Depression is the most common illness observed in the elderly, adults and children. Antidepressants prescribed are usually synthetic drugs and these can sometimes cause a wide range of unpleasant side effects. Current research is focussed on natural products from plants as they are a rich source of potent new drug leads. Besides Hypericum perforatum (St. John's wort), the plants studied include Passiflora incarnata L. (passion flower), Mitragyna speciosa (kratom), Piper methysticum G. Forst (kava) and Valeriana officinalis L. Harman, harmol, harmine, harmalol and harmaline are indole alkaloids isolated from P. incarnata, while mytragynine is isolated from M. speciosa. The structure of isolated compounds from P. methysticum G. Forst and V. officinalis L. contains an indole moiety. The indole moeity is related to the neurotransmitter serotonin which is widely implicated for brain function and cognition as the endogenous receptor agonist. An imbalance in serotonin levels may influence mood in a way that leads to depression. The moiety is present in a number of antidepressants already on the market. Hence, the objective of this review is to discuss bioactive compounds containing the indole moeity from plants that can serve as potent antidepressants.

Quaternary alkaloids are the major alkaloids isolated from Tinospora species. A previous study pointed to the necessary presence of quaternary nitrogens for strong acetylcholinesterase (AChE) inhibitory activity in such alkaloids. Repeated column chromatography of the vine of Tinospora crispa extract led to the isolation of one new protoberberine alkaloid, 4,13-dihydroxy-2,8,9-trimethoxydibenzo[a,g]quinolizinium (1), along with six known alkaloids—dihydrodiscretamine (2), columbamine (3), magnoflorine (4), N-formylannonaine (5), N-formylnornuciferine (6), and N-trans-feruloyltyramine (7). The seven compounds were isolated and structurally elucidated by spectroscopic analysis. Two known alkaloids, namely, dihydrodiscretamine and columbamine are reported for the first time for this plant. The compounds were tested for AChE inhibitory activity using Ellman’s method. In the AChE inhibition assay, only columbamine (3) showed strong activity with IC₅₀ 48.1 µM. The structure–activity relationships derived from these results suggest that the quaternary nitrogen in the skeleton has some effect, but that a high degree of methoxylation is more important for acetylcholinesterase inhibition.

Rhodomyrtus tomentosa is a common wood, prevalent in areas with undemanding soil conditions and resistant toward pests and diseases. The plantcan be found in China, Taiwan, Philippines, Malaysia, Indonesia, and Vietnam. Literature and artwork indicate that R. tomentosa played an importantholistic role in the daily lives of several ancient cultures, providing medicinal benefits. R. tomentosa exhibits a wide spectrum of pharmacologicaleffects and has been used to treat colic diarrhea, wounds, heartburn, abscesses, gynecopathy, and as a pain killer. R. tomentosa was used in traditionalChinese medicine to treat urinary tract infection. 42 compounds have been isolated from this plant and structurally elucidated. They comprisephloroglucinol, flavonoid, terpenoid, anthracene glycoside, tannin, and other compounds. Rhodomyrtone, a member of the acylphloroglucinolsdemonstrated a significant activity against a wide range of Gram-positive bacteria. Rhodomyrtone exhibited both antimicrobial and anti-infectiveactivities. Several biological activities have been documented as antibacterial, antifungal, antimalarial, osteogenic, antioxidant, and anti-inflammatory.R. tomentosa has been studied extensively for alternative antimicrobial agents. Although rhodomyrtone exhibited potential activity with a very lowminimum inhibitory concentration value, the mechanisms of action of this compound are still unclear. Furthermore, toxicity studies on it extract tovalidate pharmacological activities are required.Keywords: Rhodomyrtus tomentosa, Kemunting, Phytochemical, Pharmacological, Biological activities, Chemical constituents.