高碘酸盐氧化1,6-二-O-三苯甲基-D-甘露醇的区选性

合成了模型化合物1,6-二-O-三苯甲基-D-甘露醇(TPMM),研究了它在混合溶剂中的高碘酸盐氧化反应的区选性。对氧化产物进行了分离鉴定。取得了最终氧化产物α-O-三苯甲基乙醛,制得了重要有机合成原料α-羟基乙醛。     

Darstellung von 2,3,4,5-tetrakis(dimethyl)sulfocyclo-pentasilan und 2,3,4,5-etrakis(dimethyl)selenacyclopenta-silan

Octamethylcyclotetrasillan reacts with elemental sulfur or selenium in benzene at 80°C to give the five-membered ring products, cyclo-(Me₂Si)₄S and cyclo-(Me₂Si)₄Se.     

2,3,4,6-四-O-乙酰基-β-D-吡喃葡萄糖基异硫氰酸酯的合成及晶体结构

采用葡萄糖作原料经乙酰化、溴化和硫氰酸化三步合成了2,3,4,6-四-O-乙酰基-β-D-吡喃葡萄糖基异硫氰酸酯,培养出了单晶,用X射线衍射分析了其晶体结构.结果表明,晶体为正交晶系,P212121空间群,a=0.72624(2)nm,b=1.17508(2)nm,c=2.17210(5)nm,α=β=γ=90°,V=1.85365(7)nm,Z=4,R=0.0531,wR=0.1359.     

Reduction of 2,3,4,5-tetraphenylcyclopentadienone (tetracyclone)

A convenient route for the reduction of tetracyclone (1) to 1,2,3,4-tetraphenylcyclopentadiene (2) is to heat a mixture of 1, hydrazine hydrate (excess), and hydrazine dihydrochloride in diethylene glycol for 4 h. In the absence of the solvent diethylene glycol the product obtained was shown from the IR, NMR and mass spectral data to be the enone 3.     

Solid-state structure and condensation reaction of (triphenylmethyl)silanetriol

(Triphenylmethyl)silanetriol [1, (Ph₃C)Si(OH)₃] was obtained in 98% yield by the hydrolysis of (triphenylmethyl)trichlorosilane with ice-water in diethyl ether. Single crystal of [1 · acetone] for X-ray crystallographic determination was grown from a saturated acetone solution. In the single crystal X-ray structure analysis, the silanetriol 1 crystallizes in the centrosymmetric triclinic space group with two independent molecules in the asymmetric unit. Two independent molecules of the silanetriols 1 interact with each other and with acetones by intermolecular hydrogen bondings. Such hydrogen-bonding interactions lead to a one-dimensional columnar polymeric tube. Finally, this tube interacts with others to make sheets alternating hydrophobic organic part and hydrophilic hydroxy groups of the molecules 1 and the oxygen of acetones arranged regularly. The silanetriol 1 is very stable compound in solution and in solid states at room temperature, but decomposed in the presence of KOH, and undergoes a condensation reaction with dicyclohexylcarbodiimide (DCC) as strong dehydrating agent to give polysiloxane. The silanetriol 1 reacts with trimethylchlorosilane to give three type siloxane products (Ph₃C)Si(OH)_3−n(OSiMe₃)_n (n = 1, 2, 3). The number (n) of silylation of hydroxy groups on the silanetriol 1 increase with increasing the mol ratio of trimethylchlorosilane used.     

Relaxation pathways of excited N-(triphenylmethyl)salicylidenimine in solutions

Excited state relaxation of N-(triphenylmethyl)-salicylidenimine (MS1) in protic and aprotic solvents has been investigated by means of absorption pump-probe spectroscopy with femtosecond time resolution and fluorescence spectroscopy with picosecond time resolution. Short-lived excited states and long-lived photoproducts have been identified from the differential absorption spectra. Excited states and photoproducts were different under excitation of enol-closed and cis-keto tautomers. As a result, the commonly accepted excited state relaxation model of aromatic anils, which assumes an ultrafast transformation of excited enol-closed tautomers into cis-keto tautomers, has been modified. Performed quantum chemical calculations suggest that hydrogen-bonded ethanol molecules facilitate formation of cis-keto tautomers and are responsible for their different relaxation pathways in comparison with relaxation of excited enol-closed tauromers. Fluorescence decay on a nanosecond time scale was attributed to aggregated MS1 molecules.     

The triphenylmethyl (trityl) group and its uses in nucleotide chemistry

The triphenylmethyl (trityl) group can be removed from 5′-trityl 2′-deoxynucleosides (and their N-acyl derivatives) under aprotic neutral conditions without causing any side reactions. An efficient method for tritylation of N-acyl 2′-deoxynucleosides is described. Potential use of such derivatives for stepwise synthesis of deoxyoligonucleotides is discussed.     

Selective sialylation of 2,3-di-O-(β-d-galactopyranosyl)-d-galactose catalyzed by Trypanosoma cruzi trans-sialidase

Trypanosoma cruzi, the agent of Chagas’ disease, expresses on its surface a trans-sialidase (TcTS) that transfers sialic acid from host glycoconjugates to terminal β-galactopyranosyl units of parasite mucins. This process is involved in infection and pathogenesis. The trisaccharide 2,3-di-O-(β-d-galactopyranosyl)-d-galactose 1 is an external unit in the larger oligosaccharides of the mucins and a site for sialylation. The trisaccharide was previously synthesized in our laboratory. The last step of the synthesis was the hydrogenolysis of the crystalline benzyl trisaccharide. Herein we prove that the trisaccharide 1, its alditol 3 and the benzyl glycoside 2 are good acceptors of sialic acid and effective inhibitors of the sialylation of N-acetyllactosamine catalyzed by TcTS. Furthermore, selective sialylation of the 1→3 linked galactopyranose in glycoside 2 was determined by one and two-dimensional NMR analysis. In contrast, the flexible 2,3-di-O-(β-d-galactopyranosyl)-d-galactitol 3 is sialylated in either one of the two possible sites.     

Triethyl- (or trimethyl-)silyl triflate-catalyzed reductive cleavage of triphenylmethyl (trityl) ethers with triethylsilane

[reaction: see text] A triphenylmethyl (trityl) ether was reductively and instantaneously cleaved by triethylsilane in the presence of a catalytic amount of TES- (or TMS)-triflate. The reaction conditions are mild enough to achieve reduction in the presence of a variety of acid-sensitive functional groups. Upon a mild acidic treatment of the crude product, the corresponding alcohol is obtained in high yield.