Studies on antibiotics antiviral activity of compounds related to pterygospermin

Abstract

Chapter I: General Introduction The current concepts and avenues to viral chemotherapy have been briefly reviewed. The extreme parasitism of viruses-as defined by their size, habitat, mode of replication, and complete dependence on host cell metabolism for multiplication-limits chemotherapeutic approaches for their control, since their restricted enzymic make up offers fewer possibilities for selectively interfering with viral growth without impairing vital host cell reactions. Viral classification, composition, infectivity, and the possible modes of interference by potential antiviral agents during various phases of viral multiplication in the host cell, as well as the widely dissimilar chemical types (Appendix I) hitherto screened for antiviral activity, have been discussed briefly. Present investigations: Several synthetic compounds containing the structural sequence N-C-S, as in pterygospermin and its decomposition product benzyl isothiocyanate, were previously examined in this laboratory (Appendix II) for antivaccinia and anti influenza activity. The present studies extend these observations, primarily with respect to the effect of substitution in benzyl isothiocyanate residues on antimicrobial responses.

Chapter II: Experimental Techniques The experimental methods and procedures used for determining antivaccinia, anti influenza, antibacterial, and antifungal activities of the compounds described in Chapter III are outlined. Although tissue culture techniques are widely used in viral studies and are convenient, they were not adopted here in order to maintain comparability with earlier work in this laboratory. Instead, classical chick embryo techniques using egg adapted vaccinia and influenza (PR8) viruses were employed for primary antiviral screening. Secondary screening was carried out on mouse influenza and rabbit vaccinia infections. Serial dilution assays, routinely used in this laboratory, were adopted for antibacterial and antifungal tests.

Chapter III: Preparation of Substituted Benzylaminothiomethane Sulphonic Acids and Other Compounds The following compounds-some of them prepared for the first time-were synthesised using standard procedures for antimicrobial assays: (a) Substituted isothiocyanates Benzyl ; o , m , and p monomethyl ; o , m , and p monomethoxy ; o isopropyl ; m nitro ; 2,3 , 2,4 , and 2,5 dimethyl benzyl ; phenylethyl ; phenylpropyl ; benzhydryl ; and and naphthylmethyl isothiocyanates. (b) Potassium salts of substituted aminothiomethane sulphonates Benzyl ; o , m , and p monomethyl ; o , m , and p monomethoxy ; o isopropyl ; m nitro ; 2,4 , and 2,5 dimethyl benzyl ; phenyl ; phenylethyl ; phenylpropyl ; and and naphthylmethyl aminothiomethane sulphonates. (c) Substituted thioureas o Xylyl , di o xylyl , di p xylyl , di p methylphenyl , and dibenzyl thioureas. (d) 4 Substituted thiosemicarbazides 4 o Methylbenzyl , 4 p methylbenzyl , 4 p methoxybenzyl , 4 phenyl , 4 benzyl , 4 o methylphenyl , 4 p methylphenyl , 4 methyl , 4 formyl , and 4 benzhydryl thiosemicarbazides. (e) 5 Substituted aminothiatriazoles and amine X 5 Aminothiatriazole; 5 phenyl , 5 benzyl , 5 p methylphenyl , 5 o methylphenyl , 5 p methylbenzyl , 5 o methylbenzyl , and 5 methyl aminothiatriazoles; and “amine X”. (f) Thiosemicarbazones Benzaldehyde ; o , m , and p hydroxy ; o , m , and p methoxy ; o nitro ; o amino ; and p dimethylamino benzaldehyde thiosemicarbazones; and isatin 3 thiosemicarbazone. (g) 1 Substituted tetrazole 5 thiols 1 Phenyl and 1 benzyl tetrazole 5 thiols. (h) N Alkylbenzylamines N methyl , N ethyl , and N isopropyl benzylamines. Attempts to prepare and characterise the active compound earlier designated amine X are also described.

Chapter IV: Antiviral Activity of Substituted Potassium Benzylaminothiomethane Sulphonates and Other Compounds The antiviral, antibacterial, and antifungal responses of substituted benzyl isothiocyanates, their bisulphite addition compounds, and other derivatives are analysed relative to their structural features. The activities support the earlier “isothiocyanate hypothesis” (Kurup and Rao, Indian J. Med. Res., 1957):

Substitution on the side chain methylene by methyl, ethyl, or phenyl reduces activity markedly. Activity is largely retained with o methyl or p methyl substitution, but lost when both positions are substituted. Methoxy groups lower activity; o isopropyl abolishes activity. Dimethyl or nitro substitution eliminates antimicrobial activity. Replacing the benzene ring with or naphthyl groups produces inactive compounds. The sulphur atom in the N-C-S sequence is essential. Thioureas and thiosemicarbazones are generally inactive. Two structurally unrelated compounds-5 benzylaminothiatriazole and amine X-show antiviral but not antibacterial or antifungal activity.

Therapeutic findings:

p Methyl BAC is toxic; MO, o methyl MO, and amine X show therapeutic activity in vaccinia infections in rabbits. Amine X does not act against mouse influenza, unlike the others. MO and o methyl BAC exert prophylactic antiviral action in eggs, effective when administered 24 hours before inoculation.

Mode of antiviral action:

MO and o methyl MO reduce the virulence of vaccinia virus without altering virus yield, effective when given within 5 hours post infection or 1 hour pre infection suggests interference with the eclipse phase. Amine X inhibits virus production, acting during the first 12 hours after infection indicates a different mechanism.

Biochemical interactions:

Antimicrobial activity of MO, o methyl MO, and p methyl BAC is specifically antagonised by aneurin (vitamin B ); partly influenced by glutamic acid; marginally affected by pyridoxine; unaffected by other B vitamins or amino acids. They do not significantly affect glucose oxidation by Staphylococcus or succinate oxidase in rat liver mitochondria.

Toxicity:

p Methyl BAC: 45 ± 3.2 mg/kg (mice, intraperitoneal). o Methyl BAC: 168 ± 2.5 mg/kg (mice), comparable to MO. Amine X: intravenous doses of 50 mg/kg/day for 3 days tolerated in rabbits.

The findings extend the isothiocyanate hypothesis by highlighting a possible isosteric relationship with aneurin, influencing biological activity.