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.

2-Amino-6-arylsulfonylbenzonitriles as non-nucleoside reverse transcriptase inhibitors of HIV-1

A series of 2-amino-5-arylthiobenzonitriles (1) was found to be active against HIV-1. Structural modifications led to the sulfoxides (2) and sulfones (3). The sulfoxides generally showed antiviral activity against HIV-1 similar to that of 1. The sulfones, however, were the most potent series of analogues, a number having activity against HIV-1 in the nanomolar range. Structural-activity relationship (SAR) studies suggested that a meta substituent, particularly a meta methyl substituent, invariably increased antiviral activities. However, optimal antiviral activities were manifested by compounds where both meta groups in the arylsulfonyl moiety were substituted and one of the substituents was a methyl group. Such a disubstitution led to compounds 3v, 3w, 3x, and 3y having IC50 values against HIV-1 in the low nanomolar range. When gauged for their broad-spectrum antiviral activity against key non-nucleoside reverse transcriptase inhibitor (NNRTI) related mutants, all the di-meta-substituted sulfones 3u-z and the 2-naphthyl analogue 3ee generally showed single-digit nanomolar activity against the V106A and P236L strains and submicromolar to low nanomolar activity against strains E138K, V108I, and Y188C. However, they showed a lack of activity against the K103N and Y181C mutant viruses. The elucidation of the X-ray crystal structure of the complex of 3v (739W94) in HIV-1 reverse transcriptase showed an overlap in the binding domain when compared with the complex of nevirapine in HIV-1 reverse transcriptase. The X-ray structure allowed for the rationalization of SAR data and potencies of the compounds against the mutants.

Inhibition of uridine phosphorylase. Synthesis and structure-activity relationships of aryl-substituted 1-((2-hydroxyethoxy)methyl)-5-(3-phenoxybenzyl)uracil

Structure-activity relationship studies on a series of 1-((2-hydroxyethoxy)methyl)-5-(3-(substituted-phenoxy)benzyl)uracils as inhibitors of murine liver uridine phosphorylase have led to compounds with IC50s as low as 1.4 nM. The two most potent compounds, 10j (3-cyanophenoxy) and 11f (3-chlorophenoxy) were tested in vivo for effects on steady-state concentrations of circulating uridine in mice and rats. Both compounds were substantially more efficacious than BAU (5-benzylacyclouridine) both in vitro and in vivo.

Inhibition of uridine phosphorylase: synthesis and structure-activity relationships of aryl-substituted 5-benzyluracils and 1-[(2-hydroxyethoxy)methyl]-5-benzyluracils

A series of 1-[(2-hydroxyethoxy)methyl]-5-benzyluracils were synthesized and tested for inhibition of murine liver uridine phosphorylase (UrdPase). Inhibitors of UrdPase are reported to enhance the chemotherapeutic utility of 5-fluoro-2'-deoxyuridine and 5-fluorouracil and to ameliorate zidovudine-induced anemia in animal models. We prepared a series of 5-aryl-substituted analogues of 5-benzylacyclouridine (BAU), a good inhibitor of UrdPase (IC50 of 0.46 microM), to develop a compound with enhanced potency and improved pharmacokinetics. The first phase of structure-activity relationship studies on a series of 32 aryl-substituted 5-benzyluracils found several 5-(3-alkoxybenzyl) analogues of 5-benzyluracil with enhanced potency. The acyclovir side chain, the (2-hydroxyethoxy)methyl group, was substituted on the more potent aryl-substituted 5-benzyluracils. The two most potent compounds, 10y (3-propoxy) and 10dd (3-sec-butoxy), were inhibitors of UrdPase with IC50s of 0.047 and 0.027 microM, respectively. Six compounds were tested in vivo for effects on steady-state concentrations of circulating uridine in rats. Plasma uridine levels were elevated 3-9-fold by compound levels that ranged from 8 to 50 microM.

Nucleotide analogue inhibitors of purine nucleoside phosphorylase

The diphosphate of the antiherpetic agent acyclovir [9-[(2-hydroxyethoxy)methyl]guanine] has been shown to inhibit purine nucleoside phosphorylase with unique potency (Tuttle, J. V., and Krenitsky, T. A. (1984) J. Biol. Chem. 259, 4065-4069). A major factor contributing to the superior inhibition by this diphosphate over the corresponding mono- and triphosphates is revealed here. Homologues of acyclovir mono- and diphosphate that extend the ethoxy moiety by one to four methylene groups were synthesized. These homologues were evaluated for their ability to inhibit human purine nucleoside phosphorylase. Within the diphosphate series, the Ki values increased progressively with increasing chain length. With the monophosphates, the Ki values reached a minimum with the homologue containing a pentoxy moiety. A plot of chain length versus Ki values for both mono- and diphosphates showed that both series had similar optimal distances between the aminal carbon and the terminal oxygen anion. Monophosphates with optimal positioning were somewhat less potent than diphosphates with similar positioning. Nevertheless, it was clear that a major factor in determining potency of inhibition was the distance of the terminal phosphate from the guanine moiety.

Neogymnomyces, a new genus of the Gymnoascaceae

Four strains of Gymnoascus demonbreunii have been studied on various media at room temperature and at 37 °C. Ascocarps were produced on most media and naked mature asci on some media. No growth was demonstrated by any of the strains at 37 °C. Spore suspensions of the various strains were injected intraperitoneally into mice; most of the strains were recovered, but no lesions or other abnormalities were observed in any tissues.G. demonbreunii is shown to have no taxonomic relationship with Histoplasma capsulatum and is not the sexual state of that fungus. Comparisons of G. demonbreunii with species of Gymnoascus revealed significant morphological differences that require the inclusion of G. demonbreunii in a new genus, Neogymnomyces.

THE GENUS MYXOTRICHUM KUNZE

The genus Myxotrichum Kunze is monographed and limited to seven valid species. Twenty-five previously described species of Myxotrichum are excluded from the genus and placed in other Gymnoascaceous genera or elsewhere. Two new combinations are described. Myxotrichum is considered to be represented by M. chartarum (Nees) Kunze, M. aeruginosum Montagne, M. deflexum Berkeley, M. ochraceum Berkeley and Broome, M. setosum (Eidam) comb, nov., M. stipitatum (Lindfors) comb, nov., and M. carminoparum Robak.

A NEW GENUS OF THE GYMNOASCACEAE WITH SWOLLEN PERIDIAL SEPTA

A new genus of the Gymnoascaceae, Auxarthron, is established to include certain species previously excluded from Gymnoascus and Myxolrichum. The genus is characterized by the presence of (1) enlargements at the septa in the peridial hyphae; (2) ascospores globose, subglobose to ovoid, asperulate to echinulate-reticulate, and hyaline to pale orange-yellow-brown; (3) the presence of either short spines or elongate appendages, or both; (4) lightly colored, elongate appendages which are non-septate except for one, two, or three basal septa with characteristic swellings at such septa; (5) orange-yellow-brown colored to brown ascocarps with a peridial network of more or less dichotomously anastomosed hyphae. Seven species are included in the genus as follows: Auxarthron californiense sp. nov. (the type species), A. reticulatum (Zukal) comb, nov., A. zuffianum (Morini) comb, nov., A. umbrinum (Boudier) comb, nov., A. brunneum (Rostrup) comb, nov., A. conjugatum (Kuehn) comb, nov., and A. conipactum sp. nov.