Abstract:
Infectious diseases account for most deaths globally, far beyond the damage incurred by
warfare and food shortages. 10 million deaths have resulted from infectious diseases
worldwide; lower respiratory tract infections are the largest, followed by diarrhoea,
tuberculosis, HIV-AIDS, and Malaria. 70,000 deaths have resulted due to the increased
drug resistance in malaria, antibacterial, and antifungal drugs. Bioactive compounds are
continually being explored for the prophylaxis and treatment of these infectious diseases
and also to manage drug resistance limitations acquired by some of the currently used
drugs. This study aimed to characterize phytochemicals from the Chamaecrista nigricans
plant and the Ximenia americana roots with antiplasmodial and antimicrobial activities.
The grounded plant of C. nigricans and X. americana roots were extracted via cold
extraction using a 1:1 methanol: DCM solvent volume ratio. Fractionation and purification
were done using the silica column chromatography technique, and Sephadex LH20 was
used to purify some compounds further. Chemical structures were identified using FTIR,
GC-MS, and NMR spectroscopic techniques. C. nigricans yielded previously reported
compounds compounds: chrysophanol (1,8-dihydroxy-3-methylanthraquinone) (SAO-04),
(1,6,8-trihydroxy-3-methylanthraquinone) (SAO-05), and physcion (1,8-dihydroxy-3-
methyl-6-methoxyanthraquinone) (SAO-06). X. americana yielded seven compounds:
Octahydro-3-isopropyl-4a,5-dimethylnaphthalen-2 (1H)-one, Trans-2-dodecenedioic acid,
Octadecanoic acid, 1,2-dihexadecanoylglycerol, Methyl-14-methylpentadecanoate, (Z)-7-
tetradecenal and (Z)-9-hexadecenal. The crude extracts from the two plants had IC50 values
of > 47.6 μg/ml against both P. falciparum D6 (chloroquine sensitive) and W2
(chloroquine-resistant). The compounds isolated from the two plants exhibited
antiplasmodial activity with IC50 values of > 4.76 μg/ml against both P. falciparum D6
(chloroquine sensitive) and W2 (chloroquine-resistant). The crude extracts of the two plants
displayed reduced toxicity with an IC50 value of > 47.6 μg/ml, while the compounds from
the two plants were cytotoxic with IC50 values ranging between 3.8378-> 4.76 μg/ml
against the normal VERO cells. Crude extract of X. americana had mild activity against
Cryptococcus neoformans with IC50 value >200 μg/ml. Crude extract of C.nigricans had no
activity against Cryptococcus neoformans, while compounds isolated from it exhibited
activity with IC50 values ranging from 4.19-8.63 μg/ml. An alkaloid fraction (SAO-07)
from X. americana portrayed potent activity against E. coli (IC50 value of 1.45 μg/ml)
compared to the control drug Meropenem (IC50 value of 7.57μg/ml). Compounds isolated
from C.nigricans had notable activity against methicillin-resistant Staphylococcus aureus
with IC50 values ranging between 6.93-16.99 μg/ml in comparison to control drugs whose
IC50 values ranged between 2.63-17.57 μg/ml. In conclusion, it was observed that
compounds from C.nigricans have antimicrobial activity against methicillin-resistant S.
aureus, while an alkaloid isolated from X. americana exhibited activity against E. coli. It
was also established that both crude extracts of the two plants had minimal antiplasmodial
activity and toxicity while their isolated compounds were cytotoxic. The findings also
ascertain that these plants harbour antimicrobial and antiplasmodial compounds and should
be further investigated for novel antimalarial and antimicrobial drugs.