Automated solvent system screening for the preparative countercurrent chromatography of pharmaceutical discovery compounds

A fully automated countercurrent chromatography system has been constructed to rapidly screen the commonly used heptane/ethyl acetate/methanol/water solvent system series and translate the results to preparative scale separations. The system utilizes “on‐demand” preparation of the heptane/ethyl acetate/methanol/water solvent system upper and lower phases. Elution‐extrusion countercurrent chromatography was combined with non‐dynamic equilibrium injection reducing the screening time for each heptane/ethyl acetate/methanol/water system to 17 min. The result enabled solvent system development to be reduced to under 2 h. The countercurrent chromatography system was interfaced with a mass spectrometer to allow selective detection of target components in crude medicinal chemistry reaction mixtures. Mass‐directed preparative countercurrent chromatography purification was demonstrated for the first time using a synthetic tetrazole epoxide derived from a routine medicinal chemistry support workflow.     

Nickel‐Catalyzed Barton Decarboxylation and Giese Reactions: A Practical Take on Classic Transforms

Two named reactions of fundamental importance and paramount utility in organic synthesis have been reinvestigated, the Barton decarboxylation and Giese radical conjugate addition. N ‐hydroxyphthalimide (NHPI) based redox‐active esters were found to be convenient starting materials for simple, thermal, Ni‐catalyzed radical formation and subsequent trapping with either a hydrogen atom source (PhSiH₃) or an electron‐deficient olefin. These reactions feature operational simplicity, inexpensive reagents, and enhanced scope as evidenced by examples in the realm of peptide chemistry.     

Relationships between the canonical ascending and descending central series of ideals of an associative algebra

We consider the canonical descending and ascending central series of ideals of an associative algebra. In particular, we prove that some ideal in the descending central series is finite-dimensional if and only if some ideal in the ascending central series is finite-codimensional. This result is the associative algebra analogue of results due to Reinhold Baer and Philip Hall in group theory and Ian Stewart in Lie algebra. We also prove various related results.     

Density functional modelling of silicate and aluminosilicate dimerisation solution chemistry

Common throughout sol-gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density functional theory (DFT), and are compared with: (i) existing values reported in the literature, and (ii) new and previously published DFT-derived data for similar silicate reactions at near-neutral pH. From the results it is seen that the energetics of deprotonation and dimerisation reactions depend greatly on the pH value, and these results correlate well with existing experimental values and trends. Hence, this investigation exemplifies that an accurate replication of the solution environment is crucial for obtaining useful theoretical results for species dissolved in non-ideal environments.     

Packed column supercritical fluid chromatography of isomeric polypeptide pairs

The characterization and determination of peptides is of great importance in the pharmaceutical industry as is the ability to rapidly perform targeted determinations of bioactive peptides in complex matrices. The purpose of the presented work is to assess the feasibility of packed column supercritical fluid chromatography (SFC) for the separation of two-pairs of water soluble peptides of identical mass, composition and charge that differ only in amino acid sequence. Upon evaluating a variety of conditions, trifluoroacetic acid (HTFA) in conjunction with methanol as the modifier proved to be, in general, the most successful mobile phase additive for elution of the two isomeric peptide pairs from all nitrogenous stationary phases. In contrast, water and ammonium acetate gave distorted peak shapes and therefore proved to be less satisfactory as neutral additives. The basic additive, iso-propylamine (IPAm), coupled with HA-Pyridine yielded the highest resolution factor for the complete study. Aminopropyl and HA-Pyridine columns with 5 μm particle size and 60 Å pore size were found to be best for resolution of each peptide pair. Bare silica and phenyl-hexyl stationary phases did not afford any separation. The primary roles of the carbon dioxide and methanol modifier are believed to provide (a) stationary phase solvation and (b) peptide solubility and transport; while, HTFA is postulated to fully protonate each peptide and form ion pairs between its conjugate base and cationic peptide analyte. The separation process, therefore, is best viewed as ion pair supercritical fluid chromatography (IP-SFC). For the case where IPAm gave good resolution on the HA-Pyridine column, the peptides are probably in the neutral state.     

Temperature dependence of the crystal structure and g-values of trans-diaquabis(methoxyacetato)copper(II): evidence for a thermal equilibrium between complexes with tetragonally elongated and compressed geometries

The crystal structures of trans-diaquabis(methoxyacetato)copper(II) and the isostructural nickel(II) complex have been determined over a wide temperature range. In conjunction with the reported behavior of the g-values, the structural data suggest that the copper(II) compound exhibits a thermal equilibrium between three structural forms, two having orthorhombically distorted, tetragonally elongated geometries but with the long and intermediate bonds to different atoms, and the third with a tetragonally compressed geometry. This is apparently the first reported example of a copper(II) complex undergoing an equilibrium between tetragonally elongated and compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metal-ligand bonding parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each structural form at every temperature. When combined with estimates of the Jahn-Teller distortions of the different forms, the latter produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model based upon Jahn-Teller coupling. It is suggested that cooperative effects may cause the development of the population of tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may oversimplify the diversity of structural forms present at high temperature.     

Rapid spectrofluorimetric determination of plasma salicylate with edta and terbium

A rapid single-reagent spectrofluorimetric assay for salicylate in human blood plasma is reported. The method is based on ternary complex formation with terbium and EDTA in alkaline solution; it requires only 10 μl of plasma, and protein precipitation is not necessary. Within-assay relative standard deviations were better than 2.5%, and correlation with the Trinder method was excellent. The procedure is particularly suited for emergency use in cases of suspected aspirin poisoning.