Ligand binding stereoselectivity

DIASTEREOMERS STEREOSELECTIVITY STEREOSPECIFICITY STERIC-APPROACH CONTROL STERIC HINDRANCE Steric hindrance effect on ligand binding, SCATCHARD RLOT Stern layer,... 

Since the co-crystallized enantiomers showed distinct binding patterns, this information raised the assumption of stereoselectivity of P-gp in its ligand binding quality (Aller et al, 2009). Stereoselectivity has also been shown for flupentixol (Dey et al., 1999) and propafenone derivatives (Jabeen et al., 2011). On the other hand there are also ample reports on equal activity of enantiomeres. Thus, as for niguldipine and verapamil both enantiomers showed equivalent activities (Hollt et al., 1992 Luurtsema et al., 2003), the distomers with respect to cardiovascular activity were used for clinical studies. 

When an appropriate chiral phosphine ligand and proper reaction conditions are chosen, high enantioselectivity is achievable. If a diphosphine ligand with C2 symmetry is used, two diastereomers for the enamide-coordinated complex can be formed because the olefin can interact with the metal from either the Re- or Sf-face. Therefore, enantioselectivity is determined by the relative concentrations and reactivities of the diastereomeric substrate-Rh complexes. It should be mentioned that in most cases it is not the preferred mode of initial binding of the prochiral olefinic substrate to the catalyst that dictates the final stereoselectivity of these catalyst systems. The determining factor is the differ-... 

Gillespie, A.M. and White, D.P. (2001) Understanding the steric control of stereoselective olefin binding in cyclopentadienyl complexes of rhenium an application of de novo ligand design. Organometallics, 20, 5149. 

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