MECHANISMS FOR THE REACTIONS OF THE ANOMERIC TETRA-O-ACETYL-D-GLUCOPYRANOSYL BROMIDES WITH PYRIDINE AND 2-PYRIDONE

Abstract

Reaction of tetra-0-acetyl-or-D-glucopyranosyl bromide (I) with pyridine a t high dilution gives a high yield of N-(tetra-0-acetyl-8-D-glucopyranosyl)-pyridium bromide (11). The addition of tetra-n-butylammonium bromide diverts the reaction to the formation of the highly strained or-anomer (111) of 11. I t is contended that 111 arises from the 8-anomer (IV) of I by way of a rearrangement of an intermediate formed between pyridine and the 1,2-acetoxonium ion (VIII) which readily arises by dissociation of IV. The formation of 2-pyridyl tetra-0-acetyl-or-D-glucopyranoside in >60% yield in the reactions of I with either 2-ethoxypyridine or 2-pyridone in the presence of tetra-72-butylammoniui~~ bromide is taken as supporting evidence for this novel type of rearrangement.

A One-Pot Synthesis of 1-α- And 1-β-D-Arabinofuranosyl-2-Nitroimidazoles: Synthons to the Markers of Tumor Hypoxia

“…The precise function of stannic chloride remains obscure but the formation of 4b can be loosely based upon a proposal by Lemieux and Morgan [13] that involves reduced formation of 1,2-benzoxonium ion due to trans location of 1-O-acetyl and 2-O-benzoyl groups in 2a in comparison to 2b. Nonetheless, the coupling reaction yielded an isomeric preference for a-product 4 (b:a = 2:1).…”

A One-Pot Synthesis of 1-α- And 1-β-D-Arabinofuranosyl-2-Nitroimidazoles: Synthons to the Markers of Tumor Hypoxia

“…This implies that the trans rule, although suppressed due to the weaker electronic effect of the acetyl C-1' carbonyl, still applies under these conditions. The precise function of stannic chloride remains obscure but the formation of 4b can be loosely based upon a proposal by Lemieux and Morgan [13] that involves reduced formation of 1,2-benzoxonium ion due to trans location of 1-O-acetyl and 2-O-benzoyl groups in 2a in comparison to 2b. Therefore, approach of a possible tautomer of the intermediate imidazole nitronate ester [14] at 1'-b-position progresses, albeit not in the same isomeric proportions.…”

“…H NMR (CDCl 3 ) d 7.08-8.13 (m, 17 H, H-4, 5, and Ar -H), 7.06 (d, J = 4.27 Hz, 1 H, H-1'), 6.13 (d, J = 4.27 Hz, 1 H, H-2'), 5.67 (s, 1 H, H-3'), 4.98 (dd, J = 11.9, 6.41 Hz, 1 H, H-5'a), 4.86 (dd, J = 11.9, 3.66 Hz, 1 H, H-5'b), 4.69 (m, 1 H, H-4') 13. C NMR (CDCl 3 ) d 166.13, 165.23, 164.09, 144.10, 154.76, 134.5, 133.88, 133.41, 129.96, 129.72, 129.60, 129.29, 128.70, 128.61, 128.49, 128.40, 128.27, 127.65, 123.37, 88.42, 82.03, 75.39, 63.06.…”

Synthesis of Lipid-Linked Oligosaccharides (LLOs) and Their Phosphonate Analogues as Probes To Study Protein Glycosylation Enzymes

“…Various conditions have been used to prepare oxazoline GlcNAc, such as treatment of peracetylated GlcNAc with iron(III) chloride, 28 anhydrous stannic chloride as catalyst, 29 or a two-step procedure involving chloride ion catalysis, 30 by forming α-chloro GlcNAc with hydrogen chloride and acetyl chloride, 31 followed by equilibration of the anomeric chloride using tetraethylammonium chloride as catalyst, and finally oxazoline formation of the β-chloro GlcNAc with a base, here sodium bicarbonate. 32 Oxazoline intermediates were also obtained by treatment of 1-propenyl β-glycoside with mercury(II) chloride and mercury oxide.…”