C-13-LABELED ALDOPENTOSES - DETECTION AND QUANTITATION OF CYCLIC AND ACYCLIC FORMS BY HETERONUCLEAR 1D AND 2D NMR-SPECTROSCOPY

H-1-Decoupled C-13 NMR spectra (150 MHz) of the simple aldopentoses (M solutions in (H2O)-H-2, 28 degrees C) selectively labeled with C-13 a t C-1 (D-(1-C-13)arabinose 1, D-(1-C-13)lyxose 2, D-(1-C-13)ribose 3, D-(1-C-13)xylose 4) contain six enriched C-1 signals that were attribu ted to four cyclic (alpha- and beta- furanoses and pyranoses) and two acyclic (aldehyde, hydrate) forms. Spectral data were collected and pr ocessed in a fashion to permit accurate quantitation of the cyclic and acyclic forms. Percentages of forms varied with pentose structure: al pha-furanose (0.8-7.4%), beta-furanose (0.6-13.2%), alpha-pyranose (20 .2-70.8%), beta-pyranose (26.9-62.0%), hydrate (0.063-0.095%), aldehyd e (0.009-0.042%). Aldehyde was least abundant in solutions of D-xylose and most abundant in solutions of D-ribose, and the hydrate/aldehyde ratio was higher for D-arabinose, D-lyxose, and D-xylose (6.3-7.8) tha n for D-ribose (2.1). Heteronuclear 2D HMQC-TOCSY and HCCH-TOCSY spect ra were also obtained on several selectively and uniformly C-13-labele d model saccharides, respectively, to evaluate the advantages and limi tations of these isotope-aided methods to detect H-1 signals of specif ic forms in solution. These methodologies can be extended to studies o f suitably C-13-labeled oligosaccharides and oligonucleotides. (C) 199 8 Elsevier Science Ltd. All rights reserved.