Long‐range protoncarbon‐13 coupling constants of monosaccharides by selective heteronuclear 2D‐J NMR spectroscopy

Abstract

Long-range J(CH) values were measured for six glycoside derivatives by a selective 2D-J heteronuclear sequence. The values obtained are discussed in terms of conformational effects and constitute a valuable contribution to ' 5 and 3J comprehension. KEY WORDS 2D-J NMR heteronuclear spectroscopy Selective irradiation Long-range protonxarbon couplingsGlycoside derivatives

Structural Elucidation of the Biological Repeating Unit of O-specific Polysaccharide from Citrobacter Serotype O41

“…As pointed out by Abeygunawardana et al (1991), long-range correlations show up for those proton -carbon pairs, for which 'H-13C coupling constants of several hertz can be expected according to the stereochemistry of the given sugar residue. These may be predicted from couplings reported for peracetylated methyl glycosides of the corresponding hexoses (Morat et al, 1988). In the spectrum of PlA, crosspeaks were generally found for carbon-proton pairs, for which JH, > 4 Hz were reported for the corresponding hexoses (Morat et al, 1988).…”

“…These may be predicted from couplings reported for peracetylated methyl glycosides of the corresponding hexoses (Morat et al, 1988). In the spectrum of PlA, crosspeaks were generally found for carbon-proton pairs, for which JH, > 4 Hz were reported for the corresponding hexoses (Morat et al, 1988). Since 'J,,, c3 = 4.7 Hz and 3JH4, c2 = 5.2 Hz was reported for a residue having the P-galucto configuration, C2 of I1 was assigned from the crosspeak between H4 (3.961 ppm) and the carbon signal at 6 73.60 ppm; whereas the weaker crosspeak at 6 71.58 ppm was ascribed to the two-bond connectivity between H4 and the C3.…”

“…73.60 ppm was attributed to intraresidue connectivity to C3 of VI (expected, see Morat et al, 1988) and possibly also interresidue connectivity to C2 of residue 11. Evidence supporting this interresidue linkage assignment comes from NOE contacts observed in the NOESY spectrum (Fig.…”

Configurational assignment in alkyl‐branched sugars via the geminal C,H coupling constants

“…One important prerequisite for performing configurational assignments through geminal C,H couplings, however, is the knowledge of the number of oxygen atoms bound to either one of the two carbon centers in the 2 J coupling pathway C A -C B -H. Earlier cases, in which geminal C,H couplings have been calculated using molecular orbital calculations, involved only compounds that have at least one O-substituent at each carbon atom 11,12 or two O-substituents at C A . 5,10 Calculations on a structure where C B represents a CH 3 group have also been performed, 13 but they cannot be considered here, since they study a coupling with three chemically equivalent methyl protons.…”

Stereospecific assignment of exocyclic methylene protons in panose by 13C‐filtered 1D TOCSY

“…To accomplish this, one needs to be able to measure the pertinent vicinal 3J(H-5,H-6~) and 3J(H-5, H-6s) coupling constants in conjunction with either the H-4 c, H-~R,s nuclear Overhauser enhancement WOE) effects4*' or the 3J(C-4,H-6~) and 3J(C-4,H-6s) scalar couplings. 6 Measuring long-range heteronuclear coupling constants, particularly in molecules with I3C in natural abundance, is one of the more challenging problems in today's high-resolution NMR spectroscopy. Recently, a variety of sensitive, H-detected experiments designed to measure 'J(C,H), 'J(C,H) and even 4J(C,H) have been applied to carbohydrates.…”