INDOR technique

Only two normal Erythrina alkaloids have been isolated from Cocculus species, dihydroerysodine (47) (75) and dihydroerysovine (44), the latter recently from C. trilobus (57). Neither alkaloid has been found in Erythrina species. The structure 44 for dihydroerysovine was deduced from the spectroscopic evidence and by methylation using diazomethane to give the known dihydroerysotrine (38). The positions of the aromatic substituents were determined by detailed NMR experiments using NOE and INDOR techniques (see Section II,C,2d). 

At the beginning of the C-nmr era Olah el al. used the INDOR-technique and obtained some very interesting results with ions containing C in natural abundance. Today C-nmr-spectra of carbocations are obtained routinely with dilute samples of carbocations which contain only natural abundance... 

The C-nmr spectrum of ion [100] obtained by the INDOR-technique showed equivalent methylene carbon absorptions at S -l- 138 1 (ref. CSa 7i,p = 180 5 Hz). The methine carbon appears at -1-85 but Ji, was not obtainable by the experimental technique used. It was concluded that the ion has two sets of equivalent methylene protons both of which are coupled to equivalent carbon atoms. It must either have high symmetry or be a set of rapidly equilibrating ions. 

More modem one-dimensional (ID) sequences such as INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) or DEPT (Distortionless Enhancement by Polarization Transfer) [6,13-15] have not been used extensively [16]. This type of experiment seems to be more powerful than the old INDOR technique. 

The INDOR technique of decoupling 14N from H (150) has been shown to yield two different values of /(N-H) in formamide, but the experimental errors are much larger than those found in the measurement of 13N-H couplings. 

Due to the high receptivity of F, E nf correlation spectroscopy became available very early in the history of NMR spectroscopy. Using the INDOR technique on a cw-spectrometer, McFarlane and coworkers gave the first report whatsoever on the use of "X, "Y correlated spectroscopy for indirect observation via of the resonances in complexes of the type WF6 0R and WOp4L. Beside the first chemical shift determination for a low-7 transition metal, which was at that time not feasible by any other technique, further the indirect determination of y( W, P), and the assignment of relative coupling signs, was reported. 

With the aid of decoupling experiments and the INDOR technique, it was possible to define completely the structure and stereochemistry of erythristemine (1) with the exception of the configuration at C-11." In order to obtain the latter information, recourse was taken to A-ray analysis on the 2-bromo-4,6-dinitrophenolate salt of (1). This constitutes a new method and may be applicable elsewhere. Details of the structural and stereochemical elucidation of the interesting insecticidal alkaloid (2), which may be regarded as a ring-D degraded erythroidine structure, have appeared. ... 

The methyl resonances of several oleanene derivatives have been assigned using lanthanide shifts and homonuclear INDOR techniques to measure the nuclear Overhauser effects between methyl signals. The assignments of the resonances of a series of 18jSH- and 18aH-oleanenes have been published. The potential use of molecular rotation differences in the identification of triterpenoid structures has been discussed. ... 

Andranginine was obtained from Craspidospermum verticillatum Boj. var. petiolare (125), but the mass spectral and CMR spectral data did not allow deduction of its carbon skeleton. Using the INDOR technique the structure was deduced to be 338 (126). 

Anteunis group have reported the n.m.r. spectral parameters of some 4-alkyl-6-methyI-l,3-oxaselenans using INDOR techniques. Low-temperature studies show that the conformational equilibria in the trans-senes are markedly one-sided, with the methyl next to selenium strongly preferring to be axial (AG ca. 1.5 kcal mol ) (71). Ring-inversion barriers were measured (AGfoo = 8.3 kcal mol" ). 

In addition to allowing the determination of the P chemical shift this double resonance method provides a means by which the relative signs of coupling involving P can be determined. The primary advantage of the INDOR technique lies in its use of relatively sensitive nuclei to obtain data on less receptive systems. 

Sn. As a result, all three are relatively easy to study, except where long relaxation times or the null signal problem make for difficulties. Therefore, the relevant NMR literature is extensive. In the three years 1978-80, Si, Sn, and Pb proved to be the 7th, 18th, and 26th most popular nuclei, respectively, for chemical NMR studies, with at least 85, 28, and 9 publications, respectively (including solid state studies). There seems to have been only one publication (6) involving Ge (measured via the INDOR technique) in the same period, and there do not appear to have been any in 1981. 

Kikuchi, T., M. Niwa, M. Takayama, T. Yokoi, and T. Shingu Application of Homonuclear INDOR Technique. Structure of an Acid-Induced Rearrangement Product of 16-Keto-friedel-3-ene. Tetrahedron Letters 1973, 1987. 

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