Abstract
The Co(III) complex containing an optically active cyclen, (2R, 5R, 8R, 11R)-2, 5, 8, 11tetraethyl-I, 4, 7, 10-tetraazacyclododecane, reacts with a-amino-a-methylmalonic acid (AMM)to give the title compound as the sole product. The molecular structure of the complex was determined by X-ray analysis. Crystal data were monoclinic, space group P21, a=13.985(6), b=11.768 (13), c=9.626 (3) A, β= 108.36 ( 3 )°, U=1504 (2)A3, and Z=2. Least-squares refinement converged at R=0.055 for 2977 unique reflections. The complex revealed a cis-octahedral geometry with the macrocycle coordinated in folded manner, and the chiralities of four nitrogen atoms of the macrocycle were S, S, S, R as found in the starting complex (Fig, 3). The AMM coordinates to Co(III) by the pro R carboxylate and the amino group in β form with δ conformation, and the absolute configuration of the chiral center in the AMM moiety is R. The uncoordinated carboxyl group forms an intramolecular hydrogen bond to one of the nitrogens in the cyclen ligand. Thus the starting complex recognizes the prochiral center in AMM through three-point attachment. Decarboxylation of the AMM complex resulted in the formation of alaninato complexes, whose R:S ratio was 28:72. The cycle of asymmetric synthesis of alanine was performed under mild reaction conditions by the releasing alanine from the alaninato complex and by recovering the complex as the starting compound [1] (Fig.6).
