ASYMMETRIC TETRACOORDINATE PENTACOVALENT ORGANOPHOSPHORUS COMPOUNDS: THEIR RESOLUTION AND DETERMINATION OF ENANTIOMERIC PURITY

Solid-phase synthesis of stereoregular oligodeoxyribonucleoside phosphorothioates using bicyclic oxazaphospholidine derivatives as monomer units

Nucleoside 3'-O-bicylic oxazaphospholidine derivatives were designed as monomer units for a solid-phase synthesis of stereoregular oligodeoxyribonucleoside phosphorothioates (PS-ODNs). The trans-isomers of appropriately designed nucleoside 3'-O-bicyclic oxazaphospholidine derivatives were generated exclusively by the reaction between the 3'-OH of the corresponding protected nucleosides and 2-chloro-1,3,2-oxazaphospholidine derivatives. The resultant trans-oxazaphospholidine isomers were configurationally stable, and their diastereopurity was not impaired by epimerization in the presence of an acidic activator during the condensation on a solid support. As a result, the formation of both (Rp)- and (Sp)-phosphorothioate internucleotide linkages by using the oxazaphospholidine monomers and the acidic activator proceeded without any loss of diastereopurity (diastereoselectivity > or = 99:1). In addition, ab initio molecular orbital calculations showed that the epimerization of oxazaphospholidine derivatives was most likely to proceed via an edge inversion process that was accelerated by N-protonation. The calculations rationalized not only the relations between the ring structure and the configurational stability of the oxazaphospholidines observed in this study but also the observations reported in the literature that the inversion of tricoordinated organophosphorus compounds were accelerated by acids or nucleophiles.

Stereoselective inhibition of glutamate carboxypeptidase by organophosphorus derivatives of glutamic acid

A series of alkyl and aryl phosphonyl, thiophosphonyl, and dithiophosphonyl derivatives of (S)- and (R)-glutamic acid were prepared and examined for inhibitory potency against glutamate carboxypeptidase (carboxypeptidase G). The acquisition of the phosphonamidodithioic acids and the individual phosphonamidothioic acid diastereomers was achieved through a common phosphonamidothiolate precursor, which also allowed for the chromatographic resolution of the chiral phosphorus center of the phosphonamidothioic acids. The most potent inhibitor of the series was the n-butylphosphonamidate derivative of the natural isomer of glutamic acid. Although each diastereomeric pair of three phosphonamidothionates exhibited stereoselective inhibition consistent with the configuration of the chiral phosphorus center, this effect was generally not remarkable. More important, was the effect of carbon stereochemistry upon glutamate carboxypeptidase inhibition as exemplified by a limited series of enantiomeric pairs of phosphonamidate and phosphonamidodithionate derivatives of glutamic acid. The phosphonamidate analogs derived from the unnatural stereoisomer of glutamic acid were devoid of inhibitory potency in contrast to their enantiomers. Surprisingly, the phosphonamidodithionates derived from the unnatural stereoisomer of glutamic acid demonstrated greater inhibitory potency than their naturally-derived antipodes.