HOHAHA-HMQC

The assignment of structures by NMR in the highly hydrogenated skeleton is not straightforward due to the similar chemical environment of the methylene groups. In the H-NMR spectrum ((see Fig. (2)) the upfield region (0.5-4 ppm) is severely congested and methods that have been applied to new structure elucidation, such as HMQC (or HSQC), HMBC, INEPT, COSY, NOESY, ROESY, TOCSY (HOHAHA), HMQC-TOCSY, are needed. A particularly useful method is HMQC-TOCSY (see... 

An unprecedented manzamine dimer, kauluamine (90), was isolated from the Indonesian marine sponge Prianos sp. 90 is an unsymmetrical dimer composed of tetracyclic and pentacyclic ring systems. Efforts to obtain a crystalline structure or to run an INADEQUATE experiment were unsuccessful. Thus the structure was elucidated by NMR methods, mainly on the basis of extensive 2D-NMR experiments, DQFCOSY, HOHAHA, HMQC, HMBC, and HMQC-HOHAHA [102,103]. 

NMR data of 47, including the H H COSY, HOHAHA, HMQC, and HMBC spectra, and the FABMS/MS fragmentation, corroborated well with those of the imine (C-20 and N) form of 46. The treatment of 47 with NaBH4 afforded senepodine A (46) by... 

Ammalahti, E. Brunow, G. Bardet, M. Robert, D. Kilpelainen, I. Identification of side-chain structures in a poplar lignin using three-dimensional HMQC-HOHAHA NMR spectroscopy. J. Agric. Food Chem. 1998, 46, 5113-5117. 

The addition of a HOHAHA mixing step to a heteronuclear multiple-quantum correlation (HMQC) experiment (Bax et al., 1983) yields two-dimensional HMQC-HOHAHA experiments (Lerner and Bax, 1986 Davis, 1989b Oh et al., 1989 Gronenborn et al., 1989b John et al., 1991 Willker et al., 1993a). Domke and McIntyre (1992) combined heteronuclear Hartmann-Hahn transfer with multiplicity editing techniques. 

Kilpelainen, L, Ammalahti, E., Brunow, G., and Robert, D. (1994) Application of three-dimensional HMQC-HOHAHA NMR spectroscopy to wood lignin, a natural polymer. Tetrahedron Lett. 35(49), 9267-9270. 

NMR is the tool most widely used to identify the structure of triterpenes. Different one-dimension and two-dimension techniques are usually used to study the structures of new compounds. Correlation via H-H coupling with square symmetry ( H- H COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC), distortionless enhancement by polarisation transfer (DEPT), incredible natural abundance double quantum transfer experiment (INADEQUATE) and nuclear Overhauser effect spectroscopy (NOESY) allow us to examine the proton and carbon chemical shift, carbon types, coupling constants, carbon-carbon and proton-carbon connectivities, and establish the relative stereochemistry of the chiral centres. 

For the determination of the sequence and substitution positions of the different monosaccharides of a saponin, a series of proton and carbon 2D-NMR techniques can provide valuable information about the usually crowded regions of the conventional ID spectra. Thus, integrated approaches including ID or 2D H- H homonuclear NMR shift-correlation experiments (DQF- and TQF-COSY, TOCSY or HOHAHA, NOESY, ROESY or CAMELSPIN), and H-detected H-,3C heteronuclear shift correlation (HMQC, HMBC) have proved to be extremely useful. 

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