FERROCENOYL AMINO-ACIDS - A SYNTHETIC AND STRUCTURAL STUDY

A series of ester-protected amino acids were coupled to ferrocenecarbo xylic acid (1) using the DCC/HOBt protocol to give ferrocenoyl N-amino acids (amino acid = Glu(OBz)(2) (2a), Gly(OEt) (2b), Pro(OBz) (2c), C ys(SBz)OMe (2d), Ala(OBz) (2e), Tyr(OBz) (2f), Phe(OBz) (2g)). All pro ducts were fully characterized. The intermediate hydroxybenzotriazole active ester FcCOOBt (3) was isolated and fully characterized. The sol id state structures of 2a, 2d, and 3 were determined by single-crystal X-ray diffraction. 2a: monoclinic P2(1) with a = 11.8142(5) Angstrom, b = 9.7560(5) Angstrom, c = 22.9456(10) Angstrom, beta = 90.246(5)deg rees, V = 2644.7(2) Angstrom(3), Z = 2, R = 0.046. 2d: orthorhombic P2 (1)2(1)2(1) with a = 9.957(2) Angstrom, b = 11.680(2) Angstrom, c = 36 .452(2) Angstrom, V = 4239.5(13) Angstrom(3), Z = 4, R = 0.065. The so lid state structures of 2a and 2d show extensive C=O ... H-N hydrogen bonding. 3: triclinic <P(1)over bar> with a 7.0391(5) Angstrom, b = 10 .7922(7) Angstrom, c = 11.1690(7) Angstrom, alpha = 108.071(5)degrees, beta = 107.957(5)degrees, gamma = 103.896(5)degrees, V = 712.5(2) Ang strom(3), Z = 2, R = 0.030. The long ester bond distance of 1.427(2) A ngstrom provides a rationale for its inherent reactivity toward primar y and secondary amines.