28074-71-7Relevant academic research and scientific papers
Glycosylation with ulosonates under Mitsunobu conditions: Scope and limitations
Kánya, Nándor,Kun, Sándor,Batta, Gyula,Somsák, László
, p. 14463 - 14476 (2020)
A systematic study was performed by using Mitsunobu conditions (diethyl azodicarboxylate, Ph3P or n-Bu3P in THF or CH3CN) for glycosylations with methyl 3,4,5,7-tetra-O-benzoyl-α-d-gluco-hept-2-ulopyranosonate. From a set of 47 O-, N-, S- and C-nucleophiles, phenols and N-hydroxy compounds with a pKa of 5-8, phthalimide, benzotriazole, 6-chloropurine, an oxazolidinedione and several tetrazoles with a pKa of 4-8, and thiophenol gave the corresponding products in moderate to very good yields, while C-nucleophiles were unreactive. Trihaloacetanilides underwent O-glycosylation to give O-glycosyl-N-aryl trihaloacetimidates which could not be made by conventional O-imidoylations. All reactions were highly stereoselective to produce the β(d) anomers only. With methyl (5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-d-glycero-d-galacto-2-nonulopyranose)onate phenols and benzotriazole resulted in the expected products, but all other nucleophiles failed to react. While these transformations gave anomeric mixtures in a ratio close to 1?:?1 at room temperature, the α-selectivity increased to 92?:?8 at -30 °C. An o-nitrophenyl sialoside was converted to a spiro-benzoxazinone derivative by reduction of the nitro group and subsequent spontaneous ring closure.
Unexpected stability of aryl β-N-acetylneuraminides in neutral solution: Biological implications for sialyl transfer reactions
Dookhun, Veedeeta,Bennet, Andrew J.
, p. 7458 - 7465 (2007/10/03)
A reagent panel comprised of seven aryl β-D-N-acetylneuraminides was synthesized and then used to probe the mechanisms of nonenzymatic hydrolysis. These reactions proceeded via four independent pathways: (1) acid-catalyzed hydrolysis of the neutral molecule; (2) acid-catalyzed hydrolysis of the anionic form, or its kinetic equivalent spontaneous hydrolysis of the neutral form; (3) spontaneous hydrolysis of the anionic form; and (4) a base-promoted pathway. The pH-independent spontaneous hydrolysis of 4-nitrophenyl α-D-N- acetylneuraminide (5) occurs at a rate that is over 100 times faster than that of the corresponding reaction of 4-nitrophenyl β-D-N-acetylneuraminide (4a). Spontaneous hydrolyses of four aryl β-D-N-acetylneuraminides displayed a βIg value of -1.24 ± 0.16 (pH = 8.1, T = 100 °C), and at a pH value of 1.0 (50 °C), all seven panel members gave a βIg value of 0.14 ± 0.08. The aqueous ethanolyses of 4a and 5 gave similar products and displayed sensitivity parameters (m) in a standard Winstein-Grunwald analysis of -0.04 ± 0.01 and ± 0.23 ± 0.02, respectively. These results, plus the activation parameters calculated for the spontaneous hydrolyses of the anionic forms of 5 (ΔH? = 116 ± 2 kJ mol-1 and ΔS? = 27 ± 4 J mol-1 K-1) and 4a (ΔH? = 138 ± 3 kJ mol-1 and ΔS? = 59 ± 8 J mol -1 K-1), are inconsistent with anomeric carboxylate assistance occurring during the hydrolysis reactions, and the likely cause for the enhanced reactivity of 5 in comparison to that of 4a is an increase in ground-state steric strain.
