Thiopeptide antibiotics: retrospective and recent advances

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

Highly efficient, multigram and enantiopure synthesis of (S)-2-(2,4′-bithiazol-2-yl)pyrrolidine

(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

Fmoc-2-Mercaptobenzothiazole (MBT), for the Introduction of the Fmoc Moiety Free of Side-Reactions

A double side-reaction, consisting in the formation of Fmoc--Ala-OH and Fmoc--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 -amino function of the amino acids

Samarium(II) folding cascades involving hydrogen atom transfer for the synthesis of complex polycycles

The expedient assembly of complex, natural product-like small molecules can deliver new chemical entities with the potential to interact with biological systems and inspire the development of new drugs and probes for biology. Diversity-oriented synthesis is a particularly attractive strategy for the delivery of complex molecules in which the 3-dimensional architecture varies across the collection. Here we describe a folding cascade approach to complex polycyclic systems bearing multiple stereocentres mediated by reductive single electron transfer (SET) from SmI2. Simple, linear substrates undergo three different folding pathways triggered by reductive SET. Two of the radical cascade pathways involve the activation and functionalization of otherwise inert secondary alkyl and benzylic groups by 1,5-hydrogen atom transfer (HAT). Combination of SmI2, a privileged reagent for cascade reactions, and 1,5-HAT can lead to complexity-generating radical sequences that unlock access to diverse structures not readily accessible by other means

Palladium catalysed C-H arylation of pyrenes: access to a new class of exfoliating agents for water-based graphene dispersions.

From Europe PMC via Jisc Publications RouterHistory: ppub 2020-01-01, epub 2020-01-28Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; Grant(s): 1781838, EP/P00119X/1A new and diverse family of pyrene derivatives was synthesised via palladium-catalysed C-H ortho-arylation of pyrene-1-carboxylic acid. The strategy affords easy access to a broad scope of 2-substituted and 1,2-disubstituted pyrenes. The C1-substituent can be easily transformed into carboxylic acid, iodide, alkynyl, aryl or alkyl functionalities. This approach gives access to arylated pyrene ammonium salts, which outperformed their non-arylated parent compound during aqueous Liquid Phase Exfoliation (LPE) of graphite and compare favourably to state-of-the-art sodium pyrene-1-sulfonate PS1. This allowed the production of concentrated and stable suspensions of graphene flakes in water

Controlling Antibacterial Activity Exclusively with Visible Light: Introducing a Tetra-ortho-Chloro-Azobenzene Amino Acid

The introduction of a novel tetra-ortho-chloroazobenzene amino acid (CEBA) has enabled photoswitching of the antimicrobial activity of tyrocidine A analogues by using exclusively visible light, granting spatiotemporal control under benign conditions. Compounds bearing this photo- switchable amino acid become active upon irradiation with red light, but quickly turn-off upon exposure to other visible light wavelengths. Critically, sunlight quickly triggers isomerisation of the red light-activated compounds into their original trans form, offering an ideal platform for self-deactivation upon release into the environment. Linear analogues of tyrocidine A were found to provide the best photocontrol of their antimicrobial activity, leading to compounds active against Acinetobacter baumannii upon isomerisation. Exploration of their N- and C-termini has provided insights into key elements of their structure and has allowed obtaining new antimicrobials displaying excellent strain selectivity and photocontrol

Biocatalytic Conversion of Cyclic Ketones Bearing α-Quaternary Stereocenters into Lactones in an Enantioselective Radical Approach to Medium-Sized Carbocycles

Cyclic ketones bearing alpha-quaternary stereocenters undergo efficient kinetic resolution using cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus. Lactones possessing tetrasubstituted stereocenters are obtained with high enantioselectivity (up to >99% ee) and complete chemoselectivity. Preparative scale biotransformations were exploited in conjunction with a SmI2-mediated cyclization process to access complex, enantiomerically enriched cycloheptan- and cycloctan-1,4-diols. In a parallel approach to structurally distinct products, enantioenriched ketones from the resolution bearing an alpha- all carbon quaternary stereocenter were used in a SmI2-mediated cyclization process to give cyclobutanol products (up to >99% ee)

Thiopeptides: Synthesis and Structure-Activity Relationship Studies

[spa]En la presente tesis doctoral se ha llevado a cabo el desarrollo de una nueva estrategia sintética para la obtención de un nuevo miembro de la familia de antibióticos conocida como tiopéptidos, o tiazolil péptidos. Este nuevo miembro, la baringolina, fue aislado y caracterizado por la empresa farmacéutica española Biomar S.A., la cual no elucidó la estereoquímica del compuesto. Así, el propósito inicial de esta tesis es múltiple; por un lado se pretende desarrollar una estrategia que permita su obtención de forma directa y modular, facilitando la futura síntesis de análogos; por otro lado, la obtención de la baringolina sintética debe ofrecer una confirmación definitiva de su estructura y su estereoquímica. La estrategia desarrollada se basó en reacciones de acoplamiento cruzado, lo cual requería la preparación de los fragmentos necesarios y la optimización de la metodología a utilizar. Además, se escogió utilizar amino ácidos de la serie L como única fuente de quiralidad en la molécula, la cual presumiblemente está formada a partir de estos, dado el origen ribosomal de los tiopéptidos. Con la metodología puesta a punto y los fragmentos correspondientes preparados, se pudo llevar a cabo su ensamblaje, dando lugar a la baringolina sintética, la cual resultó ser idéntica a la natural, confirmándose así su estructura y estereoquímica. Dado el éxito de la síntesis total, se procedió a la síntesis de una pequeña librería de análogos, en la cual se modificaron dos zonas diferentes de la molécula, el anillo de tiazolina y la cola peptídica. Como resultado de la evaluación de la capacidad de inhibición de cultivos de bacterios Gram positivo, se extrajeron diversas conclusiones relativas a las relaciones estructura-actividad de las partes modificadas. En primer lugar, la tiazolina demostró ser necesaria para mantener un amplio espectro de actividad frente a diversas cepas, ya que su substitución por un anillo de tiazol, más rígido, prácticamente solo mantuvo el mismo nivel de potencia frente a S.aureus. Por otro lado, el papel de la cola peptídica resultó ser limitado, ya que su acortamiento no causó grandes diferencias de actividad y potencia. Por último, se substituyó la cola por un grupo de ácido ciclohexanoico en la versión que poseía un anillo de tiazol en lugar de tiazolina, lo cual resultó en el restablecimiento de la actividad frente a todas las cepas y un aumento de potencia frente a la mayoría de éstas.[eng]The present doctoral thesis has been devoted to the development of a new synthetic strategy to obtain a new member of the thiopeptide, or thiazolyl peptide, family of antibiotics. This new member, baringolin, was isolated and characterized by the Spanish pharmaceutical company Instituto Biomar S.A. Although a structure was proposed, no stereochemical information was provided. Thus, this thesis has several objectives; first, a novel modular and straightforward strategy must be developed to achieve its total synthesis, but also to facilitate the preparation of analogues. The achievement of the total synthesis of baringolin should serve as the final confirmation of its structure and stereochemistry. The strategy developed herein is based in cross-coupling reactions and required the preparation of suitable building blocks and optimization of the required methodology. Moreover, L –series amino acids were chosen as the sole source of chirality to be introduced in the molecule, which is presumably synthesized in the ribosome of the producing bacteria. Once the synthetic methodology was set up and building blocks were ready, condensation of all fragments and final steps gave rise to synthetic baringolin, which was identical to its natural counterpart, confrming its structure and stereochemistry. Comparison of both products was made by spectroscopic methods and biological function assessment. Given the successful outcome of our synthetic plan, a small library of analogues was designed. Two different moieties of the molecule were modified: the thiazoline ring and the peptidic tail. As a result of minimum inhibitory concentration of Gram positive bacteria growth assessment of the library, different conclusions could be drawn from the results thus obtained. First, thiazoline was shown to be crucial to keep a broad activity profile against many strains; its substitution for a more rigid thiazole ring resulted in loss of activity towards most strains, while potency was only maintained against S. aureus. On the other hand, shortening of the peptidic tail had almost no effect in either activity or potency. Substitution of the peptidic tail with a cyclohexanoic acid moiety in the thiazole series resulted in recovery of activity against all strains and a potency increase against most of them. The good results obtained are good evidence of the efficiency of the synthetic strategy developed during this thesis and demonstrate that chemical synthesis is a useful tool for both structure determination and structure-activity relationship studies

Thiopeptides: Synthesis and Structure-Activity Relationship Studies

[spa]En la presente tesis doctoral se ha llevado a cabo el desarrollo de una nueva estrategia sintética para la obtención de un nuevo miembro de la familia de antibióticos conocida como tiopéptidos, o tiazolil péptidos. Este nuevo miembro, la baringolina, fue aislado y caracterizado por la empresa farmacéutica española Biomar S.A., la cual no elucidó la estereoquímica del compuesto. Así, el propósito inicial de esta tesis es múltiple; por un lado se pretende desarrollar una estrategia que permita su obtención de forma directa y modular, facilitando la futura síntesis de análogos; por otro lado, la obtención de la baringolina sintética debe ofrecer una confirmación definitiva de su estructura y su estereoquímica. La estrategia desarrollada se basó en reacciones de acoplamiento cruzado, lo cual requería la preparación de los fragmentos necesarios y la optimización de la metodología a utilizar. Además, se escogió utilizar amino ácidos de la serie L como única fuente de quiralidad en la molécula, la cual presumiblemente está formada a partir de estos, dado el origen ribosomal de los tiopéptidos. Con la metodología puesta a punto y los fragmentos correspondientes preparados, se pudo llevar a cabo su ensamblaje, dando lugar a la baringolina sintética, la cual resultó ser idéntica a la natural, confirmándose así su estructura y estereoquímica. Dado el éxito de la síntesis total, se procedió a la síntesis de una pequeña librería de análogos, en la cual se modificaron dos zonas diferentes de la molécula, el anillo de tiazolina y la cola peptídica. Como resultado de la evaluación de la capacidad de inhibición de cultivos de bacterios Gram positivo, se extrajeron diversas conclusiones relativas a las relaciones estructura-actividad de las partes modificadas. En primer lugar, la tiazolina demostró ser necesaria para mantener un amplio espectro de actividad frente a diversas cepas, ya que su substitución por un anillo de tiazol, más rígido, prácticamente solo mantuvo el mismo nivel de potencia frente a S.aureus. Por otro lado, el papel de la cola peptídica resultó ser limitado, ya que su acortamiento no causó grandes diferencias de actividad y potencia. Por último, se substituyó la cola por un grupo de ácido ciclohexanoico en la versión que poseía un anillo de tiazol en lugar de tiazolina, lo cual resultó en el restablecimiento de la actividad frente a todas las cepas y un aumento de potencia frente a la mayoría de éstas.[eng]The present doctoral thesis has been devoted to the development of a new synthetic strategy to obtain a new member of the thiopeptide, or thiazolyl peptide, family of antibiotics. This new member, baringolin, was isolated and characterized by the Spanish pharmaceutical company Instituto Biomar S.A. Although a structure was proposed, no stereochemical information was provided. Thus, this thesis has several objectives; first, a novel modular and straightforward strategy must be developed to achieve its total synthesis, but also to facilitate the preparation of analogues. The achievement of the total synthesis of baringolin should serve as the final confirmation of its structure and stereochemistry. The strategy developed herein is based in cross-coupling reactions and required the preparation of suitable building blocks and optimization of the required methodology. Moreover, L –series amino acids were chosen as the sole source of chirality to be introduced in the molecule, which is presumably synthesized in the ribosome of the producing bacteria. Once the synthetic methodology was set up and building blocks were ready, condensation of all fragments and final steps gave rise to synthetic baringolin, which was identical to its natural counterpart, confrming its structure and stereochemistry. Comparison of both products was made by spectroscopic methods and biological function assessment. Given the successful outcome of our synthetic plan, a small library of analogues was designed. Two different moieties of the molecule were modified: the thiazoline ring and the peptidic tail. As a result of minimum inhibitory concentration of Gram positive bacteria growth assessment of the library, different conclusions could be drawn from the results thus obtained. First, thiazoline was shown to be crucial to keep a broad activity profile against many strains; its substitution for a more rigid thiazole ring resulted in loss of activity towards most strains, while potency was only maintained against S. aureus. On the other hand, shortening of the peptidic tail had almost no effect in either activity or potency. Substitution of the peptidic tail with a cyclohexanoic acid moiety in the thiazole series resulted in recovery of activity against all strains and a potency increase against most of them. The good results obtained are good evidence of the efficiency of the synthetic strategy developed during this thesis and demonstrate that chemical synthesis is a useful tool for both structure determination and structure-activity relationship studies

Thiopeptide Antibiotics: Retrospective and Recent Advances

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