Enamide binding, selectivity

Extended X-ray absorption fine structure spectroscopy has been applied to obtain structural information on intermediates in solution in Rh(I)-catalyzed asymmetric hydrogenations. Further information comes from P nmr studies which have shown that the enamides PhCH= C(NHC0Ph)C02Me bind selectively to rhodium complexes of (4a) whereas itaconic acid derivatives CH2=C(C02R )CH2C02R bind weakly, the reverse being true for complexes of (4b). The kinetics of the... 

A1 and concanamycin A—two established V-ATPase inhibitors.163 This observation was confirmed by both in vitro enzyme assays and in vivo activity studies in mutant yeast. These studies indicated that, while the benzolactone enamides were potent V-ATPase inhibitors, a profound selectivity occurred between the mammalian and fungal enzymes. Subsequent studies by De Brabander determined that salicylihalamide A binds irreversibly to the trans-membranous proton-translocating domain via A-acyliminium chemistry.164... 

The geometry of a chiral 6-membered chelate ring is not conducive to effective asymmetric catalysis. Consider square-planar complexes of d[, l-2,3-diphenyl-l,3 bis (diphenylphosphino) propane (24), which are presumed to exist in chair conformation (Scheme 6) with rapid ring inversion. The close approximation to a-symmetry in the environment of the metal suggests that there will be little discrimination between the diastereomeric modes of binding of a prochiral bidentate ligand, since substituents on the olefin experience similar steric interactions in both isomers. The expectation of low selectivity is borne out in practice, for in some cases enamide complexes derived from this phosphine exist in two diastereomeric forms (Figure 3). 

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