LR-HSQMBC: a sensitive NMR technique to probe very long-range heteronuclear coupling pathways.
HMBC is one of the most often used and vital NMR experiments for the structure elucidation of organic and inorganic molecules. We have developed a new, high sensitivity NMR pulse sequence that overcomes the typical (2,3)JCH limitation of HMBC by extending the visualization of long-range correlation data to 4-, 5-, and even 6-bond long-range (n)JCH heteronuclear couplings. This technique should prove to be an effective experiment to complement HMBC for probing the structure of proton-deficient molecules. The LR-HSQMBC NMR experiment can, in effect, extend the range of HMBC to provide data similar to that afforded by 1,n-ADEQUATE even in sample-limited situations. This is accomplished by optimizing responses for very small (n)JCH coupings as opposed to relying on the markedly less sensitive detection of long-range coupled (13)C-(13)C homonuclear pairs at natural abundance. DFT calculations were employed to determine whether the very long-range correlations observed for cervinomycin A2 were reasonable on the basis of the calculated long-range couplings.
Discovery & Preclinical Sciences, Process & Analytical Chemistry, Structure Elucidation Group, Merck & Co. Inc. , Rahway, New Jersey 07065, United States.
R Thomas
RT
Williamson
Alexei V
AV
Buevich
Gary E
GE
Martin
Teodor
T
Parella
D018943:Anthracyclines / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D011789:Quantum Theory; D012015:Reference Standards
D018943:Anthracyclines; C035628:cervinomycin A2