel concept for the direct oxidation of cycloalkanes to the corresponding cyclic ketones in a one‐pot synthesis in water with molecular oxygen as sole oxidizing agent was reported recently. Based on this concept we have developed a new strategy for the double oxidation of n‐heptane to enable a biocatalytic resolution for the direct synthesis of heptanone and (R)‐heptanols in a one‐pot reaction. The bicatalytic cascade employs an NADH driven P450 BM3 monooxygenase variant (WTNADH, 19A12NADH or CM1NADH) and an (S)‐enantioselective alcohol dehydrogenase (RE‐ADH). In the initial step n‐heptane is hydroxylated under consumption of NADH to produce (R/S)‐heptanol. In the second oxidation step the (S)‐heptanol enantiomers are transformed to the corresponding ketones, reducing and thereby regenerating the cofactor. Characterization of initial hydroxylation step revealed high turnover frequencies (TOF) of up to 600 min−1, as well as high coupling efficiencies using NADH as cofactor (up to 44%). In the cascade reaction a nearly 2‐fold improved product formation was achieved, compared to the single hydroxylation reaction. The total product concentration reached 1.1 mM, corresponding to a total turnover number (TTN) of 2500. Implementation of an additional cofactor regeneration system (D‐glucose/glucose dehydrogenase) enabled a further enhancement in product formation with a total product concentration of 1.8 mM and a TTN of 3500.
Amphetamine (speed), methamphetamine (crystal meth), and 3,4-methylenedioxy-Nmethylamphetamine (MDMA, ecstasy) represent the most frequently abused amphetamine-type stimulants (ATS). Differences in pharmacological potency and metabolism have been shown for the enantiomers of all three stimulants. Legal consequences in cases of drug possession may also differ according to the German law depending on the enantiomeric composition of the seized drug. Therefore, enantioselective monitoring of seized specimens is crucial for legal and forensic casework.Various kinds of samples of amphetamine (n = 143), MDMA (n = 94), and methamphetamine (n = 528) that were seized in southern Germany in 2019 and 2020 were analyzed for their chiral composition using different chromatographic methods.Whereas all samples of amphetamine and MDMA were racemic mixtures, the chiral composition of the methamphetamine specimens was diverse. Although the vast majority (n = 502) was present as (S)-methamphetamine, also specimens containing pure (R)-methamphetamine (n = 7) were found. Furthermore, few samples (n = 8) were of racemic nature or contained non-racemic mixtures of both enantiomers (n = 10).Because methamphetamine appears in varying enantiomeric compositions, any seizure should be analyzed using an enantioselective method. Amphetamine and MDMA, on the other hand, currently appear to be synthesized exclusively via racemic pathways and are not chirally purified. Nevertheless, regular monitoring of the chiral composition should be ensured.
SummaryThe hydroxylation of n-alkanes, which proceeds in the presence of a P450-monooxygenase advantageously at temperatures significantly below room temperature, is described. In addition, an enzymatic hydroxylation of the “liquid gas” n-butane with in situ cofactor regeneration, which does not require high-pressure conditions, was developed. The resulting 2-butanol was obtained as the only regioisomer, at a product concentration of 0.16 g/L.
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