Heteronuclear Multiple Bond Connectivity

Because of the complexity of the polyether antibiotics tittle progress has been made in stmcture determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early stmcture elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and H (192) and nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for stmcture determinations. Eor example, heteronuclear multiple bond connectivity (hmbc) and homonuclear Hartmann-Hahn spectroscopy were used to solve the stmcture of portimicin (14) (193). East atom bombardment mass spectrometry was used in solving the stmctures of maduramicin alpha and co-factors (58). 

Heteronuclear Multiple-Bond Connectivity (HMBC) Spectra... 

Hirota and coworkers41 reported a planar structure of new polyene macrolide antibiotic YS-822A (65), which they isolated. XH and 13C NMR spectra of 65 showed a number of broad and overlapping signals, but the 1H-1H and 13C- H COSY spectra implied the existence of a mycosamine moiety and several other partial structures. The connectivity of these partial structures was established by extensive 2D NMR experiments, including homonuclear Hartmann-Hahn and heteronuclear multiple-bond connectivity measurements, which led to the determination of the gross planar structure of 65. 

A. Bax and M. F. Summer, and C assignments from sensitivity-enhanced detection of heteronuclear multiple-bond connectivity by 2D multiple quantum NMR,/Am. Chem. Soc. 108 (1986),2093-2094. 

R74 R. Araya-Maturana, T. Delgado-Castro, W. Cardona and B. E. Weiss-Lopez, Use of Long-Range C-H ( J n>3) Heteronuclear Multiple Bond Connectivity in the Assignment of C NMR Spectra of Complex Organic Molecules , p. 253... 

Bax A, Summers MF (1986) Proton and Carbon-13 Assignments from Sensitivity-Enhanced Detection of Heteronuclear Multiple-Bond Connectivity by 2D Multiple Quantum NMR. J Amer Chem Soc 108 2093... 

A H(detected)- C shift correlation spectrum (common acronym HMQC, for heteronuclear multiple quantum coherence, but sometimes also called COSY) is a rapid way to assign peaks from protonated carbons, once the hydrogen peaks are identified. With changes in pulse timings, this can also become the HMBC (heteronuclear multiple bond connectivity) experiment, where the correlations are made via the... 

Bax A, Davis DG (1985) MLEV-17 Based two-dimensional homonuclear magnetization transfer spectroscopy. J Magn Reson 65 355-360 Bax A, Drobny G (1985) Optimization of two-dimensional homonuclear relayed coherence transfer NMR spectroscopy. J Magn Reson 61 306-320 Bax A, Marion D (1988) Improved resolution and sensitivity in H-detected heteronuclear multiple-bond correlation spectroscopy. J Magn Reson 78 186-191 Bax A, Subramanian S (1986) Sensitivity-enhanced two-dimensional heteronuclear chemical shift correlation NMR spectroscopy. J Magn Reson 67 565-569 Bax A, Summers MF (1986) and Assignments from sensitivity-enhanced detection of heteronuclear multiple bond connectivity by 2D multiple-quantum NMR. J Am Chem Soc 108 2093-2094... 

---