Enantioselective Synthesis of (−)-Acetylapoaranotin

The first enantioselective total synthesis of the epipolythiodiketopiperazine (ETP) natural product (−)-acetylapoaranotin (3) is reported. The concise synthesis was enabled by an eight-step synthesis of a key cyclohexadienol-containing amino ester building block. The absolute stereochemistry of both amino ester building blocks used in the synthesis is set through catalytic asymmetric (1,3)-dipolar cycloaddition reactions. The formal syntheses of (−)-emethallicin E and (−)-haemotocin are also achieved through the preparation of a symmetric cyclohexadienol-containing diketopiperazine

Customized bioreactor enables the production of 3D diaphragmatic constructs influencing matrix remodeling and fibroblast overgrowth

The production of skeletal muscle constructs useful for replacing large defects in vivo, such as in congenital diaphragmatic hernia (CDH), is still considered a challenge. The standard application of prosthetic material presents major limitations, such as hernia recurrences in a remarkable number of CDH patients. With this work, we developed a tissue engineering approach based on decellularized diaphragmatic muscle and human cells for the in vitro generation of diaphragmatic-like tissues as a proof-of-concept of a new option for the surgical treatment of large diaphragm defects. A customized bioreactor for diaphragmatic muscle was designed to control mechanical stimulation and promote radial stretching during the construct engineering. In vitro tests demonstrated that both ECM remodeling and fibroblast overgrowth were positively influenced by the bioreactor culture. Mechanically stimulated constructs also increased tissue maturation, with the formation of new oriented and aligned muscle fibers. Moreover, after in vivo orthotopic implantation in a surgical CDH mouse model, mechanically stimulated muscles maintained the presence of human cells within myofibers and hernia recurrence did not occur, suggesting the value of this approach for treating diaphragm defects

Intramolecular stabilization of 2,6-diarylphenylsilylium ions by π-arene and lone pair-halogen coordination

Silyliumionen sind höhere Analoge von Carbokationen der Struktur R3Si+. Was sie vor allem auszeichnet, ist ihre enorme Elektrophilie. Die Erzeugung langlebiger silylkationen hat deshalb die Entwicklung neuartiger synthetischer Wege und schwach nucleophile Reaktionsbedingungen bedingt. Erst 2002 wurden mit der Kristallstruktur eines Triarylsilyliumions letzte Zweifel an der Existenz dreifach koordinierter Siliziumkationen ausgeräumt. In den vergangenen Jahren haben verschiedene Forschungsgruppen Silyliumionen erfolgreich zur Erzeugung reaktiver Zwischenstufen und in der Lewissäure-Katalyse angewandt. Das Ziel dieser Arbeit ist die Erweiterung der Familie dieser Terphenylsilyiumionen, die in der Siegel Gruppe bereits entwickelt wurden. Die Terphenylgrundstruktur bietet sterische Abschirmung von der positiven Ladun des Siliciumkerns sowie eine komplette thermodynamsiche Stabilisierung durch die pie-Koordination. Um die Lewis-Acidität zu regeln, wurde die Elektronendichte der benachbarten Ringe reduziert. Zuerst wurden Halogenatome an der ortho-Position dieser benachbarten Ringe eingeführt Diese mindern die Koordination der pie-Arene, so dass eine bevorzugte Koordination zwischen dem Halogen und dem Silicium stattfinden. Diese Konformation wurde durch NMR, X-Ray und Berechnungsmethoden bestätigt. Eine zweite Generation von Terphenylsilyliumionen wurde synthetisiert, mit Halogenatome in para-Position zu der benachbarten Ringen. Somit sollte eine Koordination am lateralen Ring und an den Halogenatomen vermieden werden wodurch das Silyiumion entschirmt wird. Durch Verwendung von X-Ray- Kristallographie wurde gezeigt, dass die intramolekulare Koordination des positiv geladenen Kerns mit den benachbarten Ringen tatsächlich reduziert wurde und dass die intermolekulare Koordination mit dem Gegenion konkurriert. Durch ein grosses Interesse die Energetik der pie-Arene-Koordinationen detailliert zu erforschen, wurden eine Reihe von Kationen aus 2,6-Difluoro- und 2,6-Dimethyl-substitutierte Ringe synthetisiert. Somit wurde die Koordination zwischen den abgeschiedenen Halogenpaar zu Silicium verglichen. Dabei wurde bedeutsamerweise eine Konkurrenz anstatt einer Kooperation zwischen den beiden Stabilisierungsmethoden erkannt. Eine Interaktion von F=>Si wird durch methylierte Ringe mit niedrigere Basizität, wohingegen eine pie-Koordination mit duryl- und pentamethylphenyl-Substituenten bevorzugt wird. In dieser Arbeit wurde erfolgreich eine neue Art der Phenylsilyiumionen, die sterisch zugänglichere trikoordinierte Triarylsilyliumionen widerspiegeln, synthetisiert und untersucht. Diese Strukturen weisen niedrige Resonanzverschiebung in 29Si- NMR Spektroskopie auf, was ein klares Zeichen von abgeschirmten kationischen Zentren darstellt. Die Stabilität dieser „nackten“ Silyliumionen ist auf die agostische Wechselwirkung mit den benachbarten aliphatischen Gruppen zurückzuführen. Eine erst kürzlich aufgesetzte Hypothese befasst sich mit Kationen, die in eine stabilere Triarylsilylkation-Struktur neu geordnet werden. Diese sind verantwortlich für eine niedrige chemische Resonanzverschiebung. Weitere Untersuchungen werden nun folgen, um die Mechanismen dieser Neuanordnung aufzuklären. Summary Silylium ions are group 14 analogs of carbocation of the general structure R3Si+. Their most striking feature is their extreme electrophilicity. The generation of long-lived silyl cationic species has therefore necessitated the development of novel synthetic approaches and weakly nucleophilic conditions. It was only in 2002 that the first crystal structure of a triarylsilylium ion dispelled any doubt about the existence of tricoordinated silyl cations in the condensed phase. In the recent years, several research groups have succeeded in applying silylium ion chemistry to the preparation of other reactive intermediates and to the field of Lewis acid catalysis. The aim of this thesis is to expand the family of terphenylsilylium ions previously developed in the Siegel group. The terphenyl skeleton provides steric shielding of the positively charged cavity as well as an overall thermodynamic stabilization by internal !-coordination. A systematic study was performed in order to tune the Lewis acidity at silicon by reducing the electron density of the flanking rings. At first, halogen atoms were introduced at the ortho positions of the flanking rings with the effect of quenching !-arene coordination in favor of lone pair-halogen coordination to silicon. This coordination mode was confirmed via NMR, X-ray and computational studies. A second generation of terphenylsilylium ions, featuring halogen atoms in the para position of the flanking rings, was synthesized with the aim of avoiding both lateral ring and halogen coordination, in favor of a very deshielded silylium ion. As a result, the intramolecular coordination of the positively charged cavity by the flanking rings was effectively reduced but the intermolecular coordination by the counterion became competitive, as shown by X-ray crystallography. We became interested in probing the energetic details of !-arene coordination compared to lone pair-halogen coordination to silicon, and therefore a series of cations bearing 2,6-difluoro- and 2,6-dimethyl-substituted rings were synthesized. Remarkably, a competition, rather than a cooperation, is established between the two modes of stabilization: with methylated rings of lower basicity the preferred interaction is F=>Si, while with duryl and pentamethylphenyl substituents !-coordination is favored. In the search of silylium ions as active as the truly tricoordinated triarylsilylium ion, but sterically more accessible, a new family of phenylsilylium ions featuring aliphatic chains in place of the flanking aromatic rings was synthesized and studied. These compounds exhibited very low field-shifted resonances in Si NMR spectroscopy, sign of a very deshielded cationic center. At first, the stability of these “naked” silylium ions, which did not display significant solvent or anion coordination, was attributed to agostic interactions with the nearby aliphatic groups. Recently, a new hypothesis has been formulated regarding a rearrangement of the initial cations into more stable triarylsilyl cationic structures, which are responsible for the low field-shifted resonances. Further investigations are now ongoing to elucidate the mechanism of this rearrangement

Through-space interactions in enshroudedm-terphenylsilanes

A series of m-terphenyl-substituted silanes was prepared and studied with regard to the steric and electronic interactions between the silyl core and the terphenyl shroud. Only weak conformational preferences were observed for the core, but the π-basicity of the lateral rings led to distinct nuclear magnetic resonance shifts, and o-fluorine atoms led to through-space coupling effects

The Pediatric Emergency Care Applied Research Network intermediate-risk predictors were not associated with scanning decisions for minor head injuries

Aim: This study determined the predictors associated with the decision to perform a computed tomography (CT) scan in children with a minor head injury (MHI). We focused on those facing an intermediate risk of clinically important traumatic brain injury (ciTBI), according to the Pediatric Emergency Care Applied Research Network (PECARN) prediction rule. Methods: A 1-year, cross-sectional study was performed in an Italian paediatric emergency department, focusing on children presenting within 24 h of an MHI and meeting the PECARN intermediate-risk criteria. Results: We included 308 children, and 47% were younger than 2 years of age. CT scans were carried out on 13%, 1.3% had a ciTBI and one was initially missed but did not need neurosurgery following diagnosis. Single and multiple PECARN intermediate-risk predictors were not associated with whether a CT scan was carried out. The only clinical variable associated with the decision to perform a CT scan was if the child was <3 months of age (OR 18.1, 95% CI, 4.91-66.61). Conclusion: The PECARN intermediate-risk predictors did not play a major role in the decision to perform a CT scan. The only factor significantly associated with the decision to perform a CT scan was when the patient was younger than 3 months of age

Bariatric surgery improves atherogenic LDL profile by triglyceride reduction

BACKGROUND: Small dense low-density lipoprotein (LDL) are atherogenic particles frequently observed in obese patients. Fatty acids modulate LDL. Objective of this study was to determine the relations between plasma phospholipid fatty acid composition and the presence of small dense LDL particles in morbidly obese patients treated with laparoscopic gastric banding (LAGB). METHODS: Small dense LDL, plasma lipids, lipoproteins, apoproteins, and phospholipid fatty acid composition (a marker of dietary fatty acid intake) were quantified before and 12 months after surgery in four men and 11 women who were morbidly obese and (BMI > 40 kg/m(2)) eligible for surgery, consecutively treated with LAGB at the Department of Medical and Surgical Sciences of the University of Padova. RESULTS: BMI was 48.3 +/- 4.8 kg/m(2) before and 36.1 +/- 5.5 kg/m(2) after LAGB. Plasma triglycerides and apoprotein E levels significantly decreased, while HDL cholesterol significantly increased after LAGB. A reduction of small dense LDL with an increase of LDL relative flotation (0.34 +/- 0.04 before vs 0.38 +/- 0.03 after LAGB, p < 0.001) was also observed. These modifications were neither related to weight reduction nor to changes in phospholipid fatty acid composition, but they were associated to triglyceride reduction, which explained 76.7% of the LDL relative flotation variation. CONCLUSION: Weight loss obtained by LAGB in morbidly obese subjects was accompanied by triglyceride reduction, high-density lipoprotein increase, and an improvement of the atherogenic LDL profile. Triglyceride reduction, but not the extent of weight loss or dietary fatty acid modifications, is the determinant of modifications of LDL physical properties in these patients

A self-assembling peptide hydrogel for ultrarapid 3D bioassays

A peptide soft hydrogel is used as a 3D matrix for flash microarray bioassays

Preservation strategies for decellularized pericardial scaffolds for off-the-shelf availability

Decellularized biological scaffolds hold great promise in cardiovascular surgery. In order to ensure off-the-shelf availability, routine use of decellularized scaffolds requires tissue banking. In this study, the suitability of cryopreservation, vitrification and freeze-drying for the preservation of decellularized bovine pericardial (DBP) scaffolds was evaluated. Cryopreservation was conducted using 10% DMSO and slow-rate freezing. Vitrification was performed using vitrification solution (VS83) and rapid cooling. Freeze-drying was done using a programmable freeze-dryer and sucrose as lyoprotectant. The impact of the preservation methods on the DBP extracellular matrix structure, integrity and composition was assessed using histology, biomechanical testing, spectroscopic and thermal analysis, and biochemistry. In addition, the cytocompatibility of the preserved scaffolds was also assessed. All preservation methods were found to be suitable to preserve the extracellular matrix structure and its components, with no apparent signs of collagen deterioration or denaturation, or loss of elastin and glycosaminoglycans. Biomechanical testing, however, showed that the cryopreserved DBP displayed a loss of extensibility compared to vitrified or freeze-dried scaffolds, which both displayed similar biomechanical behavior compared to non-preserved control scaffolds. In conclusion, cryopreservation altered the biomechanical behavior of the DBP scaffolds, which might lead to graft dysfunction in vivo. In contrast to cryopreservation and vitrification, freeze-drying is performed with non-toxic protective agents and does not require storage at ultra-low temperatures, thus allowing for a cost-effective and easy storage and transport. Due to these advantages, freeze-drying is a preferable method for the preservation of decellularized pericardium

Preservation strategies for decellularized pericardial scaffolds for off-the-shelf availability

© 2018 Decellularized biological scaffolds hold great promise in cardiovascular surgery. In order to ensure off-the-shelf availability, routine use of decellularized scaffolds requires tissue banking. In this study, the suitability of cryopreservation, vitrification and freeze-drying for the preservation of decellularized bovine pericardial (DBP) scaffolds was evaluated. Cryopreservation was conducted using 10% DMSO and slow-rate freezing. Vitrification was performed using vitrification solution (VS83) and rapid cooling. Freeze-drying was done using a programmable freeze-dryer and sucrose as lyoprotectant. The impact of the preservation methods on the DBP extracellular matrix structure, integrity and composition was assessed using histology, biomechanical testing, spectroscopic and thermal analysis, and biochemistry. In addition, the cytocompatibility of the preserved scaffolds was also assessed. All preservation methods were found to be suitable to preserve the extracellular matrix structure and its components, with no apparent signs of collagen deterioration or denaturation, or loss of elastin and glycosaminoglycans. Biomechanical testing, however, showed that the cryopreserved DBP displayed a loss of extensibility compared to vitrified or freeze-dried scaffolds, which both displayed similar biomechanical behavior compared to non-preserved control scaffolds. In conclusion, cryopreservation altered the biomechanical behavior of the DBP scaffolds, which might lead to graft dysfunction in vivo. In contrast to cryopreservation and vitrification, freeze-drying is performed with non-toxic protective agents and does not require storage at ultra-low temperatures, thus allowing for a cost-effective and easy storage and transport. Due to these advantages, freeze-drying is a preferable method for the preservation of decellularized pericardium. Statement of Significance: Clinical use of DBP scaffolds for surgical reconstructions or substitutions requires development of a preservation technology that does not alter scaffold properties during long-term storage. Conclusive investigation on adverse impacts of the preservation methods on DBP matrix integrity is still missing. This work is aiming to close this gap by studying three potential preservation technologies, cryopreservation, vitrification and freeze-drying, in order to achieve the off-the-shelf availability of DBP patches for clinical application. Furthermore, it provides novel insights for dry-preservation of decellularized xenogeneic scaffolds that can be used in the routine clinical cardiovascular practice, allowing the surgeon the opportunity to choose an ideal implant matching with the needs of each patient