Anomeric deoxy and unsaturated methyl pentofuranosides and pentopyranosides

Abstract

Both the anomers for methyl 2,3-dideoxy-D-glycero-pent-2-enofuranoside were characterized and hydrogenated to the corresppnding methyl 2,3-dideoxy-D-glycero-pentofuranosides. The similar compounds were prepared in the pyranoside ring form but in the L-glycero configuration. The anomeric forms for methyl 3-deoxy-L-erytlrro-pentopyranoside are reported together with a number of their derivatives of interest for the study of solvation effects on conformational equilibria (21). The molar rotations of the deoxy and unsaturated glycosides are discussed as are the conformational properties of the various compounds.Canadian Journal of Chemistry, 47, 4413 (1969) In a previous communication (I), the preparation of the four stereoisomeric methyl 4,6-0-benzylidene-2,3-dideoxy-D-hex-2-enopyranosides was accomplished, in each case, by opening of the epoxide ring of a parent 2,3-anhydro derivative to the corresponding iodohydrin which was treated with either p-toluenesulfonyl (tosyl) or methanesulfonyl (mesyl) chloride in pyridine. We wish to report a modified procedure which allowed the preparation of the anomeric forms both for methyl 2,3-dideoxy-D-glycero-pent-2-enofuranoside (4c and 9c) and for methyl 2,3-dideoxy-L-glycero-pent-2-enopyranoside (17c and 18c).Methyl 5-0-benzoyl-2,3-dideoxy-P-D-glyceropent-2-enofuranoside (9a) was first prepared by reaction of 3,5-di-0-benzoyl-D-erythro-pent-1-enofuranose with methanol (2). The p-D-configuration was later assigned by an alternative synthesis (3,4) involving reduction of methyl 5-0-benzoyl-2,3-di-0-tosyl-P-D-ribofuranoside by the method of Tipson and Cohen (5). The physical constants and nuclear magnetic resonance (n.m.r.) spectrum reported for 9a indicate that this compound was not pure. Also, the n.m.r. signal for Hz was erroneously assigned to HI. It is of interest to note that several 2',3'-unsaturated nucleosides have been prepared (6-10).The 5-0-benzoyl derivative (la) of the readily available methyl 2,3-anhydro-a-D-lyxofuranoside (I 1) was treated with sodium iodide in acetone in the presence of acetic acid and sodium acetate as described previously (1). The spectrum of the sirupy product (2a) required high purity. That the epoxide opening followed the normal course (attack at the 3-position) for a 2,3-anhydrofuranoside (12,13) was established by benzoylation of the iodohydrin 2a to 2c followed by hydrogenolysis to yield crystalline methyl 2,5-di-0-benzoyl-3-deoxy-a-D-theo pentofuranoside (3). This 3-deoxy structure was required since the anomeric proton (singlet at r 4.85) was not appreciably coupled to either of the methylene protons at r 7.35 and 8.05. The quartet at .r 5.35 was assigned to Hz and the spacings indicated 6.5 Hz coupling with the methylene proton (H,) at r 7.35, and 1.6 Hz coupling with that (H,) at r 8.05. Spin decoupling also showed the methylenic protons to be coupled with a signal forming part of a multiplet (H4, H,, and H,,) centered at r 5.5 and assigned to H,.Following the previously reported procedure for the reduction of iodohydrins to olef...

Influence of solvent on the magnitude of the anomeric effect

“…On the other hand, the population of 16e is significantly greater in CD3CN than in CDC13 (0.58 versus 0.49). This is as expected, since hydrogen bonding of the hydroxyl group of 16 with a solvent molecule must enrich the electron density on the oxygen atom (20) and thereby increase the exo-anomeric effects, but more so that for the equatorial conformer (16e). Thus, the proton-accepting solvent should, as was observed, enrich the population of the equatorial conformer (16e).…”

“…This result is attributed to a greater strengthening of the exoanomeric effects, but more so for 16e as the result of the hydrogen bonding with water as is indicated in the formula for 16e. Experimental evidence exists for increased electron density on an oxygen atom of an hydroxyl group as the result of hydrogen bond formation (20), and Jeffrey and Mitra To better establish the influence of hydrogen bonding on the conformational equilibrium for 16, a study was made of the effect of the addition of dimethylsulfoxide to solutions in Ccl4-C6D6 (10%). The results, presented in Fig.…”

“…For example, the conformational equilibrium for methyl 3-deoxy-P-L-erythropentopyranoside was more sensitive to the chemical nature of the solvent than to its polarity (20). Similarly, specific solvation effects were found to influence the conformational equilibrium for 2-methoxytetrahydropyran (2-MeO-THP) (3) (1 1).…”

An Apparent Stereochemical Effect in MnO2 Oxidation of Some Allylic Alcohols

“…appeared in which conformations of the methyl 2,3-dideoxy a-L and P-L-glycero-pent-2-enopyranosides were discussed (14). We prepared the were identical in all respects with those kindly supplied by Professor Lemieux (14).…”

The conformational behaviour of 2-aryloxytetrahydropyrans and 2-acetoxytetrahydropyran, and barrier to ring inversion

“…51t is well known that the anomeric effect decreases with increasing polarity of the solvent (27,(33)(34)(35)(36) conformational equilibria studied by 'H nrnr were highly biased (axial preference of 98-99%) and were estimated by an approximate method of analysis so that the small influence of the substituent on the phenyl ring could not be detected.…”