A conformational study of methyl β-cellobioside-d₈ by ¹³C nuclear magnetic resonance spectroscopy: dihedral angle dependence of ³J_C–H in ¹³C—O—C—¹H arrays

Abstract

Methyl β-cellobioside (2) has been deuterated at positions C-2, -3, -3′, -4, -6, and -6′ by 1H–2H exchange with deuterium oxide in the presence of Raney nickel catalyst. The resulting simplification in the 13C nmr spectrum of this isotopically-labelled compound has facilitated the measurement of interresidue 13C–1H coupling, as a means of determining the orientation of the glycosidic linkage in 2. Three-bond coupling across the linkage between 13C-4′ and H-1 is found to be 4.3 Hz and that between 13C-4′ and H-1, 4.2 Hz. By reference to other 13C–1H coupling data, which exhibit a Karplus type of relationship between the magnitude of 3JC—H and dihedral angle in 13C—O—C—1H arrays of bonded atoms, it appears that torsion angles [Formula: see text] and ψ of the disaccharide in aqueous solution are in the region of 25–30°, i.e., close to the angles of crystalline 2. Corresponding data for the hepta-O-acetyl derivative indicate that ψ is smaller by ∼10° and [Formula: see text] is unchanged. An analysis of the 1H-coupled 13C spectrum of cyclohexaamylose-2,3,6,6′-d4 is presented in relation to these findings. Computer simulations of the observed spectra have been used to determine coupling constants and to assess the importance of second-order effects on the measurement of JC—H.

Three‐dimensional structure of the oligosaccharide terminus of globotriaosylceramide and isoglobotriaosylceramide in solution

“…The 4 and y angles (44.6, -13.7) found for crystalline cellobiose 1561 also fall within the range marked in Fig. 8, closer to the former of the two minima, whereas conformational analysis of methyl P-('H8)cellobioside based on interglycosidic 'Hi' 3C coupling constants gave 4, y values within the range 25 -30" for both of these angles [57]; these values would agree better with a conformation that is dynamically averaged between the two conformational states indicated in Fig. 8.…”

A Karplus equation for 3JHCCN in amino sugar derivatives

“…1D and 2D 1 H/ 15 N heteronuclear single quantum, multiple bond correlation (HSQMBC) NMR spectra33 , 34 were acquired by using a Bruker hsqcetf3gpjclrnd pulse sequence, which included shaped, 180° chirp pulses of 500 μs and 2 ms for inversion and refocusing, respectively, at the 15 N frequency. A pulse sequence execution error in the form of nonprogressive accumulation of data was eliminated by setting separate, but equal phase programs (ph14 = 0 0 0 0 2 2 2 2 and ph4 = 0 0 0 0 2 2 2 2) for the shaped 15 N refocusing pulse and the following 15 N 90° high power pulse, respectively. The 1/2J delay was calculated from 1 J NH 93 Hz, whereas the evolution delay for long-range 1 H-15 N coupling constants was 83 ms. 1D HSQMBC was conducted by using 16384 point data sets, linearly predicted to 65536 points.…”

“…Measurement of the coupling constants was performed by 1D 1 H NMR of 15 N-labeled amino sugars30 , 31 , 36 -38 and/or 1D and 2D 1 H/ 15 N HSQMBC33 , 34 of amino sugars having 15 N either enriched or at natural abundance. The latter experiments were facilitated by the enhanced sensitivity of a 1 H/ 13 C/ 15 N inverse NMR cryoprobe which yielded excellent HSQMBC spectra from 1 mg of 15 N-labeled derivative, or from 20-30 mg having 15 N at natural abundance.…”

“…1 We are interested in extending the use of 15 N NMR parameters for the structural, stereochemical, and conformational analysis of biological materials, in this instance, by definition of the dependence of vicinal 1 H- 15 N coupling constants ( 3 J HCCN ) on the 1 H/ 15 N atomic dihedral angle in amino sugars. The dependence of vicinal 1 H-1 H coupling constants on the dihedral angle2 , 3 and on a number of other molecular parameters is now well established for carbohydrates4 -6 and other molecules.7 -12 Considerable data exist also for the dependence of three-bond 1 H- 13 C coupling constants, for both the HCOC13 -21 and HCCC14 , 22 -24 moieties.…”

“…However, the dependence of 3 J HCCN on dihedral angle and on other molecular parameters is less well defined,25 especially in amino sugars. Our approach has been to measure the 3 J HCCN values of amino sugar derivatives in fixed or known conformations, in which the 1 H and 15 N nuclei have defined orientations. Many of our model compounds are methyl 2-(and 3-) amino-4,6-O-benzylidene-2-(and 3-)deoxy-α-D-hexopyranosides, which are known for their conformational purity in chair conformations,26 or occasionally a skew form.27 -29 Like trans-decalin, trans fusion of the 4,6-O-benzylidene ring to the pyranose ring restricts the number of conformational possibilities, so that the latter ring cannot adopt an alternative chair form.…”