Synthetic L-pyrrolysine of formula I, and derivatives thereof, chemical methods of preparing these amino acids and derivatives, and methods of derivatizing these amino acids after incorporation into a peptide or protein. ##STR1## Also provided are derivatives and methods of preparing derivatives, including addition of substituents at any substitutable position; modifications to the lysine alkyl chain; modifications of the pyrroline ring. Also provided are methods of adding labels to the pyrrolysine or derivative thereof.
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
 This work was supported at least in part by grants from the National Science Foundation (MCB-9808914); the Department of Energy (DE-FG02-92ER20042); and the National Institutes of Health (GM 061796). The Federal Government may have certain rights in this invention.