New Strategies for Organic Catalysis: The First Enantioselective Organocatalytic 1,3-Dipolar Cycloaddition

Our laboratory has been engaged in the design of broadly useful new strategies for enantioselective catalysis that utilize organic chemicals as reaction catalysts. In our recent study, we reported that the LUMO-lowering activation of α,β-unsaturated aldehydes using the reversible formation of iminium ions with chiral imidazolidinones 1 (eq 1) is a valuable platform for the development of enantioselective organocatalytic Diels−Alder reactions (eq 2). In this work, we reveal that this catalytic strategy is also amenable to [3 + 2] cycloadditions between nitrones and α,β-unsaturated aldehydes to provide isoxazolidines (eq 3), useful synthons for the construction of biologically important amino acids, β-lactams, amino carbohydrates, and alkaloids. To our knowledge, this is the first example of an organocatalytic 1,3-dipolar cycloaddition. Moreover, this study further documents that chiral amines can be employed as asymmetric catalysts for a range of transformations that traditionally utilize metal salts

Rare variants in tenascin genes in a cohort of children with primary vesicoureteric reflux

Primary vesicoureteral reflux (PVUR) is the most common malformation of the kidney and urinary tract and reflux nephropathy is a major cause of chronic kidney disease in children. Recently, we reported mutations in tenascin XB (TNXB) as a cause of PVUR with joint hypermobility

A new algorithm for computing distance matrix and Wiener index of zig-zag polyhex nanotubes

The Wiener index of a graph G is defined as the sum of all distances between distinct vertices of G. In this paper an algorithm for constructing distance matrix of a zig-zag polyhex nanotube is introduced. As a consequence, the Wiener index of this nanotube is computed

A simple device for studying macromolecular crystals under moderate gas pressures (0.1-10 MPa)

A simple device for studying crystalline samples under moderate gas pressure (0.1-10 MPa) has been developed. The device employs a modified Cajon ultra-torr fitting to ensure a gas-tight seal around an X-ray capillary. The cell accommodates standard X-ray capillaries that require no modification. The device is straightforward to utilize and samples can be mounted with routine techniques and pressurized in a matter of seconds. In a subsequent development, a complete purging and pressurization system has been designed and constructed for use on beamline 7-1 at the Stanford Synchrotron Radiation Laboratory. This paper describes the construction of both the pressure cell and the delivery system and presents results of the use of this cell for the preparation of xenon derivatives to be used in phase determination by the multiple isomorphous replacement method

Machine Learning in Automated Text Categorization

The automated categorization (or classification) of texts into predefined categories has witnessed a booming interest in the last ten years, due to the increased availability of documents in digital form and the ensuing need to organize them. In the research community the dominant approach to this problem is based on machine learning techniques: a general inductive process automatically builds a classifier by learning, from a set of preclassified documents, the characteristics of the categories. The advantages of this approach over the knowledge engineering approach (consisting in the manual definition of a classifier by domain experts) are a very good effectiveness, considerable savings in terms of expert manpower, and straightforward portability to different domains. This survey discusses the main approaches to text categorization that fall within the machine learning paradigm. We will discuss in detail issues pertaining to three different problems, namely document representation, classifier construction, and classifier evaluation.Comment: Accepted for publication on ACM Computing Survey

Molecular basis of Lys11-polyubiquitin specificity in the deubiquitinase Cezanne

The post-translational modification of proteins with polyubiquitin regulates virtually all aspects of cell biology. Eight distinct chain linkage types in polyubiquitin co-exist and are independently regulated in cells. This ‘ubiquitin code’ determines the fate of the modified protein1. Deubiquitinating enzymes of the Ovarian Tumour (OTU) family regulate cellular signalling by targeting distinct linkage types within polyubiquitin2, and understanding their mechanisms of linkage specificity gives fundamental insights into the ubiquitin system. We here reveal how the deubiquitinase Cezanne/OTUD7B specifically targets Lys11-linked polyubiquitin. Crystal structures of Cezanne alone and in complex with mono- and Lys11-linked diubiquitin, in combination with hydrogen-deuterium exchange mass spectrometry, enable reconstruction of the enzymatic cycle in exquisite detail. An intricate mechanism of ubiquitin-assisted conformational changes activate the enzyme, and while all chain types interact with the enzymatic S1 site, only Lys11-linked chains can bind productively across the active site and stimulate catalytic turnover. Our work highlights the fascinating plasticity of deubiquitinases, and indicates that new conformational states can occur when a true substrate, such as diubiquitin, is bound at the active site

Aggressive treatment of metastatic squamous cell carcinoma of the rectum to the liver: a case report and a brief review of the literature

BACKGROUND: Rectal squamous cell carcinoma (SCC) is a rare tumor. The incidence of this malignancy has been reported to be 0.25 to 1 per 1000 colorectal carcinomas. From a review of the English literature 55 cases of SCC of the rectum have been published. In this study we report a rectal metastatic SCC to the liver, discussing the efficacy of aggressive adjuvant and neo-adjuvant therapies on survival and prognosis. CASE PRESENTATION: A 39-year-old female patient with a pure SCC of the rectum diagnosed endoscopically is presented. The patient underwent initially neoadjuvant chemo-radiotherapy and then abdominoperineal resection with concomitant bilateral oophorectomy and hysterectomy, followed by adjuvant chemo-radiotherapy. Five months after the initial operation liver metastasis was demonstrated and a liver resection was carried out, followed by adjuvant chemotherapy. Eighteen months after the initial operation the patient is alive. CONCLUSION: Although prognosis of rectal SCC is worse than that of adenocarcinoma, an aggressive therapeutic approach with surgery as the primary treatment, followed by combined neo- and adjuvant chemo-radiotherapy, may be necessary in order to improve survival and prognosis