Search

A series of new 3,4-ethylenedioxy-2-thenyl (EDOTn) derived alcohols have been synthesized and evaluated as super acid labile carboxylic acid protecting groups. All the derivatives are labile to very low concentrations of TFA (0.01–0.5%).

Azathiocoraline synthesis has been developed and optimized by using the solid-phase approach. This convenient solid-phase methodology, which involves more steps on solid-phase, has been successfully applied for generating Azathiocoraline analogues. The solid-phase approach consolidates a rapid and efficient way to explore synthetic strategies for new bioactive, highly non-proteinogenic complex depsipeptides and is an essential tool to shorten the development time required for new therapeutic compounds.

A double side-reaction, consisting in the formation of Fmoc-beta-Ala-OH and Fmoc-beta-Ala-AA-OH, during the preparation of Fmoc protected amino acids (Fmoc-AA-OH) with Fmoc-OSu is discussed. Furthermore, the new Fmoc-2-MBT reagent is proposed for avoiding these side-reactions as well as the formation of the Fmoc-dipeptides (Fmoc-AA-AA-OH) and even tripeptides, which is another important side-reaction when chloroformates such as Fmoc-Cl is used for the protection of the alpha-amino function of the amino acids.

p-Nitrobenzyloxycarbonyl (pNZ) is used for the permanent protection of ornithine in the synthesis of derivatives of the anti-tumor cyclodepsipeptide Kahalalide F that contain acid labile residues.

Semipermanent side-chain protection of Orn and Lys with p-nitrobenzyloxycarbonyl (pNZ) for Fmoc/tBu chemistry does not result in the unwanted removal of α-Fmoc that occurs when groups such as Alloc are used for the same application. Furthermore, pNZ can be used in conjuction with p-nitrobenzyl ester (pNB) to prepare cyclic peptides.

Efficient modular synthetic routes to open chain marine alkaloids such as lamellarins have been developed. 5,6-Dihydropyrrolo[2,1-b]isoquinoline scaffolds were prepared, and protocols enabling regioselective bromination followed by Suzuki cross-coupling were established for the introduction of aryl groups onto the 2- and 3-positions.

An efficient solid phase synthesis of the pyrrole-based alkaloids lamellarins Q and O using Merrifield resin and N-protected methyl 3,4-dibromopyrrole-2-carboxylate as a scaffold is described.

An effective solid-phase preparation of the pharmaceutically interesting 4 H -2-(3-hydroxy-4-methoxyphenyl)-naphtho[1,2- b ]pyran-1-one system from an anchored bisarylacetylene is described.

[reaction: see text] Syntheses of 2-substituted furo[3,2-b]pyridines and furo[3,2-h]quinolines have been achieved for the first time in the solid-phase mode. The central enabling steps involved concomitant deprotection/cyclization promoted by the mild base K(2)CO(3). Reactions were monitored "in situ" in real time by a variety of spectroscopic techniques, which allowed full and accurate control of progress in these syntheses.

[reaction: see text] A total solid-phase synthesis of lamellarins U and L has been achieved. The conversion of an aldehyde group into a formate by a Baeyer-Villiger reaction and a intramolecular [3 + 2] cycloaddition of a 3,4-dihydroisoquinolinium salt over a triple bond comprise the key steps of the process. Each transformation has been controlled with the proper spectroscopic and analytical methods.

(S)-2-(4-Bromo-2,4′-bithiazole)-1-(tert-butoxycarbonyl)pyrrolidine ((S)-1) was obtained as a single enantiomer and in high yield by means of a two-step modified Hantzsch thiazole synthesis reaction when bromoketone 3 and thioamide (S)-4 were used. Further conversion of (S)-1 into trimethyltin derivative (S)-2 broadens the scope for further cross-coupling reactions.

Ethyl quinolin-4-one-3-carboxylate has been converted in 4 steps into 4H-pyrano[3,4-c]quinolin-4-one and 3-methoxyquinolin-4-one has been converted in 3 steps into 3H-pyrano[2,3-c]quinolin-3-one. Neither of these tricyclic lactones corresponds to natural cherimoline.

Thiopeptides, or thiazolyl peptides, are a relatively new family of antibiotics that already counts with more than one hundred different entities. Although they are mainly isolated from soil bacteria, during the last decade, new members have been isolated from marine samples. Far from being limited to their innate antibacterial activity, thiopeptides have been found to possess a wide range of biological properties, including anticancer, antiplasmodial, immunosuppressive, etc. In spite of their ribosomal origin, these highly posttranslationally processed peptides have posed a fascinating synthetic challenge, prompting the development of various methodologies and strategies. Regardless of their limited solubility, intensive investigations are bringing thiopeptide derivatives closer to the clinic, where they are likely to show their veritable therapeutic potential.

6-Methoxy-4-methylquinoline was converted into 8-methoxy-1,3,4,5-tetrahydropyrrolo[4,3,2-de]quinoline by a six reaction sequence in which the last step was the formation of the indole ring.

The first total synthesis of Aeruginazole A, prepared via a convergent strategy that involved both solid-phase peptide synthesis and solution phase chemistry and that enabled conservation of the stereochemistry of the intermediates, is reported.

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 anti-tumor activity. It reviews work published from January 2008 to December 2010.

For the first time, an enantioselective synthesis of both 1R,4S-isagarin 1a and 1S,4R-isagarin 1b was achieved starting from 1,4-dimethoxy-2-vinylnaphthalene 2. The key steps involve a Sharpless asymmetric dihydroxylation and reaction with an acetonylating pyridinium ylid. The different optical rotations and melting points of the enantiopure 1R,4S-isagarin 1a and 1S,4R-isagarin 1b with respect to the isolated natural product will be addressed.

The use of methyl 2-(1,3-dithian-2-yl)benzoate as a member of a new group of bidentate synthons in an improved annelation method, yielding polycyclic systems with three differentiated carbonyl groups, is described.

The protection of arginine (Arg) side chains is a crucial issue in peptide chemistry because of the propensity of the basic guanidinium group to produce side reactions. Currently, sulfonyl-type protecting groups, such as 2,2,5,7,8-pentamethylchroman (Pmc) and 2,2,4,6,7-pentamethyldihydrobenzofurane (Pbf), are the most widely used for this purpose. Nevertheless, Arg side chain protection remains problematic as a result of the acid stability of these two compounds. This issue is even more relevant in Arg-rich sequences, acid-sensitive peptides and large-scale syntheses. The 1,2-dimethylindole-3-sulfonyl (MIS) group is more acid-labile than Pmc and Pbf and can therefore be a better option for Arg side chain protection. In addition, MIS is compatible with tryptophan-containing peptides.

The detection of toxins in shellfish through reliable methods is essential for human health preservation and prevention of economic losses in the aquaculture industry. Although no human intoxication has been unequivocally linked to gymnodimines or spirolides, these phycotoxins are highly toxic by intraperitoneal injection causing false positives in lipophilic toxin detection by the mouse bioassay. Based on the detection of molecular interactions by fluorescence polarization an inhibition assay was developed using fluorescent alpha-bungarotoxin and nicotinic acetylcholine receptor-enriched membranes of Torpedo marmorata to detect gymnodimine and 13-desmethyl C spirolide. Both toxins, classified into the cyclic imine group, inhibit the interaction of alpha-bungarotoxin with Torpedo nicotinic acetylcholine receptors in the nM range. In this study we analyze the matrix effect of four shellfish species on the fluorescence polarization assay. Mussels, clams, cockles and scallops were extracted with acetone and sequentially partitioned with n-hexane and chloroform. The interference of these shellfish extracts with the alpha-bungarotoxin fluorescence or its binding to the nicotinic acetylcholine receptor was lower than 11%. The average recovery rates of gymnodimine and 13-desmethyl C spirolide using these solvents were 90.6+/-7.8% and 89.6+/-3.2%, respectively with variations among species. The quantification range of this fluorescence polarization assay for gymnodimine and 13-desmethyl C spirolide in all tested species was 80-2000 microg kg(-1) and 85-700 microg kg(-1) of shellfish meat, respectively. This assay format can be used to detect gymnodimine and 13-desmethyl C spirolide in shellfish as a screening assay.

Several analogues of the cytotoxic thiopeptide IB-01211 or mechercharmycin A (1) have been synthesized. The cytotoxicity of 1 and the synthesized analogues were evaluated against a panel of three human tumor cell lines. Thiopeptide 1 and the most active derivatives 2 and 3c were chosen for further studies on effects on cell cycle progression and induction of apoptosis. Interestingly, the inhibition of cell division and activation of a programmed cell death by apoptosis were detected.

Treatment of dithioacetals 1a–c, 3, and 4 with DMTSF accomplishes cyclization upon the indole 3-position to give the Strychnos -type pentacles 2a–c, 10, and 11 , respectively.

In recent years, backbone protection has allowed the synthesis of complex peptidic sequences of high interest by preventing chain aggregation and aspartimides formation. Nevertheless, the backbone protectors currently used have some drawbacks: they are difficult to remove and show high steric hindrance. The new backbone protectors presented in this study (EDOTn and MIM) represent an improvement in both aspects.

Oxathiocoraline, a member of the quinoxaline antibiotic family, has been synthesized on solid-phase. The depsipeptide exhibits high synthetic complexity owing to the presence of consecutive NMe amino acids, two ester moieties, a disulfide bridge, and two SMe Cys residues. Because of internal diketopiperazine formation, standard stepwise or convergent approaches failed to deliver the linear octadepsipeptide precursor. Therefore, an alternative methodology where an intermolecular disulfide dimer is formed on solid-phase was developed. Cleavage of the dimer from the solid-phase and subsequent bismacrolactamization followed by incorporation of the heterocyclic unit afforded the target compound. Oxathiocoraline showed antitumoral activity in three tumor cell lines.

[reaction: see text] p-Nitromandelic acid as a safety-catch linker for Boc/Bzl-SPPS of base-labile compounds like peptides and depsipeptides is described. This linker permits acidic removal of side-chain protection groups from the resin. For cleavage from the solid support, the p-nitro group was reduced with tin(II) chloride. After washing off the reducing agents, the (depsi)peptide acids with or without the side-chain protection schemes were obtained by microwave irradiation at 50 degrees C with 5% TFA in dioxane.

The pyrrolo[2,3-c]carbazole 1, the common core of the marine alkaloids known as the dictyodendrins, has been synthesised. The sequence is based on a Suzuki cross-coupling reaction between the pyrrole fragment 2 and the indole fragment 3, followed by tandem photochemical 6π-electrocyclisation/aromatisation.

6,7-Dimethoxy-4-methylquinoline has been converted in nine steps into the sulfur-containing pyrrolo[4,3,2- de ]quinoline marine alkaloid isobatzelline B. This constitutes the first total synthesis of an alkaloid of the group which contains a methylthio substituent.

A synthetic way for the construction of the tetracyclic 1,2,3,4,5,6-hexabydro-1,5-methanoazocino[4,3- b ]indo1e system I, having a methoxycarbonyl substituent at the C-6 position, is reported. The synthesis implies methoxycarbonylation of the Interannular methylene carbon of an appropriate 2-(4-pyridylmethyl)indole, followed by alkylation of the pyridine nitrogen, catalytic hydrogenation and, finally, oxidative cyclization of the resulting 2-(4-piperidylmethyl)indo1e.

A short, new route to the title tetracyclic substructure of Strychnos alkaloids, consisting in the nucleophilic attack of an ester α-anion to a pyridinium salt, acid-induced cyclization of the resultant 1,4-dihydropyridine, and stereospecific elaboration of the ethylidene substituent, is reported.

Important links exist between the process of pre-mRNA splicing and cancer, as illustrated by the frequent mutation of splicing factors in tumors and the emergence of various families of antitumor drugs that target components of the splicing machinery, notably SF3B1, a protein subunit of spliceosomal U2 small nuclear ribonucleoprotein particle (snRNP). Sudemycins are synthetic compounds that harbor a pharmacophore common to various classes of splicing inhibitors. Here, we describe the synthesis and functional characterization of novel sudemycin analogues that functionally probe key chemical groups within this pharmacophore. Our results confirm the importance of a conjugated diene group and in addition reveal significant spatial flexibility in this region of the molecule. Sudemycin K, a derivative that replaces the pharmacophore's oxycarbonyl by an amide group, displays improved potency as an inhibitor of cancer cell proliferation, as a regulator of alternative splicing in cultured cells and as an inhibitor of in vitro spliceosome assembly. Sudemycin K displays higher stability, likely related to the replacement of the oxycarbonyl group, which can be a substrate of esterases, by an amide group. The activity and special reactivity of sudemycin K can pave the way to the synthesis and evaluation of a variety of novel sudemycin derivatives. This study was supported by Fundación Botín, Banco de Santander through its Santander Universities Global Division, Consolider RNAREG, AGAUR, MINECO and the European Research Council. We acknowledge support of the Spanish Ministry of Economy and Competitiveness, ‘Centro de Excelencia Severo Ochoa 2013-2017.’ This work was partially funded by the CICYT (CTQ2015-67870P) and Generalitat de Catalunya (2014 SGR 137)

Herein is described the synthesis of several analogs of the natural product IB-01211 from concatenated azoles, via a biomimetic pathway based on cyclization–oxidation of serine containing peptides combined with the Hantzsch synthesis. The macrocyclization of rigid peptide compounds 1 and 2 to give IB-01211 and its epimer 12b was explored, and the results are compared here to those previously obtained for the macrocyclization of more flexible structures in the syntheses of YM-216391, telomestatin, and IB-01211. Lastly, the preliminary results of anti-tumor activity screening of the synthesized analogs are discussed.