The invention provides compound which is an
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F-radiolabelled S-propylhomocysteine or a derivative thereof. The compound has an enantiomeric purity of at least about 90%.
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F-radiolabelled S-propylhomocysteine may be made by treating an N-protected ester of a substituted S-propylhomocysteine with a complexed F″ salt in the presence of a base to form a protected product and then deprotecting the protected product to form the
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F-radiolabelled S-propylhomocysteine. In this method the N-protected ester has a leaving group on the S-propyl group and has an enantiomeric purity of at least about 90%. The base should be such that it does not cause racemisation of the protected product.
Reactions of protection-free a-amino acids with aldehydes or ketones in the presence of sodium cyanoborohydride afforded the N-monoalkylated amino acids in inorganic salt-free form. Application of this method to the synthesis of N-alkyl derivatives of biologically important amino acids is also described.