In this study, two previously unreported lignans [4 '-O-demetylsuchilactone-8 '-ol (<bold>1</bold>), 7-O-(3-methyl-2,3-dihydroxy-butyl)isodaurinol] (<bold>2</bold>), four new alkaloids (haplomegalanthine (<bold>3</bold>), megalantin (<bold>4</bold>), megalanthamide (<bold>5</bold>), glycoisohaplopine (<bold>6</bold>) and thirty-five known compounds (<bold>7-41</bold>) were isolated from Haplophyllum megalanthum Bornm. (Rutaceae). Pinoresinol (<bold>23</bold>), epipinoresinol (<bold>24</bold>), indole-3-carbaldehyde (<bold>29</bold>), N-[2-(4-hydroxyphenyl)ethyl]-3-methylbut-2-enamide (<bold>34</bold>), 7,8-dimethoxyfuroquinoline-4-one (<bold>35</bold>), cis-khellactone (<bold>36</bold>), 4,4 '-dihydroxy-3,3 ',9-trimethoxy-9,9 '-epoxylignan (<bold>37</bold>), ulopterol (<bold>39</bold>) and trans-decursidinol (<bold>40</bold>) were identified for the first time in the genus Haplophyllum. Also, 4 '-O-demethylsuchilactone (<bold>16</bold>) and N-(4-hydroxyphenethyl)benzamide (<bold>32</bold>) were found for the first time within the family Rutaceae. Structures of the compounds were elucidated by the use of HRMS, UHPLC-MS and 1D/2D NMR analyses. Furthermore, cytotoxic activity of the crude extract and previously unreported compounds (1-3, 5, 6) on colon cancer cell line HT29 were tested by the MTT method. IC50 values were determined for these five compounds and the crude extract as 18.48 +/- 0.94 mu g/ml, 52.62 +/- 7.27 mu g/ml, 23.15 +/- 6.70 mu g/ml, 21.45 +/- 2.48 mu g/ml, 5.06 +/- 0.19 mu g/ml and 2.82 +/- 0.012 mu g/ml, respectively. The present report is the first detailed phytochemical investigation of the title plant pointing out that it comprises a rich source of diverse chemical constituents including new compounds with promising cytotoxic activity.
