Construction of challenging proline–proline junctions via diselenide–selenoester ligation chemistry

Polyproline sequences are highly abundant in prokaryotic 10 and eukaryotic proteins, where they serve as key components of 11 secondary structure. To date, construction of the proline−proline motif 12 has not been possible owing to steric congestion at the ligation junction, 13 together with an n → π* electronic interaction that reduces the 14 reactivity of acylated proline residues at the C-terminus of peptides. 15 Here, we harness the enhanced reactivity of prolyl selenoesters and a 16 trans-γ-selenoproline moiety to access the elusive proline−proline 17 junction for the first time through a diselenide−selenoester ligation− 18 deselenization manifold. The efficient nature of this chemistry is 19 highlighted in the high-yielding one-pot assembly of two proline-rich 20 polypeptide targets, submaxillary gland androgen regulated protein 3B 21 and lumbricin-1. This method provides access to the most challenging of ligation junctions, thus enabling the construction of 22 previously intractable peptide and protein targets of increasing structural complexity

Accelerated protein synthesis via one–pot ligation–deselenization chemistry

Peptide ligation chemistry has revolutionized protein science by facilitating access to synthetic proteins. Here, we describe the development of additive-free ligation-deselenization chemistry at β-selenoaspartate and γ-selenoglutamate that enables the generation of native polypeptide products on unprecedented timescales. The deselenization step is chemoselective in the presence of unprotected selenocysteine, which is highlighted in the synthesis of selenoprotein K. The power of the methodology is also showcased through the synthesis of three tick-derived thrombin-inhibiting proteins, each of which were assembled, purified, and isolated for biological assays within a few hours. The methodology described here should serve as a powerful means of accessing synthetic proteins, including therapeutic leads, in the future

Accelerated protein synthesis via one–pot ligation–deselenization chemistry

Peptide ligation chemistry has revolutionized protein science by facilitating access to synthetic proteins. Here, we describe the development of additive-free ligation-deselenization chemistry at β-selenoaspartate and γ-selenoglutamate that enables the generation of native polypeptide products on unprecedented timescales. The deselenization step is chemoselective in the presence of unprotected selenocysteine, which is highlighted in the synthesis of selenoprotein K. The power of the methodology is also showcased through the synthesis of three tick-derived thrombin-inhibiting proteins, each of which were assembled, purified, and isolated for biological assays within a few hours. The methodology described here should serve as a powerful means of accessing synthetic proteins, including therapeutic leads, in the future

Immobilisation and application of bifunctional iminophosphorane organocatalysts

Bifunctional iminophosphoranes, containing a triaryl-substituted iminophosphorane and bis(3,5- trifluoromethyl)phenyl thiourea on a single enantiomer scaffold are novel asymmetric superbase organocatalysts reported by the Dixon group in 2014. This thesis describes our efforts to expand their scope and utility in a variety of challenging chemical transformations. Chapter 2 describes the development and application of immobilised bifunctional iminophosphorane organocatalysts. We have successfully immobilised bifunctional iminophosphoranes on a crosslinked polystyrene support and applied this sold-supported catalyst to three challenging asymmetric reactions; namely the nitro-Mannich reaction of phosphinoyl ketimines and the conjugate addition of alkylmalonates and N,N-dimethyl β-keto amides to nitrostyrene. Very good yields, enantio- and diasteroselectivities were obtained in all cases. We have also demonstrated their use in a range of conjugate additions of cyclic 1,3-dicarbonyl compounds to nitroalkenes, which suffered from very slow reaction rates under tertiary amine-based bifunctional catalysis. In all cases, the immobilised bifunctional iminophosphoranes performed very well in comparison to their homogeneous counterparts. We have also demonstrated catalyst recycling over 10 cycles and application in a continuous flow system with a productivity of 7.20 mmol producth-1gcatalyst-1. to the ring-opening polymerisation (ROP) of cyclic esters. We have demonstrated the performance of bifunctional iminophosphorane organocatalysts in the ROP of L-lactide (LA), δ-valerolactone (VL) and ε-caprolactone (CL). The polymerisation of LA and VL proceeded rapidly and was well controlled, while only short lengths (&gt; 100 DP) of poly(CL) could be prepared in a controlled fashion due to hypothesised competing initiation from the catalyst. We have shown that the polymerisation of LA using our catalyst may be considered a living polymerisation. Di-block co-polymers could also be successfully prepared via sequential monomer addition or through the use of macroinitiators. We then investigated the roles of the iminophosphorane and the thiourea component of the catalyst.</p

Immobilisation and application of bifunctional iminophosphorane organocatalysts

Bifunctional iminophosphoranes, containing a triaryl-substituted iminophosphorane and bis(3,5- trifluoromethyl)phenyl thiourea on a single enantiomer scaffold are novel asymmetric superbase organocatalysts reported by the Dixon group in 2014. This thesis describes our efforts to expand their scope and utility in a variety of challenging chemical transformations. Chapter 2 describes the development and application of immobilised bifunctional iminophosphorane organocatalysts. We have successfully immobilised bifunctional iminophosphoranes on a crosslinked polystyrene support and applied this sold-supported catalyst to three challenging asymmetric reactions; namely the nitro-Mannich reaction of phosphinoyl ketimines and the conjugate addition of alkylmalonates and N,N-dimethyl &beta;-keto amides to nitrostyrene. Very good yields, enantio- and diasteroselectivities were obtained in all cases. We have also demonstrated their use in a range of conjugate additions of cyclic 1,3-dicarbonyl compounds to nitroalkenes, which suffered from very slow reaction rates under tertiary amine-based bifunctional catalysis. In all cases, the immobilised bifunctional iminophosphoranes performed very well in comparison to their homogeneous counterparts. We have also demonstrated catalyst recycling over 10 cycles and application in a continuous flow system with a productivity of 7.20 mmol producth-1gcatalyst-1. to the ring-opening polymerisation (ROP) of cyclic esters. We have demonstrated the performance of bifunctional iminophosphorane organocatalysts in the ROP of L-lactide (LA), δ-valerolactone (VL) and ε-caprolactone (CL). The polymerisation of LA and VL proceeded rapidly and was well controlled, while only short lengths (&gt; 100 DP) of poly(CL) could be prepared in a controlled fashion due to hypothesised competing initiation from the catalyst. We have shown that the polymerisation of LA using our catalyst may be considered a living polymerisation. Di-block co-polymers could also be successfully prepared via sequential monomer addition or through the use of macroinitiators. We then investigated the roles of the iminophosphorane and the thiourea component of the catalyst.This thesis is not currently available in OR

Carta manuscrita de Paco (Manchester) a Pere Pascual comentant diversos aspectes de beques i del GIFT

Highly active bifunctional iminophosphorane catalysts have been applied to the organocatalytic ring-opening polymerization (ROP) of l-lactide (LA), δ-valerolactone (VL), and ε-caprolactone (CL). LA polymerization using catalyst <b>2</b> at 1 mol % loading rapidly gave poly­(LA) in full conversion and with excellent control over the molecular weight distribution. VL and CL were polymerized under the control of catalyst <b>3</b> at 5 mol % loading. Poly­(VL) was obtained in high conversion and with very good control over the molecular weight distribution. The catalyst system was suitable for the formation of short lengths of poly­(CL), with good control over the molecular weight distribution. The formation of block copolymers by sequential monomer addition and the use of macroinitiators such as monomethoxy-terminated poly­(ethylene glycol) (mPEG) were also demonstrated using the catalyst system. Control experiments using nonbifunctional <i>N</i>-alkyl iminophosphorane <b>5</b> demonstrated the roles of both components of the bifunctional catalyst in the ROP reaction. Notably, the bifunctional iminophosphorane catalysts are moisture-stable and nonhygroscopic, enabling the assembly of ROP reactions on the open bench

Combining ionising radiation with nanoconstructs: towards new options in cancer therapy

Engineered nanomaterials that produce reactive oxygen species while exposed to X- and gamma rays offer promise of a novel cancer treatment strategy. Similar to photodynamic therapy (PDT) but suitable for deep tumours, the new approach called X-PDT is highly effective at clinically low radiation doses. The X-PDT nanomaterials can enhance cancer radiotherapy, by increasing its selectivity, and decreasing side effects. Additionally, the nanomaterial platform offers therapeutically valuable functionalities such as molecular targeting, the capability for drug/gene delivery, adaptive responses allowing triggering of drug release and more. The potential of such nanomaterials to be combined with radiotherapy has been widely recognised, as apparent in an explosion of new advances in X-PDT. So far, the field seems to develop organically, by a combinatorial approach, and optimally designed materials and quantitative approaches remain scarce. In order for further breakthroughs to be made, and to facilitate clinical translation the applicable principles and fundamentals should be articulated. We will introduce mechanisms and principles underpinning rational material design for X-PDT. The understanding of these principles will enable novel ways to optimise the ROS yields and the ensuing cytotoxicity which is directly related to therapy success. The X-PDT nanomaterials will be discussed though the lens of catalytical processes at solid surfaces. Drawing on analogies between photo- and radio-catalysis, we propose that future authors build on selected advances in the areas of clean energy, water splitting and environmental remediation. Traditionally, in PDT photosensitizer drugs act as molecular catalysts. In the X-PDT approach, catalysis takes place on the solid surface of nanomaterials. Many aspects of such surfaces are well established in solid state physics, but disciplinary barriers prevent wider utilisation of that knowledge to build optimised X-PDT agents. We discuss optimising of charge transfer catalysis where ROS are formed by redox reactions. The alternative process of energy transfer catalysis is also highly relevant, while much less understood; we discuss resonant tuning of X-PDT offered by energy transfer processes which offers unprecendented amplification. Functionalisations and coatings are a ubiquitous feature of engineered nanomaterials and these layers can be used for facile tuning of X-PDT. We discuss how ionic organisation of fluid at the solid-liquid interface affects the potential profile, and how this, in turn, allows to easily adjust the matching of electron and hole energies with relevant redox potentials. We then focus on nanomaterials where coatings contain clinical photosensitizers (a development analogous to surface-immobilised organocatalysts in chemistry). These offer additional dimension to optimise X-PDT, as they can utilise energy transduction (X-rays into visible light) and also Cherenkov radiation produced during radiotherapy. Furthermore we explore clinical translation of these materials where we discuss biocompatible nanocarriers (liposomes and PLGA nanoparticles) as well as mesoporous silica etc. Critically, the photosensitizers respond with ROS not only to light but also to radiation. We explain the underpinning mechanism which makes it possible to create X-PDT nanoparticles with sophisticated functionalities such as X-ray triggering exclusively from FDA-approved components, a step that brings closer their clinical translation. Finally in this section we draw attention of the reader to novel photosensitizers derived from aggregation-induced-emission (AIE) molecular species. We explain how their violation of the Kasha rule enables exceptionally high ROS yields, suggesting that they may help build uniquely powerful and clinically compatible nanoconstructs for X-PDT. We then turn attention to cells and explore ways in which cells fight back the ROS attacks which is necessary for their survival. Effective X-PDT agents should be able to weaken or, ideally, disable this cellular protection. We focus on DNA damage and its repair, as well as on maintaining the redox status through the cellular antioxidant system based on glutathione system. Both DNA damage and the antioxidants can be interfered with using functional nanoparticles. As a conclusion we present a roadmap for designing nanomaterials with optimised X-PDT performance

Forgotten French. Exiles in the British Isles, 1940-44

A new family of bifunctional H-bond donor phase-transfer catalysts derived from cinchona alkaloids has been developed and evaluated in the enantio- and diastereoselective nitro-Mannich reaction of in situ generated <i>N</i>-Boc-protected imines of aliphatic, aromatic, and heteroaromatic aldehydes. Under optimal conditions, good reactivity and high diastereoselectivities (up to 24:1 dr) and enantioselectivities (up to 95% ee) were obtained using a 9-amino-9-deoxyepiquinidine-derived phase-transfer catalyst possessing a 3,5-bis(trifluoromethyl)phenylurea H-bond donor group at the 9-position

Chick Embryo Experimental Platform for Micrometastases Research in a 3D Tissue Engineering Model: Cancer Biology, Drug Development, and Nanotechnology Applications

Colonization of distant organs by tumor cells is a critical step of cancer progression. The initial avascular stage of this process (micrometastasis) remains almost inaccessible to study due to the lack of relevant experimental approaches. Herein, we introduce an in vitro/in vivo model of organ-specific micrometastases of triple-negative breast cancer (TNBC) that is fully implemented in a cost-efficient chick embryo (CE) experimental platform. The model was built as three-dimensional (3D) tissue engineering constructs (TECs) combining human MDA-MB-231 cells and decellularized CE organ-specific scaffolds. TNBC cells colonized CE organ-specific scaffolds in 2&ndash;3 weeks, forming tissue-like structures. The feasibility of this methodology for basic cancer research, drug development, and nanomedicine was demonstrated on a model of hepatic micrometastasis of TNBC. We revealed that MDA-MB-231 differentially colonize parenchymal and stromal compartments of the liver-specific extracellular matrix (LS-ECM) and become more resistant to the treatment with molecular doxorubicin (Dox) and Dox-loaded mesoporous silica nanoparticles than in monolayer cultures. When grafted on CE chorioallantoic membrane, LS-ECM-based TECs induced angiogenic switch. These findings may have important implications for the diagnosis and treatment of TNBC. The methodology established here is scalable and adaptable for pharmacological testing and cancer biology research of various metastatic and primary tumors