Abstract:
A method of forming a thiohydantoin from an N-protected amino acid is described. The method employs a phosphate compound selected from the group consisting of (R. sub. 1 O)(R. sub. 2 O)P(. dbd. O)X and (R. sub. 1 O)(R. sub. 2 O)P(. dbd. O)--O--P(. dbd. O)(OR. sub. 3)(OR. sub. 4) to form acylphosphate moieties from the carboxyl groups of internal aspartic acid and glutamic acid residues and an acylphosphate moiety at a C-terminal carboxyl. The later acylphosphate, unlike the internal acylphosphates, spontaneously cyclizes to an oxazolone, which is less reactive with nucleophilic reagents. R. sub. 1 and R. sub. 2 are each alkyl, aryl, or alkaryl groups which are the same or different and which may be covalently linked to each other; R. sub. 3 and R. sub. 4 are each alkyl, aryl, or alkaryl groups which are the same or different and which may be covalently linked to each other; and X is a leaving group, such as chlorine or bromine, which is substantially unreactive towards thiohydantoins. The acylphosphate and oxazolone moieties are then reacted with a thiocyanate reagent under conditions effective to convert the internal acylphosphates to amides and the terminal oxazolone to thiohydantoin, thereby permitting selective C-terminal thiodantionation of aspartic acid- and/or glutamic acid-containing proteins.