One new limonoid, named siamensinolide (1), together with two known limonoids (2 and 3) and eight carbazole alkaloids (4–11) were isolated from the twigs of Chalcas siamensis Tanaka. Their structures were elucidated by spectroscopic methods, mainly 1D and 2D NMR spectroscopy. O-methylclausenolide (2) displayed strong cytotoxicity against A2780 cell lines with the IC₅₀ value of 9.2 µM, while clausenolide (3) exhibited strong antibacterial activity against methicillin-resistant Staphylococcus aureus with the MIC value of 0.5 µg/mL.

Background/Objectives: Wannachawee recipe (WCR) has been listed in the Hospital Traditional Medicine Formulary and has been used as a Thai medicine to treat psoriasis in the Thai Traditional Medicine Clinic of Prapokklao Hospital since 2006. Previous reports have found that WCR demonstrates good results for the treatment of patients with psoriasis. Among 136 Thai psoriasis patients who received WCR, 92.80% responded well. Although WCR is effective, there is still a lack of scientific data, especially relating to the bioactive compound in WCR. Therefore, this study aims to evaluate the phytochemicals in WCR via bioassay-guided isolation. Methods: In this study, the WCR was extracted via decoction with water, in a process based on traditional Thai medicine. The water extract was concentrated and dried using a spray dryer. The crude water extract was isolated using the partition technique with organic solvents, namely petroleum ether and ethyl acetate. These fractions were then separated and tested for anti-inflammatory activity using the bioassay-guided fractionation method. Results: Two particular types of pro-inflammatory cytokines are involved in inflammation and are among the factors that cause psoriasis—TNF-α and IL-6. Thus, we evaluated the isolated samples in terms of anti-inflammatory activity. The isolation resulted in two pure compounds—p-coumaryl aldehyde and trans-p-coumaryl alcohol. In the efficacy test of the isolated compounds, compared to the standard indomethacin at the same concentration of 12.5 ug/mL, trans-p-coumaryl alcohol was found to have the best efficacy, inhibiting TNF-α by 29.28% and IL-6 by 36.75%, with the standard compound showing inhibitions rates of 15.80% for TNF-α and 27.44% for IL-6. Conclusions: This study is the first report to identify the bioactive compound of WCR as trans-p-coumaryl alcohol or 4-hydroxycinnamyl alcohol.