Remarkable remote chiral recognition in a reaction mediated by a catalytic antibody

The crystal structures of catalytic antibody D2.3 Fab with the two enantiomers, 7D and 7L, which represent transition state analogues for the hydrolysis of the corresponding esters, 6D and 6L, were determined to better understand remarkable reactivity differences: the L-ester displayed significantly tighter binding (K(M)) and increased catalytic activity (k(cat)) with D2.3, even though the chiral center is 7 bonds distant from the reaction center. Surprisingly, the electron densities of the liganded phosphonates, 7D and 7L, within the D2.3 binding/reaction site were essentially identical, highlighting the subtle influences of protein interactions on chemical behavior.     

X-Ray structures of two families of hydrolytic antibodies

The catalytic mechanisms of two esterase-like catalytic antibodies (Abs) have been determined, based on kinetic data and on structures of the complexes with transition-state analogs and with a stable substrate analog of the reactions they catalyze. Both Abs stabilize the oxyanion intermediate close to the transition state in ester hydrolysis. The different geometries of the hydrogen bonds that participate in this stabilization account for most of the difference between the efficiencies of these two Abs.     

The absolute configuration of tri-o-thymotide and its “cage” clathrate inclusion cavity

The absolute configuration of tri-$\text{o}$-thymotide (TOT) has been determined by X-ray crystal structure determinations of two cage-type clathrate inclusion compounds (+)-TOTS·S-(+)-2-bromobutane and (?)-TOT·RR-(+)-2,3-dimethylthiirane; (+)-TOT has a $\text{P}$ propeller-like configuration     

Stereospecific reactions and interactions in tri-ortho-thymotide clathrates

The emphasis in this paper is on the interpretation of physicochemical phenomena occurring in tri-ortho-thymotide (TOT) clathrates in the light of crystallographic data.Enantiomeric discrimination of guest included in the cageP3₁21 clathrates, first suggested by H. M. Powell, has been studied for about twenty guest molecules. Practical applications include preparative resolution and determination of the absolute configuration of guest molecules via TOT clathrates. The observation of similar position and orientation within the cage of stereochemically related guests, provides a clue for the chiral discrimination in terms of crystallographic data. The influence of different factors (guest size, crystallographic disorder, etc.) is analyzed, as well as the difficulties in obtaining a precise assignment of the chirality of host/guest interactions.TOT clathrates including stilbene and cinnamic acid as guest undergo photoisomerization reactions whose pathway is different from that observed in solution or in the pure guest crystal, due to the different microenvironment around the olefinic molecule.It is shown that symmetry, as well as crystallographic disorder, is the most important factors governing these phenomena. The analysis of these factors bears similarities with the problems arising in chiral discrimination. In particular, the flexibility of the TOT molecule is probably strongly correlated with the physicochemical phenomena so far studied, as well as with the large variety of crystal forms. The comparison of the TOT molecular configurations in five different crystallographic environments allows a critical discussion on the pertinent molecular parameters which reflect the TOT flexibility.Dedicated to Professor H. M. Powell.