Quantitative ¹H NMR. Development and Potential of an Analytical Method: An Update

Covering the literature from mid-2004 until the end of 2011, this review continues a previous literature overview on quantitative ¹H NMR (qHNMR) methodology and its applications in the analysis of natural products. Among the foremost advantages of qHNMR is its accurate function with external calibration, the lack of any requirement for identical reference materials, a high precision and accuracy when properly validated, and an ability to quantitate multiple analytes simultaneously. As a result of the inclusion of over 170 new references, this updated review summarizes a wealth of detailed experiential evidence and newly developed methodology that supports qHNMR as a valuable and unbiased analytical tool for natural product and other areas of research

Quantum Mechanics-Based Structure Analysis of Cyclic Monoterpene Glycosides from Rhodiola Rosea

NMR- and MS-guided metabolomic mining for new phytoconstituents from a widely used dietary supplement, Rhodiola rosea, yielded two new (+)-myrtenol glycosides, 1 and 2, and two new cuminol glycosides (3 and 4), along with three known analogues (5–7). The structures of the new compounds were determined by extensive spectroscopic analysis. Quantum Mechanics-driven 1H iterative Full Spin Analysis (QM-HiFSA) decoded the spatial arrangement of the methyl groups in 1 and 2, as well as other features not recognizable by conventional methods, including higher order spin-coupling effects. The application of QM-HiFSA will provide a definitive reference point for future phytochemical and biological studies of R. rosea as a resilience botanical. Application of a new NMR data analysis software package, CT, for QM-based iteration of NMR spectra is also discussed

Structural Resolution Of The Stereochemistry Of A Spirooxirane Derived From An Alpha-Arylidene Heterocyclic Carbonyl - The Crystal And Molecular-Structure Of 2-(Para-Chlorophenyl)-5-Phenyl-7-Methyl-1-Oxa-5,6-Diazaspiro 2.4 Hept-6- En-4-One

The stereochemical assignment of molecular geometry for α‐arylidene carbonyl compounds and spirooxirane derived from them have continued to be a challenging problem for which the most satisfactory solution continues to be an x‐ray diffraction structure determination. In that regard, the title compound (a spirooxirane) has been found to crystallize in the monoclinic space group P2 1/c with cell dimensions of a = 5.989(1)Å, b = 27.625(4)Å, c = 9.374(2)Å, β = 99.06(1)°. The structure of the compound has been determined, with the refinement to R = 0.059. The previous, tentative assignment of structure has been confirmed substantiating our prediction that the oxidation of the enone system proceeds with rotation of the phenyl group on the β‐carbon away from the carbonyl group, minimizing adverse steric interactions and allowing orbitals of the carbonyl group to overlap with those of the carbanionic center during the closure of the oxirane ring. The agreement between predictions based on nmr data and the x‐ray diffraction determination will support a stronger reliance on the nmr data predictions in subsequent studies

Structural resolution of the stereochemistry of a spirooxirane derived from an α‐arylidene heterocyclic carbonyl. The crystal and molecular structure of 2‐( p ‐chlorophenyl)‐5‐phenyl‐7‐methyl‐1‐oxa‐5,6‐diazaspiro[2.4]hept‐6‐en‐4‐one

The stereochemical assignment of molecular geometry for α‐arylidene carbonyl compounds and spirooxirane derived from them have continued to be a challenging problem for which the most satisfactory solution continues to be an x‐ray diffraction structure determination. In that regard, the title compound (a spirooxirane) has been found to crystallize in the monoclinic space group P2 1/c with cell dimensions of a = 5.989(1)Å, b = 27.625(4)Å, c = 9.374(2)Å, β = 99.06(1)°. The structure of the compound has been determined, with the refinement to R = 0.059. The previous, tentative assignment of structure has been confirmed substantiating our prediction that the oxidation of the enone system proceeds with rotation of the phenyl group on the β‐carbon away from the carbonyl group, minimizing adverse steric interactions and allowing orbitals of the carbonyl group to overlap with those of the carbanionic center during the closure of the oxirane ring. The agreement between predictions based on nmr data and the x‐ray diffraction determination will support a stronger reliance on the nmr data predictions in subsequent studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96401/1/5570200314_ftp.pd