One-pot ligation strategy for atypical ubiquitin chains synthesis by using the trifluoroacetamidomethyl-protected isopeptide-linked Ub (Tfacm-isoUb) unit

Protein chemical synthesis can provide the homogeneous atypical ubiquitin chains that are usually difficult to obtain by other methods. Herein, we report a new one-pot ligation approach for the synthesis of atypical Ub chains based on the Tfacm-protected isoUb building block with operational simplicity and high efficiency. The key intermediate, the Tfacm-protected isoUb building block can be readily prepared by Fmoc SPPS. The practicality and efficiency of the new method is demonstrated by the successful preparation of K11-linked di-Ub.     

Clustering Multivariate Longitudinal Observations: The Contaminated Gaussian Hidden Markov Model

The Gaussian hidden Markov model (HMM) is widely considered for the analysis of heterogenous continuous multivariate longitudinal data. To robustify this approach with respect to possible elliptical heavy-tailed departures from normality, due to the presence of outliers, spurious points, or noise (collectively referred to as bad points herein), the contaminated Gaussian HMM is here introduced. The contaminated Gaussian distribution represents an elliptical generalization of the Gaussian distribution and allows for automatic detection of bad points in the same natural way as observations are typically assigned to the latent states in the HMM context. Once the model is fitted, each observation has a posterior probability of belonging to a particular state and, inside each state, of being a bad point or not. In addition to the parameters of the classical Gaussian HMM, for each state we have two more parameters, both with a specific and useful interpretation: one controls the proportion of bad points and one specifies their degree of atypicality. A sufficient condition for the identifiability of the model is given, an expectation-conditional maximization algorithm is outlined for parameter estimation and various operational issues are discussed. Using a large-scale simulation study, but also an illustrative artificial dataset, we demonstrate the effectiveness of the proposed model in comparison with HMMs of different elliptical distributions, and we also evaluate the performance of some well-known information criteria in selecting the true number of latent states. The model is finally used to fit data on criminal activities in Italian provinces. Supplementary materials for this article are available online     

CLASSIFICATION OF INFINITE DIMENSIONAL WEIGHT MODULES OVER THE LIE SUPERALGEBRA sl(2/1)

We give a complete classification of infinite dimensional indecomposable weight modules over the Lie superalgebra sl(2/1).     

A Note on Restricted Representations of the Witt Superalgebras

Let F be an algebraically closed field of prime characteristic p 〉 3, and W（n） the Witt superalgebra over F, which is the Lie superalgebra of superderivations of the Grassmann algebra in n indeterminates. The dimensions of simple atypical modules in the restricted supermodule category for W（n） are precisely calculated in this paper, and thereby the dimensions of all simple modules can be precisely given. Moreover, the restricted supermodule category for W（n） is proved to have one block.     

Isolation and characterization of process related impurities of olanzapine using HPLC and ESI-MS/MS

An RP-HPLC method for the simultaneous separation and determination of olanzapine (OLZ) and its process impurities in bulk drugs and pharmaceutical formulations was developed. The separation was accomplished on Inertsil ODS 3V (4.6 mm x 250 mm; particle size 5 microm) column using 0.2 M ammonium acetate (pH = 4.50) and ACN as mobile phase in gradient elution mode. The analytes were monitored by a photo diode array (PDA) detector set at 254 nm and the flow rate was kept at 1.0 mL/min. The chromatographic behavior of all the compounds was examined under variable compositions of different solvents, buffer concentrations, and pH. The method was validated in terms of accuracy, precision, and linearity. Four unknown process impurities observed consistently during the analysis of different batches of OLZ were isolated and characterized by ESI-MS/MS, (1)H NMR, and FT-IR. The proposed RP-HPLC method was successfully applied to the analysis of commercial formulations. The method could be of use not only for rapid and routine evaluation of the quality of OLZ in bulk drug manufacturing units but also for the detection of its impurities in pharmaceutical formulations.     

Acid-sensitive auxiliary assisted atypical diubiquitin synthesis exploiting thiol-ene coupling

Atypical ubiquitin (Ub) chains are generally involved in intracellular physiological processes, while the molecular mechanisms underlying their regulation remain unclear. In this work, we report an acid-sensitive auxiliary group based bifunctional handle that can prepare Lys27-, Lys29- and Lys33-diUb analogs by thiol-ene coupling (TEC) in combination with native chemical ligation (NCL). A prominent advantage of this method is the rapid and effective removal of acid-sensitive auxiliary groups after the formation of the isopeptide bond mimic. Collectively, this work illustrates the utility of the new strategy in the simple and efficient production of homogeneous atypical diUb analogs for biochemical and biophysical studies.     

Discussion

Abstract

Visualization is increasingly being recognized as an effective and efficient way not only to communicate patterns in scientific data, but to discover them as well. In the low dimensions of everyday experience, the human ability to find meaningful order in noisy data may never be matched by automatons. So the introduction of a useful visualization procedure, as provided here by Furnas and Buja, is indeed a welcome development. They show that low-dimensional patterns extracted by a combined projection and section operation (a prosection) can imply the existence of similar higher-dimensional structure. In exploratory or inductive data analyses, then, prosections could be used to generate hypotheses about relationships between sampled variables. However, the familiar curse of dimensionality may confine their practical application to point clouds of only moderate dimension.     

New synthetic approach to atypical retinoids: application of a versatile annulation procedure

A new approach to an atypical retinoid is presented. The C₁₅ skeleton was built up by exploiting a step-by-step sequence: the C₉ fragment of an intermediate was homologated by reaction with a C₄ phosphorane, and then submitted to a benzannulation reaction. The last two carbon atoms were inserted by a Wittig reaction with the C₂ phosphorane of ethyl bromoacetate. Manipulation of functional groups was then performed.     

An instance of temperature-dependent elution order of enantiomers from a chiral brush-type HPLC column

Typically, reduction of column temperature increases the enantioselectivity of a chiral stationary phase. An instance in which progressive reduction of temperature initially reduces enantioselectivity, then inverts the elution order of the enantiomers, and finally causes enantioselectivity to increase has been observed. This behavior is related to the nature and concentration of the polar modifier in the mobile phase, and requires particular chiral phase-analyte-mobile phase combinations. A rationalization is presented as to the possible origin of this behavior. This rationale may aid in finding other examples of this temperature-dependent elution order of enantiomers and ultimately increase our understanding of chiral recognition processes.