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

Abstract

The C-6-methylene protons in the internal ghcosyl unit of panose, ~-G l~-a ( l + 6)-~-Glc-a(l+ 4)-D-Glc(a,B), were stereospecifically assigned. The assignment strategy involved the measurement of the long-range 3J(C-4, H -~R ) and 'J(C-4,HaS) coupling constants for this residue in panose, with natural "C isotope abundance, using a newly designed "C-filtered 1D TOCSY experiment.

Distinguishing diastereomeric organic compounds based on the concerted use of3J(C,H) and3J(N,H) values

“…10 An example of the 1D spectrum from which 15 N-1 H coupling constants were measured is shown in Fig. 2.…”

“…An additional sensitivity gain of p 2 was achieved by the post-acquisition symmetrization protocol. 10 For the purpose of determining which set of experimental coupling constants (A and B in Table 1) belongs to which diastereoisomer in Scheme 1, it was very helpful to build a look-up …”

“…Three-bond coupling constants are also averaged; however, a set of such couplings for different pairs of nuclei is often sufficient for unambiguous identification of the relative stereochemistry. 4 Vicinal coupling constants have been used for stereochemical assignment of diastereotopic groups or atoms in peptides 5 and oligosaccharides 6 and recently for the determination of the absolute configuration in natural products. 7 Scheme 1 shows the reason for this study.…”

“…10 The pulse sequence is depicted in Fig. 1 where the hard 90°and selective 180°pulse flanked by two…”

α/β-ge-SELINCOR-TOCSY, a New Method for the Determination of H,C Coupling Constants

“…Two soft pulses are used: The first one selects the structural information. Obtaining the coupling constant (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). One may carbon resonance under proton decoupling, and a second soft pulse determines the spin state.…”