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The use of chemical ionization mass spectrometry for the characterization of analogues of methotreate, N-[4-[[(2,4-diamino-6-pteridinyl)methyl]amino]benzoyl]-L-glutamic acid, has been studied. With methane as reactant gas, abundant [MH]+ions were generally not produced. However, with ammonia, especially in conjunction with thermal desorption from a platinum wire, significant amounts of [MH]+ions were formed by methotrexate, the a-, ?- and diamide analogues, and series of a- and ?-monoalkylamide derivatives. The t-butyl esters of the various monoamides behaved similarly to the corresponding monoamides, except for the ready loss of isobutylene. Fragment ions from both methane and ammonia chemical ionization were formed by cleavages ‘benzylic’ to the pteridine ring, by bond breakage at the amide bond between the aminobenzoyl and glutamyl moieties, and by fragmentations on both sides of this amide bond. Fragment ions from these processes, in conjunction with further disintegration of the glutamyl moiety, are diagnostic of the pteridine, aminobenzoyl and glutamyl moieties of the analogues. Examples of application to structural determination are given.

The majority (85%) of 394 monarch butterflies sampled from overwintering sites in Mexico contain the same epoxy cardenolide glycosides, including most conspicuously a novel polar glycoside with a single genin-sugar bridge (aspecioside), as occur in the milkweedsAsclepias speciosa andA. syriaca. This cardenolide commonality was established by isolating aspecioside and syriobioside from the wings of overwintering monarchs and the two plant species, and comparing Chromatographie and NMR spectrometric characteristics of the isolates. When combined with the migratory pattern of monarchs and the distribution of these two milkweed species, this chemical evidence lends strong support to the hypothesis thatA. syriaca is the major late summer food plant of monarchs in eastern North America. This finding may be of ecological importance, forA. syriaca contributes less cardenolide and cardenolides of lower emetic potency to monarchs than most milkweeds studied to date.

The conformation of a small molecule in its binding site on a protein is a major factor in the specificity of the interaction between them. In this paper, we report the use of 1H and 13C NMR spectroscopy to study the fluctuations in conformation of the anti-bacterial drug trimethoprim when it is bound to its "target," dihydrofolate reductase. 13C relaxation measurements reveal dihedral angle changes of +/- 25 degrees to +/- 35 degrees on the subnanosecond time scale, while 13C line-shape analysis demonstrates dihedral angle changes of at least +/- 65 degrees on the millisecond time scale. 1H NMR shows that a specific hydrogen bond between the inhibitor and enzyme, which is believed to make an important contribution to binding, makes and breaks rapidly at room temperature.

332 species of plants from the colony of Hong Kong have been tested for the presence of alkaloids. 38 gave strong positive reactions.

Under the reaction conditions indicated, the diones (Ia) and (Ib) afford the hydroxylation products (Ic) and (Id) together with the degradation product (II) (yields given in mg).

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An attempt was made in children to identify a urinary halothane—cysteine conjugate which had been described previously in adult patients following administration of halothane. If this conjugate was found it would indicate that a reductive metabolite of halothane binds covalently with the sulphydryl-containing amino acid, cysteine, a reaction which could lead to hepatic injury. The potential halothane—cysteine conjugate, N-acetyl-S-(2-bromo-2-chloro-1, 1-difluoroethyl)-L-cysteine (acetyl BCFEC), was prepared and the identity of the compound established using hydrogen-1 and carbon-13 NMR spectroscopy and methane chemical ionization mass spectrometry. A measurement technique for acetyl BCFEC was developed using HPLC with u.v. detection at 200 nm. In six children after halothane anaesthesia, one child being studied twice, urine was collected for up to 1 week and analysed for acetyl BCFEC. Little or no acetyl BCFEC was detected in any of the 43 urine samples tested, indicating that in children it is not a significant urinary metabolite of halothane.

The cardenolide glycosides (Ia) (calactin), (Ib) (calotropin), (Ic) (calotoxin), (Id) (afroside), (IIIa) (gofruside), and (IIIb) (frugoside), the genin (IIa) (calotropagenin) as well as the novel glycosides (IIb) and (IIc) (the glucosides of calotropagenin or gomphogenin, resp.) are isolated from the title species.