T. R. Watson

Structure-activity relationships of benzimidazole carbamates as inhibitors of mammalian tubulin, in vitro

The structure-activity relationships of thirty-two methyl (5(6)-substituted benzimidazol-2yl) carbamates as inhibitors of the rate of polymerisation of mammalian tubulin have been investigated. The size or some colinear physico-chemical characteristic of the substituent in the 5 (or 6)-position has a profound effect on potency. The presence of branching with or without a commensurate increase in the polarity of the 5(6)-substituent adjacent to the benzimidazole ring (alpha-position) resulted in a loss of activity. The nature of the overall site, as reflected by the quantitative models, could relate to either the hydrophobicity or molar volume of the 5 (or 6)-substituents.

The disposition of biphenylacetic acid following topical application

SummaryPlasma and synovial fluid concentrations of biphenylacetic acid were determined following application of 3 g of 3% biphenylacetic acid gel to one knee of patients suffering from rheumatoid arthritis.The mean peak plasma concentration was 34 ng/ml. Synovial fluid concentrations tended to follow plasma concentrations but at a somewhat lower level, the mean peak synovial fluid concentration was 21 ng/ml. The average ratio of synovial fluid AUC (0–24 h) to plasma AUC (0–24 h) was 0.58, r=0.97.Where patients had bilateral effusions, the concentration in the ipsilateral knee at each time point examined was not significantly different to that in the contralateral knee, suggesting that absorption was initially into the plasma and subsequently into the synovium.

Two high-performance liquid chromatographic determinations for mebendazole and its metabolites in human plasma using a rapid Sep Pak C18 extraction

A rapid extraction procedure for mebendazole and its metabolites from plasma using Sep Pak C18 is described. This method eliminates the need for solvent extractions as such. Two reversed-phase high-performance liquid chromatographic determinations for these extracts, one isocratic elution and the other gradient elution, using an analytical wavelength of 254 nm are also presented. The gradient elution system provides superior resolution of these compounds and consequently has improved determination limits. For mebendazole the determination limits are 20 ng/ml (isocratic system) and 10 ng/ml (gradient system).

Interactions in phenol‐sodium dodecyl sulphate‐water systems

Changes in environment resulting from micelle formation and solubilization can be followed by observing chemical shifts in the nuclear-magnetic-resonance spectra of the components. We have used nmr spectroscopy to study interactions between phenol, water and the surfactant sodium dodecyl sulphate. Spectra were obtained in D,O:H,O (60:40) at 35 using a Perkin-Elmer R-12 high resolution spectrometer. Chemical shifts were determined by locking to tetramethylsilane as an external standard and expanding the field to 50 or 100 Hz per chart width; the accuracy of the shifts is within about f0.2 Hz. Corrections for diamagnetic susceptibilities were made where necessary. A change of medium from a polarizing to a more inert environment (such as the hydrocarbon environment of a micelle of the surfactant) may cause a considerable high-field shift (Eriksson & Gillberg, 1966). Fig. la shows the high-field shift for the phenol ring protons with increasing surfactant concentration. As this concentration increases, the ratio of micellar phenol to free phenol increases. Since the observed chemical shift is the weighted average of the free and solubilized peak positions this gives rise to a high-field shift. Extrapolation of the phenolic proton shifts to zero chemical shift gives an intercept

The biliary metabolism of butylated hydroxytoluene (3, 5‐di‐t‐butyl‐4‐hydroxy‐toluene) and its derivatives in the rat

The biliary metabolism of 3, 5‐di‐t‐butyl‐4‐hydroxybenzyl alcohol (BHT‐CH2OH), 3, 5‐di‐t‐butyl‐4‐hydroxybenzaldehyde (BHT‐CHO) and 3, 5‐di‐t‐butyl‐4‐hydroxybenzoic acid (BHT‐COOH) after parenteral administration has been examined in the rat and compared to that of 3, 5‐di‐t‐butyl‐4‐hydroxytoluene. Quantitative excretion and chemical examination of bile showed that in the enterohepatic circulation BHT‐COOH or its ester glucuronide is the recirculating compound from the four compounds studied. Biliary excretion data are also presented for 1, 2‐bis(3, 5‐di‐t‐butyl‐4‐hydroxyphenyl)ethane.

The metabolism of butylated hydroxytoluene, (3, 5‐di‐t‐butyl‐4‐hydroxytoluene) in man

The urinary metabolites of [14C]-3,5-di-t-butyl-4-hydroxytoluene (BHT) in man have been estimated by Daniel, Gage & others (1967), who found that over 50% of a 40 mg oral dose is excreted in the urine during the 24 h after dosing. The major metabolite (present to the extent of 35% of the dose) was later identified as a glucuronide of 4-carboxy-2-( 1 -carboxy-I -methylethyl)-6-( 1 -formyl-1 -methylethyl)-

Identification of biliary metabolites of Mebendazole in the rat

SummaryThree metabolites of mebendazole were isolated from the bile of rats dosed with a mixture of mebendazole and pentadeutero-mebendazole. The identification was based upon the appearance of the characteristic doublet in the mass spectrum of the compounds and the comparison of their fragmentations with those of authentic compounds. Cochromatography of the metabolites with the authentic compounds on HPLC supported the identification. Methyl-5(6)-(α-hydroxybenzyl)-2-benzimidazole carbamate, 2-amino-5(6)-(α-hydroxybenzyl) benzimidazole and 2-amino-5(6)-benzoylbenzimidazole were identified as metabolites after enzymic conjugate hydrolysis. Some unmetabolized mebendazole was also found.

In vivo and in vitro metabolism of gomphoside, a cardiotonic steroid with doubly-linked sugar

The metabolism of gomphoside, a cardiotonic steroid glycoside with doubly-linked 4,6-dideoxyhexosulose sugar was studied in vivo in rats, and in vitro using rat liver microsomes. The biliary excretion of metabolites, following intraperitoneal administrative of [3H]gomphoside, was rapid with 68% of radioactivity being collected over 8 h. The metabolites in the bile were principally a water-soluble glucuronide conjugate of gomphoside, and a small amount of chloroform-soluble metabolites. Conversion of [3H]gomphoside to metabolites by microsomes at 37 degrees C reached a maximum of 16% under optimum conditions, producing the same set of metabolites as those in the chloroform-soluble fraction of the bile. The major chloroform-soluble metabolite was the aglycone of gomphoside, viz. gomphogenin or 2 alpha,3 beta, 14-trihydroxy-5 alpha-card-20(22)-enolide. The other major component was recovered gomphoside. Other metabolites were calactin, calotropin, and 2 alpha-hydroxyuzarigenin 3-(4,6-dideoxy-beta-D-arabino-hexopyranoside). Another metabolite, which is a new cardenolide was shown to be 3-epi-gomphogenin or 2 alpha,3 alpha, 14-trihydroxy-5 alpha-card-20(22)-enolide. Gomphoside glucuronide was shown spectroscopically to have the glucuronide residue attached to position 3 of the hexosulose sugar. It was cleaved by beta-D-glucuronidase to gomphoside, and is thus gomphoside 3-beta-D-glucuronide. The metabolic transformations of gomphoside are summarized in Fig. 5.

The metabolic and pharmacokinetic disposition of mebendazole in the rat.

SummaryThe metabolism and pharmacokinetics of mebendazole was studied in rats using [2′-3H]-mebendazole (biologically stable; specific activity 383.9 (mCi/mMol) and [2-l4C]-mebendazole (specific activity 2.57 mCi/mMol). Analyses were performed by high pressure liquid chromatography and liquid scintillation spectrometry. About 85% of an intravenous dose was eliminated with the bile and the remainder with the urine. The majority of the dose was recovered as conjugated metabolites. The major metabolite (methyl-5(6)-(α-hyciroxybenzyl)-2-benzimidazole carbamate) accounted for about 77 % of the total recovered and 99 % of it was conjugated. Anaerobic metabolism studies conductedin vitro with intestinal micro-organisms obtained from rats indicated that metabolism of mebendazole did not occur in the gut, but that the intestinal microflora was able to hydrolyse conjugated metabolites which were eliminated with the bile. Mebendazole was found to have a biphasic elimination profile after intravenous administration. Its terminal plasma elimination half-life was 3.2 hours and its re-distribution half-life was 0.4 hour. After oral administration, as a solution in aqueous dimethyl sulphoxide, a bioavailability of 53 % was obtained.

4-Amino-3-(3'-methoxycarbonyl-2'-thioureido)benzophenone, a prodrug of mebendazole.

SummaryThe compound 4-amino-3-(3′-methoxycarbonyl-2′-thioureido) benzophenone has shown promise as a prodrug of the anthelmintic mebendazole. The compound is stable in acid and neutral media and is rapidly hydrolysed in base. An HPLC assay procedure for mebendazole, the prodrug and their known or expected metabolites and degradation products in aqueous media and rat blood has been developed. The prodrug administered orally to rats is rapidly converted to mebendazole. The area under the blood level versus time curve of mebendazole, in rats dosed with the prodrug, is more than twice that obtained after dosing rats with an equimolar amount of mebendazole. Only the prodrug, mebendazole and known metabolites of mebendazole are detected in rats dosed with the prodrug.