Compound 10b, 6-acetamido-6,8-dideoxy-D-erythro-beta-D- galacto-octopyranosyl-1-oxyacetic acid sodium salt, was synthesised by hydrazinolysis of Lincomycin, acetylation of methylthiolincosaminide (MTL) 9a, and by subsequent glycosylation of acetate 9b with methyl glycolate under mild conditions (NIS/TfOH). The methyl ester 10a was hydrolysed by treatment with Amberlite Ira-4OO (OH-) resin and aqueous sodium hydroxide, followed by neutralisation with Dowex-50 W x 8 (H+) resin and lyophilisation to give 10b. This carboxylate may represent the first derivative in a novel series of sialidase inhibitors utilising carbohydrate natural products. The phosphonate 11c, prepared under the same experimental conditions with dibenzyl(hydroxymethyl)phosphonate as acceptor, also displays an inhibitory activity towards Clostridium perfringens sialidase (Ki in mM range as with Neu5Ac).

Acetates↗

PubMedDate not supplied

Opioid dependence in myenteric neurons innervating the circular muscle of guinea-pig ileum.

Guinea-pigs were treated with morphine for 6-8 days by subcutaneous implantation of pellets, each containing a mixture of morphine base (120 mg) and morphine hydrochloride (35 mg). Each guinea-pig received a single pellet. Mechanical activity of the circular muscle was recorded in vitro in preparations comprising the circular muscle and myenteric plexus. Exposure to morphine was maintained by addition of 1 microM morphine to the organ baths. After 90 min, morphine was withdrawn, either by repeatedly washing tissues in morphine-free Krebs' solution, or by addition of naloxone to reduce the occupancy of the opioid receptors by morphine. Withdrawal of morphine resulted in markedly enhanced contractile activity compared with that in circular muscle-myenteric plexus preparations from untreated control guinea-pigs. The withdrawal contractions were abolished by tetrodotoxin (600 nM) and greatly reduced by hyoscine (1 microM), indicating that they resulted from action potential discharge in myenteric neurons that release acetylcholine onto the circular muscle. Activation of the cholinergic excitatory motor neurons was not secondary to synaptic activation by cholinergic interneurons, because hexamethonium (100 microM) did not affect withdrawal contractions. The withdrawal response may therefore arise in the cholinergic excitatory motor neurons themselves, or in neurons that activate them via noncholinergic mechanisms.

Animals↗

PubMedDate not supplied

Effect of nickel(II) on DNA-protein interactions.

Alterations in DNA-protein interactions (DPI) may play an important role in carcinogenesis. Although the mechanism of nickel carcinogenesis is unknown, nickel reportedly affects DPI. A microfiltration, nitrocellulose filter assay was utilized to study DPI in intact Chinese hamster ovary (CHO) cells and in isolated nuclei. Prior to exposure of CHO cells or isolated CHO cell nuclei, DNA and proteins were radiolabeled using 3H-thymidine and 35S-methionine, respectively. Nuclei were exposed to NiCl2 in 10 mM HEPES buffer (pH 6.8). CHO cells were exposed in either complete or a salts-glucose medium. Following exposure, nuclei or cells were incubated at 37 degrees C for 20 min in a high salt lysis solution; aliquots were loaded onto nitrocellulose filters and washed with a low salt solution. DNA (3H) retained on each filter was normalized to protein (35S) bound on the filter. Exposure of either whole cells or isolated nuclei to increasing, noncytotoxic concentrations of NiCl2 resulted in a dose dependent decrease in DPI. The effect of nickel on specific DNA-protein interactions was examined using a band shift assay and a cloned satellite DNA sequence. Nickel inhibited specific protein binding to the satellite DNA probe. The results of these two independent assays, which were conducted at physiological pH, indicate that NiCl2 inhibits specific DNA-protein interactions.

Animals↗