Peptides tritium incorporation

Other dehydro amino acids conveniently used in the same way include A " -proline and 2,6-diaminohex-3-ynoic acid (for [ H]lysine) °. These residues usually give more nearly stoichiometric tritium incorporation upon reduction than does A" -leucine. The tritiation of A -amino acids (or peptides containing them) would require stereoselective reductions in order to obtain the desired (R)- or (5)-forms (as discussed later in this section). 

Alternatively, incorporation of Phe(4-NHBoc) into a peptide is followed by deprotection to regenerate the 4-amino group. Iodination generates the Phe(3,5-I2,4-NH2)-containing peptide, which is then converted into the tritium-labeled Phe(3,5-3H2,4-NH2) for the formation of the [(Asu)21 6,Phe2(3,5-3H2,4-NH2),Arg8]-VP.[31]... 

Of even more practical relevance is the incorporation of excess tritium during the catalytic tritiation of 4,5-dehydroleucine (A -Leu) and of peptides containing this precursor of [ HJleucine, leading to specific activities of up to 200 Ci/mmol. N-Boc-A -Leu (5) has been subjected to catalytic tritiation using palladium catalysts then the... 

Abe s group (Abe, 1971 Abe et al, 1970) isolated L-leucyl-D-proline lactam and L-phenylalanyl-D- and L-proline lactam from cultures in which ergokryptine and ergotamine, respectively, were the major peptide alkaloids. The time course of production of the lactams was consistent with their involvement in peptide alkaloid biosynthesis (Abe et al, 1970). The role of the lactams as precursors of the peptide alkaloids was tested by carrying out incubations with the tritium-labeled lactams. Incorporation of L-leucyl-D- and -L-proline lactam into ergokryptine plus ergokryptinine was 0.06-1.45%, and incorporation of L-phenylalanine-D- and -L-proline lactam... 

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