P nuclear magnetic resonance spectroscopy of lipopolysaccharides from pseudomonas aeruginosa

Intact lipopolysaccharide antigens isolated from seven different immunotypes of Pseudomonas aeruginosa have been examined by ³¹P-NMR spectroscopy. These macromolecular complexes contain phosphorus covalently attached to the carbohydrate residues present in the lipid A moiety and the ‘core’ oligosaccharide region. The spectral signals for various ortho- and pyro-phosphoric esters were observed. All phosphate groups appeared to be mono-esterified. Certain shifts characteristic for phosphate diester groups, observed in lipopolysaccharide complexes from other Gram-negative bacteria, were absent. Furthermore, no evidence was found to indicate that phosphate groups are involved in the covalent linkage of individual lipopolysaccharide complexes to form dimers or trimers.     

31P nuclear magnetic resonance spectroscopy of lipopolysaccharides from pseudomonas aeruginosa

Intact lipopolysaccharide antigens isolated from seven different immunotypes of Pseudomonas aeruginosa have been examined by ³¹P-NMR spectroscopy. These macromolecular complexes contain phosphorus covalently attached to the carbohydrate residues present in the lipid A moiety and the ‘core’ oligosaccharide region. The spectral signals for various ortho- and pyro-phosphoric esters were observed. All phosphate groups appeared to be mono-esterified. Certain shifts characteristic for phosphate diester groups, observed in lipopolysaccharide complexes from other Gram-negative bacteria, were absent. Furthermore, no evidence was found to indicate that phosphate groups are involved in the covalent linkage of individual lipopolysaccharide complexes to form dimers or trimers.     

Synthesis of C-substituted triazoles,isoxazoles, and pyrazoles by 1,3-dipolar cycloaddition to acetylenic sugars

Addition of phenyl azide to 3,5-di-O-acetyl-6,7-dideoxy-1,2-O-isopropylidene-β-l-idio-hept-6-ynofuranose (1) and subsequent saponification gave a 4-substituted 1-phenyl-1,2,3-triazole derivative (3) whose optical rotatory dispersion (o.r.d.) curve was positive. The α-d-gluco analog (5) of 1 similarly gave the 5-epimer (7) of 3; its o.r.d. curve was negative. Both 3 and 7 were degraded to the known 1-phenyl-1,2,3-triazole-4-carboxaldehyde. Similarly, addition of 2,4,6-trimethylbenzonitrile N-oxide to 1 or 5 gave the corresponding, crystalline 3-mesitylisoxazoles as single products; ¹³C-n.m.r. spectroscopy was used to establish the orientation of addition. Related 3-mesitylisoxazoles (11 and 13) were obtained from 1,2:3,4-di-O-isopropylidene-d-glycero-α-d-galacto-oct-7-ynopyranose (10) and its l-glycero 6-epimer (12), respectively; 11 showed the expected, large levorotation, and the 6-epimer 13 was also levorotatory. Benzonitrile (N-phenyl)imine, prepared in situ from 1-(α-chlorobenzylidene)-2-phenylhydrazine and base, did not react with 10 (or its 6-epimer 12), but did react with the 6-keto analog to give a 5-substituted 1,3-diphenyl-1,2-diazole.     

Reaction of derivatives of methyl 2,3-O-benzylidene-6-deoxy-α-L-mannopyranoside with butyllithium: Synthesis of methyl 2, 6-dideoxy-4-O-methyl-α-L-erytho-hexopyranosid-3-ulose

Methyl 2,3-O-benzylidene-6-deoxy-α-L-mannopyranoside (2) reacted with butyllithium to give a mixture of 1,5-anhydro-3-C-butyl-1,2,6-trideoxy-L-ribo-hex-1-enitol (3) and its L-arabino analogue (4), together with methyl 2,3,6-trideoxy-α-L-erythro-hex-2-enopyranoside (5). In contrast, the 4-O-methyl analogue (8) of 2 was converted by butyllithium into methyl 2,6-dideoxy-4-O-methyl-α-L-erythro-hexo-pyranosid-3-ulose (9), which was further characterized as its oxime 10. The 4-O-benzyl analogue of 8, obtained as two separate diastereoisomers (6 and 7) differing in configuration at C-2 of the dioxolane ring, gave a complex mixture of products on treatment with butyllithium.     

THE CONVULSANT ACTION OF METHYLDITHIOCARBAZINATE: A COMPARISON WITH OTHER SULPHUR-CONTAINING HYDRAZIDES

—The convulsant action of methyldithiocarbazinate (MDTC), thiocarbohydrazide (TCH) and thiosemicarbazide (TSC) has been studied in mice. The relationship between dose and time to convulsions indicated that MDTC has a dual action and is more potent than TSC. Pretreatment of mice with pyridoxal phosphate (0.25 mmol/kg) protected against convulsions and death produced by low doses of MDTC or TCH, and low or high doses of TSC. Pretreatment with pyridoxine hydrochloride (0.25 mmol/kg) protected mice against TSC but not against TCH. It protected against low doses of MDTC (0.12 mmol/kg), but shortened the latency to convulsions after intermediate doses of MDTC (0.37 mmol/kg). Glutamate decarboxylase activity (GAD, EC 4.1.1.15) in whole brain homogenates from mice killed at the onset of seizures, was significantly reduced by all 3 drugs at all doses. This inhibition did not exceed 30% after any dose of TSC or TCH, but was 64% in mice killed 4 min after the injection of MDTC (0.98 mmol/kg). The addition of pyridoxal phosphate to brain homogenates abolished GAD inhibition after MDTC but not after TCH. In vitro brain GAD was 50% inhibited by 10⁻⁴m -MDTC, 18% by 10⁻⁴m -TSC and 8% by 10 ⁻⁴m -TCH. Kinetic studies suggested that at low concentrations MDTC inhibits by competing with pyridoxal phosphate. At the onset of convulsions the cerebral content of pyridoxal phosphate was reduced after low or high doses of TSC (0.27 and 2.2 mmol/kg) and after high doses of MDTC (0.98 mmol/kg). All three drugs (at 10⁻⁵−10⁻⁴m ) inhibited pyridoxal phosphokinase (EC 2.7.1.35) in vitro. Short latency convulsions after MDTC (0.37–0.98 mmol/kg) very probably arise from inhibition of cerebral GAD, due to competition for coenzymic sites and/or unavailability of coenzyme. Long-latency convulsions after MDTC (0.12–0.37 mmol/kg) are comparable to those seen after TSC (0.27–2.2 mmol/kg) and may depend on a mechanism additional to inhibition of GAD.     

Blocking VLDL secretion causes hepatic steatosis but does not affect peripheral lipid stores or insulin sensitivity in mice

The liver secretes triglyceride-rich VLDLs, and the triglycerides in these particles are taken up by peripheral tissues, mainly heart, skeletal muscle, and adipose tissue. Blocking hepatic VLDL secretion interferes with the delivery of liver-derived triglycerides to peripheral tissues and results in an accumulation of triglycerides in the liver. However, it is unclear how interfering with hepatic triglyceride secretion affects adiposity, muscle triglyceride stores, and insulin sensitivity. To explore these issues, we examined mice that cannot secrete VLDL [due to the absence of microsomal triglyceride transfer protein (Mttp) in the liver]. These mice exhibit markedly reduced levels of apolipoprotein B-100 in the plasma, along with reduced levels of triglycerides in the plasma. Despite the low plasma triglyceride levels, triglyceride levels in skeletal muscle were unaffected. Adiposity and adipose tissue triglyceride synthesis rates were also normal, and body weight curves were unaffected. Even though the blockade of VLDL secretion caused hepatic steatosis accompanied by increased ceramides and diacylglycerols in the liver, the mice exhibited normal glucose tolerance and were sensitive to insulin at the whole-body level, as judged by hyperinsulinemic euglycemic clamp studies. Normal hepatic glucose production and insulin signaling were also maintained in the fatty liver induced by Mttp deletion. Thus, blocking VLDL secretion causes hepatic steatosis without insulin resistance, and there is little effect on muscle triglyceride stores or adiposity.