Inverse-Detected Two-Dimensional Nmr Methods: Applications in Natural Products Chemistry

Abstract

Applications of inverse-detected 2D nmr methods are reviewed. Sequences presently available for direct (one-bond) heteronuclear correlation via / (HMQC and others) are discussed individually followed by examples of applications to natural products presented by class. Correlations of heteronuclear pairs other than 'H-13C and *H-15N are briefly considered. Optimization of parameters necessary in the acquisition of inverse-detected heteronuclear chemical shift correlation data are considered, followed by an illustration using the degradation product of 1-bromomaaliol. Methods for performing HMQC-COSY (RELAY) and HMQC-TOCSY experiments are considered with examples. Various ways of utilizing HMQC-TOCSY data are discussed followed by an illustration of the assembly of the protonated portion of the carbon skeleton of the degradation product of 1-bromomaaliol by varying the mixing times in a series of HMQC-TOCSY experiments. Long-range proton-detected heteronuclear chemical shift correlation experiments (HMBC) are presented with extensive examples of the application of these experiments to a diverse assortment of natural products, which are presented by class of compounds. A practical example of the application of the HMBC experiment to the degradation product of 1-bromomaaliol follows. The relatively new HMQC-NOESY experiment is presented followed by a discussion of the relatively few examples of this experiment presently contained in the literature. Finally, examples of proton-detected one-dimensional analogues of 2D nmr experiments are described; these include SELINCOR, selective one-dimensional HMQC-TOCSY, and SIMBA (selective inverse multiple bond analysis).

Teichoic acid and lipoteichoic acid of Streptococcus pneumoniae possess identical chain structures

“…The 'H'3C-heteronuclear-multiple-quantum coherence (HMQC) spectra were recorded using a pulse sequence with bilinear-rotation-decoupling pulse to suppress signals from protons connected to ' ' C [33]. A block size of 2K in Fz and 1024 increments, each with 32 scans in F , , were used in time-proportional-phase-increment mode, followed by zero filling of the 2K*2K matrix, processing with a n/2 phaseshifted sine filter and phase correction in F2 and F,.…”

Structural Elucidation with NMR Spectroscopy: Practical Strategies for Organic Chemists

“…When inverse detected heteronuclear correlation techniques (much more sensitive than their directly detected counterparts) were developed in the 1980s, [1] NMR became a practical alternative to X-ray crystallography for the elucidation of natural products. For example, these methods soon allowed the assignment of kauradienoic acid, [2] a complex diterpene, and even vitamin B 12 .…”

“…Recent work has uncovered the structural details of not only natural products of every class but also synthetic creations. Well-characterized examples include platensimycin (1), [4] a broad spectrum nonmevalonate terpenoid antibiotic, maoecrystal V (2), [5] an antitumor diterpenoid, chlorofusin, a peptide-based fungal metabolite with anticancer properties, [6] daphlongeranine B (3), [7] an unusual polycyclic alkaloid, and cytosporic acid (4), [8] a polyketide-derived HIV-1 integrase inhibitor, as well as β,βЈ-disilyl-substituted vinyl cations 5 [9] and cyanoresorc [5]arene 6. [10] For simple unknowns, straightforward experiments such as 1D 1 H and 13 C NMR, COSY (correlation spectroscopy), and NOESY (nuclear Overhauser spectroscopy) suffice.…”

The intercellular adhesin involved in biofilm accumulation of Staphylococcus epidermidis is a linear beta-1,6-linked glucosaminoglycan: purification and structural analysis

“…A block size of 1K in f2 and 512 increments, each with 256 scans in f1, were used in time-proportional-phaseincrement mode, followed by zero filling of a 1K ϫ 1K matrix, processing with a /2 phase-shifted sine filter, and phase correction in f2 and f1 (46).…”