Investigating microcrystalline cellulose crystallinity using Raman spectroscopy.

Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity variability can result in downstream process variability. The aim of this study was to develop models to determine MCC crystallinity index (%CI) from Raman spectra of 30 commercial batches using Raman probes with spot sizes of 100 µm (MR probe) and 6 mm (PhAT probe). A principal component analysis model separated Raman spectra of the same samples captured using the different probes. The %CI was determined using a previously reported univariate model based on the ratio of the peaks at 380 and 1096 cm-1. The univariate model was adjusted for each probe. The %CI was also predicted from spectral data from each probe using partial least squares regression models (where Raman spectra and univariate %CI were the dependent and independent variables, respectively). Both models showed adequate predictive power. For these models a general reference amorphous spectrum was proposed for each instrument. The development of the PLS model substantially reduced the analysis time as it eliminates the need for spectral deconvolution. A web application containing all the models was developed. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10570-021-04093-1.

Development of a continuous process for α-thio-ß-chloroacrylamide synthesis with enhanced control of a cascade transformation.

A continuous process strategy has been developed for the preparation of α-thio-ß-chloroacrylamides, a class of highly versatile synthetic intermediates. Flow platforms to generate the α-chloroamide and α-thioamide precursors were successfully adopted, progressing from the previously employed batch chemistry, and in both instances afford a readily scalable methodology. The implementation of the key α-thio-ß-chloroacrylamide casade as a continuous flow reaction on a multi-gram scale is described, while the tuneable nature of the cascade, facilitated by continuous processing, is highlighted by selective generation of established intermediates and byproducts.

Selective nanomolar detection of dopamine using a boron-doped diamond electrode modified with an electropolymerized sulfobutylether-beta-cyclodextrin-doped poly(N-acetyltyramine) and polypyrrole composite film.

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.

Stepwise dissolution and composition determination of samples of multiple crystals using a dissolution medium containing aqueous alcohol and fluorocarbon phases.

Crystallisations are widely used in pharmaceutical and fine chemical manufacturing to control impurity levels, however crystallisations do not always reduce impurities to acceptable levels. Information on the location and distribution of impurities in crystallised materials would be helpful in such cases. A two phase dissolution medium featuring a fluorocarbon non-solvent vehicle and a aqueous ethanol solvent phase has been used to determine the composition of multi-particle crystalline samples through a partial dissolution approach combined with particle sizing and HPLC analysis. 4-Chloro-2-nitroacetanilide (1) was chosen as the host compound for this study, with 4-methyl-2-nitroacetanilide (2) and 4-tert-butyl-2-nitroacetanilide (3) chosen as the guest impurities that were added to supersaturated toluene solutions of 1 at levels up to 5 mol%. The crystals that formed were subjected to a series of partial dissolution steps carried out using the biphasic dissolution medium composed of a 50% aqueous ethanol solvent phase and a perfluorohexane continuous phase. To inhibit particle agglomeration, the mixture also contained 13,13,14,14,15,15,16,16,17,17,18,18-dodecafluoro-2,5,8,11-tetraoxaoctadecane (4) as a non-ionic surfactant. The partial dissolution steps showed a relatively even dissolution with each sequential step as determined from particle sizing. Analysis of the solutions by HPLC from each partial dissolution step allowed the level of impurity to be determined, and when combined with the particle sizing data this allowed an impurity distribution to be generated. Impurity 2 was found to be relatively evenly distributed while impurity 3 was localised on or near the surfaces of crystals.

Structural determinants of opioid activity in derivatives of 14-aminomorphinones: effect of substitution in the aromatic ring of cinnamoylaminomorphinones and codeinones.

In recent years there has been substantial interest in the 14-aminodihydromorphinone derivatives methoclocinnamox (MC-CAM) and clocinnamox (C-CAM). To investigate the importance of the cinnamoyl ring substituent, a series of analogues have been prepared with chloro, methyl, and nitro substituents in the 2' and 4' positions. Despite some discrepancies between the in vitro and in vivo data, a clear SAR could be observed where the 2'-chloro and 2'-methyl ligands consistently displayed higher efficacy than their 4'-substituted analogues. The new series also followed the well-established SAR that 17-methyl ligands have greater efficacy at the mu opioid receptor than their 17-cyclopropylmethyl counterparts.

Methyl tetra-O-acetyl-α-D-glucopyranuronate: crystal structure and influence on the crystallisation of the ß anomer.

Methyl tetra-O-acetyl-ß-D-glucopyranuronate (1) and methyl tetra-O-acetyl-α-D-glucopyranuronate (3) were isolated as crystalline solids and their crystal structures were obtained. That of the ß anomer (1) was the same as that reported by Root et al., while anomer (3) was found to crystallise in the orthorhombic space group P212121 with two independent molecules in the asymmetric unit. No other crystal forms were found for either compound upon recrystallisation from a range of solvents. The α anomer (3) was found to be an impurity in initially precipitated batches of ß-anomer (1) in quantities <3%; however, it was possible to remove the α impurity either by recrystallisation or by efficient washing, i.e. the α anomer is not incorporated inside the ß anomer crystals. The ß anomer (1) was found to grow as prisms or needles elongated in the a crystallographic direction in the absence of the α impurity, while the presence of the α anomer (3) enhanced this elongation.

The impact of storage conditions upon gentamicin coated antimicrobial implants.

A systematic approach was developed to investigate the stability of gentamicin sulfate (GS) and GS/poly (lactic-co-glycolic acid) (PLGA) coatings on hydroxyapatite surfaces. The influence of environmental factors (light, humidity, oxidation and heat) upon degradation of the drug in the coatings was investigated using liquid chromatography with evaporative light scattering detection and mass spectrometry. GS coated rods were found to be stable across the range of environments assessed, with only an oxidizing atmosphere resulting in significant changes to the gentamicin composition. In contrast, rods coated with GS/PLGA were more sensitive to storage conditions with compositional changes being detected after storage at 60 °C, 75% relative humidity or exposure to light. The effect of γ-irradiation on the coated rods was also investigated and found to have no significant effect. Finally, liquid chromatography-mass spectrometry analysis revealed that known gentamines C1, C1a and C2 were the major degradants formed. Forced degradation of gentamicin coatings did not produce any unexpected degradants or impurities.

Exploring the Scope of Asymmetric Synthesis of ß-Hydroxy-γ-lactams via Noyori-type Reductions.

Enantio- and diastereoselective hydrogenation of ß-keto-γ-lactams with a ruthenium-BINAP catalyst, involving dynamic kinetic resolution, has been employed to provide a general, asymmetric approach to ß-hydroxy-γ-lactams, a structural motif common to several bioactive compounds. Full conversion to the desired ß-hydroxy-γ-lactams was achieved with high diastereoselectivity (up to >98% de) by addition of catalytic HCl and LiCl, while ß-branching of the ketone substituent demonstrated a pronounced effect on the modest to excellent enantioselectivity (up to 97% ee) obtained.

Preparation and stereochemical integrity of certain thioesters of 2-arylpropionic acids and related compounds.

2-Arylpropionate thioesters 5, 6a/6b and 7a/7b, 2-aryloxypropionate thioesters 8a/8b and 2-alkoxy-2-arylacetate thioesters 9a/9b were prepared from thiol 4 and the corresponding carboxylic acids. Thioesters 6a/6b, 7a/7b, 8a/8b and 9a/9b were monitored for evidence of inter-conversion between epimers in acetonitrile solvent at 40 degrees C, by optical activity in the cases of 6a/6b and 7a/7b, and by 1H NMR spectroscopy in the cases of 8a/8b and 9a/9b. Only in the case of thioesters 9a/9b was significant inter-conversion between epimers observed.

Spectroscopic characterisation of the monoclinic and orthorhombic forms of paracetamol.

The metastable orthorhombic form of paracetamol was prepared from the melt of the commercially available monoclinic form. Distinct differences were observed in the infrared spectra of both forms, especially in the region 1260-1225 cm(-1), in which is observed three strong absorptions of approximately equal intensity in spectra of the monoclinic form, and two absorptions, one strong and one medium, in spectra of the orthorhombic form. No diagnostically useful differences were observed in the Raman spectra of the two forms. A 13C CP/MAS solid-state NMR spectrum of the monoclinic form and a spectrum of a mixture of forms prepared from a melt were obtained. A spectrum of the orthorhombic form was obtained from these spectra by difference spectroscopy. The spectra show that the carbons in the paracetamol molecules are all in unique chemical environments in both crystalline forms, and that clear well-resolved differences in the chemical shifts of particular carbons in both forms can be observed.

Supramolecular stacking motifs in the solid state of amide and triazole derivatives of cellobiose.

1-Acetamido-1-deoxy-(4-O-ß-d-glucopyranosyl-ß-d-glucopyranose) (5) and 1-deoxy-1-(4-phenyl-1,2,3-triazolyl)-(4-O-ß-d-glucopyranosyl-ß-d-glucopyranose) (7) were synthesised from 1-azido-1-deoxy-(4-O-ß-d-glucopyranosyl-ß-d-glucopyranose) (2) and crystallised as dihydrates. Crystal structural analysis of 5·2H2O displayed an acetamide C(4) chain and stacked cellobiose residues. The structure of 7·2H2O featured π-π stacking and stacking of the cellobiose residues.

Hydrogen bonding in crystal forms of primary amide functionalised glucose and cellobiose.

A glucoside and cellobioside of glycolamide were synthesised and the crystal chemistry of these compounds investigated. The amidoglucoside crystallised in the P2(1) space group. The primary amide group participates in C(7) and C(17) chains also involving the pyranose oxygen and hydroxyl groups. The amidocellobioside crystallised as a methanol solvate in the P2(1) space group. The amide N-H groups donate hydrogen bonds to oxygen atoms on the cellobiose units, while intramolecular hydrogen bonds give rise to S(7) and S(9) motifs in addition to a R3(3) (9) motif. A tetra-O-acetylglucoside derivative of thioglycolamide and its sulfoxide derivative were synthesised to examine the effect of protecting the glucopyranose hydroxyl groups. The thioglycolamido derivative, which crystallised in the P2(1)2(1)2(1) space group, featured amide N-H groups donating to the glucopyranose oxygen and an acetyloxy group. The sulfoxy derivative crystallised in the P2(1) space group and featured the primary amide groups forming R2(3)(8) motifs generating a 2(1) ladder.

Preparation and characterisation of solid state forms of paracetamol-O-glucuronide.

The synthesis and crystallisation of the pharmaceutically important metabolite, paracetamol-O-glucuronide, is described. Hydrated and anhydrous forms of the target molecule have been characterised by PXRD, DSC and TGA. In addition, a methanol solvate has been analysed, including single crystal analysis, which represents the first structure solution for this system.

Fumaroylamino-4,5-epoxymorphinans and related opioids with irreversible µ opioid receptor antagonist effects.

We have previously shown that cinnamoyl derivatives of 14ß-amino-17-cyclopropylmethyl-7,8-dihydronormorphinone and 7α-aminomethyl-6,14-endoethanonororipavine have pronounced pseudoirreversible µ opioid receptor (MOR) antagonism. The present communication describes the synthesis and evaluation of fumaroylamino analogues of these cinnamoylamino derivatives together with some related fumaroyl derivatives. The predominant activity of the new ligands was MOR antagonism. The fumaroylamino analogues (2a, 5a) of the pseudoirreversible antagonist cinnamoylamino morphinones and oripavines (2b, 5b) were themselves irreversible antagonists in vivo. However the fumaroylamino derivatives had significantly higher MOR efficacy than the cinnamoylamino derivatives in mouse antinociceptive tests. Comparison of 2a and 5a with the prototypic fumaroylamino opioid ß-FNA (1a) shows that they have similar MOR irreversible antagonist actions but differ in the nature of their opioid receptor agonist effects; 2a is a predominant MOR agonist and 5a shows no opioid receptor selectivity, whereas the agonist effect of ß-FNA is clearly κ opioid receptor (KOR) mediated.

Evaluation of the Bruker SMART X2S: crystallography for the nonspecialist?

An evaluation of the Bruker SMART X2S for the collection of crystallographic diffraction data, structure solution and refinement is carried out with a variety of materials with different electron densities, presenting some of the successes and challenges of automation in chemical crystallography.

Potentiometric evaluation of calix[4]arene anion receptors in membrane electrodes: phosphate detection.

Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-N'-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-(N'-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO(4)(2-) in the concentration range 5.0 x 10(-5) to 1.0 x 10(-1)M, with near-Nernstian response slopes of -33.0 and -28.0 mV dec(-1) for ionophores I and II, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO(4)(2-) with respect to the other anions, including sulfate and nitrate.

Crystal polymorphism of pharmaceuticals: probing crystal nucleation at the molecular level.

Paracetamol, sulfathiazole and L-glutamic acid are presented as examples of pharmaceutical crystal polymorphic systems. The effect of N-acylated sulfathiazole derivatives (3-6) on sulfathiazole crystallisation is discussed, and possible modes of action presented. Methods for the control of the crystal polymorphism of L-glutamic acid which utilise the principles of conformation mimicry and co-operative binding are presented. The preparation of a series of bis-amides of EDTA derived from sulfathiazole, 5-aminoisophthalic acid and 4-hydroxyaniline (i.e. compounds 9a-c) is presented, as is data on the effect of these compounds on the crystallisation of, respectively, sulfathiazole, L-glutamic acid and paracetamol.