Evaluation of steric effects on the exocyclic conformations of 6-C-methyl-substituted 2-acetamido-2-deoxy-β-d-glucopyranosides

Achkar, Jihane; Sanchez-Larraza, Isabel; Wei, Alexander

doi:10.1016/s0008-6215(01)00295-6

Cited by 3 publications

(8 citation statements)

References 24 publications

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“…Purification by silica gel flash chromatography with an EtOAc-hexanes gradient afforded the acetate in nearly quantitative yield. 6, 159.5, 138.2, 137.9, 133.6, 132.0, 129.8, 129.7, 128.8, 128.5, 128.4, 128.2, 127.9, 127.8, 127.7, 127.6, 113.9, 87.5, 86.7, 80.9, 77.1, 76.9, 75.8, 75.5, 74.7, 63.2, 55.2, 20.8;IR (thin film) 1742IR (thin film) , 1613IR (thin film) , 1514IR (thin film) , 1455IR (thin film) , 1362IR (thin film) , 1249IR (thin film) , 1066IR (thin film) , 1030 7, 159.2, 138.1, 137.8, 133.5, 131.9, 130.1, 129.4, 128.9, 128.4, 128.3, 127.9, 127.7, 127.6, 127.5, 113.7, 87.5, 84.0, 80.6, 77.6, 75.5, 75.4, 73.2, 70.8, 69.5, 55.2, 20.8;IR (thin film) 1746IR (thin film) , 1613IR (thin film) , 1584IR (thin film) , 1513IR (thin film) , 1455IR (thin film) , 1362IR (thin film) , 1231IR (thin film) , 1175IR (thin film) , 1050 6, 165.3, 159.3, 138.0, 133.0, 130.2, 129.9, 129.6, 129.4, 129.2, 128.3, 113.8, 99.5, 68.8, 78.0, 77.1, 76.8, 74.9, 72.3, 63.1, 55.2, 29.6, 25.6, 21.1, 20.8, 1.0; [R] 3.81 (s, 3 H), 3.53-3.63 (m, 3 H), 2.29 (s, 3 H), 1.97 (s, 3 H), 0.71 (s, 9 H), -0.03 (s, 3 H), -0.20 (s, 3 H); 13 C NMR (125 MHz, CDCl3) δ 169.7 165. 1, 159.2, 137.9, 133.1, 132.8, 130.2, 130.0, 129.9, 129.6, 129.5, 129.2, 128.4, 113.7, 96.5, 86.8, 77.7, 74.6, 73.3, 73.2, 72.4, 70.0, 55.3, 29.7, 21.2, 21.1, 17.7, -4.1, -4.6;IR (thin film) 1734IR (thin film) , 1613IR (thin film) , 1514IR (thin film) , 1493IR (thin film) , 1373IR (thin film) , 1250IR (thin film) , 1228IR (thin film) , 1176IR (thin film) , 1146IR (thin film) , 1092IR (thin film) , 1057 (300 MHz,2 H),2 H),…”

Section: Methodsmentioning

confidence: 99%

“…1, 159.2, 137.9, 133.1, 132.8, 130.2, 130.0, 129.9, 129.6, 129.5, 129.2, 128.4, 113.7, 96.5, 86.8, 77.7, 74.6, 73.3, 73.2, 72.4, 70.0, 55.3, 29.7, 21.2, 21.1, 17.7, -4.1, -4.6;IR (thin film) 1734IR (thin film) , 1613IR (thin film) , 1514IR (thin film) , 1493IR (thin film) , 1373IR (thin film) , 1250IR (thin film) , 1228IR (thin film) , 1176IR (thin film) , 1146IR (thin film) , 1092IR (thin film) , 1057 (300 MHz,2 H),2 H),2 H),3 H),7.15 13 C NMR (75 MHz, CDCl3) δ 170. 5, 169.9, 159.5, 134.4, 134.1, 133.1, 131.3, 129.5, 129.4, 128.8, 128.2, 123.7, 123.4, 113.9, 99.9, 82.7, 75.7, 74.2, 62.9, 55.2, 54.0, 20.8, 20.6;IR (thin film) 1777IR (thin film) , 1745IR (thin film) , 718, 1612IR (thin film) , 1514IR (thin film) , 1385IR (thin film) , 1225IR (thin film) , 1088IR (thin film) , 1034 (300 MHz,2 H),2 H),2 H),5 H),6.89 (d,2 H, J ) 8.7 Hz), 5.82 (t, 1 H, J ) 9.6 Hz), 5.74 (d, 1 H, J ) 10.5 Hz), 5.16 (t, 1 H, J ) 9.6 Hz), 4.52 (d, 1 H, J ) 11.4 Hz), 4.45 (d, 1 H, J ) 11.7 Hz), 4.38 (t, 1 H, J ) 10.5 Hz), 3.89 (m, 1 H), 3.84 (s, 3 H), 3.63 (d, 2 H, J ) 4.2 Hz), 1.92 (s, 3 H), 1.83 (s, 3 H); 13 C NMR (75 MHz, CDCl3) δ 170.2, 169. 6, 159.2, 134.3, 132.8, 131.4, 129.9, 129.4, 128.9, 128.1, 123.6, 113.7, 83.1, 77.5, 73.2, 71.8, 69.6, 68.8, 55.3, 53.7, 20.6, 20.4;IR (thin film) 1777IR (thin film) , 1751IR (thin film) , 1718IR (thin film) , 1612IR (thin film) , 151...…”

Section: Methodsmentioning

confidence: 99%

“…12 However, at 0 °C the BH 3 /Bu 2 BOTf conditions were found not to be compatible with alkenes, such as allyl ethers. 13 Here we report that the reductive cleavage of anisylidene acetals by BH 3 /Bu 2 BOTf can selectively produce either regioisomer, simply by adjusting the reaction temperatures and reagent concentrations. Strictly anhydrous conditions are not required because any traces of water are consumed by excess borane, obviating the need for molecular sieves.…”

Section: Introductionmentioning

confidence: 92%

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Temperature-Controlled Regioselectivity in the Reductive Cleavage of p-Methoxybenzylidene Acetals

2004

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The regioselective ring opening of pyranosidic 4,6-p-methoxybenzylidene acetals with BH(3)/Bu(2)BOTf in THF can be tuned by adjusting the reaction temperature and reagent concentrations. Reductive cleavage at 0 degrees C resulted in the exclusive formation of 4-O-p-methoxybenzyl (PMB) ethers, whereas reaction at -78 degrees C produced 6-O-PMB ethers in high yields. The latter condition was observed to be compatible with a variety of acid-sensitive functional groups, including allyl and enol ethers. The presence of water does not interfere with reductive ring opening and may contribute toward in situ generation of H(+) as a catalyst for 6-O-PMB ether formation. Reductive cleavage under rigorously aprotic conditions is greatly decelerated, and yields only the 4-O-PMB ether. The temperature-dependent reductive cleavage of the 4,6-acetal can be described in terms of kinetic versus thermodynamic control: Lewis-acid coordination of the more accessible O-6 is favored at higher temperatures, whereas protonation of the more basic but sterically encumbered O-4 predominates at low temperatures.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

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Temperature-Controlled Regioselectivity in the Reductive Cleavage of p-Methoxybenzylidene Acetals

2004

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“…Here we describe the conformational analysis of 6- C -monodeuterated and 6- C -methyl-substituted 2-acetamido-2-deoxy-β- d -glucopyranosyl (β- d -GlcNAc) monosaccharides ( 1a − 3a ) and their corresponding 1,4-linked disaccharides ( 1b − 3b ), using vicinal coupling constants from variable-temperature nuclear magnetic resonance (VT-NMR) spectroscopy. A previous analysis of these compounds at 298 K in methanol- d 4 has established that the stereodefined 6- C -methyl group imposes a strong conformational bias on the C-5−C-6 bond, with predictable outcomes for the lowest energy conformations . In this article, further evaluation of 3 J H,H coupling constants over a wide temperature range (229−320 K) permits these conformational preferences to be described in thermodynamic terms with use of three-state conformer models.…”

Section: Introductionmentioning

confidence: 91%

Synthesis and Conformational Analysis of 6-C-Methyl-Substituted 2-Acetamido-2-deoxy-β-d-glucopyranosyl Mono- and Disaccharides

et al. 2004

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Several 6-C-substituted 2-acetamido-2-deoxy-β-D-glucopyranosides (β-D-GlcNAc monosaccharides 1a-3a and 1,4-linked disaccharides 1b-3b) were studied by solution NMR spectroscopy. Conformational analysis of the (6S)-and (6R)-C-methyl-substituted β-D-GlcNAc monosaccharides indicates that the stereodefined methyl groups impose predictable conformational biases on the exocyclic C-5-C-6 bond, as determined by 1 H-1 H and 13 C-1 H coupling constants. Variabletemperature NMR experiments in methanol-d 4 were performed to determine ΔΔH and ΔΔS values derived from the two lowest energy conformers. These indicate that while the influence of 6-C-methyl substitution on conformational enthalpy is in accord with the classic principles of steric interactions, conformational preference in solution can also be strongly affected by other factors such as solventsolute interactions and solvent reorganization.

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“…Furthermore, this method can be applied on partially protected carbohydrates ( 52 ). Allyl ethers, however, were found to be incompatible with this methodology at 0 °C or above …”

Section: Pyransmentioning

confidence: 99%

Regioselective Ring Opening of 1,3‐Dioxane‐Type Acetals in Carbohydrates

et al. 2018

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The (regio)selective manipulation of hydroxyl groups in carbohydrates has been a long‐standing challenge in (bio)organic chemistry and continues to trigger the creative minds of many chemists. Among the various strategies that have been developed to address these issues, mostly relying on multistep procedures involving the use of protecting groups, the regioselective ring opening of 1,3‐dioxane‐type acetals has emerged as a powerful tool. Since the first papers on this subject appeared in the 1960s, a large variety in both acetal types and reagents for their partial cleavage has come to the fore. This review aims to give an overview of the different carbohydrate‐derived ring systems, ranging from four‐ to seven‐membered rings, on which regioselective ring‐openings have been performed, along with the appropriate reagents and combinations thereof. The transformations on 1,3‐dioxane acetals fit in a larger group of ring opening reactions of structurally related cyclic functional groups, including 1,3‐dioxolanes, 1,3‐oxathianes, orthoesters, cyclic carbonates and silylene acetals, which will not be discussed in this review.

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Evaluation of steric effects on the exocyclic conformations of 6-C-methyl-substituted 2-acetamido-2-deoxy-β-d-glucopyranosides

Cited by 3 publications

References 24 publications

Temperature-Controlled Regioselectivity in the Reductive Cleavage of p-Methoxybenzylidene Acetals

Temperature-Controlled Regioselectivity in the Reductive Cleavage of p-Methoxybenzylidene Acetals

Synthesis and Conformational Analysis of 6-C-Methyl-Substituted 2-Acetamido-2-deoxy-β-d-glucopyranosyl Mono- and Disaccharides

Regioselective Ring Opening of 1,3‐Dioxane‐Type Acetals in Carbohydrates

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