1,1′-ferrocenoyl-oligoprolines.: A synthetic, structural and electrochemical study

The preparations of the eight ferrocenoyl oligopeptides, 1,1'-(Pro-OBzl)(2)-Fc (1), 1,1'-(Pro-OMe)(2)-Fc (1a), 1,1'-(PrO2- OBzl)(2)-Fc (2), 1,1'-(Pro(3)-OBzl)(2)-Fc (3), 1,1'-(Pro(4)-OBzl)(2)-Fc (4), 1-(Pro(2)-OBzl)- 1'-(OBt)-Fc (5), 1-(Pro(3)-OBzl)-1'-(OBt)-Fc (6), 1-(Pro(4)-OBzl)-1'-(OBt)-Fc (7) are described. Crystallographic studies were carried out for 1a, showing a 1,3'-configuration of the two substitutents. The growing oligoproline chain adopts a helical polyproline-II conformation in solution. Compounds 1-4 exhibit reversible one-electron oxidations of the ferrocene moiety, which is influenced by the length of the oligoproline chain. With growing peptide length, the molecule becomes easier to oxidize. For the mixed OBt - ester- oligoprolines, 5, 6 and 7, quasi-reversible oxidations are observed at slow scan rates, which vary with the oligoproline chain length. (C) 2001 Elsevier Science B.V. All rights reserved.