RACEMIZATION OF ISOVALINE BY GAMMA-RADIATION - COSMOLOGICAL IMPLICATIONS

Isovaline (a-amino-a-methylbutyric acid) is of considerable cosmological interest since (I) it is one of the 12 nonprotein amino acids isolated and identified from the Murchison carbonaceous chondrite1 and (2) it has no a hydrogen at its asymmetric center and has been shown2 to be incapable of racemization by the mechanisms accounting for the racemization of ordinary α-amino acids. It had previously been suggested3 that the enantiomeric composition of the Murchison isovaline should represent that prevailing at the time of its original synthesis in the meteorite, thus giving a clue as to the primordial enantiomeric composition of the other amino acids in the meteorite regardless of their present composition. Recently we reported4-6 that ionizing radiation could cause —radioracemization– of α-amino acids both in the solid state and in solution, along with their well-known radiolysis.7 We now have found that such radiation is capable of racemizing isovaline as well.© 1979, American Chemical Society. All rights reserved.