Lilia M. Beauchamp

Amino acid ester prodrugs of acyclovir

Eighteen amino acid esters of the antiherpetic drug, acyclovir, were synthesized as potential prodrugs for oral administration. The esters were examined for in vitro antiviral activity against herpes simplex virus Type 1 (HSV-1). They were found to have less potency than the parent compound. Their efficiencies as prodrugs were evaluated in rats by measuring the urinary recovery of acyclovir. Ten prodrugs produced greater amounts of the parent drug in the urine. The L-amino acid esters were better prodrugs than the corresponding D- or D, L-isomers, suggesting the involvement of a stereoselective transporter. The L-valyl ester, 256U87, was the best prodrug. Sixty three per cent of its administered dose was excreted as acyclovir in the urine, a considerable improvement over acyclovir itself, for which this value was 19%. Since 256U87 was stable in aqueous solutions, its conversion to acyclovir in vivo was probably enzyme catalyzed. This L-valyl ester prodrug of acyclovir is now undergoing clinical evaluation.

Enzymatic phosphorylation of acyclic nucleoside analogs and correlations with antiherpetic activities

Abstract The inhibitor and substrate specificities of deoxythymidine (dThd) kinase purified from herpes simplex virus (HSV Type 1) were studied. A number of nucleosides and nucleoside analogs were phosphorylated by the virus coded enzyme. These included several compounds structurally related to 9-(2-hydroxyethoxymethyl)guanine (acyclovir), a potent inhibitor of HSV replication. Some contained guanine with 9-substituents differing from that of acyclovir by methylene additions, methylene and thioether substitutions for the ether oxygen, and branching on the distal side of the ether oxygen. Others were various 2-substituted 6-hydroxypurines with the 9-(2-hydroxyethoxymethyl) substituent. A limitation of the specificity of the enzyme with guanine derivatives was the lack of phosphorylation of any derivative with an acyclic moiety branched on the proximal side of the ether oxygen. Many of the compounds that were phosphorylated were subsequently found to inhibit HSV replication. Such compounds apparently inhibited HSV replication via the same route of activation previously described for acyclovir [G. B. Elion, P. A. Furman, J. A. Fyfe, P. de Miranda, L. Beauchamp and H. J. Schaeffer, Proc. natn. Acad. Sci. U.S.A. 74 , 5716 (1977)]. Moreover, several compounds not phosphorylated by the enzyme did not inhibit replication. However, some other acyclic nucleoside analogs that were phosphorylated were not good antivirals, indicating that phosphorylation catalyzed by the HSV dThd kinase was not sufficient for inhibition of viral replication to occur. These results emphasize the importance of the specificity of cellular kinases and the HSV DNA polymerase to the mechanism of antiviral activity. The dThd kinase from Vero cells was also purified. With this host cell enzyme, kinetic constants of known antiviral compounds were determined and compared to those of dThd (relative V ′ max ; k ′ m ): dThd (100; 1.3 μM), 5-iodo-2′-deoxyuridine (87; 1.8 μM), 5-trifluoromethyl-2′-deoxyuridine (91; 1.2 μM), 5-bromo-2′-deoxycytidine (5; 580 μM), and 9-β- d -arabinofuransoylthymine (23; 2300 μM). None of the purine acyclic nucleoside analogs tested (at 1000 μM) was detectably phosphorylated by the Vero cell enzyme, and all had apparent K i values >300 μM. The phosphorylation catalyzed by host cell dThd kinase correlated with the toxicity of some pyrimidine nucleoside analogs.

Anxiolytic activity of analogues of 4-benzylamino-2-methyl-7H-pyrrolo[2,3-d]pyrimidines

Abstract An extensive series of analogues of the lead anxiolytic 4-benzylamino-2-methylpyrrolo[2,3-d]pyrimidine 1 was synthesized and evaluated in the Geller-Seifter conflict test for anxiolytic activity to discover a less toxic derivative. Analysis of the SAR revealed that the most potent compounds were those with meta substituents on the benzylamino ring. In this group the most promising derivatives were 4-[bis(3,5-dimethylamino)]benzylamino-2-methyl-7H-pyrrolo[2,3-d]pyrimidine 12 and 4-(3,5-dimethylbenzyl-amino)-2-rnethyl-7H-pyrrolo[2,3-d]pyrimidine 24. Potential metabolites of 12 were synthesized and checked for their anxiolytic activity. Less toxic analogues of the second lead 24 were prepared by extending the alkyl groups attached to the benzene ring moiety. The addition of a fluoro substituent to the benzene moiety in the extended alkyl chain analogue 4-(3,5-diethyl-2-fluorobenzylamino)-2-methyl-7H-pyrrolo[2,3-d]pyrimidine 34 resulted in a compound with a longer duration of activity relative to its analogue 4-(3,5-diethylbenzylamino)-2-methyl-7H-pyrrolo[2,3-d]pyrimidine 26.

Chapter 15. Antiviral Agents

Publisher Summary Important advances in antiviral chemotherapy have been made with the food and drug administration (FDA) approval of idoxuridine, vidarabine, and trifluridine for the topical treatment of herpetic keratitis and of amantadine for oral treatment of all influenza A virus infections. Acyclovir, with its unique mechanism of action, although it was possible to share to some degree by a number of new antiviral pyrimidine nucleosides, may mark the beginning of a period of development of drugs with selective antiviral activity against several classes of viruses. This chapter discusses both new and old compounds with activity against DNA viruses and includes a brief update of the advances in the RNA area. Of the DNA viruses, the herpes group is the source of the most common viral illnesses in man. The family consists of herpes simplex virus (HSV) types 1 and 2 (cause of “cold sores,” encephalitis, eye, and genital infections), varicella zoster (VZV) (chickenpox and shingles), cytomegalovirus (CMV) (pneumonia, CNS diseases, and disseminated infections especially in neonates), and Epstein-Barr virus (EBV) (mononucleosis). All the herpesviruses share the characteristic of undergoing periods of dormancy. During that, they reside either in ganglionic sites or, in the case of EBV and possibly CMV, in lymphocytes. For reasons that are not well understood, these latent viruses may be reactivated to initiate recurrent or new forms of illness. Significant progress has also been made in the clinical use and development of agents active against RNA viruses. Clinical efficacy with both amantadine and rimantadine for the treatment of influenza A infections has been further substantiated. Ribovirin appears to be effective against influenza when administered by the inhalation of a small-particle aerosol through a face mask. A new compound, sodium 5-aminosulfonyl-2,4-dichlorobenzoateI has good in vitro activity against several strains of influenza virus and has been effective in reducing mortality in mice. Several other agents have been reported with potent in vitro activity against rhinovirus.

The antiinfluenza activity of pyrrolo[2,3-d]pyrimidines

Abstract From a group of pyrrolo[2,3- d ]pyrimidine compounds that have been screened against influenza virus, one derivative, 4-(3-piperidinyl benzylamino)-2-methyl-7 H -pyrrolo[2,3- d ]pyrimidine ( 9 ), has shown promising activity against both the A and B strains. The compound had activity comparable to amantadine, but was inactive when given orally. 4-(Substitutedphenyl ethylamino)-2-methyl-7 H -pyrrolo[2,3- d ]pyrimidines showed no improved activity.

Phosphorylation of ganciclovir phosphonate by cellular GMP kinase determines the stereoselectivity of anti-human cytomegalovirus activity.

Abstract A racemic mixture of ganciclovir phosphonate was resolved by stereoselective phosphorylation using GMP kinase. The R-enantiomer of ganciclovir phosphonate was active against human cytomegalovirus but the S-enantiomer was less active. We show that enantiomeric selectivity of antiviral activity for ganciclovir phosphonate was conferred by stereoselective phosphorylations by mammalian enzymes, not by stereoslective inhibition of DNA polymerase from human cytomegalovirus.

Acyclic Nucleosides. Synthesis and Antiherpetic Activity of 9-[[[2-Hydroxy-1-(Hydroxymethyl)Ethyl]Thio]Methyl]Guanine and 1-[[[2-Hydroxy-1-(Hydroxymethyl)Ethyl]Thio]Methyl]Cytosine

Abstract The synthesis and antiherpetic activity of 9-[[[2-hydroxy-1-(hydroxymethyl)ethyl]thio]methy1]guanine (4) and 1-[[[2-hydroxy-1-(hydroxymethyl)ethyl]thio]methy]cytosine (6), the side-chain thio analogues of ganciclovir (3) and BW A1117U (5), are described. The sidechain synthon 1,3-bis(benzyloxy)-2-[(chloromethyl)thio]propane (11) was prepared in four steps from 1,3-bis(benzyloxy)-2-propanol (7). Alkylation of 2-amino-6-chloro-9H-purine with 11 provided the intermediate 9-substituted-2-amino-6-chloropurine 12, which was conveniently converted to 4 in two steps. Reaction of a fivefold excess of cytosine with 11 provided the desired 1-isomer 14, which was debenzylated to give 6. In contrast with ganciclovir (3) and BW A1117U (5), neither 4 nor 6 had significant in vitro activity against human cytomegalovirus.

Synthesis of a Fluorinated Ganciclovir Analog

Abstract The synthesis of a new ganciclovir analog with a trifluoromethyl group in the acyclic chain is described.

An Efficient Synthesis of 2-[(4-Amino∼1,2-dihyro-2-oxo-1- pyrimidinyl)methoxyi-l,3-propanediyl-di-L-valinate an Anti-cytomegalovirus Agent

Abstract A novel synthesis of 1-(β-D-pentopyranosyl)pyridinethione nucleosides utilizing pyridine-2(1H)-thiones and α-bromoxylose or β-bromoarabinose triacetate as starting components is described. The free nucleosides were tested for their potential activity against HIV and different types of tumor virus.