Enantioselective synthesis of (10S)- and (10R)-methyl-anandamides

For the development of novel endocannabinoid templates with potential resistance to hydrolytic and oxidative metabolism, we are targeting the bis-allylic carbons of the arachidonoyl skeleton. Toward this end, we recently disclosed the synthesis and preliminary biological data for the (13S)-methyl-anandamide. We report now the total synthesis of the (10S)- and (10R)-methyl-counterparts. Our synthetic approach is stereospecific, efficient, and provides the analogs without the need for resolution. Peptide coupling, P-2 nickel partial hydrogenation, and cis-selective Wittig olefination are the key steps.     

Numerical Simulation of Turbulent Flow and Heat Transfer in a Three-Dimensional Channel Coupled with Flow Through Porous Structures

This study investigates numerically the turbulent flow and heat transfer characteristics of a T-junction mixing, where a porous media flow is vertically discharged in a 3D fully developed channel flow. The fluid equations for the porous medium are solved in a pore structure level using an Speziale, Sarkar and Gatski turbulence model and validated with open literature data. Overall, two types of porous structures, consisted of square pores, are investigated over a wide range of Reynolds numbers: an in-line and a staggered pore structure arrangement. The flow patterns, including the reattachment length in the channel, the velocity field inside the porous medium as well as the fluctuation velocity at the interface, are found to be strongly affected by the velocity ratio between the transversely interacting flow streams. In addition, the heat transfer examination of the flow domain reveals that the temperature distribution in the porous structure is more uniform for the staggered array. The local heat transfer distributions inside the porous structure are also studied, and the general heat transfer rates are correlated in terms of area-averaged Nusselt number accounting for the effects of Reynolds number, velocity ratio as well as the geometrical arrangement of the porous structures.     

Statics and dynamics of 2D colloidal crystals in a random pinning potential

We report the first experimental study of a model system of a two-dimensional colloidal crystal in a random pinning potential. The colloidal crystal consists of monodispersed charged polystyrene microspheres suspended in deionized aqueous media and confined near a rough charged surface. It is found that the static orientational correlation function g6(r) decays exponentially for intermediate and strong pinning, in agreement with theories. The driven depinning is dominated by thermally activated creep motion along 1D-like channels between regions with short-range order. A coexistence model is proposed for describing the observations.     

A chiral phosphazane reagent strategy for the determination of enantiomeric excess of amines

Methods for measuring enantiomeric excess (ee) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which is reacted with the mixture of enantiomers under investigation. However, these CDAs have almost exclusively been based on carbon frameworks, which are generally costly and/or difficult to prepare. In this work, a methodology based on the readily prepared inorganic cyclodiphosph(iii)azane CDA ClP(μ-N^tBu)₂POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be highly effective in the measurement of ee’s of chiral amines, involving in situ reaction of the chiral amines (R*NH₂) with the P–Cl bond of the CDA followed by quaternization of the phosphorus framework with methyl iodide. This results in sharp ³¹P NMR signals with distinct chemical shift differences between the diastereomers that are formed, which can be used to obtain the ee directly by integration. Spectroscopic, X-ray structural and DFT studies suggest that the NMR chemical shift differences between diastereomers is steric in origin, with the sharpness of these signals resulting from conformational locking of the bornyl group relative to the P₂N₂ ring induced by the presence of the P(v)-bonded amino group (R*NH). This study showcases cheap inorganic phosphazane CDAs as simple alternatives to organic variants for the rapid determination of ee.

The simple inorganic cyclodiphosph(iii)azane chiral derivatisation agent ClP(μ-^tBuN)₂POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of ee’s of chiral amines using ³¹P NMR spectroscopy.     

Nonlinear constitutive force model selection,update and uncertainty quantification for periodically sequential impact applications

Nonlinear Dynamics - Contact–impact events frequently occur between solid contact interfaces in complex dynamic mechanical systems and engineering applications. Impact force models are used...     

Synthesis of esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone

The esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone were prepared by reaction of urea with the esters of 2-hydroxy-2-phosphinylethanal in acidic medium. The ir, ¹H nmr and ³¹P nmr spectral data of the products are reported. All the isolated products had cis configuration. The stereochemistry of their formation is discussed.     

Studies toward diazonamide A: initial synthetic forays directed toward the originally proposed structure

A brief introduction into the chemistry of diazonamide A (1) is followed by first-generation sequences to access the originally proposed structure for this unusual marine natural product. These explorations identified a route capable of delivering a model compound possessing the complete heteroaromatic core of the natural product, highlighting in the process several unanticipated synthetic challenges which led both to new methodology as well as an improved synthetic plan that was successfully applied to fully functionalized intermediates.     

Studies toward diazonamide A: development of a hetero-pinacol macrocyclization cascade for the construction of the bis-macrocyclic framework of the originally proposed structure

In this article, we describe further studies toward the originally proposed structure of diazonamide A (1). After confronting a number of failures in synthesizing the heterocyclic core of that structure, success was finally realized through the development of a novel hetero-pinacol-based macrocyclization cascade sequence. Subsequent elaboration led to an advanced compound bearing both of the 12-membered rings of the target molecule. In addition, preliminary biological studies with intermediates and simplified analogues obtained via the developed sequences are also described.     

Interactions of complementary PEGylated liposomes and characterization of the resulting aggregates

The interaction of complementary liposomes bearing both recognizable and protective ligands at their external surface has been investigated. Aggregation of hydrogenated phosphatidyl choline/cholesterol (2:1 molar ratio) based liposomes was mediated by the molecular recognition of the complementary phosphate and guanidinium groups incorporated in separate unilamellar liposomes. The phosphate group was incorporated in the bilayer employing dihexadecyl phosphate, while the guanidinium moiety was introduced in the membrane through the incorporation of various guanidinium lipids. For the latter, anchoring ability and primarily introduction of a spacer group between their lipophilic part and the guanidinium group was found to affect the ability for molecular recognition. Also, poly(ethylene glycol) (PEG) introduced in both types of liposomes at various concentrations and up to 15% with respect to cholesterol modifies the interaction effectiveness and morphology of the obtained aggregates. Interaction of these complementary liposomes leads to large precipitating aggregates or fused liposomes, as shown by phase contrast microscopy and dynamic light scattering. Specifically, fusion of liposomes takes place under a nonleaking process involving lipid mixing, as demonstrated by calcein entrapment and resonance energy transfer experiments. Calorimetric parameters also correlate with the processes of aggregation and fusion. The interactions of non-PEGylated liposomes involve exothermic processes of higher enthalpic content than those of the PEGylated counterparts.