thiourea and thiocyanate

The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at -78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α-selectivity. The high selectivity extends to the 4-O-benzyl-protected 3-OH acceptors, which are typically less reactive and selective than galactose 3,4-diols. Treatment of the α-sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5-N5 bond by a C-H or a C-C bond. The reaction of the isothiocyanate-protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α-selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5-position.

Topics: Deamination; Glycosides; Guanidine; N-Acetylneuraminic Acid; Silanes; Stereoisomerism; Thiocyanates; Thiourea

Syntheses and single crystal X-ray structural characterizations, together with infrared spectroscopic studies, are recorded for 1 : 1 adducts of silver(I) thiocyanate with thiourea ('tu') and N,N'-diethylthiourea ('detu' identical with (EtNH)(2)CS). The two complexes display novel and different polymeric forms. That formed with tu is a double-stranded form, comprising a pair of Ag(mu-S-tu)Ag(mu-... strands linked by pairs of mu-SCN anions, the whole array having quasi-2 symmetry about the polymer axis. The detu adduct takes the ionic form [Ag(detu)2](infinity|infinity)[Ag(SCN)2](infinity|infinity), both cation and anion being one-dimensional polymers lying in parallel, and both of the form ...Ag(mu-S-L)2Ag(mu-... (L = SCN or detu), disposed about crystallographic 4 axes. Redeterminations of the structures of AgSCN : tu, etu (1 : 2) ('etu' = ethylenethiourea, (CH2NH)2CS)) with quasi-trigonal silver atom environments (the etu adduct the more closely so), are also recorded as a basis for an IR spectroscopic characterization of the [(NCS)Ag(S-xtu)2] array. A mechanochemical/infrared study of the AgSCN:etu (1 : 1) system showed that no 1 : 1 complex exists in this case, the product being a mixture of the 1 : 2 complex and a novel 1 : 0.5 complex. The latter complex was prepared both mechanochemically and from solution, and characterized by infrared spectroscopy. Diagnostic ligand and metal-ligand bands in the IR and far-IR spectra are assigned for all of the complexes studied and for AgSCN and are discussed in relation to the structures of the complexes. The double degeneracy of the delta(SCN) mode of the coordinated thiocyanate is lifted and the first overtone of this band at gains intensity in the IR in the 1 : 1 complexes, behaviour that is not observed for the terminal bonding mode that is present in the 1 : 2 complexes.

Topics: Crystallography, X-Ray; Ligands; Models, Molecular; Organometallic Compounds; Silver; Spectrophotometry, Infrared; Thiocyanates; Thiourea

An anion exchange monolithic silica capillary column was prepared by surface modification of a hybrid monolithic silica capillary column prepared from a mixture of tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMS). The surface modification was carried out by on-column copolymerization of N-[3-(dimethylamino)propyl]acrylamide methyl chloride-quaternary salt (DMAPAA-Q) with 3-methacryloxypropyl moieties bonded as an anchor to the silica surface to form a strong anion exchange stationary phase. The columns were examined for their performance in liquid chromatography (LC) and capillary electrochromatography (CEC) separations of common anions. The ions were separated using 50 mM phosphate buffer at pH 6.6. Evaluation by LC produced an average of 30,000 theoretical plates (33 cm column length) for the inorganic anions and nucleotides. Evaluation by CEC, using the same buffer, produced enhanced chromatographic performance of up to ca. 90,000 theoretical plates and a theoretical plate height of ca. 4 mum. Although reduced efficiency was observed for inorganic anions that were retained a long time, the results of this study highlight the potential utility of the DMAPAA-Q stationary phase for anion separations.

Topics: Acrylamides; Anions; Bromates; Chromatography, Gel; Iodates; Iodides; Methyl Chloride; Silanes; Silicon Dioxide; Thiocyanates; Thiourea

Inhibitors of the initial step (H2-antagonist) and of the final step (thiocyanate, SCN-; and nitrite, NO2-) were used to study the dynamics of acid secretion in isolated frog gastric mucosa. Tissues were mounted in flow-through chambers, and the acid secretion rate (SR) was recorded on a pH-stat microprocessor. Continuous presence of H2-antagonist decreases the SR to a lower steady state, and on removal the SR returns to basal SR, causing a net loss of acid, the nonconservative effect. The amount of lost acid is a unique function of exposure, thus, independent of the patterns (pulses or steps) of inhibition. In contrast, continuous presence of SCN- or NO2- (below 3 mM) results in an undershoot in SR with a return to basal SR, whereas at higher concentrations there is no return. Removal of these inhibitors causes an overshoot in SR with return to basal SR. The rebound acid is equal to acid suppressed by NO2- and low concentration of SCN-, resulting in no net loss of acid, the conservative effect, whereas at high concentrations of SCN- there is an apparent loss of acid. In maximally secreting tissue the overshoot of SR is not observed. However, the acid is not lost, merely delayed. In resting tissue NO2- also merely delays the exit of the acid produced in response to forskolin. The rebound acid is proposed to reside in a sequestered "acid" pool that is stable for at least 120 min. Results with NO2- and SCN- suggest an effect on a saturable exit enzyme, possibly the K+-H+-ATPase.

Topics: Animals; Gastric Acid; Histamine; In Vitro Techniques; Metiamide; Nitrites; Rana catesbeiana; Stimulation, Chemical; Thiocyanates; Thiourea

Topics: Antithyroid Agents; Azides; Carbon Isotopes; Cyanides; Cysteine; Glutathione; Iodides; Kidney; Liver; Oxidation-Reduction; Perchlorates; Peroxidases; Pharmacology; Research; Saliva; Spectrophotometry; Sulfites; Sulfur Isotopes; Thiocyanates; Thiosulfates; Thiourea; Thyroid Gland

Topics: Halogens; Humans; Iodine; Iodine Radioisotopes; Propylthiouracil; Thiocyanates; Thiourea; Thyroid Gland

Topics: Animals; Propylthiouracil; Rats; Thiocyanates; Thiourea