Antiviral (RNA) activity of selected Amaryllidaceae isoquinoline constituents and synthesis of related substances.

A series of 23 Amaryllidaceae isoquinoline alkaloids and related synthetic analogues were isolated or synthesized and subsequently evaluated in cell culture against the RNA-containing flaviviruses (Japanese encephalitis, yellow fever, and dengue viruses), bunyaviruses (Punta Toro, sandfly fever, and Rift Valley fever viruses), alphavirus (Venezuelan equine encephalomyelitis virus), lentivirus (human immunodeficiency virus-type 1) and the DNA-containing vaccinia virus. Narciclasine [1], lycoricidine [2], pancratistatin [4], 7-deoxypancratistatin [5], and acetates 6-8, isonarciclasine [13a], cis-dihydronarciclasine [14a], trans-dihydronarciclasine [15a], their 7-deoxy analogues 13b-15b, lycorines 16 and 17, and pretazettine [18] exhibited consistent in vitro activity against all three flaviviruses and against the bunyaviruses, Punta Toro and Rift Valley fever virus. Activity against sandfly fever virus was only observed with 7-deoxy analogues. In most cases, however, selectivity of the active compounds was low, with toxicity in uninfected cells (TC50) occurring at concentrations within 10-fold that of the viral inhibitory concentrations (IC50). No activity was observed against human immunodeficiency virus-type 1, Venezuelan equine encephalomyelitis virus, or vaccinia viruses. Pancratistatin [4] and its 7-deoxy analogue 5 were evaluated in two murine Japanese encephalitis mouse models (differing in viral dose challenge, among other factors). In two experiments (low LD50 viral challenge, variant I), prophylactic administration of 4 at 4 and 6 mg/kg/day (2% EtOH/saline, sc, once daily for 7 days, day -1 to +5) increased survival of Japanese-encephalitis-virus-infected mice to 100% and 90%, respectively. In the same model, prophylactic administration of 5 at 40 mg/kg/day in hydroxypropylcellulose (sc, once daily for 7 days, day -1 to +5) increased survival of Japanese-encephalitis-virus-infected mice to 80%. In a second variant (high LD50 viral challenge), administration of 4 at 6 mg/kg/day (ip, twice daily for 9 days, day -1 to +7) resulted in a 50% survival rate. In all cases, there was no survival in the diluent-treated control mice. Thus, 4 and 5 demonstrated activity in mice infected with Japanese encephalitis virus but only at near toxic concentrations. To our knowledge, however, this represents a rare demonstration of chemotherapeutic efficacy (by a substance other than an interferon inducer) in a Japanese-encephalitis-virus-infected mouse model.

Synthesis and antiviral evaluation of N-carboxamidine-substituted analogues of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamidine hydrochloride.

Ten, hitherto unreported, analogues of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamidine hydrochloride (2a, ribamidine) and methyl carboximidate 5 have been synthesized. These include the N-cyano (2b), N-alkyl (2c-e), N-amino acid (2f-h), N,N'-disubstituted (6, 7a,b), and the N-methylated carboxamide (1f) analogues of ribavirin. In addition, a new facile synthesis of carboxamidine 2a was also developed. All compounds were evaluated for biological activity against the following RNA viruses: Punta Toro (PT) and sandfly fever (SF) viruses (bunyaviruses); Japanese encephalitis (JE), yellow fever (YF), and dengue-4 viruses (flaviviruses); parainfluenza type 3 (PIV3), respiratory syncytial virus (RSV), and measles viruses (paramyxoviruses); influenza A and influenza B viruses (orthomyxoviruses); Venezuelan equine encephalomyelitis virus (VEE, alphavirus); human immunodeficiency virus type-1 (HIV-1, lentivirus); the DNA-containing vaccinia (VV) virus (poxvirus); and adeno type 5 (Ad5) viruses. All of the compounds except for 2b and 7a,b exhibited activity against the bunyaviruses such as that observed with 2a; however, higher IC50 values were generally observed. Glycine analogue 2f showed activity in PT-virus-infected mice in terms of increased survivors and decreased markers of viral pathogenicity. Carboxamidine 2a, carboximidate 5, and dimethyl amidine 6 exhibited activity against dengue type-4 virus. Monomethyl amidine 2c demonstrated activity against RSV, PIV3, and, to a lesser extent, influenza A and B. Activity of 2c generally required higher IC50 values than unsubstituted 2a. The latter exhibited hitherto unreported activity against RSV; therapeutic indices for 2a against RSV and PIV3 were greater than 64 and greater than 21. No substantial in vitro activity was observed for any of the compounds tested against Ad5, measles, JE, YF, VEE, or HIV-1. In addition, evidence is presented which argues in favor of a distinct antiviral mechanism of action for carboxamidines, e.g. 6, in contrast to a role as a carboxamide precursor.