This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Article pubs.acs.org/jnp Marine Terpenoid Diacylguanidines: Structure, Synthesis, and Biological Evaluation of Naturally Occurring Actinofide and Synthetic Analogues † † ‡ ‡ ‡ † Marianna Carbone, M. Letizia Ciavatta, Veroniqué Mathieu, Aude Ingels, Robert Kiss, Paola Pascale, † § ⊥ † Ernesto Mollo, Nicon Ungur, Yue-Wei Guo,*, and Margherita Gavagnin*, † Consiglio Nazionale delle Ricerche (CNR), Istituto di Chimica Biomolecolare (ICB), Via Campi Flegrei, 34, 80078 Pozzuoli (Na), Italy ‡ Laboratoire de Cancerologié et de Toxicologie Experimentale,́ Facultéde Pharmacie, UniversitéLibre de Bruxelles (ULB), Campus de la Plaine, Boulevard du Triomphe, 1050 Brussels, Belgium § Institute of Chemistry, Moldova Academy of Sciences, Academiei str. 3, MD-2028 Chisinau, Republic of Moldova ⊥ State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, P.R. China *S Supporting Information ABSTRACT: A new diacylguanidine, actinofide (1), has been isolated from the marine mollusk Actinocyclus papillatus. The structure, exhibiting a guanidine moiety acylated by two terpenoid acid units, has been established by spectroscopic methods and secured by synthesis. Following this, a series of structural analogues have been synthesized using the same procedure. All of the compounds have been evaluated in vitro for the growth inhibitory activity against a variety of cancer cell lines. uanidine compounds present a wide species distribution, Our continuing chemical studies on marine shell-less G both in terrestrial and in marine environments. mollusks aim to identify new bioactive metabolites.10 As such, Structurally, natural guanidines include pyrimidine derivatives, we have previously described two indole guanidines, peptides, polyketides, and terpenes.1 In guanidines isolated phidianidines A and B from the aeolidacean nudibranch from marine organisms, in particular, the guanidine moiety is Phidiana militaris collected at the South China Sea, that exhibited very promising biological properties.11 Herein, we very often incorporated in peptide, polyketide, and aromatic fi metabolites, whereas terpenoid guanidines are less frequently report a diacylguanidine compound, actino de (1), from the isolated.2,3 skin of the dorid nudibranch Actinocyclus papillatus, collected at the same location. The previous chemical investigation of this Guanidines are highly valued in various biological, bio- 4 mollusk had resulted in the identification of the main chemical, and medical applications. Potent biological activities, 12 metabolite of the skin extract, actisonitrile, which is not such as anti-inflammatory, antiprotozoal, anti-HIV, chemo- 5,6 structurally related to 1. therapeutic, and antidiabetic, have been shown by numerous With the aim at both securing the structure and obtaining a natural and synthetic guanidines. Among them, acylguanidines larger amount of compound for biological screening, the are greatly appreciated because they may be considered as synthesis of actinofide (1) was performed as described below. considerably less basic bioisosteres of guanidines with improved In addition, the interesting growth inhibitory activity against pharmacokinetics and pharmacodynamics on various biological various cancer cell lines observed for compound 1 prompted 7,8 targets. The basicity of the acylguanidines (pKa values around the preparation of a series of structural analogues 2−9 to be 8) is 4−5 orders of magnitude lower than that of the assayed along with 1 (Chart 1). Finally, the related terpenoid corresponding guanidines. Hence, on one hand, acylguanidines diacylguanidine dotofide (10), previously described from the 13 are sufficiently basic to undergo key interactions with acidic aeolidacean nudibranch Doto pinnatifida by König et al., was residues of the receptor, whereas, on the other hand, a considerable portion remains uncharged at physiological pH, Received: October 13, 2016 thus facilitating diffusion across membranes.9 Published: April 13, 2017 © 2017 American Chemical Society and American Society of Pharmacognosy 1339 DOI: 10.1021/acs.jnatprod.6b00941 J. Nat. Prod. 2017, 80, 1339−1346 Journal of Natural Products Article Chart 1 fi fi 13 puri ed from a collection of D. pinnati da caught in the bay of carbonyl functions. In the C NMR spectrum (CD3OD), eight fi δ Naples and submitted to the same biological screening. ole nic carbon signals were recognized at C 160.3 (C, C-3), 156.6 (C, C-3′), 136.6 (C, C-7), 132.2 (C, C-11), 125.3 (CH, ■ RESULTS AND DISCUSSION C-10), 124.4 (CH, C-6), 121.9 (CH, C-2″), and 121.7 (CH, C- fi fi 2), consistent with the presence of four trisubstituted double Actino de (1) was puri ed from the skin extract of a single α β individual of A. papillatus, collected by SCUBA along the coast bonds, two of which were , -unsaturated. According to this, the 1H NMR spectrum displayed signals due to four vinylic of Wei Zhou Island (South China Sea) during May 2007. As δ ″ 12 protons [ H 5.85 (2H, br s, H-2 and H-2 ), 5.15 (1H, m, H-6), already described, the Et2O soluble portion (172.1 mg) of the δ 5.12 (1H, m, H-10)] and to six vinyl methyl groups [ H 2.21 acetone extract of the skin had been fractionated by Sephadex ″ ″ (6H, br s, H3-15 and H3-5 ), 1.94 (3H, s, H3-4 ), 1.69 (3H, s, LH20 followed by silica gel chromatography to isolate the main 1 metabolite, actisonitrile. Selected fractions recovered from the H3-12), 1.65 (3H, s, H3-14), 1.62 (3H, s, H3-13)]. The H 12 NMR spectrum was completed by multiplets at δ 2.25−1.98 SiO2 column that were not considered in the previous work H have been now analyzed and submitted to preparative TLC that were attributable to four methylenes adjacent to double fi bonds. These data were consistent with two linear unsaturated puri cation (petroleum ether/Et2O, 1:1) to obtain pure actinofide (1, 1.3 mg). An additional aliquot (2.7 mg) of isoprenoid arrangements each containing a carbonyl residue. compound 1 was isolated as the protonated form by purifying Analysis of 2D NMR experiments, which were recorded in both fractions of the extract on reversed-phase high-performance CDCl3 and CD3OD, led us to recognize farnesoyl and 3,3- liquid chromatography (HPLC, Supelco Discovery C18 dimethylacryloyl (senecioyl) moieties. The remaining structural column, MeOH/H2O gradient with 0.1% of TFA). fragment CH3N3 required by the molecular formula was fi The molecular formula of actino de (1), C21H33N3O2, was suggested to have the Y-shaped arrangement of a guanidine + δ deduced from the [M + H] peak at 360.2645 m/z in the functional group ( CN 159.2) and to be connected to both HRESIMS spectrum. The IR spectrum showed bands at 3345, terpenoyl moieties by an acyl linkage as depicted in structure 1. −1 δ 1731, and 1633 cm according to the presence of amino and The signal resonating at C 175.4 (CD3OD) and 172.7 1340 DOI: 10.1021/acs.jnatprod.6b00941 J. Nat. Prod. 2017, 80, 1339−1346 Journal of Natural Products Article a Scheme 1. Synthesis of Actinofide (1) aConditions: (i) CDI, DMF then addition to a guanidine solution in DMF/dioxane; (ii) 3,3-dimethyl acrylic acid, N-methylpyrrolidone, 2-chloro-1- methyl pyridinium iodide, rt, 30 min, 50 °C, 1 h, then addition of guanidine derivative 2 and DIEA at rt, 12 h. Table 1. Determination of the Antiproliferative Activities (GI values, μM) of Compounds 1−10 Using the MTT Colorimetric a b 50 Assay , glioma carcinoma melanoma compound Hs683c U373 A549 MCF7 SKMEL-28 B16F10 1 8.3 ± 1.8 15.7 ± 10.1 23.4 ± 5.5 23.4 ± 5.9 24.2 ± 8.2 7.5 ± 3.1 2 10.0 21.0 13.7 22.0 20.1 9.2 3 39.4 46.0 76.5 52.2 56.3 17.1 4 >100 >100 >100 >100 >100 92.8 5 6.8 9.2 18.5 30.3 42.7 5.7 6 32.7 38.9 46.9 42.4 61.9 23.8 7 60.3 45.6 75.6 59.7 >100 21.3 8 31.5 36.2 37.4 41.5 53.4 25.0 9 37.4 35.0 38.9 51.2 57.3 18.9 10 18.1 28.8 29.4 28.1 60.5 9.6 etoposided 1.5 24.9 1.7 4.0 3.2 nde carboplatind 45.6 27.6 53.5 nde 68.6 34.9 a μ Data are represented as the GI50 concentration ( M), i.e., the compound concentration that reduces by 50% the growth of a given cell line (as compared to the control value) after having cultured the cells for 72 h with the compound of interest. bEach experiment was carried out once in six replicates, except for compound 1, for which the presented results are the mean of two independent assays conducted each in sextuplicate. cThe origin and histological type of each cell line analyzed are as follows. Human glioma model lines included the Hs683 oligodendroglioma (ATCC code HTB-138) and the U373 glioblastoma (ECACC code 08061901) cell lines. Melanoma models included the human SKMEL-28 (ATCC code HTB- 72) and the mouse B16F10 (ATCC code CRL-6475) cell lines. Human carcinoma models included the A549 NSCLC (DSMZ code ACC107) and d the MCF-7 breast (DSMZ code ACC115). The selected positive control compounds are drugs routinely used in cancer treatment. The GI50 concentrations reported in the table were obtained partly in our previous experiments.10,32 eNot determined. ″ 8,9 (CDCl3) was determined to represent both C-1 and C-1 sea. Although terpenoid guanidines are not so frequently carbonyls by analysis of diagnostic HMBC correlations with encountered in marine organisms, a number of these δ ″ δ ff distinguishable H-2 ( H 5.77) and H-2 ( H 5.78) protons in compounds have been isolated from di erent higher plant fi the CDCl3 spectrum of 1.