The methods described in the previous section are aimed at coupling of aspartic acid and PheOMe without protection; the methods described in this section do not depend on aspartic acid as the starting material. Because aspartic acid can be produced by ammonia addition to fumaric acid by an ammonia lyase, APM synthesis from fumaric acid, PheOMe, and ammonia as starting materials was proposed by TOSOH (41). PseudomonasputidaTS-15001 was found to be catalyzing the coupling of the three substrates simultaneously. Although all details of this reaction system have not been studied, this system seems to consist of two reactions in the cells. At first, aspartic acid is produced from fumarate by the ammonia addition reaction by an ammonia lyase; second, aspartic acid is coupled with PheOMe by an aminopeptidase. The low production yield seems to result from the hydrolysis of APM by the ami-nopeptidase in the same way as in the first example of the direct production.
Production of APM from similar substrates was proposed by Showa Denko Corporation (42), where APM was derived from fumaric-PheOMe (FPM) by ammonia addition reaction by certain bacterial cells that produced an ammonia lyase, as shown in Scheme 6. In this proposal, FPM was derived from its cis-trans isomer, maleic-PheOMe (MPM) which is more easily produced by the coupling reaction of maleic anhydride and PheOMe than by the direct production of FPM by the coupling reaction of fumaric acid and PheOMe. When fumaric acid and PheOMe are coupled directly, use of a coupling reagent is required, such as oxalyl chloride, thionyl chloride, or car-bodiimide. However, the coupling of maleic anhydride and h2n
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