L-tert-leucine

Figure 4.18 Enzyme membrane reactor synthesis of L-tert-leucine from trimethylpyruvic acid in an continuously operated enzyme membrane reactor with ultrafiltration followed by a crystallization step...

L-tert-leucine trimethylpyruvate leucine dehydrogenase + formate dehydroenase... 

Recently, a lipase-catalysed kinetic resolution has been developed to produce L-tert-leucine via a lactone of its A-benzoyl derivative. There is also reputed to be another bioroute to L-terMeucine using transaminase technology. 

Some of the products formed are functional ingredients in their own right, such as high fmctose syraps, cefuroxime etc. Others are intermediates that can be either freely traded, such as acrylamide as a pre-polymer and 6-APA and p-hydroxyphenylglycine as precursors of semi-synthetic antibiotics. Alternatively some intermediates tend to be used in-house by the company producing them such as fS)-2-chloropropanoate and L-tert-leucine. 

Reactions possible that are not possible using chemistry. HFCS, cefuroxime, L-tert-leucine, (S)-2-chloropropanoic acid. If -decalactone... 

Synthesis of (S)-Benzyl-L-tert-Leucine Butyl Ester... 

Figure 7.16 Reductive amination of tri methyl pyruvate to L-tert-leucine (L-Tle).

Leucine dH is the enzyme used as the biocatalyst in the process commercialized by Degussa AG (Hanau, Germany) to produce L-tert-leucine (L-Tle).28-60 This UAA has found widespread use in peptidomimetic drugs in development, and the demand for this unique amino acid continues to increase.61-62 This process, which has been the subject of much study, requires a co-factor recycling system (Scheme 19.4, R = Me3C).63-64 Similar to phenylalanine dH, leucine dH has been used to prepare numerous UAAs because of its broad substrate specificity.43-65-66... 

Figure 5.5 Reaction calorimetry results from the addition of methyl chloroformate (slight excess) to L-tert-leucine (by courtesy of ACS) [34],...

Examples of Small-Scale and Industrial Applications 9.1 L-tert-Leucine as an Example of Ton-Scale Synthesis... 

Fig. 35 Production of L-tert-leucine by reductive amination of trimethyl pyruvic acid catalyzed by leucine dehydrogenase (LeuDH) and formate dehydrogenase (FDH) for cofactor regeneration...

Fig. 3.45 L-tert-leucine production by cofactor-dependent reductive amination.

While the production of D-amino acids is well established the preparation of L-amino acids is difficult due to the limited selectivity and narrow substrate spectrum of L-hydantoinases. This can be circumvented by employing rather un-selective hydantoinases in combination with very enantioselective L-carbamoyl-ases and carbamoyl racemases [90]. Furthermore, a D-hydantoinase has been genetically modified and converted into a L-hydantoinase. This enzyme can be used on a 100-kg scale for the production of L-tert-leucine [34]. Finally, the fact that the X-ray structure of an L-hydantoinase is known gives hope that side-directed mutagenesis will lead to improved L-hydantoinases [91]. 

Kragl, U. VasicRacki, D. Wandrey, C. Continuous production of L-tert-leucine in series of two enzyme membrane reactors— modelling and computer simulation. Bioprocess Eng. 1996, 14 (6), 291-297. 

Researchers at Johnson and Johnson have reported the use of microreactors in the drug development process. They utilized a commercially available CYTOS benchtop system, shown in Fig. 15, to examine several reactions. One such reaction was the highly exothermic reaction to form A-methoxycarbonyl-L-rert-leucine by the addition of methylchloroformate to L-tert leucine. Such highly exothermic reactions present safety hazards in large-scale systems. Utilizing the CYTOS system, they were able to perform this reaction in the laboratory and achieved 91% yield. ... 

L-tert-Leucine [L-ter/-Butylglycine 2-Amino-3,3-dimethylbutyric acid] C6H13NO2... 

A typical example for an efficient transamination process is the production of l-alanine, l-25, which is carried out in a continuous manner starting from pyruvate, 24, and L-glutamate, l-22, with a high space-time yield of 4.8kg/(L-d) (Fig. 13) [28], In addition, several non-proteinogenic a-amino acids, e.g., L-phosphinothri-cine, L-homophenylalanine, and L-tert-leucine have been also produced via transamination. 

Dealing with complex systems (two or more coupled enzymatic reactions or reactions with coenzyme regeneration) a complete kinetic investigation and computer simulation of the reaction system is very helpful to achieve the desired selectivity and yield of reaction (e. g. by choosing a sensible substrate and coenzyme concentration, enzyme ratio and reaction time). A case study is available[42, 431 exemplifying the production of L-tert-leucine by reductive animation and simultaneous coenzyme regeneration. 

A very common variation of the CSTR is a cascade of n CSTRs. With an increasing number of reaction vessels, the cascade approximates to the plug-flow reactor. The product concentration increases stepwise from vessel to vessel. For example, a two-stage cascade can be used to overcome effects of product inhibition, e.g. in the synthesis of L-tert-leucine 1421 or GDP-Manl144, 145l The basis for calculating reactor operation conditions is the formulation of mass balances for all reaction components for the distinct reactor type. The mass balances for the above reactors can be formulated as follows ... 

In particular, the non-naturally occurring amino acid L-tert-leucine has received significant attention due to several pharmaceutically active compounds into which it is incorporated[1). HIV-protease inhibitors developed by Novartis and Abbott are based on L-tert-leudne 2, 3. Roche has developed the anti-arthritic compound Ro 31-9790 based on its potent inhibition of collagenase 41 and a key component in the synthesis of Ro 31-9790 is the methylamide of L-tert-leucine. Boehringer Ingelheim developed a series of compounds that inhibit the ribonucleotide redudase of Herpes... 

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