Universal NMR Databases for Contiguous Polyols

Abstract

On the basis of 1,2,3-triols 1a approximately d, 1,2,3,4-tetraols 2a approximately h, and 1,2,3,4,5-pentaols 3a approximately p, NMR databases with four types of profile-descriptors ((13)C-, (1)H-, and (1)H(OH)-chemical shifts and vicinal spin-coupling constants) for contiguous polyols are reported. To systematically assess the relative values of these databases, a case study has been conducted on heptaols 4a approximately d, through which the gamma- and delta-effects have been recognized to refine the (13)C and (1)H chemical shift profile predicted via an application of the concept of self-contained nature. The magnitudes of gamma- and delta-effects depend on a specific stereochemical arrangement of the functional groups present in both the inside and outside of a self-contained box and are significant only for the stereoisomers belonging to a specific sub-group. With the exception of the stereochemical arrangement of functional groups belonging to a specific sub-group, the gamma- and delta-effects can, at the first order of approximation, be ignored for the stereochemical analysis of unknown compounds. For the stereoisomers belonging to a specific sub-group, it is necessary to refine, with incorporation of the gamma- and delta-effects, the profile predicted at the first order of approximation. With use of heptaols 4a approximately d, the values of (3)J(H,H) profiles have been assessed. Two methods, one using profiles consisting of three contiguous (3)J(H,H) constants and the other using profiles consisting of two contiguous (3)J(H,H) constants, have been developed. A stereochemical analysis based on three, or two, contiguous (3)J(H,H) profiles is operationally simpler than one based on (13)C and (1)H chemical shift profiles. Therefore, it is recommended to use a (3)J(H,H) profile as the primary device to predict the stereochemistry of unknown polyols and (13)C and (1)H chemical shift profiles as the secondary devices to confirm the predicted stereochemistry.

Chemical Synthesis of the GHIJK Ring System and Further Experimental Support for the Originally Assigned Structure of Maitotoxin

“…[4,7] Concurrent with this objective, we had in mind the development of synthetic strategies suitable for an eventual total synthesis of larger fragments of maitotoxin for biological investigations. The devised synthetic plan for the construction of the GHIJK ring system 2 required the coupling and elaboration of fragments 13 (Scheme 2) and 33 (Scheme 5) to the targeted structure.…”

Stereochemical Assignment in Acyclic Lipids Across Long Distance by Circular Dichroism: Absolute Stereochemistry of the Aglycone of Caminoside A

“…The requirement (and limitation) of these methods is that stereotopicity of the signals of intervening CH 2 groups must be made by measurements of J coupling constants under favorable conditions of NMR spectroscopy signal dispersion and dihedral angles that conform to all‐staggered molecular conformations. These methods, although usually successful for polyketides bearing contiguous 1,2 or 1,3‐disubstituted stereoelements, become less reliable for molecules containing two or more stereocenters separated by three or more methylene bridges because the two diastereotopic chain segments subtended at each stereocenter cannot always be differentiated by NMR spectroscopy 7…”

Nuclear Magnetic Resonance Spectroscopy for Structural Characterization of Bioactive Compounds

“…It is an empirical procedure that relies on the comparison of the observed chemical shifts of compounds with unknown vicinal or proximal centers with libraries of configurationally known stereomodels. These 1 H and 13 C NMR databases were first created for the stereochemical assignment of 1,3,5-triols [37,38,40] and then extended for 1,2,3-triols, 1,2,3,4-tetraols, and 1,2,3,4,5-pentaols [41][42][43]. Using this strategy, the relative configuration of 1,3-diol system at C7/C-9 of caylobolide B 12 was assigned as a syn-arrangement since it fits with the carbon chemical shifts of a 1,3-diol model system.…”