Crystal Structure and Absolute Configuration of the Hydrobromide Salt of ( - ) - 2 - exo -
نویسنده
چکیده
The configuration of one of the four isomers of 2-aminonorbornane-2-carboxylic acid (C8H1302N) has been determined to be (lR,2R,4S) by X-ray crystallography, utilizing anomalous scattering. The hydrobromide salt of this isomer, (-)-2-exo-aminonorbornane-2-carboxylic acid, cryst$lizes in space group P212121 with four molecules per unit cell of dimensions a = 6.986, b = 22.669, and c = 6.150 A. The structure was determined by the heavy atom method and refined us. 923 unique observed reflections to a final R factor of 0.04. The bond angles and distances in the bicycloheptane ring agree well with those observed in other norbornane compounds, but the location of the carboxyl group in the endo position is counter to certain chemical predictions. Determination of the absolute configuration relates this norbornane amino acid to (-)-norbornanone (1 R). he unnatural amino acid, 2-aminonorbornane-2T carboxylic acid, or BCH,' has been prepared by both the Strecker and the Bucherer syntheses,2 and shown to possess several interesting biological activities. BCH inhibits the Na+-independent transport of nonpolar amino acids across cell membranes; like leucine, it acts as an insulin-releasing factor in the rat,3 and it inhibits the flavoprotein amino acid oxidase^.^ The chemical syntheses from (* )-norbornanone yield a mixture of four isomers, the (-) and (+) enantiomers of the exo-amino (I and 11) and endo-amino forms. The &* 4 4 5
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