Embellicines A and B: Absolute Configuration and NF-κB Transcriptional Inhibitory Activity Weaam Ebrahim, †,○ Amal H. Aly, † Victor Wray, ‡ Attila Ma ́ ndi, § Marie-He ́ le ̀ ne Teiten, ∥ Franc ̧ ois Gaascht, ∥ Barbora Orlikova, ∥ Matthias U. Kassack, # WenHan Lin, ▽ Marc Diederich, ∥,⊥ Tibor Kurta ́ n, § Abdessamad Debbab,* ,† and Peter Proksch* ,† † Institut fü r Pharmazeutische Biologie und Biotechnologie, Heinrich-Heine-Universitä t Dü sseldorf, Universitä tsstrasse 1, Geb. 26.23, D-40225 Dü sseldorf, Germany ‡ Helmholtz Centre for Infection Research, Inhoffenstraße 7, D-38124 Braunschweig, Germany § Department of Organic Chemistry, University of Debrecen, POB 20, 4010 Debrecen, Hungary ∥ Laboratoire de Biologie Mole ́ culaire et Cellulaire du Cancer, Hô pital Kirchberg 9, rue Edward Steichen L-2540 Luxembourg, Luxembourg ⊥ Department of Pharmacy, College of Pharmacy, Seoul National University, 599 Kwanak-ro, Kwanak-gu, Seoul, 151-742, Korea # Institut fü r Pharmazeutische und Medizinische Chemie, Heinrich-Heine-Universitä t, Universitä tsstrasse 1, Geb. 26.23, D-40225 Dü sseldorf, Germany ▽ National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Health Science Center, 100083 Beijing, People’s Republic of China ABSTRACT: Two new metabolites, embellicines A and B (1 and 2), were isolated from the EtOAc extract of the fungus Embellisia eureka, an endophyte of the Moroccan plant Cladanthus arabicus (Asteraceae). The structures of these new compounds were determined on the basis of extensive one- and two- dimensional NMR spectroscopy as well as by high-resolution mass spectrometry. The absolute configuration of embellicine A (1) was determined by TDDFT ECD calculations of solution conformers, whereas that of embellicine B (2) was deduced based on ROESY correlations and on biogenetic considerations in comparison to 1. Both embellicines (1 and 2) are cytostatic, cytotoxic, and inhibit NF-κB transcriptional activity, indicating that inhibition of NF-κB may be a possible mechanism of action of these compounds. Embellicine B (2) was the most active compound encountered in this study and acts at nanomolar concentrations without affecting tumor microenvironment. ■ INTRODUCTION Increasing resistance to chemotherapy is tightly linked to aberrant activation of nuclear factor kappa B (NF-κB) signaling implicated both in inflammation and in initiation, promotion, and progression of tumorigenesis. 1−3 Suppression of this proinflammatory pathway may provide opportunities for prevention and treatment of cancer so that the NF-κB signaling pathway became an interesting target for new bioactive compounds. 4−6 Natural products and their semisynthetic derivatives have been a rich source of inspiration for chemists and pharmacologists, which allowed them to retain their immense impact on drug discovery over the years, even with the growing advances in high-throughput synthesis and combinatorial chemistry. In the last decades, major efforts have been undertaken with regard to bioprospecting of microorganisms, especially endophytic fungi, that are known for their production of structurally diverse natural products with an amazing array of bioactivities. 7−10 A recent overview indicated that 51% of bioactive substances isolated from endophytic fungi were previously unknown, 11 thus highlighting the vast opportunities for bioprospecting in this group of microorganisms. In the course of our search for new bioactive secondary metabolites from endophytic fungi, 12−15 the fungus Embellisia eureka (internal strain no. CATS2) was isolated, after surface sterilization, from healthy stem tissues of Cladanthus arabicus (Asteraceae) collected in Morocco. To date, the chemical constituents of fungi belonging to the genus Embellisia have received only scant attention. Literature survey showed that a heptatrienoic acid-substituted bicyclic ketone derivative 16 and terpestacin 17 were isolated from Embellisia chlamydospora. Moreover, hydroxylated indolizidine alkaloids were obtained from Embellisia oxytropis. 18 In the present study, we report the isolation and structure elucidation of two new alkaloids, embellicines A (1) and B (2), produced by E. eureka, and Received: January 8, 2013 Published: March 14, 2013 Article pubs.acs.org/jmc © 2013 American Chemical Society 2991 dx.doi.org/10.1021/jm400034b | J. Med. Chem. 2013, 56, 2991−2999