Synthesis of redox derivatives of lysine and related peptides containing phenothiazine or tris(2,2′‐bipyridine)ruthenium(II)

Boc‐ l ‐Lysine derivatives and lysine‐containing peptides bearing the electron donor 10 H ‐phenothiazine (PTZ) or the redox chromophore tris(2,2′‐bipyridine)ruthenium(II) dication ([Rub 3 ,] 2H , where b is 2,2‐bipyridine) have been synthesized and characterized. SeO 2 oxidation (53% yield) of 4,4′‐dimethyl‐2,2′‐bipyridine, Ag 2: O oxidation (85% yield) of the monoaldehyde, complexation (96% yield) of 4′‐methyl‐2,2′‐bipyridine‐4‐carboxylic acid (m‐OH) with Rub 2 Cl 2: . activation (81% yield) of the acid [Rub 2 m‐OH] 2+ (PF 6 − ) 2 , and condensation (83% yield) of the succinimido ester [Rub 2 m‐OSu] 2+ (PF 6 − ) 2 with Boc‐Lys furnished the protected redox‐chromophore module [Boc‐Lys(Rub 2 m)‐OH] 2+ (PF 6 − ) 2 in 29% overall yield over five steps. The first two steps constitute the first practical synthesis of the monocarboxylic acid m‐OH (45% overall yield). Also prepared were m‐OSu, Boc‐Lys(m)‐OH, Boc‐Lys(m)‐OCH 3 , and [Rub 2 m‐NHCH 3 ] 2+ (PF 6 − ) 2: . Activation (91% yield) of 3‐(10 H ‐phenothiazine‐10)propanoic acid (PTZpn‐OH) and condensation (92% yield) of the succinimido ester PTZpn‐OSu with Boc‐Lys furnished the protected electron‐donor module Boc‐Lys(PTZpn)‐OH (84% overall yield). The latter was used in solid‐phase syntheses of two redox tripeptides. CH 3 CO‐Ala‐Lys(PTZpn)‐Ala‐OH and [Rub 2 m‐Ala‐Lys(PTZpn)‐Ala‐OH] 2 (PF 6 − ) 2 . The electrochemical properties of these redox amino acids and peptides were similar to those of PTZpn‐OH, [Rub 2 m‐OH]2 + (PF 6 ) 2 . or [Rub 2 m‐NHCH 3 ] 2+ (PF 6 − ) 2 . Lys(PTZpn). [Lys(Rub 2 m)] 2+ (PF 6 ) 2: . and other redox modules may be useful for engineering light‐harvesting proteins, photovoltaic cells, and other molecular electronic devices.