In order to characterize a sample obtained from an important medicinal plant we applied
nuclear magnetic resonance to access quantitative data of its bioactive compounds.
Piper rivinoides has been a focus of our interests due to the disclosed vasodilator activity found
for its extracts and purifies compounds. Following an usual trend for Piper species we were able to identify four benzofuran neolignans, namely Eupomatenoid
V, Eupomatenoid VI, (2R,3R)-2,3-dihydro-2-(4-hydroxy-3-methoxyphenyl)-3-methyl-5-(E)-propenylbenzofuran and Conocarpan. In this paper we aim to characterize the bioactive
fractions and the raw extract under quantitative analysis. A fundamental feature of
NMR spectroscopy is that the intensity of a single resonance obtained will have direct
relation with the number of spins and so with the concentration. Thus, since each
of the intensity interfering parameter is optimized the integrated signal becomes
directly correlated to the concentration of a certain compound. Then, key known resonances
from Eupomatenoid VI (1 H, d 3JHH = 8.18 Hz, 7.66 ppm; H-6'), Eupomatenoid V (1 H,
s, 7.37 ppm; H-6) and Conocarpan (1 H, d JHH = 8.10 Hz, 6.76 ppm; H-3) related to
one proton each were found to be isolated, and so, capable of being quantified. The
integrals of each of the selected resonances were used as their absolute values for
quantitative calculations; manalito=(Ianalito/Ipadrão) * (MManalito/MMpadrão) * (Nanalito/Npadrão) * (1/mpadrão). Dimethylbenzaldehyde resonance at 9.85 ppm (aldehyde proton, 1 H, s) was used as
internal standard. The results found with basis on the equation (1) show that the
evaluated extract contains 15.29% of Eupomatenoid VI, 29.81% of Eupomatenoid V, 5,52%
of Conocarpan; percentages were calculated for the total powdered and dry plant material.
By means of two signals from 6.15 ppm to 6.40 ppm related to two typical protons of
benzofuran neolignans we could define to total benzofuran neolignans concentration
in the sample.
Fig. 1
