Anti-Parkinson drug, L-Dopa

Action on organs other than the target organ (e.g., peripheral tachycardic and hypertensive effects of dopamine after systemic application of the anti-Parkinson drug L-dopa, sedative side effects of lipophilic histamine Hj antagonists). 

In addition to carbon-carbon bond formation, transition metal catalysts can also generate a stereogenic center. The first reaction of this type in which useful amounts of asymmetric induction were observed was an asymmetric hydrogenation to make phenylalanine and the method has been used for many years to synthesize the anti-Parkinsons drug, L-Dopa (3) (Fig. 7) (142, 143). 

The a-amino acids prepared by the synthetic methods just described are racemic unless a resolution step is included, enantiomerically enriched reactants are used, or the reaction is modified so as to become enantioselective. Considerable progress has been made in the last of these methods, allowing chemists to prepare not only L-amino acids, but also their much rarer D-enantiomers. We have already seen one example of this approach in the synthesis of the anti-parkinsonism drug L-dopa by enantioselective hydrogenation (see Section 14.14). A variation of the Strecker synthesis using a chiral catalyst has recently been developed that gives a-amino acids with greater than 99% enantioselectivity. 

The synthesis of the anti-Parkinson drug L-dopa by enantioseiective hydrogenation was described earlier in Section 14.12. 

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