Abstract
The UV-vis spectra of isocorydine 1, norisocorydine 2 and boldine 3 were studied in 2% v/v acetonitrile, at constant ionic strength (0.1 M NaCl, 35 degree Celsius). The pKa values of isocorydine 1 and norisocorydine 2 were 11.75 and 12.07, respectively. Boldine 3 gave a pKa value of 9.16 and 10.44. All of the alkaloids 1–3 were stable at physiological pH; thereby all of them will not ionize, thus permitting the basic nitrogen to be protonated and accumulated within the acidic food vacuole of Plasmodium via pH trapping. Subsequently, acidic food vacuoles that have been neutralized by alkaloids would result in enhancement of the antiplasmodial activity. The alkaloids showed antiplasmodial activity against Plasmodium falciparum and antioxidant activities; DPPH radical scavenging, metal chelating and ferric reducing power. The antioxidant properties of the alkaloids under investigation revealed that in addition to the antiplasmodial activity, the alkaloids can also prevent oxidative damage. It can be prevented by binding free heme and neutralizing the electrons produced during the Plasmodium falciparum mediated haemoglobin destruction in the host. Slightly basic properties of the aforementioned alkaloids, along with their antioxidant activities, are advantageous in improving the suppression of malaria infection that cause less damage to the host.
Highlights
IntroductionAcidity constants (Ka values) of a reactant in a medium are useful physicochemical measurement to describe the extent of dissociation of functional groups with respect to pH
The majority of the antimalarial drugs were derived from plants; which have provided a good source of lead for drug discovery[11]
The importance of the antioxidant activity is to reverse or minimize the oxidative damage to the hosts caused by Plasmodium parasites from malaria infection
Summary
Acidity constants (Ka values) of a reactant in a medium are useful physicochemical measurement to describe the extent of dissociation of functional groups with respect to pH These parameters are important in selecting appropriate acidic or basic reagents in drug delivery studies. Parasites such as Plasmodium possesses acidic food vacuole, which is an important organelle involved in the digestion of the host haemoglobin. The same approach was employed in this work to determine the acid-base behaviour of the alkaloids against varying pH and temperature dependence[14] In this communication, we report the antiplasmodial and antioxidant activities for isocorydine 1 and norisocorydine 2 (Table 1). All graphs of the pH-absorbance of alkaloids 1–3 can be found as supplementary Fig. S2–S4 online
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