On Nitrogen Coordination in Vincadifformine-Type Alkaloids

Determination of Active Ingredients, Mineral Composition and Antioxidant Properties of Hydroalcoholic Macerates of Vinca minor L. Plant from the Dobrogea Area

In recent decades, new alternative therapies using drugs containing active ingredients of natural origin have been a hot topic for medical research. Based on the confirmed therapeutic potential of the Vinca minor plant, considered in the specialized literature to be of pharmaceutical interest, the purpose of this study is to determine the chemical and mineral composition of the Vinca minor plant grown in the Dobrogea area, with a view to its use in the formulation of dermal preparations. For this purpose, plant materials were collected from the mentioned area and hydroalcoholic macerates of different concentrations were obtained: 40%, 70% and 96% from leaves (F40, F70, F96) and stems (T40, T70, T96) of Vinca minor plant to determine the optimal extraction solvent. The hydroalcoholic macerates were analyzed via the HPLC method for the identification and quantification of the main bioactive compounds, and two methods were used to evaluate their antioxidant properties: the DPPH radical scavenging test and the photochemiluminescence method. HPLC analysis showed the presence of four indole alkaloids: vincamine, 1,2-dehydroaspidospermidine, vincaminoreine and eburnamonine. Vincamine was the alkaloid found in the highest concentration in Vinca leaves (2.459 ± 0.035 mg/100 g d.w.). The antioxidant activity of Vinca minor hydroalcoholic macerates showed values between 737.626-1123.500 mg GAE/100 g d.w (DPPH test) and 77.439-187.817 mg TE/100 g d.w (photochemiluminescence method). The concentrations of toxic metals Cd, Cu, Ni, Pb in dried leaves and stems of Vinca minor, determined by AAS, were below detection limits.

Molecular Rotation Spectrum of Tetracyclic Quinolizidines: Observation of trans-Matrine and the Elusive cis-Matrine

We characterized the bis-quinolizidine tetracyclic alkaloid (5S, 6S, 7R, 11R)-matrine in a supersonic jet expansion, using chirped-pulsed broadband microwave spectroscopy. Previous crystal diffraction analyses suggested 16 diastereoisomers associated with matrine's four carbon stereocenters but were inconclusive whether the lactamic nitrogen atom would additionally produce separated trans-/cis- diastereoisomers or if both species may interconvert through low potential barriers. Our experiment simultaneously detected trans- and cis-matrine through their rotational spectrum, confirming the possibility of conformational rearrangement in matrine alkaloids. The two matrine conformers mainly differ in the envelope or half-chair lactamic ring, as evidenced by the experimental rotational and nuclear quadrupole coupling parameters. Molecular orbital calculations with ab initio (MP2) and density functional methods (B3LYP-D3(BJ) and MN15) were tested against the experiment, additionally offering an estimation of the cis-/trans- barrier of 24.9-26.9 kJ mol^-1. The experiment illustrates the structural potential of chirped-pulsed broadband microwave spectroscopy for high-resolution rotational studies of biomolecules in the range of 20-40 atoms.