Synthesis of Nitrogen-Containing Goniothalamin Analogues with Higher Cytotoxic Activity and Selectivity against Cancer Cells Matheus A. Meirelles, Carolyne B. Braga, Catia Ornelas, and Ronaldo A. Pilli* [a] Introduction According to the World Health Organization, cancer was re- sponsible for an estimated 9.6 million deaths in 2018, and is the second-leading cause of death worldwide. Drug resistance remains a challenge in cancer therapy, resulting in a continu- ous need for new bioactive compounds. [1] Over the past de- cades, global efforts have been directed to access more selec- tive molecules that display fewer side effects during cancer treatment. [2, 3] In this regard, natural products are considered a privileged source of new bioactive substances, as they play an important role in drug discovery programs. [4, 5] Styryl lactones are secondary metabolites found mostly in the genus Goniothalamus, and are known to display several biological activities, including antineoplastic activity. The im- portance of this family of natural products was first reviewed in 1999 by Blµzquez et al., who covered the isolation, structure elucidation, biogenesis, and biological activity of styryl lac- tones. [6] Since then, several authors have updated the informa- tion about these biologically active compounds. [7–11] Recently, we reviewed the chemical and biological aspects of goniotha- lamin-related styryl lactones, [12] highlighting the relevance of these natural products in drug discovery. Goniothalamin (1) is a styryl lactone first isolated by Hlubu- cek and Robertson from the bark of Cryptocarya caloneura, [13] and it is by far the most extensively studied compound of this family of natural products due to its wide biological profile, with its antitumor activity being the most notable (Figure 1). [12] This compound is active against several cancer cell lines and has been shown to be particularly promising for ovarian, pros- tate, and pancreatic cancers. [14–16] Moreover, no evidence for toxicity was observed when 1 was administered to mice bear- ing Ehrlich tumors during in vivo studies, [17–19] demonstrating its good biocompatibility and absence of side effects while in- hibiting tumor growth. Since its isolation, goniothalamin (1) has been a lead com- pound in the search for more potent and selective molecules. Previous works have demonstrated that both endo and exo double bonds in the dihydropyranone ring are important for its cytotoxic activity (Figure 2). The a,b-unsaturated lactone acts as a Michael acceptor, and its absence results in the com- plete loss of cytotoxic activity against cancer cells, while the exo double bond provides the required rigidity for higher ac- tivity. [20, 21] Thus, the benzene ring remains the most evident site for structural modifications, and a great amount of effort has been made in this direction. [14, 20–23] Our research group pre- viously found that (R)-, (S)-, and rac-goniothalamin show no Two series of racemic goniothalamin analogues displaying ni- trogen-containing groups were designed and synthesized. A total of 19 novel analogues were evaluated against a panel of four different cancer cell lines, along with the normal prostate cell line PNT2 to determine their selectivity. Among them, go- niothalamin chloroacrylamide 13 e displayed the lowest IC 50 values for both MCF-7 (0.5 mm) and PC3 (0.3 mm) cells, about 26-fold more potent than goniothalamin (1). Besides its higher potency, compound 13 e also displayed much higher selectivity than goniothalamin. In contrast, goniothalamin isobutyramide 13 c was the most potent analogue against Caco-2 cells (IC 50 = 0.8 mm), about 10-fold more potent and 17-fold more selective than 1. These results reveal the potential of compounds 13 c and 13 e for further in vivo studies, representing the first go- niothalamin analogues with IC 50 values in the low micromolar range and high selectivity against MCF-7, Caco-2, and PC3 cancer cell lines. [a] M. A. Meirelles, Dr. C. B. Braga, Prof. C. Ornelas, Prof. R. A. Pilli Department of Organic Chemistry, Institute of Chemistry, University of Cam- pinas, UNICAMP CEP 13083-970, Campinas, S¼o Paulo (Brazil) E-mail : rapilli@unicamp.br Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/cmdc.201900281. Figure 1. Representative natural products belonging to the family of styryl lactones. ChemMedChem 2019, 14, 1403 – 1417  2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1403 Full Papers DOI: 10.1002/cmdc.201900281