A bidirectional approach to the synthesis of polypropionates: synthesis of C1-C13 fragment of zincophorin and related isomers

The structure-activity study of a bioactive natural product containing polypropionate subunits requires that its stereoisomers also be evaluated. Therefore, a general approach to synthesize these motifs is necessary. We describe herein the synthesis of the C1-C13 polypropionate subunit of zincophorin and isomers thereof using a two-reaction sequence: an aldol reaction using a mixture of tetrasubstituted enoxysilanes and a hydrogen-transfer reaction, both under Lewis acid control. Selection of the appropriate Lewis acid dictates the stereochemical outcome of these reactions. From a tactical standpoint, this study shows how a polypropionate sequence can be read and constructed in two directions, either the east-west or the west-east approaches. The choice of the optimal route is influenced by the number of complexation sites that can interfere in the aldol step under bidentate Lewis acid control.     

A C-glycoside route to leukotrienes

The stereospecific syntheses of three isomers of 7-hydroxy-5,6-epoxy heptanoic acid methyl ester, $\text{7}$, $\text{12b}$ and $\text{19}$, have been achieved via a $\text{C}$-glycoside route.     

Gas Chromatographic Fingerprint Analysis for the Comparison of Seized Cannabis Samples

Cannabis sativa L. is widely used as recreational illegal drugs. Illicit Cannabis profiling, comparing seized samples, is challenging due to natural Cannabis heterogeneity. The aim of this study was to use GC–FID and GC–MS herbal fingerprints for intra (within)- and inter (between)-location variability evaluation. This study focused on finding an acceptable threshold to link seized samples. Through Pearson correlation-coefficient calculations between intra-location samples, ‘linked’ thresholds were derived using 95% and 99% confidence limits. False negative (FN) and false positive (FP) error rate calculations, aiming at obtaining the lowest possible FP value, were performed for different data pre-treatments. Fingerprint-alignment parameters were optimized using Automated Correlation-Optimized Warping (ACOW) or Design of Experiments (DoE), which presented similar results. Hence, ACOW data, as reference, showed 54% and 65% FP values (95 and 99% confidence, respectively). An additional fourth root normalization pre-treatment provided the best results for both the GC–FID and GC–MS datasets. For GC–FID, which showed the best improved FP error rate, 54 and 65% FP for the reference data decreased to 24 and 32%, respectively, after fourth root transformation. Cross-validation showed FP values similar as the entire calibration set, indicating the representativeness of the thresholds. A noteworthy improvement in discrimination between seized Cannabis samples could be concluded.     

Electrochemical oxidation of La2CuO4 thin films grown by molecular beam epitaxy

Thin insulating and c-axis oriented films of La₂CuO₄ are grown using a molecular beam epitaxy technique. Subsequently, these films are oxidized electrochemically using a 1N KOH solution. This approach is used to induce superconductivity, leading to a maximum T_c0 of 31 K,, measured both resistively and inductively. The surface morphology, lattice constants and the resistivity before and after the electrochemical treatment are compared.     

Singular vectors of the Neveu-Schwarz algebra

We give an explicit expression for some singular vectors of highest weight representations of the Neveu-Schwarz algebra.     

Chromatographic behavior of mPEG-papaya proteinases conjugates examined on ion-exchange and hydrophobic gel media

The four cysteine proteinases, papain, chymopapain, caricain, and endoproteinase Gly-C were isolated and purified as the catalytically competent species from the commercially available latex of the tropical treeCarica papaya L. Their free thiol function (cysteine-25), which is essential for activity, was protected in the form of a mixed disulfide containing a 5 kDa polyethylene glycol (PEG) chain. The second (nonessential) free thiol function (cysteine-117) of chymopapain was blocked similarly. Caricain was also derivatized through acylation of its amino functions by PEG chains (average: 15 moles of PEG per mole of enzyme). The Chromatographic behavior of these conjugates was examined on ion-exchange and hydrophobic gels and compared to the Chromatographic behavior of the unpegylated proteinases. The results indicated that charge-shielding effects by PEG chain(s), surrounding the different proteinases, plays(play) a key role in the course of separation of pegylated and unpegylated species by ion-exchange chromatography. Similarly, PEG chain(s) is(are) able to mask hydrophobic regions on the surface of the proteinases. However, the affinity showed by PEG itself for the hydrophobic ligands immobilized on the matrix is the preponderant factor determining the behavior of the PEG-proteinases conjugates on Fractogel TSKButyl-650.     

Quantitative MRS study of Baló's concentric sclerosis lesions

Baló's concentric sclerosis (BCS) lesions display specific metabolite changes detected by magnetic resonance spectroscopy (MRS). We report on two cases of BCS lesions examined by MRS; the first case was evaluated 36 days after the onset of symptoms, whereas the second case was evaluated 9 days after the onset of symptoms. MRS data were obtained from single voxels located in the lesion and in the contralateral region. Relative to the creatine/phosphocreatine peak, BCS lesions displayed decreases of N-acetyl aspartate and increases of choline, myo-inositol (mI), glutamine/glutamate (Glx), lactate and lipid+macromolecule signals, in agreement with previous reports. In addition, previously unreported decreases of mI (-19% to -29%) and increases of Glx (+55% to +198%) were measured; these could be useful in characterizing BCS lesions.     

Chromatographic analysis of salicylic compounds in different species of the genus Salix

The separation of nine phenol glycosides--salicin, salicortin, 2'-acetylsalicortin, populin, tremulacin, salidroside, triandrin, picein and helicin--by normal phase (NP), reversed phase (RP) HPLC techniques and a coupling of NP and RP monolithic silica columns was studied. Among the above nine compounds only five--salicin, populin, tremulacin, salidroside and triandrin--were resolved in an NP system with a mobile phase comprising hexane/isopropanol/methanol (87:12:1, v/v/v). Optimized separation was performed with two coupled monolithic silica columns of different polarity (bare silica and RP-18). The method was applied to verify the presence of salicylic compounds and other phenolic derivatives in the bark of six species from the genus Salix, namely S. purpurea, S. daphnoides clone 1095, S. alba clone 1100, S. triandra, S. viminalis, and S. herbacea. Gradient elution with a mobile phase composed of acetonitrile and water containing 0.05% of trifluoroacetic acid, with increasing acetonitrile concentration from 3% to 48%, was chosen as optimal. For the selective detection of the salicylic compounds, an evaporative light scattering detector was employed along with a UV detector. The differences in the composition of phenols in the different plant materials were confirmed. Additionally, it must be emphasized that for the first time the presence of 2'-acetylsalicortin was revealed in S. alba clone 1100. Furthermore, an SPE-HPLC method was developed for the rapid analysis of the salicin content, analyzed as free and total fraction, in willow barks. The determined concentrations of total salicin varied from 25.4 mg/g in S. alba clone 1100 to 96.47 mg/g in S. daphnoides clone 1095.