NMR of Natural Products as Potential Drugs

Abstract

This review outlines methods to investigate the structure of natural products with emphasis on intramolecular hydrogen bonding, tautomerism and ionic structures using NMR techniques. The focus is on 1H chemical shifts, isotope effects on chemical shifts and diffusion ordered spectroscopy. In addition, density functional theory calculations are performed to support NMR results. The review demonstrates how hydrogen bonding may lead to specific structures and how chemical equilibria, as well as tautomeric equilibria and ionic structures, can be detected. All these features are important for biological activity and a prerequisite for correct docking experiments and future use as drugs.

Structural Studies of β-Diketones and Their Implications on Biological Effects

“…An interesting structure that seems to cause diverse biological effects is shown in Figure 11. This structural element is part of tetracyclines, and in this case, the equilibrium is shifted towards the a-form [8]. Furthermore, it has shown promising effects in comparison with mycobacteria [57].…”

“…A recent study [42] investigated a large series of curcumin analogues (Figure 12). Probabilities to act as antineoplastic, prostate cancer treatment, and anticarcinogenic agents was studied theoretically by applying a se- This structural element is part of tetracyclines, and in this case, the equilibrium is shifted towards the a-form [8]. Furthermore, it has shown promising effects in comparison with mycobacteria [57].…”

“…The dihydroanthracen-1(4H) one (Figure 16) isolated from Rubia philippinensis is an inhibitor of soluble epoxide hydrolase (sEH). The structure was given as a single tautomer [68] but has been suggested to exist as a tautomeric equilibrium [8]. Tetramic acid is also combined with ampicillin to form a hybrid in order to improve the effect against Gram-negative bacteria [77].…”

“…The synthesis of the simple β-diketones is usually not complicated [1,2]. A number of reviews have discussed tautomerism and biological effects [3][4][5][6][7][8].…”

Long range deuterium isotope effects on 13C NMR chemical shifts of 2-alkanones in CD3OD solutions of imidazolium acetate ionic liquids

“…Deuterium isotope effects (DIE) are an effective tool for studying the structure and dynamics of organic and biological molecules, 1–3 and for drug design. 4 They are very useful for spectral interpretation and for structural elucidation in NMR spectroscopy as well. In such studies mainly DIE on 1 H and 13 C spectra over two bonds are used, but no less interesting is the transmission of the effects via three or more bonds.…”