C-3 β-lactam carbocation equivalents: versatile synthons for C-3 substituted β-lactams

An efficient and operationally simple strategy for the synthesis of differently C-3 monosubstituted (9) and disubstituted (10) monocyclic β-lactams is described. This involves reaction of β-lactam carbocation equivalents (8) with an active aromatic, aliphatic and heterocyclic substrates in the presence of a Lewis acid.     

Hydrazone- and hydrazide-containing N-substituted glycines as peptoid surrogates for expedited library synthesis: application to the preparation of Tsg101-directed HIV-1 budding antagonists

Replacing the Pro6 in the p6(Gag)-derived 9-mer "P-E-P-T-A-P-P-E-E" with N-substituted glycine (NSG) residues is problematic. However, incorporation of hydrazone amides ("peptoid hydrazones") can be readily achieved in library fashion. Furthermore, reduction of these hydrazones to N-substituted "peptoid hydrazides" affords a facile route to library diversification. This approach is demonstrated by application to Tsg101-binding compounds designed as potential HIV budding antagonists. [reaction: see text]     

Sodium dodecyl sulfate-poly(amidoamine) interactions studied by AFM imaging, conductivity, and Krafft temperature measurements

The conductivity, kappa, and Krafft temperature, TK, of sodium dodecyl sulfate (SDS) with poly(amidoamine) dendrimers (PAMAM) of 0.0, 0.5, and 1.0 generations (G) have been determined at different surfactant as well as PAMAM concentrations. The critical micelle concentration of SDS increases with the increase in the amount of each generation and the additive effect of 0.5G is maximum. TK of SDS shows a systematic decrease with maximum reduction in the presence of 0.5G. Atomic force microscopy (AFM) captures a layered pattern of 1.0G in the form of nanorods and no AFM images are detected for 1.0G in the presence of SDS. All results demonstrate that SDS has favorable interactions with ester-terminated 0.5G PAMAM rather than amine-terminated 0.0G and 1.0G.     

Asymptotic Normality of a Combined Regression Estimator

In this paper, we propose a combined regression estimator by using a parametric estimator and a nonparametric estimator of the regression function. The asymptotic distribution of this estimator is obtained for cases where the parametric regression model is correct, incorrect, and approximately correct. These distributional results imply that the combined estimator is superior to the kernel estimator in the sense that it can never do worse than the kernel estimator in terms of convergence rate and it has the same convergence rate as the parametric estimator in the case where the parametric model is correct. Unlike the parametric estimator, the combined estimator is robust to model misspecification. In addition, we also establish the asymptotic distribution of the estimator of the weight given to the parametric estimator in constructing the combined estimator. This can be used to construct consistent tests for the parametric regression model used to form the combined estimator.     

Metalation of Biginelli compounds. A general unprecedented route to C-6 functionalized 4-aryl-3,4-dihydropyrimidinones

4-Aryl-6-methyl-3,4-dihydro-2(1H)-pyrimidinone esters (DHPMs) readily undergo metalation at the C-6 methyl (vinylogous ester) position on treatment with lithium diisopropylamide at -10 degrees C. The resulting anion intermediates can be treated with electrophilic reagents to afford functionalized DHPMs that have been chemically elaborated mainly at the C-6 position. Di- and trianion formation is also possible at both the vinylogous methyl and NH positions when reactions are performed with excess equivalents of the base.     

Substituted diaryldiazomethanes and diazofluorenes: structure, reactivity and stability

The synthesis of several substituted diaryldiazomethanes and diazofluorenes, and an assessment of their structure, reactivity and stability, is reported.     

Gold nanoparticles catalyzed chemiluminescence immunoassay for detection of herbicide 2,4-dichlorophenoxyacetic acid

We present a novel immunoassay format utilizing the catalytic properties of gold nanoparticles in the luminol-silver nitrate-gold nanoparticle based chemiluminescence (CL) system for the detection of widely used herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Highly sensitive anti-2,4-D antibody was produced and conjugated with gold nanoparticles of various sizes. In the present assay format, employing a competitive inhibition approach, a well-characterized hapten-protein conjugate (2,4-D-BSA) was used to coat the microtiter plates. The analyte (2,4-D) was pre-incubated with anti-2,4-D antibody labeled with gold nanoparticles and added to each well of the microtiter plate. The gold label triggered the reaction between luminol and silver nitrate generating a luminescence signal at 425 nm. Under the optimized conditions, the CL based immunoassay showed the detection limit of 2,4-D in standard water samples around 3 ng mL(-1). The CL based immunoassay format, based on gold nanoparticles as a catalyst, could be used as a fast screening methodology (<30 min) for pesticide detection.     

Convenient Preparation of Benzylseleno‐ and Phenylselenoalkanoic Acids: Reagents for Synthesis of Organoselenium Compounds

An efficient and operationally simple route to benzylseleno‐ and phenylselenoalkanoic acids from ethyl benzyl/phenylselenoalkanoates is described. This involves preparation of ethyl benzyl/phenylselenoalkanoates as substrates by reaction of dibenzyl/diphenyl diselenide and sodium borohydride with ethyl chloroalkanoates in ethanol followed by basic hydrolysis and subsequent acidification.     

Catalytic Asymmetric Synthesis of Alkynyl Aziridines: Both Enantiomers of cis‐Aziridines from One Enantiomer of the Catalyst

Alkynyl aziridines can be obtained from the catalytic asymmetric aziridination (AZ reaction) of alkynyl imines with diazo compounds in high yields and high asymmetric inductions mediated by a chiral boroxinate or BOROX catalyst. In contrast to the AZ reaction with aryl‐ and alkyl‐substituted imines, alkynyl imines react to give cis‐substituted aziridines with both diazo esters and diazo acetamides. Remarkably, however, the two diazo compounds give different enantiomers of the cis‐aziridine from the same enantiomer of the catalyst. Theoretical considerations of the possible transition states for the enantiogenic step reveal that the switch in enantiomers results from a switch from Si‐face to Re‐face addition to the imine, which in turn is related to a switch from reaction with an E‐imine in the former and a Z‐isomer of the imine in the latter.