Reduced collagen cross links : the first synthesis of all the possible (2S,2'S)-stereoisomers of 5-hydroxylysinonorleucine and of 5,5'-dihydroxylysinonorleucine in enantiomerically pure form

The paper reports the first enantioselective synthesis of all the possible collagen reduced cross links as described: ydroxylysinonorleucines I (R1 = R3 = R4 = H, R2 = OH; R1 = R2 = R4 = H, R3 = OH) and dihydroxylysinonorleucines I (R1 = R3 = H, R2 = R4 = OH; R3 = R4 = H, R1 = R2 = OH and R2 = R4 = H, R1 = R3 = OH). The Williams' glycine template methodol. was used both for the introduction of a stereogenic at the ?-position and for an easy protection of the amino acidic functionalities during the synthesis of the dimeric amino acids.