Caloforines A-G, coumarins from the bark of Calophyllum scriblitifolium

Exploring the Recent Pioneering Developments of Small Molecules in Antimalarial Drug Armamentarium: A Chemistry Prospective Appraisal

Malaria is a very destructive and lethal parasitic disease that causes significant mortality worldwide, resulting in the loss of millions of lives annually. It is an infectious disease transmitted by mosquitoes, which is caused by different species of the parasite protozoan belonging to the genus Plasmodium. The uncontrolled intake of antimalarial drugs often employed in clinical settings has resulted in the emergence of numerous strains of plasmodium that are resistant to these drugs, including multidrug-resistant strains. This resistance significantly diminishes the effectiveness of many primary drugs used in the treatment of malaria. Hence, there is an urgent need for developing unique classes of antimalarial drugs that function with distinct mechanisms of action. In this context, the design and development of hybrid compounds that combine pharmacophoric properties from different lead molecules into a single unit gives a unique perspective towards further development of malaria drugs in the next generation. In recent years, the field of medicinal chemistry has made significant efforts resulting in the discovery and synthesis of numerous small novel compounds that exhibit potent antimalarial properties, while also demonstrating reduced toxicity and desirable efficacy. In light of this, we have reviewed the progress of hybrid antimalarial agents from 2021 up to the present. This manuscript presents a comprehensive overview of the latest advancements in the medicinal chemistry pertaining to small molecules, with a specific focus on their potential as antimalarial agents. As possible antimalarial drugs that might target both the dual stage and multi-stage stages of the parasite life cycle, these small hybrid molecules have been studied. This review explores a variety of physiologically active compounds that have been described in the literature in order to lay a strong foundation for the logical design and eventual identification of antimalarial drugs based on lead frameworks.

Vincarostine A, a novel anti-malarial trimeric monoterpenoid indole alkaloid from Catharanthus roseus

A novel trimeric monoterpenoid indole alkaloid, vincarostine A (1) consisting of an aspidosperma-iboga-aspidosperma type skeleton, was isolated from the whole plant of Catharanthus roseus. The structure including absolute stereochemistry was elucidated on the basis of 2D NMR data and CD spectrum. Vincarostine A (1) showed anti-malarial activity.

Vincazalidine A, a unique bisindole alkaloid from Catharanthus roseus

A new dimeric indole alkaloid, vincazalidine A consisting of an aspidosperma type and a modified iboga type with 1-azatricyclo ring system consisting of one azepane and two piperidine rings coupled with an oxazolidine ring was isolated from Catharanthus roseus, and the structure including absolute stereochemistry was elucidated on the basis of spectroscopic data as well as DP4 statistical analysis. Vincazalidine A induced G2 arrest and subsequent apoptosis in human lung carcinoma cell line, A549 cells.

Isovincathicine from Catharanthus roseus induces apoptosis in A549 cells

A dimeric indole alkaloid, isovincathicine consisting of an aspidosperma type and modified iboga with C-7-C-20 connection type skeletons was first isolated from Catharanthus roseus, and the structure including stereochemistry was elucidated on the basis of spectroscopic data as well as DP4 statistical analysis. Isovincathicine inhibited cell proliferation in A549 cells. We investigated the detailed mode of action of isovincathicine-induced inhibitory effects on cell proliferation in A549 cells. Flow cytometric analysis showed that isovincathicine-treated cells accumulated in the G2 phase after 24 h, and the percentage of cells showing cell death increased after 48 h. Western blotting also showed increased expression of BimEL, an apoptosis-related protein, and decreased expression of Mcl-1 and Bcl-xL. Isovincathicine was suggested to induce apoptosis in A549 cells by a mechanism is similar to that of vinblastine.

Antimalarial ceramicines Q-T from Chisocheton ceramicus

Ceramicines are a series of limonoids that were isolated from the bark of Malaysian Chisocheton ceramicus (Meliaceae) and were known to show various biological activity. Four new limonoids, ceramicines Q-T (1-4) were isolated from the barks of C. ceramicus, and their structures were determined on the basis of the 1D and 2D NMR analyses in combination with calculated 13C chemical shift data. Ceramicines Q-T (1-4) were established to be new limonoids with a cyclopentanone[α]phenanthren ring system with a β-furyl ring at C-17, and without a tetrahydrofuran ring like ceramicine B, which is characteristic of known ceramicines. Ceramicine R (2) exhibited potent antimalarial activity against Plasmodium falciparum 3D7 strain with IC50 value of 2.8 µM.

Cryptadine C, a new C27N3-type Lycopodium alkaloid from Lycopodium cryptomerinum

A new C₂₇N₃-type Lycopodium alkaloid consisting of two decahydroquinolines and a piperidine, cryptadine C (1) was isolated from Lycopodium cryptomerinum. The structure and relative configuration of 1, which is related to those of cryptadines A and B, lycoperine A, and hupercumine A, was elucidated on the basis of spectroscopic data. Cryptadine C showed moderate inhibitory activity against acetylcholinesterase.

Calofolic Acid-A from Calophyllum scriblitifolium Bark Has Vasorelaxant Activity via Indirect PKA Activation Caused by PI-3 Kinase Inhibition in Rat Vascular Smooth Muscle Cells

Previously, we isolated 2R,3S,15R-calofolic acids (CAs) from Calophyllum scriblitifolium bark, which showed vasorelaxant activity on phenylephrine (PE)-precontracted rat aortic rings. Although the effect was suggested to be induced via an extracellular Ca²⁺-independent manner and mainly acts on vascular smooth muscle, the exact mechanism of action of CAs remained unclear. Thus, this study investigated the detailed mechanism of calofolic acid-A (CA-A) induced vasorelaxation in an aortic ring specimen using rat vascular smooth muscle cells (VSMCs). The levels of PE-induced phosphorylation on MLC Ser19 decreased in VSMCs pretreated with CA-A. CA-A also decreased the phosphorylation of MYPT1 Thr696 and MYPT1 Thr853. On the other hand, CA-A increased the PE-induced phosphorylation of MYPT1 Ser695 and MYPT1 Ser668, which are reported to be phosphorylated by a cAMP-dependent protein kinase (PKA). CA-A slightly increased PKA substrate phosphorylation in a concentration-dependent manner. Furthermore, CA-A enhanced isoproterenol (ISO)-induced cAMP accumulation and PKA substrate phosphorylation. Treatment with PI-3 kinase (PI3K) inhibitor, LY294002, enhanced ISO-induced cAMP accumulation and PKA substrate phosphorylation in the same manner as CA-A treatment. Furthermore, CA-A was found to directly inhibit PI3K enzyme activity in a dose-dependent manner. Taken together, the present study indicated that CA-A induces vasorelaxation through an indirectly activated PKA-MYPT1 pathway caused by inhibition of PI3K activity.