The inhibition of S-chymotrypsin with optically active, axially and equatorially substituted frans-3-(2,4-dinitrophenoxy)-2,4-dioxa-325-phosphabicyclo[4.4.O]decan-3-ones ( = hexahydro-4H-1,3,2-benzodioxaphosphorin 3-oxides) was investigated. Their inhibitory power was determined by kinetic measurements, and the stereochemical course of the reaction of stoichiometric amounts of the enzyme and inhibitor was monitored with "P-NMR spectroscopy at pH 7.8. The irreversible inhibitors show significant enantioselectivity (the (S,)-enantiomer reacting faster) and yield diastereoisomeric, covalently phosphorylated derivatives of 6-chymotrypsin.31P-NMR Spectroscopic studies of the inhibition by the axially substituted inhibitor revealed for the racemic (*)-2a first a resonance at -4.4 ppm and later, while inhibition proceeded, a second one at -4.5 ppm. The reaction with optically active (+)-2a showed only one signal at -4.4ppm and its enantiomer (-)-2a only one signal at -4.5 ppm. Using the equatorially substituted racemic epimer (*)-2b, we observed the main resonance at -5.3 ppm and two minor ones at -4.4 and -4.5 ppm. The optically active compound (+)-2b showed two peaks at -4.5 and -5.3 ppm, whereas its antipode (-)-2b revealed two signals at -4.4 and -5.3 ppm.Comparing the 31P chemical shifts of the corresponding covalent phosphoserine derivatives 4a (-5.7 ppm, axial) and 4b (-4.5ppm, equatorial) shows the inhibition with the axial compounds 2a to proceed via neat inversion of the configuration at the P-atom, whereas the equatorial epimers 2b with a higher conformational flexibility seem to follow a different stereochemical pathway which results in both inversion and retention.

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1997 magnetic resonance, nuclear quadrupole resonance magnetic resonance, nuclear quadrupole resonance (organic substances) K 2560 -026Stereochemistry of the Inhibition of δ-Chymotrypsin with Optically Active Bicyclic Organophosphates: 31P NMR Studies.--(GANCI, W.; MEIER, E. J. M.; MERCKLING, F. A.; PRZIBILLE, G.; RINGEISEN, U.; RUEEDI, P.; Helv.