molecules Article Cytotoxic and Anti-Inflammatory Effects of Ent-Kaurane Derivatives Isolated from the Alpine Plant Sideritis hyssopifolia Axelle Aimond 1,2,† , Kevin Calabro 3,† , Coralie Audoin 2, Elodie Olivier 1 , Mélody Dutot 1 , Pauline Buron 1, Patrice Rat 1, Olivier Laprévote 1 , Soizic Prado 4 , Emmanuel Roulland 4 , Olivier P. Thomas 3,* and Grégory Genta-Jouve 1,5,* 1 Laboratoire de Chimie-Toxicologie Analytique et Cellulaire (C-TAC) UMR CNRS 8038 CiTCoM Université Paris-Descartes, 4, Avenue de l’Observatoire, 75006 Paris, France; [email protected] (A.A.); [email protected] (E.O.); [email protected] (M.D.); [email protected] (P.B.); [email protected] (P.R.); [email protected] (O.L.) 2 Laboratoires Clarins, 5 Rue Ampère, 95300 Pontoise, France; [email protected] 3 Marine Biodiscovery, School of Chemistry and Ryan Institute, National University of Ireland Galway (NUI Galway), University Road, H91 TK33 Galway, Ireland; [email protected] 4 Muséum National d’Histoire Naturelle, Unité Molécules de Communication et Adaptation des Micro-Organismes, UMR 7245, CP 54, 57 rue Cuvier, 75005 Paris, France; [email protected] (S.P.); [email protected] (E.R.) 5 Laboratoire Ecologie, Evolution, Interactions des Systèmes Amazoniens (LEEISA), USR 3456, Université De Guyane, CNRS Guyane, 275 Route de Montabo, 97334 Cayenne, French Guiana * Correspondence: [email protected] (O.P.T.); [email protected] (G.G.-J.); Tel.: +353-9149-3563 (O.P.T.); +33-153-731-585 (G.G.-J.) † These authors contributed equally to this work. Received: 13 December 2019; Accepted: 26 January 2020; Published: 29 January 2020 Abstract: This paper reports the isolation and structural characterization of four new ent-kaurane derivatives from the Lamiaceae plant Sideritis hyssopifolia. Planar structures and relative configurations were determined using both mass spectrometry and nuclear magnetic resonance (1D and 2D). Absolute configurations were determined by comparing experimental and theoretical electronic circular dichroism spectra. The cytotoxic and microbial activities of all new compounds were tested. Compounds that were non-cytotoxic were further evaluated for anti-inflammatory activity. Keywords: Sideritis hyssopifolia; ent-kaurane; anti-inflammatory; NMR 1. Introduction The cosmetics sector represents a huge potential for growth in today’s society. The quest for wellness and beauty has led to an intensive search for new products that can improve both the appearance and hygiene of an aging population. In this context, an increasing number of cosmetic companies are using nature as a unique source for their formulations. To discover new compounds of interest, the French company Laboratoires Clarins has been conducting an in-depth investigation of plants in their unique outdoor fields situated in the French Alps. Sideritis, containing around 190 species, is a widespread genus of the family Lamiaceae, which is commonly found in the Northern Hemisphere [1]. Around 250 natural products have been reported from the genus Sideritis, of which 160 are in the diterpene class, specifically in the kaurane group [2,3]. These kauranes and their enantiomers, ent-kauranes, exhibit a wide range of bioactivities, with antioxidant, anti-tyrosinase, Molecules 2020, 25, 589; doi:10.3390/molecules25030589 www.mdpi.com/journal/molecules Molecules 2020, 25, 589 2 of 10 anti-cholinesterase, and anti-inflammatory properties reported [4–6]. The focus of this study was the species Sideritis hyssopifolia grown in the French Alps. The phytochemical composition of this species is poorly described, with only two publications reporting the isolation and characterization of its flavonoids and its essential oil composition [7,8]. Except for siderol [9], diterpenoids have yet to be reported in S. hyssopifolia [10]. Because these compounds are commonly found throughout the Sideritis genus, we re-investigated the phytochemical composition of S. hyssopifolia and, as a result, isolated 12 compounds, eight of which are reported in this species for the first time, namely, siderol [9], sideridiol [9], siderone [11], ent-kaurene I [12], sideritriol [13], ent-15β,16β-epoxykauran-18-ol [14], epi-candicandiol [12], and ent-3β-7α-dihydroxykaur-16-ene [15]. Additionally, four new ent-kauranes were fully characterized (Figure1) using 1D and 2D NMR, MS, and ECD. The four novel compounds were evaluated for their cytotoxic, antimicrobial, and anti-inflammatory activities. 1212 2020 1111 1313 1717 99 1414 1616 11 22 1010 88 H 1515 33 55 77 H 44 66 RO OH O OH H H 1818 1919 1: R=H O 3 2: R=Ac H O H HO O 4 Figure 1. Structure of the new ent-kauranes compounds 1–4. 2. Results and Discussion Compound 1 was isolated as a light yellow oil. Its molecular formula was determined from the + [M+H] observed at m/z 305.2481 (calculated for C20H33O2, 305.2475, δ 1.9 ppm) in the HRESIMS spectrum acquired in positive ionization mode; the formula required five degrees of unsaturation in 1 the molecule. The H NMR spectrum exhibited four methyl singlets at δ 0.76 (s, 3H, H3-18), 0.95 (s, 3H, H3-19), 1.07 (s, 3H, H3-20), and 1.71 (s, 3H, H3-17) ppm (Tables1 and2). A signal corresponding to a trisubstituted double bond at δ 5.52 (s, 1H, H-15) was also observed, together with two hydroxylated methines at δ 3.17 (dd, J = 11.6, 4.5 Hz, 1H, H-3) and 3.54 (br s, 1H, H-7). Inspection of the 1H–1H COSY spectrum led to the identification of three spin systems. The first one started with a clear correlation of H-3 with H-2a δ 1.67 (m, 1H) and H-2b δ 1.60 (m, 1H), which, in turn, correlated with the methylene protons H-1 at δ 1.84 (1H, m) and 0.95 (1H, m). A second spin system was observed between H-7 and H-6 δ 1.66 (m, 1H) and 1.62 (m, 1H), and the last correlation was observed between H6b and H-5 at δ 1.40 (d, J = 12.0 Hz, 1H). A last spin system comprising H-9/H-11/H-12/H-13/H-14 was identified, with correlations between δ 1.28 (d, J = 4.7 Hz, 1H, H-9), 1.54 (m, 2H, H2-11), 1.51 (m, 2H, H2-12), 2.33 (br s, 1H, H-13), and 1.96 (d, J = 9.9 Hz, 1H, H-14a). A 4J cross-peak between H-15 and H-17 was also observed. Analysis of the HMBC spectrum revealed a connection between the three spin systems. The correlations of H-20 with C-1/C-5/C-9 and H-18/H-19 with C-3/C-5 indicated the presence of the first decalin ring. Two other cycles were identified using intense 2J correlations between H-7/H-9/H-14/H-15 and C-8. The last cycle was confirmed by the cross-peak between H-13 and C-16. The full three-dimensional structure was determined using the coupling constant values of the 1H NMR spectra and the NOESY correlations (see Figure2). Molecules 2020, 25, 589 3 of 10 Table 1. 1H NMR data of compounds 1–4 (1H 500 MHz). 1 a 2 b 3 b 4 b No. dH (m, J in Hz) dH (m, J in Hz) dH (m, J in Hz) dH (m, J in Hz) 1a 1.84 (dt, 13.0, 3.5) 1.82 (dt, 13.2, 3.5) 1.84 (m) 1.84 (m) 1b 0.95 (m) 1.03 (m) 1.05 (td, 13.0, 4.0) 1.07 (dd, 12.5, 3.6) 2a 1.67 (m) 1.70 (m) 1.69 (m) 1.65 (m) 2b 1.60 (m) 1.62 (m) 1.64 (m) 1.52 (m) 3a 3.17 (dd, 11.6, 4.5) 4.52 (dd, 11.6, 5.1) 4.53 (dd, 11.6, 5.0) 1.55 (m) 3b - - - 1.27 (dd, 14.3, 5.5) 4 - - - - 5 1.40 (d, 12.0) 1.49 (m) 1.55 (m) 1.86 (m) 6a 1.66 (m) 1.65 (m) 1.68 (m) 1.74 (dd, 14.4, 3.8) 6b 1.62 (m) 1.56 (m) 7 3.54 (bs) 3.63 (t, 2.9) 3.62 (t, 3.1) 4.82 (t, 3.0) 8 - - - - 9 1.28 (d, 4.7) 1.30 (d, 7.5) 1.42 (d, 6.6) 1.86 (m) 10 - - - - 11 1.54 (m) 1.49 (m) 1.56 (m) 5.36 (dd, 9.7, 3.5) 12a 1.51 (m) 1.49 (m) 1.70 (m) 6.25 (dd, 9.6, 6.5) 12b 1.49 (m) - 13 2.33 (bs) 2.37 (bs) 2.68 (m) 2.56 (m) 14a 1.96 (d, 9.9) 1.89 d (10.1) 1.82 (m) 2.01 (d, 9.4) 14b 1.35 (dd, 10.1, 5.3) 1.36 (d, 10.2, 5.2) 1.17 (dd, 11.4, 5.0) 1.50 (m) 15 5.52 (s) 5.47 (s) 2.25 (bs) 5.09 (s) 16 - - - - 17a 1.71 (s) 1.72 (bs) 4.83 (bs) 1.77 (d, 1.1) 17b - - 4.80 (bs) - 18 0.96 (s) 0.84 (s) 0.88 (s) 0.72 (s) 19a 0.76 (s) 0.85 (s) 0.86 (s) 3.36 (d, 10.8) 19b - - - 3.04 (d, 10.8) 20 1.07 (s) 1.05 (s) 1.05 (s) 1.04 (s) 21 - - - - 22 - 2.04 (s) 2.04 (s) 2.09 (s) a b CD3OD, CDCl3. The multiplicity of the signal at δ 3.17 (dd, J = 11.6, 4.5 Hz, 1H, H-3) indicated an axial orientation for H-3.