Effect of ß,γ-CHF- and ß,γ-CHCl-dGTP halogen atom stereochemistry on the transition state of DNA polymerase ß.

Recently, we synthesized the first individual ß,γ-CHX-dGTP diastereomers [(R)- or (S)-CHX, where X is F or Cl] and determined their structures in ternary complexes with DNA polymerase ß (pol ß). We now report stereospecificity by pol ß on the mixed ß,γ-CHX diastereomer pairs using nuclear magnetic resonance and on the separate diastereomers using transient kinetics. For both the F and Cl diastereomers, the R isomer is favored over the S isomer for G·C correct incorporation, with stereospecificities [(k(pol)/K(d))(R)/(k(pol)/K(d))(S)] of 3.8 and 6.3, respectively, and also for G·T misincorporation, with stereospecificities of 11 and 7.8, respectively. Stereopreference for the (R)-CHF-dGTP diastereomer was abolished for k(pol) but not K(d) with mutant pol ß (R183A). These compounds constitute a new class of stereochemical probes for active site interactions involving halogen atoms. As Arg183 is unique in family X pols, the design of CXY deoxyribonucleotide analogues to enhance interaction is a possible strategy for inhibiting BER selectively in cancer cells.

ß,γ-CHF- and ß,γ-CHCl-dGTP diastereomers: synthesis, discrete 31P NMR signatures, and absolute configurations of new stereochemical probes for DNA polymerases.

Deoxynucleoside 5'-triphosphate analogues in which the ß,γ-bridging oxygen has been replaced with a CXY group are useful chemical probes to investigate DNA polymerase catalytic and base-selection mechanisms. A limitation of such probes has been that conventional synthetic methods generate a mixture of diastereomers when the bridging carbon substitution is nonequivalent (X ≠ Y). We report here a general solution to this long-standing problem with four examples of ß,γ-CXY dNTP diastereomers: (S)- and (R)-ß,γ-CHCl-dGTP (12a-1/12a-2) and (S)- and (R)-ß,γ-CHF-dGTP (12b-1/12b-2). Central to their preparation was conversion of the prochiral parent bisphosphonic acids to the P,C-dimorpholinamide derivatives 7 of their (R)-mandelic acid monoesters, which provided access to the individual diastereomers 7a-1, 7a-2, 7b-1, and 7b-2 by preparative HPLC. Selective acidic hydrolysis of the P-N bond then afforded "portal" diastereomers, which were readily coupled to morpholine-activated dGMP. Removal of the chiral auxiliary by H(2) (Pd/C) gave the four individual diastereomeric nucleotides 12, which were characterized by (31)P, (1)H, and (19)F NMR spectroscopy and by mass spectrometry. After treatment with Chelex-100 to remove traces of paramagnetic ions, at pH ~10 the diastereomer pairs 12a,b exhibit discrete P(α) and P(ß)(31)P resonances. The more upfield P(α) and more downfield P(ß) resonances (and also the more upfield (19)F NMR resonance in 12b) are assigned to the R configuration at the P(ß)-CHX-P(γ) carbons on the basis of the absolute configurations of the individual diastereomers as determined from the X-ray crystallographic structures of their ternary complexes with DNA and polymerase ß.

Structure of cyclic nucleoside phosphonate ester prodrugs: an inquiry.

The configuration at phosphorus in cyclic (S)-HPMPC (1, cidofovir) and (S)-HPMPA (2) phenyl ester (5 and 6, respectively) diastereomers ((R(p))-5, (R(p))-6, (S(p))-6) was determined by X-ray crystallography and correlated to their (1)H and (31)P NMR spectra in solution. (R(p))-5 and (R(p))-6 have chair conformations with the nucleobase substituent equatorial and the P-OPh axial. Perhaps surprisingly, (S(p))-6 is (a, a) in the crystal and exists largely as an equilibrium of (a, a)/(e, e) conformers in chloroform or acetonitrile.

Approaches to tyrosine-linked peptidomimetic prodrugs of (S)-HPMP-based acyclic nucleoside phosphonates.

Synthetic approaches to a new class of tyrosine-linked prodrugs of two 3-hydroxy-2-(phosphonomethoxypropyl) (HPMP) nucleotide analogues ((S)-HPMPC and (S)-HPMPA) are outlined.

Tyrosine-based 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine and -adenine ((S)-HPMPC and (S)-HPMPA) prodrugs: synthesis, stability, antiviral activity, and in vivo transport studies.

Eight novel single amino acid (6-11) and dipeptide (12, 13) tyrosine P-O esters of cyclic cidofovir ((S)-cHPMPC, 4) and its cyclic adenine analogue ((S)-cHPMPA, 3) were synthesized and evaluated as prodrugs. In vitro IC(50) values for the prodrugs (<0.1-50 µM) vs vaccinia, cowpox, human cytomegalovirus, and herpes simplex type 1 virus were compared to those for the parent drugs ((S)-HPMPC, 2; (S)-HPMPA, 1; IC(50) 0.3-35 µM); there was no cytoxicity with KB or HFF cells at ≤100 µM. The prodrugs exhibited a wide range of half-lives in rat intestinal homogenate at pH 6.5 (<30-1732 min) with differences of 3-10× between phostonate diastereomers. The tyrosine alkylamide derivatives of 3 and 4 were the most stable. (l)-Tyr-NH-i-Bu cHPMPA (11) was converted in rat or mouse plasma solely to two active metabolites and had significantly enhanced oral bioavailability vs parent drug 1 in a mouse model (39% vs <5%).

Synthesis of peptidomimetic conjugates of cyclic nucleoside phosphonates.

Cyclic nucleoside phosphonates connected through a P-O-C linkage to a promoiety represent a class of prodrugs designed to overcome the low oral bioavailability of parent antiviral acyclic nucleoside phosphonates. In our prodrug approach, a nontoxic promoiety, such as an amino acid or dipeptide, is conjugated to the cyclic form of the parent drug by esterification of the phosphonic acid moiety with an alcoholic amino acid side chain (Ser, Tyr, and Thr) or a glycol linker. For the biological evaluation and investigation of the pharmacokinetic profiles of these modified nucleoside phosphonates, a reliable synthetic procedure that allows preparation of sufficient amount of potential prodrugs is needed. This unit provides a procedure for synthesizing peptidomimetic conjugates of two broad-spectrum antiviral acyclic nucleoside phosphonates: (S)-HPMPC and (S)-HPMPA. Two alternate strategies allowing synthesizing selected amino acid, dipeptide, or ethylene glycol-linked amino acid prodrugs of (S)-HPMPC and (S)-HPMPA in solution and using a solid-phase approach are presented.