Recent advances in lamellarin alkaloids: isolation, synthesis and activity

Lamellarins are a large family of marine alkaloids with potential anticancer activity that have been isolated from diverse marine organisms, mainly ascidians and sponges. All lamellarins feature a 3,4-diarylpyrrole system. Pentacyclic lamellarins, whose polyheterocyclic system has a pyrrole core, are the most active compounds. Some of these alkaloids are potently cytotoxic to various tumor cell lines. To date, Lam-D and Lam-H have been identified as lead compounds for the inhibition of topoisomerase I and HIV-1 integrase, respectively nuclear enzymes which are over-expressed in deregulation disorders. Moreover,these compounds have been reported for their efficacy in treatment of multi-drug resistant (MDR) tumors cells without mediated drug efflux, as well as their immunomodulatory activity and selectivity towards melanoma cell lines. This article is an overview of recent literature on lamellarins, encompassing their isolation, recent synthetic strategies for their total synthesis, the preparation of their analogs, studies on their mechanisms of action, and their structure-activity relationships (SAR)

The synthesis of 1,2,3,6,6a,7-hexahydro-7-methyl-5-imino-1H-pyrrolo[1,2-c]imidazolo[5,4-b]indole

N-3-(1-Methylindol-3-yl)propan-N-(2,2,2-trichloroethoxysulfonyl)guanidine was synthesized from 3-formyl-1-methylindole in six steps and subjected to conditions intended to convert the side-chain into a 2-iminotetrahydropyrimidine- containing product, of relevance to a possible synthesis of the aplicyanins. An alternative reaction course was observed, resulting in the formation of a new tetracyclic system

Synthesis and structure - Activity relationship study of potent cytotoxic analogues of the marine alkaloid Lamellarin D

The marine alkaloid, Lamellarin D (Lam-D), has shown potent cytotoxicity in numerous cancer cell lines, and was recently identified as a potent topoisomerase I inhibitor. A library of open lactone analogs of Lam-D was prepared from a methyl 5,6-dihydropyrrolo[2,1-a]isoquinoline-3- carboxylate scaffold (1) by introducing various aryl groups through sequential and regioselective bromination, followed by Pd(0)-catalyzed Suzuki cross-coupling chemistry. The compounds were obtained in a 24-44% overall yield, and tested in a panel of three human tumor cell lines, MDA-MB- 231 (breast), A-549 (lung), and HT-29 (colon), to evaluate their cytotoxic potential. From these data the SAR study concluded that more than 75% of the open-chain Lam-D analogs tested showed cytotoxicity in a low micromolar GI50 range

Lamellarin D bioconjugates I: synthesis and cellular internalization of PEG-derivatives

Herein is reported the design and synthesis of poly(ethylene glycol) derivatives of Lamellarin D with the aim of modulating their physicochemical properties, and improving the biological activity. Mono-, di- and tri-PEG conjugates with improved solubility were obtained in 18-57% overall yields from the corresponding partially protected phenolic derivatives of Lamellarin D. Conjugates 1-9 were tested in a panel of three human tumor cell lines (MDA-MB-231 breast, A-549 lung and HT-29 colon) to evaluate their cytotoxicity. Several compounds exhibited enhanced cellular internalization, and more than 85% of the derivatives showed a lower GI50 than Lam-D. Furthermore, cell cycle arrest at G2 phase, and apoptotic cell-death pathways were determined for Lamellarin D and these derivatives

Lamellarin D bioconjugates II: synthesis and cellular internalization of dendrimer and nuclear location signal derivatives

The design and synthesis of Lamellarin D conjugates with a nuclear localization signal peptide and a poly(ethylene glycol)-based dendrimer are described. Conjugates 1-4 were obtained in 8-84% overall yields from the corresponding protected Lamellarin D. Conjugates 1 and 4 are 1.4 to 3.3-fold more cytotoxic than the parent compound against three human tumor cell lines(MDA-MB-231 breast, A-549 lung, and HT-29 colon). Besides, conjugates 3, 4 showed a decrease in activity potency in BJ skin fibroblasts, a normal cell culture. Cellular internalization was analyzed and nuclear distribution pattern was observed for 4, which contains a nuclear localization signalling sequence

Síntesi total de la lamel·larina D i anàlegs de cadena oberta: estudis d'internalització cel·lular i d'inhibició de topoisomerases

[cat] Aquesta tesi comença amb la presentació de la família de Lamel·larines, uns productes naturals d'orígen marí amb interessants activitats biològiques. En el Capítol 1 se'n descriuen els últims avanços quant al seu aïllament, nova metodologia sintètica i estudis sobre l'activitat biològica i el seu mode d'acció. La consecució d'aquests mètodes sintètics ha obert la porta a la preparació del producte natural, i de molècules anàlogues. Així, en el Capítol 3 es descriu la síntesi de la Lamel·larina D amb una metodologia d'acoblaments creuats successius de Suzuki amb catàlisi de Pd(0). Amb la preparació descrita al Capítol 2 dels bromopolialcòxibenzens s'ha pogut realitzar la síntesi d'una quimioteca d'anàlegs sense lactona de la Lamel·larina D i amb la introducció de diferents patrons de substitució (es descriu al Capítol 4). S'ha assajat l'activitat biològica i estudiat les relacions estructura-activitat d'aquests compostos, cosa que ha permès posar de manifest aquells grups estructuralment importants quant a activitat. Al Capítol 5 es descriu la síntesi d'uns conjugats amb polietilenglicol de la Lamel·larina D, i més enllà al Capítol 6 es descriu la síntesi de conjugats estructuralment més complexos amb una seqüència peptídica de localització nuclear i un dendrímer. Amb els productes sintetitzats s'ha procedit a fer-ne una avaluació de la seva internalització i distribució cel·lulars, estudis co-localització dels productes amb marcatges selectius de membrana, mitocòndries i topoisomerasa.Per l'estudi del mode d'acció de la Lamel·larina D com a inhibidor de la topoisomerasa, s'ha fet ús de biosensors de pinzes òptiques i microscòpia de forces atòmiques. Aquest treball es descriu al Capítol 7 i cal destacar que aquestes novedoses tecnologies amb sensibilitats de pN i resolució nanomètrica es mostren d'elevada utilitat per a l'estudi de l'activitat de la topoisomerasa, i de la seva inhibició.[eng] Lamellarin D (Lam-D) is a marine alkaloid with antiproliferative activity against various tumor cells in the low nanomolar range. The inhibition of topoisomerase-I, a mitochondrial transmembrane potential disruption as well as promotion of apoptosis are its modes of action. Topoisomerase is an especially interesting chemotherapy target, namely because of the topoisomerase-DNA complex, which undergoes mechanical motions essential to its function (Chapter 1). The present research summary highlights the synthetic methodologies used for the synthesis of Lam-D and its related derivatives. Two synthetic strategies (A, B) had been employed for the total synthesis of Lam-D, which enable high versatility and robust methodologies for the preparation of the natural product, regioselective conjugation on its free phenolic groups and its structurally simplified derivatives.Methyl 8-isopropoxy-9-methoxy-5,6-dihydropyrrolo[2,1-a]isoquinoline-3-carboxylate was used as scaffold of strategy A. Regioselective and sequential introduction of aryl groups followed by Pd(0)-catalyzed cross coupling reactions, aromatization and ether deprotection provided the final compounds in 18-61% yields (Chapter 3). Boronic acids and borolanes were used as building blocks for the synthesis. Its preparation through regioselective bromination under mild conditions of highly activated benzenes and Pd(0)-catalyzed borylation gave the non-commercial polialcoxy synthons (7 compounds, 43-80% yields over 2 steps) for the diverted combinatorial synthesis (Chapter 2).A combinatorial library of 45 analogues of the privileged lead Lam-D was prepared using strategy A in which removal of the lactone ring were implemented in order to improve solubility, and modifications on the OMe/OH substitution pattern were explored for structure activity relationship studies. Lam-D and its analogues were obtained in 18-44% overall yields. A panel of three human tumor cell lines was used to evaluate their cytotoxic potential: A-549 lung carcinoma NSCL, HT-29 colon carcinoma cells, and MDA-MB-231 breast adenocarcinoma. Cytotoxicity was observed for numerous compounds at low micromolar concentrations, and clear SAR patterns were determined. SAR study concluded that more than 75% of the 45 open-chain Lam-D analogs tested showed cytotoxicity in a low micromolar GI50 range (Chapter 4). Strategy B, based on quaternization of the isoquinoline, further cycloaddition on the alquine and aromatization, readily gave the pentacyclic structure in good yields. A good choice of orthogonally removable protectors has been developed for the regioselective attachment of well-defined water-soluble polymeric and peptidic nuclear location signal sequence carriers to Lam-D. These chemical modifications can significantly improve both drug delivery and therapeutic efficacy due to the enhanced permeability and retention effect observed in tumor tissue. Mono-, di-, and tri-Lam-D conjugates were regioselectively synthesized through ester bond linkages in the phenolic sites. Polymeric and peptidic conjugates, respectively, have been obtained in 18-84% (2 steps) and 8-20% (2 or 3 steps) overall yields from the corresponding Lam-D protected phenolic derivatives (Chapter 5, 6).Further studies on the mechanism of action of Lamellarin D by innovative optical tweezers biosensors, served to gain a novel insight in the biological engineering of topoisomerase I enzyme and its inhibition by small drugs. Topoisomerase is an especially interesting chemotherapy target, namely because of the topoisomerase-DNA complex, which undergoes mechanical motions essential to its function during the cleavage and religation of a single strand within a duplex DNA (Chapter 7).Here we show the use of optical tweezers to study topoisomerase activity, evidenced by a large increase in the hysteresis of the force cycles resulting from the generation of ssDNA-like domains inside dsλDNA, and subsequent strand religation indicated by recovery of the characteristic dsDNA force fingerprint. In contrast, the presence of the topoisomerase inhibitor Lamellarin D results in a large increase in force hysteresis due to the initial nicking activity of Topo I and a subsequent absence of religation. These results highlight the potential of optical tweezers biosensors for the mechanistic study of DNA-modifying enzymes and for the screening of their inhibitors, and foresee profound implications in drug discovery and medical nanotechnology

Recent advances in lamellarin alkaloids: isolation, synthesis and activity

Lamellarins are a large family of marine alkaloids with potential anticancer activity that have been isolated from diverse marine organisms, mainly ascidians and sponges. All lamellarins feature a 3,4-diarylpyrrole system. Pentacyclic lamellarins, whose polyheterocyclic system has a pyrrole core, are the most active compounds. Some of these alkaloids are potently cytotoxic to various tumor cell lines. To date, Lam-D and Lam-H have been identified as lead compounds for the inhibition of topoisomerase I and HIV-1 integrase, respectively nuclear enzymes which are over-expressed in deregulation disorders. Moreover,these compounds have been reported for their efficacy in treatment of multi-drug resistant (MDR) tumors cells without mediated drug efflux, as well as their immunomodulatory activity and selectivity towards melanoma cell lines. This article is an overview of recent literature on lamellarins, encompassing their isolation, recent synthetic strategies for their total synthesis, the preparation of their analogs, studies on their mechanisms of action, and their structure-activity relationships (SAR)

Progress on Lamellarins

This review covers recent literature on the lamellarins, a family of marine natural products, and related analogs, encompassing synthetic strategies for total synthesis, structure-activity relationships (SAR), and studies on mechanisms of biological action, namely in the context of antitumor activity. It reviews work published from January 2008 to December 2010

Isolation, structural assignment and total synthesis of Barmumycin

Barmumycin was isolated from an extract of the marine actinomycete Streptomyces sp. BOSC-022A and found to be cytotoxic against various human tumor cell lines. Based on preliminary one- and two-dimensional 1H- and 13C-NMR spectra, the natural compound was initially assigned the structure of macrolactone-type compound 1, which was later prepared by two different routes. However, major spectroscopic differences between isolated barmumycin and 1 led to revision of the proposed structure as E-16. Based on synthesis of this new compound, and subsequent spectroscopic comparison of it to an authentic sample of barmumycin, the structure of the natural compound was indeed confirmed as that of E-16

The synthesis of 1,2,3,6,6a,7-hexahydro-7-methyl-5-imino-1H-pyrrolo[1,2-c]imidazolo[5,4-b]indole

N-3-(1-Methylindol-3-yl)propan-N-(2,2,2-trichloroethoxysulfonyl)guanidine was synthesized from 3-formyl-1-methylindole in six steps and subjected to conditions intended to convert the side-chain into a 2-iminotetrahydropyrimidine- containing product, of relevance to a possible synthesis of the aplicyanins. An alternative reaction course was observed, resulting in the formation of a new tetracyclic system