Conformationally defined aromatic amino acids. Synthesis and stereochemistry of 2-endo- and 2-exo-amino-1,2,3,4-tetrahydro-1,4-ethanonaphthalene-2-carboxylic acids (2-endo- and 2-exo-aminobenzobicyclo[2.2.2]octene-2-carboxylic acids)

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Abstract
The synthesis of the title compounds 1a and 1b was accomplished in good yield by conversion of ketone to the corresponding hydantoins 4a and 4b via a Bucherer-Bergs reaction, followed by barium hydroxide hydrolysis. The stereochemical assignments of 4a and 4b and the ethyl ester hydrochlorides were determined by 1H NMR analysis. Attempts toward the synthesis of 2-amino-1,4-dihydro-1,4-ethanonaphthalene-2-carboxylic acid isomers, using the pathway discussed for 1a and 1b, led only to products arising from a retro-Diels-Alder reaction. Preliminary screening of 1a and 1b as inhibitors of isolated phenylalanine hydroxylase (PH, guinea pig) and phenylalanine decarboxylase (PAD, Streptococcus faecalis) is also discussed. The use of the benzobicyclo[2.2.2]octene nucleus for the construction of conformationally defined analogs of important medicinal agents is rationalized, and 1a and 1b are compared to several other conformationally defined systems. The title compounds represent conformationally defined models of the lower energy conformations of .alpha.-methylphenylalanine.

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