Applications of¹⁵N NMR Spectroscopy in Alkaloid Chemistry

Application of 1,n-ADEQUATE and Modified Variants to Structure Elucidation and Spectral Assignment Problems

“…For nitrogenous compounds, adding 1 H-15 N HMBC to the standard suite of experiments can be extremely beneficial. 6,7 As molecules become progressively more proton-deficient, the challenge of assembling a structure increases significantly. The inherent challenge in determining the structure of proton-deficient molecules leads to what is now known among natural products chemists as the so-called Crews Rule, 8 the name derived from a work by Professor Phil Crews and a colleague.…”

A Novel Route to Recognizing Quaternary Ammonium Cations Using Electrospray Mass Spectrometry

“…As an N-H bond is not present in quats, 1 H NMR can only provide information regarding the quaternary functional group via long-range quadrupolar coupling to 14 N. These signals are frequently small and, therefore, may not be detected [20]. Although other modes of NMR may provide further information that may indicate the possible presence of a quat, they are not confirmatory or definitive [21,22]. Additionally, mass spectrometry suffers from the inability to distinguish between the M + ion of a quat and the [M + H] + ion of a non-quat in a mass spectrum.…”

1H–15N HMBC spectra of C18-diterpenoid alkaloids

“…Several reports that covered the 15 N NMR studies of many nitrogenous organic compounds including alkaloids are available [2,3]. Due to the low natural abundance of 15 N isotope, the 1 H-15 N correlation spectroscopy, which showed an about 310-fold sensitivity increase over the direct detection method, was employed in the practical applications [1].…”