Deuterium-enriched amino acids occur in the Murchison carbonaceous chondrite. Synthesis
from D-enriched interstellar precursors by Strecker reactions during aqueous alteration
of the parent body has been proposed. To test this hypothesis, we have measured the
retention of deuterium in amino acids produced from HCN, NH3, and formaldehyde-D2,
acetaldehyde-D4, and acetone-D6 in H2O. The isotopic label is 50% to 98% retained,
with variations in retentivity depending on the amino acid and the reaction conditions.
If amino acids, once formed on the parent body by the Strecker synthesis, lose no
deuterium by subsequent exchange with water or H-bearing minerals, then the observed
deuterium isotopic composition of Murchison amino acids represents as much as 50%
or more of the enrichments inherited from their interstellar precursors. Imino diacids
are prominent side products of the Strecker synthesis which have not been reported
in carbonaceous chondrites. Under the conditions of the Strecker reaction using deuterium
labeled aldehydes and ketones, unlabeled amino acids are also formed by an HCN polymerization
route indicating multiple pathways for the synthesis of amino acids in meteorites.