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Stereochemistry of the Inhibition of δ‐Chymotrypsin with Optically Active Bicyclic Organophosphates: 31 P‐NMR studies
Author(s) -
Ganci Walter,
Meier Eric J. M.,
Merckling Franco A.,
Przibille Georg,
Ringeisen Urs,
Rüedi Peter
Publication year - 1997
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19970800208
Subject(s) - chemistry , enantiomer , epimer , stereochemistry , covalent bond , racemization , proton nmr , active site , bicyclic molecule , nuclear magnetic resonance spectroscopy , yield (engineering) , resonance (particle physics) , enzyme , organic chemistry , materials science , physics , particle physics , metallurgy
Abstract The inhibition of δ‐chymotrypsin with optically active, axially and equatorially substituted trans ‐3‐(2,4‐dini‐trophenoxy)‐2,4‐dioxa‐3λ 5 ‐phospbubicyclo[4.4.0]decan‐3‐ones ( = hexahydro‐4 H ‐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 31 P‐NMR spectroscopy at pH 7.8. The irreversible inhibitors show significant enantioselectivity (the (S p )‐enantiomer reacting faster) and yield diastereoisomeric, covalently phosphorylated derivatives of δ‐chymotrypsin. 31 P‐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 –4.4 ppm 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 31 P chemical shifts of the corresponding covalent phosphoserine derivatives 4a (‐5.7 ppm, axial) and 4b (‐4.5 ppm, 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.