On the Configuration of Five‐Membered Rings: A Spin–Spin Coupling Constant Approach

Abstract

Five-membered rings are clearly among the most common structural motifs found in chemistry and biology. Nevertheless, the configuration of conformationally mobile five-membered rings is often difficult to assign from nuclear magnetic resonance (NMR) data. A simple, reliable, and efficient approach for the stereochemical analysis of five-membered rings based on the measurement of NMR coupling constants is presented. Density functional theory calculations using representative conformations of the full conformational space available to rings with different substitution patterns were used to identify differences between the accessible coupling constant values for cis and trans relative orientations of the substituents. The calculations were assessed experimentally using NMR data obtained from a number of models. This approach can be easily used to analyze different five-membered rings, such as oxolanes, cyclopentanes, furanosides and pyrrolidines, and their relative configuration can be determined without the need for making further conformational considerations.

Stereochemical Determination of Five-Membered Cyclic Ether Acetogenins Using a Spin-Spin Coupling Constant Approach and DFT Calculations

“…Nevertheless, the elucidation of some molecular architectures, like flexible five-membered rings, are still problematic. Recently, we presented a simple and efficient spin-spin coupling constant approach designed for the stereochemical analysis of five-membered rings [7]. As a result, this usually complex problem can be easily solved in most cases by the measurement of a few coupling constants without the need for any conformational consideration.…”

“…Naturally occurring C 15 tetrahydrofuranyl derivatives belong to a wider family of halogenated C 15 -acetogenins isolated from red algae of the species Laurencia [12], the majority of the structures of which have only partially had their relative configurations assigned or still need to be investigated to confirm or correct their reported structures [1,13,14]. The challenging relative configurations of the five-membered rings of compounds 1 – 5 were established by our simple and effective J -based methodology [7]. In addition, a detailed study of NMR chemical shifts by DFT calculation analysis was also undertaken with the aim of connecting remote chiralities within these tetrahydrofuranyl-acetogenins [15].…”

Branching of poly(ADP-ribose): Synthesis of the Core Motif

“…The anomeric configuration of the ribosyl residues was ascertained by measuring the value of J H1C2 using HSQC-HECADE experiments for compounds 6 and 8 (see the Supporting Information). 13 Having thus obtained the deprotected branched nucleoside of ADPr, we felt that a comparison of the spectroscopic data of our synthetic material with a compound isolated from natural sources was in order. The only available spectroscopic information on branched ADPr has been reported by Miwa and co-workers.…”

A New Inhibitor of γ-aminobutric Acid Aminotransferase from Streptomyces sp. ZZ035 Isolated from a Folk Medicinal Soil in China

“…So, 1 was identified as 5-amonimethyl-2-iminoimidazolidine-4-carboxylic acid. Further, the couple constant of 2.40 Hz between H-4 and H-5 deduced that the relative configuration at C-4/C-5 was anti [17] , and which was also confirmed by the long-range correlation between H 1"b and H-4 observed in the NOESY spectrum of 1.…”