Chemical constituents from the flowers of Anomianthus dulcis (Dunal) J. Sinclair

Abstract Phytochemical investigation of the flowers of Anomianthus dulcis led to the isolation of eleven known compounds. The isolated compounds were identified by analysis of physical and spectroscopic (IR, 1 D and 2 D NMR) data. We report five flavonoids (1–4 and 10), two chalcone-sesquiterpenoids (5 and 6), one indole alkaloid (7), one triterpenoid (8), and a mixture of two phenolic compounds (9 and 11). Remarkably, it is the second isolation of sumadain A (5) and sumadain B (6) from a natural source. Compounds 5 and 6 were evaluated against several cancer cell lines, as the previous report lacked biological activity studies. Compound 6 showed strong cytotoxicity against Hela, HT-29, HCT-116, and A549 cell lines, with IC50 values in the range of 5.43–14.64 µg/mL. Graphical Abstract


Introduction
Anomianthus dulcis is a large climbing shrub belonging to the Annonaceae family. It can be found in forests and woody grasslands of Southeast Asia (Smitinand 2014). It can reach up to 30 m in size and 20 m in height. The stems scramble over the ground and climb onto the surrounding vegetation. The flowers are salmon-orange with a strong and sweet smell. The edible fruit are red, globose (2.5 cm) and sweet (Meade and Parnell 2018). Interestingly, A. dulcis is the only species in the Anomianthus genus. A total of five phytochemical investigations of A. dulcis have been published; one focusing on the leaves (Sinz et al. 1999), one focusing on the flowers (Promchai et al. 2021), and the remaining three focusing on the stems (Sinz et al. 1998a(Sinz et al. , 1998bUbonopas et al. 2014). They describe the isolation of flavonoids, alkaloids, and chalconoids. In continuation of our efforts to identify new bioactive natural products from plants growing in Thailand (Wisetsai et al. 2019;Nathabumroong et al. 2021;Wisetsai et al. 2021aWisetsai et al. , 2021b, we decided to investigate the flowers of A. dulcis. The flowers have recently been investigated but the outcome was limited, as only 183 g of dried flowers were available.

Conclusions
Phytochemical investigation of the flowers of Anomianthus dulcis led to the identification of eleven known compounds. In terms of chemotaxonomic significance, compounds 5 and 6 are reported for the Annonaceae family for the first time, while compounds 3, 8, 9 and 11 are reported from the Anomianthus genus for the first time.
In term of biological activities, compounds 5 and 6 were evaluated against several cancer cell lines. Compound 5 showed moderate cytotoxicity against three cell lines, while compound 6 showed strong cytotoxicity against the four tested cell lines.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This work was supported by the Center of Excellence for Innovation in Chemistry (PERCH-CIC) and Khon Kaen University. This project was funded by the National Research Council of Thailand (NRCT) contract n NRCT5-TRG63003-01.