Multivalent 1,2,3‐Triazole‐Linked Carbohydrate Mimetics by Huisgen–Meldal‐Sharpless Cycloadditions of an Azidopyran

Starting from an enantiopure 3‐azido‐substituted pyran derivative and various oligo‐alkynes a series of multivalent 1,2,3‐triazole‐linked carbohydrate mimetics was synthesized. The copper‐catalyzed Huisgen–Meldal‐Sharpless cycloaddition (CuAAC) served as key coupling reaction. Cu/C in the presence of triethylamine proved to be a good catalytic system in most cases. Tri‐, tetra‐, hexa‐, and octavalent compounds with typical rigid or flexible core units were prepared. The most complex compound contains a C60‐fullerene center leading to a dodecavalent carbohydrate mimetic. Only a few of the multivalent target compounds could be converted into pure O‐sulfated derivatives that are required for their evaluation as L‐ and P‐selectin ligands. Nevertheless, preliminary experiments suggest that the dodecavalent C60‐derived compound may be a promising ligand of these biologically important proteins with IC50 values in the low nanomolar range

Fortschritte in der Synthese von Aminopyran-basierten Kohlenhydratmimetika und deren Evaluation als Selektin-Inhibitoren

Ziel dieser Arbeit war die Darstellung neuer enantiomerenreiner multivalenter Kohlenhydratmimetika und die Evaluierung ihre Aktivität als potentielle Selektin-Inhibitoren. Der zentrale Baustein wurde ausgehend von einer zuvor etablierten Methode aus lithiiertem 2-(Trimethylsilyl)ethoxyallen und einem chiralen von D-Glyceraldehyd abgeleiteten Aldonitron synthetisiert. Das erhaltene 1,2-Oxazin wurde durch eine stereoselektive Lewis-Säure-induzierte Umlagerung in ein bicyclisches Keton umgewandelt, welches dann in zwei direkten Schritten in das Kohlenhydratmimetika übergeführt wurde: die Reduktion der Carbonyl-Gruppe und die anschließende Spaltung der N-Benzyl- und der N-O-Bindungen liefert ein Aminopyran. In der vorliegenden Arbeit wurden verschiedene Transformationen mit diesem Schlüsselbaustein durchgeführt, zum Beispiel die Darstellung des entsprechenden stabilen Azidopyrans durch Kupfer- katalysierten Diazotransfer. Durch die freie Aminogruppe und adequate Linker konnte eine Vielzahl von multivalenten Verbindungen durch Schotten-Baumann- Reaktion oder durch reduktive Aminierung dargestellt werden. Zusätzlich wurden unter verschiedenen Reaktionsbedingungen der Huisgen-Meldal-Sharpless-Reaktion Verbindungen mit unterschiedlichem Grad an Multivalenz synthetisiert. Dabei wurden verschiedene Aspekte zum Einfluss auf multivalente Bindungen in Betracht gezogen, zum Beispiel Linkerlänge, Symmetrie und die Anzahl der Pyran-Liganden. Als letzten und anspruchsvollsten Schritt wurden einige der Kohlenhydratmimetika erfolgreich polysulfatiert und dann mit oder ohne Sulfatgruppen in Surface-Plasmon-Resonance- (SPR) Inhibitions-Untersuchungen als Selektin Inhibitoren getestet. Die untersuchten Verbindungen zeigten IC50-Werte im mikro- bis nanomolarem Bereich (für L- und P-Selektin), was viel versprechende Ergebnisse für niedervalente Konjugate sind. Zusammenfassend wurde eine direkte Syntheseroute für neue multivalente Kohlenhydratmimetika verwirklicht und erste Resultate der SPR-Inhibitions-Untersuchungen gaben Hinweise für die weitere Entwicklung von Selektin-Inhibitoren.The aim of this dissertation was the development of new enantiopure multivalent carbohydrate mimetics and their study as potential selectin inhibitors. The main building blocks have been synthetized following a previously established synthetic route, starting from lithiated 2-(trimethylsilyl)ethoxyallene and a chiral D-glyceraldehyde-derived aldonitrone. The obtained 1,2-oxazine undergoes a stereoselective Lewis acid- promoted rearrangement leading to a bicyclic ketone which can be transformed into the corresponding carbohydrate mimetic with two straightforward steps: reduction of the carbonyl group followed by the cleavage of the N-benzyl and N-O bonds leads to an enantiopure aminopyran derivative. In the present work several transformations were made from this key building block including the conversion to the corresponding stable azidopyran prepared by a copper- catalyzed diazotransfer. Using the amino group and choosing adequate linkers, a library of multivalent compounds was prepared via Schotten-Baumann reaction or reductive amination. Additionally, different conditions for the Huisgen- Sharpless-Meldal cycloaddition were used to synthesize carbohydrate mimetics with different degrees of multivalency. In this approach, aspects that can influence multivalency binding were considered as linker length, symmetry and number of pyran ligands. As final and most challenging step, some of the obtained carbohydrate mimetics could successfully be polysulfated and tested with and without sulfate groups in a surface plasmon resonance (SPR) inhibition assay as potential selectin inhibitors. The tested compounds showed IC50 values from micro- to nanomolar range (for L- and P-selectin), which are promising results for such conjugates. Overall, a straightforward synthetic route towards new multivalent carbohydrate mimetics was developed and the first results were obtained from the SPR inhibition assays providing some leads to further development of selectin inhibitors

Desenvolvimento de uma metodologia inovadora para a síntese de 2-C-alcenos a partir de 3-cetoaçúcares

Tese de mestrado em Química (Química, Saúde e Nutrição), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2008Neste trabalho foi investigado um método novo, simples e directo para a síntese de 2-desoxi-2-C-(etoxicarbonil) metilenoaçúcares. Será apresentada e discutida uma estratégia para sintetizar compostos deste tipo partindo de 3-cetoaçúcares, com bons rendimentos, utilizando uma reacção de Wittig com o reagente estabilizado por ressonância [(etoxicarbonil) metileno] trifenilfosforano, em acetonitrilo sob refluxo. Foi ainda desenvolvido um método geral para a oxidação de 3-cetoaçúcares utilizando PDC e anidrido acético, que ocorrem entre 5 e 15 minutos com rendimentos compreendidos entre 91 % e 94%. Partindo de -D-glucopiranósido de metilo (16) sintetizaram-se 3-cetoaçúcares acilados na posição 2 e protegidos distintamente nas restantes posições. Estes compostos foram submetidos à reacção de Wittig, dando origem a produtos de Wittig em C-2, com rendimentos entre 62% e 89%, sendo formado exclusivamente o isómero (Z). Numa segunda fase deste trabalho investigaram-se as mesmas condições reaccionais partindo de -D-galactopiranósido de metilo (24). Após protecção das posições 4,6 com o grupo benzilideno e acilação da posição 2, foi sintetizado o 3- cetoaçucar 60 e o 2-cetoaçúcar 61, que após reacção de Wittig conduziram ambos à formação do derivado 3-desoxi-3-C-[(etoxicarbonil)metileno]-D-xilo-hexopiranósido de metilo 62, sendo o único produto formado na reacção de 60 com 79% de rendimento, e o produto maioritário da mistura obtida na reacção de 61, que também contém o açúcar com ramificação em C-2 63 numa proporção de 1:0,7. O rendimento desta reacção foi de 68% . Foi feita a elucidação estrutural de todos os compostos recorrendo a espectros de 1H-NMR e 13C-NMR, e ainda aos espectros de correlação COSY, HMQC, e NOESY, sempre que necessário.In this work an easy and straightforward synthesis of 2-deoxy-2-C- (ethoxycarbonyl) methylene sugar derivatives will be investigated. We present herein a very simple strategy to synthesize this type of compounds starting from 3-keto sugars in good yield, using a Wittig reaction with the resonance stabilized reagent [(ethoxycarbonyl) methylene] triphenylphosphorane and acetonitrile as solvent, under reflux. It was also developed a general oxidation procedure leading to 3-keto sugars using PDC and acetic anhydride, with reaction times between 5 and 15 minutes, and yields between 91% and 94%. 3-Keto sugars acylated at position 2 fully protected with different groups were synthesized starting from methyl α-D-glucopyranoside (16). The Wittig reaction was carried out and Wittig products at C-2 with yields between 62% and 89% were formed. The isomer obtained was exclusively the (Z)-isomer. In a second phase of this study the same reaction conditions were investigated for compounds prepared from methyl α-D-galactopyranside (24). After protection of positions 4,6 with benzylidene and acylation at position 2, the 3-keto sugar 60 and the 2-keto sugar 61 were synthesized. The Wittig product obtained by reaction of either 60 or 61 was 3-deoxy-3-C-[(ethoxycarbonyl)methylene]-D-xylo-hexopyranoside 62, being this the single product formed in reaction of 60, isolated in 79% yield, and the major product in the reaction of 61, in which also the Wittig product in C-2 63 was formed, in the ratio 62:63 = 1:0,7. The yield of this reaction was 68%. All compounds were fully characterized by 1H-NMR, 13C-NMR, and also by COSY, HMQC, and NOESY, when necessary

Synthesis of multivalent carbohydrate mimetics with aminopolyol end groups and their evaluation as L-selectin inhibitors

In this article a series of divalent and trivalent carbohydrate mimetics on the basis of an enantiopure aminopyran and of serinol is described. These aminopolyols are connected by amide bonds to carboxylic acid derived spacer units either by Schotten–Baumann acylation or by coupling employing HATU as reagent. The O-sulfation employing the SO3·DMF complex was optimized. It was crucial to follow this process by 700 MHz 1H NMR spectroscopy to ensure full conversion and to use a refined neutralization and purification protocol. Many of the compounds could not be tested as L-selectin inhibitor by SPR due to their insolubility in water, nevertheless, a divalent and a trivalent amide showed surprisingly good activities with IC50 values in the low micromolar range

The surgical safety checklist and patient outcomes after surgery: a prospective observational cohort study, systematic review and meta-analysis

© 2017 British Journal of Anaesthesia Background: The surgical safety checklist is widely used to improve the quality of perioperative care. However, clinicians continue to debate the clinical effectiveness of this tool. Methods: Prospective analysis of data from the International Surgical Outcomes Study (ISOS), an international observational study of elective in-patient surgery, accompanied by a systematic review and meta-analysis of published literature. The exposure was surgical safety checklist use. The primary outcome was in-hospital mortality and the secondary outcome was postoperative complications. In the ISOS cohort, a multivariable multi-level generalized linear model was used to test associations. To further contextualise these findings, we included the results from the ISOS cohort in a meta-analysis. Results are reported as odds ratios (OR) with 95% confidence intervals. Results: We included 44 814 patients from 497 hospitals in 27 countries in the ISOS analysis. There were 40 245 (89.8%) patients exposed to the checklist, whilst 7508 (16.8%) sustained ≥1 postoperative complications and 207 (0.5%) died before hospital discharge. Checklist exposure was associated with reduced mortality [odds ratio (OR) 0.49 (0.32–0.77); P\u3c0.01], but no difference in complication rates [OR 1.02 (0.88–1.19); P=0.75]. In a systematic review, we screened 3732 records and identified 11 eligible studies of 453 292 patients including the ISOS cohort. Checklist exposure was associated with both reduced postoperative mortality [OR 0.75 (0.62–0.92); P\u3c0.01; I2=87%] and reduced complication rates [OR 0.73 (0.61–0.88); P\u3c0.01; I2=89%). Conclusions: Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine

Prospective observational cohort study on grading the severity of postoperative complications in global surgery research

Background The Clavien–Dindo classification is perhaps the most widely used approach for reporting postoperative complications in clinical trials. This system classifies complication severity by the treatment provided. However, it is unclear whether the Clavien–Dindo system can be used internationally in studies across differing healthcare systems in high- (HICs) and low- and middle-income countries (LMICs). Methods This was a secondary analysis of the International Surgical Outcomes Study (ISOS), a prospective observational cohort study of elective surgery in adults. Data collection occurred over a 7-day period. Severity of complications was graded using Clavien–Dindo and the simpler ISOS grading (mild, moderate or severe, based on guided investigator judgement). Severity grading was compared using the intraclass correlation coefficient (ICC). Data are presented as frequencies and ICC values (with 95 per cent c.i.). The analysis was stratified by income status of the country, comparing HICs with LMICs. Results A total of 44 814 patients were recruited from 474 hospitals in 27 countries (19 HICs and 8 LMICs). Some 7508 patients (16·8 per cent) experienced at least one postoperative complication, equivalent to 11 664 complications in total. Using the ISOS classification, 5504 of 11 664 complications (47·2 per cent) were graded as mild, 4244 (36·4 per cent) as moderate and 1916 (16·4 per cent) as severe. Using Clavien–Dindo, 6781 of 11 664 complications (58·1 per cent) were graded as I or II, 1740 (14·9 per cent) as III, 2408 (20·6 per cent) as IV and 735 (6·3 per cent) as V. Agreement between classification systems was poor overall (ICC 0·41, 95 per cent c.i. 0·20 to 0·55), and in LMICs (ICC 0·23, 0·05 to 0·38) and HICs (ICC 0·46, 0·25 to 0·59). Conclusion Caution is recommended when using a treatment approach to grade complications in global surgery studies, as this may introduce bias unintentionally

Critical care admission following elective surgery was not associated with survival benefit:prospective analysis of data from 27 countries

Purpose: As global initiatives increase patient access to surgical treatments, there is a need to define optimal levels of perioperative care. Our aim was to describe the relationship between the provision and use of critical care resources and postoperative mortality. Methods: Planned analysis of data collected during an international 7-day cohort study of adults undergoing elective in-patient surgery. We used risk-adjusted mixed-effects logistic regression models to evaluate the association between admission to critical care immediately after surgery and in-hospital mortality. We evaluated hospital-level associations between mortality and critical care admission immediately after surgery, critical care admission to treat life-threatening complications, and hospital provision of critical care beds. We evaluated the effect of national income using interaction tests. Results: 44,814 patients from 474 hospitals in 27 countries were available for analysis. Death was more frequent amongst patients admitted directly to critical care after surgery (critical care: 103/4317 patients [2%], standard ward: 99/39,566 patients [0.3%]; adjusted OR 3.01 [2.10–5.21]; p < 0.001). This association may differ with national income (high income countries OR 2.50 vs. low and middle income countries OR 4.68; p = 0.07). At hospital level, there was no association between mortality and critical care admission directly after surgery (p = 0.26), critical care admission to treat complications (p = 0.33), or provision of critical care beds (p = 0.70). Findings of the hospital-level analyses were not affected by national income status. A sensitivity analysis including only high-risk patients yielded similar findings. Conclusions: We did not identify any survival benefit from critical care admission following surgery