Esposito, Germana (2017) Stereostructural studies and biological activities of secondary metabolites from marine sources. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Lingua: English
Title: Stereostructural studies and biological activities of secondary metabolites from marine sources
Date: 6 April 2017
Number of Pages: 281
Institution: Università degli Studi di Napoli Federico II
Department: Farmacia
Dottorato: Scienza del farmaco
Ciclo di dottorato: 29
Coordinatore del Corso di dottorato:
D'auria, M.
Costantino, ValeriaUNSPECIFIED
Date: 6 April 2017
Number of Pages: 281
Uncontrolled Keywords: structural elucidation; marine natural products; bioactive compounds
Settori scientifico-disciplinari del MIUR: Area 03 - Scienze chimiche > CHIM/03 - Chimica generale e inorganica
Area 03 - Scienze chimiche > CHIM/06 - Chimica organica
Date Deposited: 03 May 2017 11:30
Last Modified: 13 Mar 2018 12:04


Within the marine ecosystem, the sessile organisms such as Porifera are considered the most interesting phylum by the natural products chemists. Because these organisms live fixed on a substrate and are lacking of any physical defence against predators, they have acquired, during their evolution, the ability to synthesize bioactive compounds that can be used as chemical weapons. Sponge derived natural products belong to many different chemical classes, including polyketides, terpenoids, peptides and alkaloids, and show a wide range of pharmacological activities such as anticancer, antibacterial, antifungal, antiviral and anti-inflammatory activities. For this reason these compounds can be used as lead compounds in drug discovery. In the last years, several drugs derived from marine natural products have appeared in the market, and others are in clinical trials. The research work described in this PhD thesis belongs to this research field. In particular, my attention was focused on the chemical analysis of the sponge of the genus Smenospongia. Two new bioactive secondary metabolites with a hybrid structure peptide/ polyketide, smenothiazoles A and B, were isolated from the sponge Smenospongia aurea. Smenothiazoles were tested against four solid tumor cell lines and showed a potent cytotoxic activity at nanomolar levels with selectivity against ovarian cancer cells and a pro-apoptotic mechanism. The analysis of the congeneric sponge species, Smenospongia conulosa, revealed the presence of two additional chlorinated compounds, conulothiazoles A and B together with smenothiazoles. However, the anticancer activity of these compounds cannot be evaluated because of the low amount isolated from the sponge. My work during these three years regarded also the chemical analysis of the MeOH crude extract of the sponge Achantostrongylophora ingens which revealed protein kinase inhibitory activity. The bioguided fractionation of this extract led to the isolation of a new halogenated alkaloid, chloromethylhalicyclamine B, together with the known natural compound halicyclamine B. The new compound is the result of the reaction between halicyclamine B and CH2Cl2 used for the extraction. However, in contrast to the known halicyclamine B, the new derivative revealed to be a selective CK1δ/ε inhibitor with an IC50 value of 6 μM. The absolute configuration of chloromethylhalicyclamine B was determined by quantum mechanical prediction of its ECD spectrum. The conformation assumed by the new molecule was also determined by computational studies and was validated by NOESY data. Docking studies were also performed in order to evaluate the accommodation of the molecule in the ATP binding site of CK1δ. Even if the globular structure of this compound is very different from that of already known CK1δ inhibitors, the analysis revealed that the accommodation in the binding site is good. Therefore, these data showed chloromethylhalicyclamine B as a new structural type of CK1δ/ε inhibitor. A deeper analysis of the chemical composition of A. ingens revealed also the presence of additional new halicyclamine derivatives but their activity has not yet been evaluated. Another part of my work has been addressed to the search for molecules involved in quorum sensing mechanism in order to control the communication between bacteria and thus their virulence. The most frequent molecules involved in this process are the acylated homoserinelactone compounds (AHLs). In collaboration with the group of Prof. Laura Steindler at the University of Haifa, Israel, I analyzed the extracts of the marine bacteria Paracoccus sp. in order to detect the presence of AHLs. Twelve saturated long-chain AHLs (3-OH-C10-HSL, 3-OH-C12-HSL, C10-HSL, 3-OH-C14-HSL, C12-HSL, 3-O-C16-HSL, 3-OHC16-HSL, C14-HSL, 3-OH-C18-HSL, C16-HSL, 3-O-C18-HSL, and C18-HSL), along with four putative unsaturated long-chain AHLs (C10 :1-HSL, 3-OH-C18 :1-HSL, C16 :1-HSL, and C18 :1-HSL) were found in Paracoccus extract confirming the possibility to have quorum sensing in particular conditions. It is noteworthy that other small molecules like diketopiperazines (DKPs) are able to influence the quorum sensing mechanism. For this reason, we determined the absolute configuration by Marfey’s method of 7 known diketopiperazine isolated from the marine sponge Acanthostrongylophora ingens. In this way we created a library of DKPs that were evaluated for their quorum quenching activity. Preliminary results showed that all compounds exhibit QS inhibitory activity against E.coli pSB1075 (long chain gene reporter) with MIC of 70 µM, while none compounds show QS inhibitory activity against E.coli pSB401 (short chain gene reporter) at low concentrations where in addition the bioluminescence increases at high concentration ≥ 70 µM.

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