Robert T. Parfitt

A high-performance liquid chromatographic method for the determination and control of the composition of gentamicin sulphate

Abstract A high-performance liquid chromatographic method for routine control of the composition of gentamicin sulphate is described. The method utilizes pre-column derivatization followed by reversed-phase chromatography with fluorescence detection and uses an internal standard for quantification. Analysis of 19 samples of gentamicin from various sources indicates that the ratio of the major components and the content of minor constituents varies with the geographical origin of the sample. The results were compared with those of a microbiological assay and the B.P. nuclear magnetic resonance (nmr) spectroscopic limit test of the same samples. The microbiological assay may be influenced by biologically active impurities whilst the nmr assay was insensitive to the presence of minor components. The method described offers a more discriminating and flexible means of monitoring the composition of gentamicin and hence of providing data upon which a realistic specification for this valuable antibiotic mixture can be prepared.

Studies on the mechanism of microbial N-demethylation of codeine by cell-free extracts of Cunninghamella bainieri

Abstract Cell-free extracts have been prepared from the fungus Cunninghamella bainieri which retain high levels of N -demethylase activity against codeine and other drug molecules. Extraction required both disruption and solubilization, indicating that the N -demethylase enzyme is probably membrane bound. The carbon monoxide-reduced u.v. difference spectrum of the extract suggests the presence of a cytochrome P -450. The effect of specific inhibitors and the generation of formaldehyde during the transformation suggest a mono-oxygenase mediated mechanism. Kinetic studies have shown that N -demethylation is unlikely to occur via the N -oxide intermediate. Instead it is proposed that N -demethylation proceeds via the transient N -hydroxymethyl intermediate.

The screening of some microorganisms for their ability to N-dealkylate drug molecules

SummarySelected microorganisms were screened for their ability to N-dealkylate drug molecules. The compounds studied enabled the investigation of N-alkyl groups in different chemical environments, including alkylaminoalkyl chains, saturated cyclic structures and in amide functions. Transformation products were extracted from the transformation mixtures, derivatised and analysed by gas liquid chromatography (GLC). For the purposes of screening, important transformation products were identified by comparison of their GLC retention data with similar derivatives of authentic standards. N-demethylation was effected by all test strains of the fungus Cunninghamella, except C. elegans, and also by three of the Streptomyces species tested. The Cunninghamella demonstrated the widest spectrum of transformation activity, N-demethylating the alkylaminoalkyl side chains of amitriptyline and chlorpromazine, the N-methylpiperidine function of codeine, and the cyclic amide function of diazepam. The N-demethylation of the latter substrate, which is only slightly water soluble, occurred in surprisingly high yield. There was no evidence that bulky groups such as N-dimethylallyl were celaved and selectivity for N-demethylation rather than O-demethylation was demonstrated when both N-and O-methyl functions were present in the same molecule. Comparisons are made with the mammalian metabolic pathways of the drug compounds studied.

Fentanyl and the 4-Anilinopiperidine Group of Analgesics

Paul Janssen’s exploitation of 4-piperidone chemistry during the early 1960s proved remarkably successful in that it led to the clinical use of both a major tranquillizer (haloperidol)(1) and a potent narcotic analgesic, fentanyl.(2) Fentanyl (1, Sublimaze, Leptanol) is related to pethidine and also to basic anilides with analgesic properties such as diampromide 2 (p. 311) and is characterized by high potency and short duration of action. Thus, in mice (tail-clip method) fentanyl is almost 200 times as active as morphine by the sc route and has a faster onset and shorter duration of action than the standard Open image in new window drug. It shows the usual morphinelike effects, namely, Straub tails, mydriasis, and constipation in mice; in dogs and cats it causes respiratory depression but is devoid of emetic action.(3) A clinical study in postsurgical patients and healthy volunteers showed 0.2 mg fentanyl to be equianalgesic with 10 mg morphine (im route) and the two drugs had similar side effects.(4) The respiratory action of fentanyl in healthy males was judged to be somewhat greater than that of pethidine at equianalgesic dose levels.(5) The rapid onset and short duration of action of fentanyl make it particularly well suited for use in neuroleptanalgesia and it has now achieved widespread use in surgical analgesia,(6) especially when given in combination with a major tranquilizer such as droperidol (3) (Thalamontal contains fentanyl, 50 μg, and droperidol, 2.5 mg/ml).(7)

The effects of column packing material and inorganic cations on the separation of fluorescent O-phthalaldehyde derivatives of gentamicin by high-performance liquid chromatography

Abstract Reported differences in the order of elution of fluorescent o-phthalaldehyde derivatives of gentamicins C1, C1a and C2 on apparently similar reversed-phase HPLC systems are explained. The differences arise from the relatively higher sensitivity of the κ value of the gentamicin C1 derivative to the presence of cations in the eluting solvent. This effect also depends on the commercial source of the bonded ODS phase used and is inversely related to the surface coverage of the silica with alkyl chains. The evidence suggests that this phenomenon results from an interaction between the residual silanol groups on the column support and secondary amino groups on the gentamicin derivatives, the C1 derivative differing from the C1a and C2 derivatives in having two rather than only one such group.

Two dibenzofuran derivatives from fruits of Rhodomyrtus macrocarpa

Abstract Two new isomers of the natural dibenzofuran derivative, rhodomyrtoxin, have been isolated from Rhodomyrtus macrocarpa fruits and their structures determined by spectroscopic methods. A third compound, possibly ψ rhodomyrtoxin was isolated in smaller quantities.

Isolation and characterization of a furostanol glycoside from fenugreek.

Abstract From the seed of fenugreek, a new glycoside has been isolated and shown to have the structure, (25 S )- 22 - O - methyl-5α-furostan-3β,22,26-triol 3- O -α-rhamnopyranosyl(1→2)[-β- d -glucopyranosyl (1→3)]-β- d - glucopyranoside-26- O -β- d -glucopyranoside.

Studies of carbon-13 n.m.r. spectroscopy in pharmaceutical analysis: the composition of commercial samples of gentamicin sulphate.

Two procedures for applying 13C n.m.r. spectroscopy to the quantitative analysis of the C1 C1a, and C2 components of gentamicin sulphate samples are described. One is based on the use of calibration plots of peak height ratios of analyte to standard (dioxan) resonance intensities recorded under conditions of full relaxation, the other upon a steady‐state experiment and the use of weighting factors. Spectrometer operating conditions are discussed, and the need for measurement of longitudinal relaxation time (T1) data described. Results for seven commercial samples are given and comparisons made between the two n.m.r. methods and an h.p.l.c. procedure in terms of accuracy, specificity and convenience.

4,5-Epoxymorphinans

The latex obtained by incision of the unripe seed capsule of the poppy, Papaver somniferum, and known as opium is the source of several pharmacologically important alkaloids. Dioskurides, in about a.d. 77, referred to both the latex (opos) and a total plant extract (mekonion) and to the use of oral and inhaled (pipe-smoked) opium to induce a state of euphoria and sedation. Since before the Christian era the therapeutic properties of opium were evident, with the first written reference to poppy juice being by Theophrastus in the third century b.c.

Synthesis and some reactions of 3,4,5,6-tetrahydro-3,6-dimethyl-2,6-.methano-3-benzazocin-1(2H)-one (2,5-dimethyl-8-oxo-6,7-benzomorphan)

Die Titelverbindung (Ib), durch Oxidation des Benzazocins (Ia) erhalten, wird uber das Oxim (Ic) durch Beckmann-Umlagerung in das Benzodiazoninon (II) ubergefuhrt, dessen Hydrolyseprodukt nach Uberfuhrung in das Salz (IIIa) als Ester (IIIb) charakterisiert wird.