A concise synthesis of (+)-artemisinin

Malaria represents one of the most medically and economically debilitating diseases present in the world today. Fortunately, there exists a highly effective treatment based on the natural product artemisinin. Despite the development of several synthetic approaches to the natural product, a streamlined synthesis that utilizes low-cost chemical inputs has yet to materialize. Here we report an efficient, cost-effective approach to artemisinin. Key to the success of the strategy was the development of mild, complexity-building reaction cascades that allowed the use of readily available, affordable cyclohexenone as the key starting material.     

Photophysical and computational investigations of bis(phosphine) organoplatinum(II) metallacycles

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D(2h) rhomboids and a D(6h) hexagon. These supramolecular polygons were obtained via self-assembly of 120° dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D(2h) rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline and a 60° organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.     

The promise of electrochemical impedance spectroscopy as novel technology for the management of patients with diabetes mellitus

Self-monitoring of blood glucose is the standard of care in management of hyperglycemia among patients with diabetes mellitus. To increase the sensitivity and specificity of current devices, a novel method of detecting glucose using electrochemical impedance spectroscopy (EIS) technology is explored. The enzyme glucose oxidase (GOx) was fixed to gold electrodes and a sine wave of sweeping frequencies was induced using a wide range of concentrations of glucose. Each frequency in the impedance sweep was analyzed for the highest response and R-squared value. The frequency with both factors optimized is specific for the glucose-GOx binding interaction and was determined to be 1.17 kHz in purified solutions in both higher and lower ranges of glucose. The correlation between the impedance response and concentration at the low range of detection (0-100 mg dL(-1) of glucose) was determined to be 3.53 ohm/ln (mg dL(-1)) with an R-squared value of 0.90 with a 39 mg dL(-1) lower limit of detection. The same frequency of 1.17 kHz was verified in whole blood under the same glucose range. The above data confirm that EIS offers a new method of glucose detection as an alternative to current technology in use by patients. Additionally, the unique frequency response of individual markers allows for modulation of signals so that several other markers important in the management of diabetes could be measured with a single sensor.     

Quantitative determination of polyphosphate in sediments using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and partial least squares regression

Phosphorus (P) is a major cause of eutrophication and subsequent loss of water quality in freshwater ecosystems. A major part of the flux of P to eutrophic lake sediments is organically bound or of biogenic origin. Despite the broad relevance of polyphosphate (Poly-P) in bioremediation and P release processes in the environment, its quantification is not yet well developed for sediment samples. Current methods possess significant disadvantages because of the difficulties associated with using a single extractant to extract a specific P compound without altering others. A fast and reliable method to estimate the quantitative contribution of microorganisms to sediment P release processes is needed, especially when an excessive P accumulation in the form of polyphosphate (Poly-P) occurs. Development of novel approaches for application of emerging spectroscopic techniques to complex environmental matrices such as sediments significantly contributes to the speciation models of P mobilization, biogeochemical nutrient cycling and development of nutrient models. In this study, for the first time Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy in combination with partial least squares (PLS) was used to quantify Poly-P in sediments. To reduce the high absorption matrix components in sediments such as silica, a physical extraction method was developed to separate sediment biological materials from abiotic particles. The aim was to achieve optimal separation of the biological materials from sediment abiotic particles with minimum chemical change in the sample matrix prior to ATR-FTIR analysis. Using a calibration set of 60 samples for the PLS prediction models in the Poly-P concentration range of 0-1 mg g(-1) d.w. (dry weight of sediment) (R(2) = 0.984 and root mean square error of prediction RMSEP = 0.041 at Factor-1) Poly-P could be detected at less than 50 μg g(-l) d.w. Using this technique, there is no solvent extraction or chemical treatment required, sample preparation is minimal and simple, and the analysis time is greatly reduced. The results from this study demonstrated the potential of ATR FT-IR spectroscopy as an alternative method to study Poly-P in sediments.     

Comparison of CID, ETD and metastable atom-activated dissociation (MAD) of doubly and triply charged phosphorylated tau peptides

The fragmentation behavior of the 2+ and 3+ charge states of eleven different phosphorylated tau peptides was studied using collision-induced dissociation (CID), electron transfer dissociation (ETD) and metastable atom-activated dissociation (MAD). The synthetic peptides studied contain up to two known phosphorylation sites on serine or threonine residues, at least two basic residues, and between four and eight potential sites of phosphorylation. CID produced mainly b-/y-type ions with abundant neutral losses of the phosphorylation modification. ETD produced c-/z-type ions in highest abundance but also showed numerous y-type ions at a frequency about 50% that of the z-type ions. The major peaks observed in the ETD spectra correspond to the charge-reduced product ions and small neutral losses from the charge-reduced peaks. ETD of the 2+ charge state of each peptide generally produced fewer backbone cleavages than the 3+ charge state, consistent with previous reports. Regardless of charge state, MAD achieved more extensive backbone cleavage than CID or ETD, while retaining the modification(s) in most cases. In all but one case, unambiguous modification site determination was achieved with MAD. MAD produced 15-20% better sequence coverage than CID and ETD for both the 2+ and 3+ charge states and very different fragmentation products indicating that the mechanism of fragmentation in MAD is unique and complementary to CID and ETD.     

Microwave‐Assisted Hydrogel Synthesis: A New Method for Crosslinking Polymers in Aqueous Solutions

It has been found that hydrogels may be formed by microwave irradiation of aqueous solutions containing appropriate combinations of polymers. This new method of hydrogel synthesis yields sterile hydrogels without the use of monomers, eliminating the need for the removal of unreacted species from the final product. Results for two particularly successful combinations, poly(vinyl alcohol) with either poly(acrylic acid) or poly(methylvinylether‐alt‐maleic anhydride), are presented. Irradiation using temperatures of 100–150 °C was found to yield hydrogels with large equilibrium swelling degrees of 500–1000 g g⁻¹. Material leached from both types of hydrogel shows little cytotoxicity towards HT29 cells.     

Mechanisms for the reaction of thiophene and methylthiophene with singlet and triplet molecular oxygen

Mechanisms for the reaction of thiophene and 2-methylthiophene with molecular oxygen on both the triplet and singlet potential energy surfaces (PESs) have been investigated using ab initio methods. Geometries of various stationary points involved in the complex reaction routes are optimized at the MP2/6-311++G(d, p) level. The barriers and energies of reaction for all product channels were refined using single-point calculations at the G4MP2 level of theory. For thiophene, CCSD(T) single point energies were also determined for comparison with the G4MP2 energies. Thiophene and 2-methylthiophene were shown to react with O(2) via two types of mechanisms, namely, direct hydrogen abstraction and addition/elimination. The barriers for reaction with triplet oxygen are all significantly large (i.e., >30 kcal mol(-1)), indicating that the direct oxidation of thiophene by ground state oxygen might be important only in high temperature processes. Reaction of thiophene with singlet oxygen via a 2 + 4 cycloaddition leading to endoperoxides is the most favorable channel. Moreover, it was found that alkylation of the thiophene ring (i.e., methyl-substituted thiophene) is capable of lowering the barrier height for the addition pathway. The implication of the current theoretical results may shed new light on the initiation mechanisms for combustion of asphaltenes.     

Efficient asymmetric synthesis of biologically important tryptophan analogues via a palladium-mediated heteroannulation reaction.

A novel and concise synthesis of optically active tryptophan derivatives was developed via a palladium-catalyzed heteroannulation reaction of substituted o-iodoanilines with an internal alkyne. The required internal alkyne 14a or 25 was prepared in greater than 96% de via alkylation of the Sch?llkopf chiral auxiliary 19 employing diphenyl phosphate as the leaving group. The Sch?llkopf chiral auxiliary was chosen here for the preparation of L-tryptophans would be available from D-valine while the D-isomers required for natural product total synthesis would originate from the inexpensive L-valine (300-g scale). Applications of the palladium-catalyzed heteroannulation reaction were extended to the first asymmetric synthesis of L-isotryptophan 38 and L-benz[f]tryptophan 39. More importantly, the optically pure 6-methoxy-D-tryptophan 62 was prepared by this protocol on a large scale (>300 g). This should permit entry into many ring-A oxygenated indole alkaloids when coupled with the asymmetric Pictet-Spengler reaction. In addition, an improved total synthesis of tryprostatin A (9a) was accomplished in 43% overall yield employing this palladium-mediated process.     

Analysis of inorganic anions by electrostatic ion chromatography using zwitterionic/cationic mixed micelles as the stationary phase

The inability to separate fluoride, phosphate and sulfate by electrostatic ion chromatography (EIC) was overcome by using an ODS silica column coated with mixed zwitterionic-cationic surfactants as the stationary phase. The best results were obtained using the zwitterionic surfactant, 3-(N,N-dimethylmyristylammonium)-propanesulfonate (C₁₉H₄₁NO₃S), and the cationic surfactant, myristyltrimethylammonium, CH₃(CH₂)₁₃N⁺(CH₃)₃, in a 10:1 molar ratio in the column coating solution. With a dilute solution of sodium tetraborate as the eluent the model analyte anions were completely separated in the following elution order: F^–, HPO₄ ^2–, SO₄ ^2–, Cl^–, NO₂ ^–, Br^–, NO₃ ^–. The very early elution of phosphate and sulfate is most unusual and is unique to this system. Detection limits better than 1.1 × 10^–4 mM and linear calibration plots up to 7.0 mM were obtained with a suppressed conductivity system.     

Synthesis of 6-amino-1,2,3-triazolo[4,5-c] pyridin-4(5H)one (8-aza-3-deazaguanine) and 6-amino-1-(β-D-ribofuranosyl)-1,2,3-triazolo[4,5-c] pyridin-4(5H)one (8-Aza-3-deazaguanosine) via novel ring closure procedures

The total synthesis of 6-amino-1,2,3-triazolo[4,5-c]pyridin-4(5H)one (8-aza-3-deazaguanine, 3 ) and 6-amino-1-(β-D-ribofuranosyl)-1,2,3-triazolo[4,5-c]pyridin-4(5H)one (8-aza-3-deazaguano-sine, 22 ) has been described for the first time by a novel base-catalyzed ring closure of 4(5)-cyanomethyl-1,2,3-triazole-5(4)carboxamide (14) and methyl 5-cyanomethyl-1-(2,3,5-tri-O-ben-zoyl-β-D-ribofuranosyl)-1,2,3-triazole-4-carboxylate (17) , respectively. Under the catalysis of DBU, 2,4-dinitrophenylhydrazone of dimethyl 1,3-acetonedicarboxylate (7) was converted to methyl 5-methoxycarbonylmethyl-1-(2,4-dinitroanilino)-1,2,3-triazole-4-carboxylate (12) via dimethyl 2-diazo-3-iminoglutarate (8) . Catalytic reduction of 12 gave methyl 4(5)methoxycar-bonylmethyl-1,2,3-triazole-5(4)carboxylate (11) from which methyl 4(5)carbamoylmethyl-1,2,3-triazole-5(4)carboxylate (10) was obtained by ammonolysis. Dehydration of 10 provided methyl 4(5)cyanomethyl-1,2,3-triazole-5(4)carboxylate (13) which on amination gave 14 . The 1,2,3-triazole nucleosides 17, 18 and 19 were obtained from the stannic chloride-catalyzed condensation of the trimethylsilyl 13 and a fully acylated β-D-ribofuranose. The yield and ratio of the ribofuranosyl derivatives of 13 markedly depends on the ratio of stannic chloride used. The structures of the nucleosides 22 and 23 were established by a combination of NOE, ¹H-nmr and ¹³C-nmr spectroscopy.