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Beauveriolides, including the main beauveriolide I {systematic name: (3R,6S,9S,13S)‐9‐benzyl‐13‐[(2S)‐hexan‐2‐yl]‐6‐methyl‐3‐(2‐methylpropyl)‐1‐oxa‐4,7,10‐triazacyclotridecane‐2,5,8,11‐tetrone, C27H41N3O5}, are a series of cyclodepsipeptides that have shown promising results in the treatment of Alzheimer's disease and in the prevention of foam cell formation in atherosclerosis. Their crystal structure studies have been difficult due to their tiny crystal size and fibre‐like morphology, until now. Recent developments in 3D electron diffraction methodology have made it possible to accurately study the crystal structures of submicron crystals by overcoming the problems of beam sensitivity and dynamical scattering. In this study, the absolute structure of beauveriolide I was determined by 3D electron diffraction. The cyclodepsipeptide crystallizes in the space group I2 with lattice parameters a = 40.2744 (4), b = 5.0976 (5), c = 27.698 (4) Å and β = 105.729 (6)°. After dynamical refinement, its absolute structure was determined by comparing the R factors and calculating the z‐scores of the two possible enantiomorphs of beauveriolide I. [ABSTRACT FROM AUTHOR]

Validation of a method for distinguishing between salts and cocrystals based on dispersion‐corrected density functional theory is presented. Existing related works (van de Streek & Neumann, 2010; LeBlanc et al., 2018) indicate that this approach is problematic and leads to incorrect results in multiple situations. The method suggested here is based on the geometry optimization of an artificially constructed wrong structure (hydrogen atom placed in salt position near the potential acceptor for cocrystals and vice versa cocrystal position with hydrogen atom placed near the potential donor of the salts). The verification of the method is based on comparison of the results with an experimentally confirmed correct hydrogen position. Calculations were performed on 173 selected structures of salts and 96 cocrystals with ΔpKa in the critical ⟨−1, 4⟩ range. The range was chosen to test the method on the most problematic structures. When the artificial wrong model did not converge to the correct one (salt to cocrystal and vice versa), it was tested whether the correct model converged to the correct one in addition. The results confirmed that the most widely used functional (PBE) tends to generate false salt results. All salts converged to the salt from cocrystal initial models. Sixteen cocrystals showed local energy minima for both the salt and cocrystal states. Eighteen cocrystals always converged to salt. Rules were identified under which the results can be considered reliable: when a cocrystal starting model converges to cocrystal, the structure is certainly cocrystal. When both the cocrystal and salt models converge to salt for a long hydrogen‐bond (longer than 2.613 Å) the structure is most likely salt. For short hydrogen bonds it is not possible to distinguished reliably between salt and cocrystal using the dispersion‐corrected PBE functional. Additional calculations were performed with more advanced functionals for 18 problematic structures detected in the screening as well as for four more mentioned in the literature. The results show that the rSCAN functional (Bartók & Yates, 2019) improves the agreement with the experiment. Further improvement was observed by using hybrid functionals (PBE0, PBE50), which were tested on structures that gave incorrect results with rSCAN. The described method for distinguishing salts from cocrystals can be useful for enhancing the information given by structure solutions from powder, the verification of structure solutions from single crystals and studies related to crystal structure prediction. [ABSTRACT FROM AUTHOR]

Beauverolides (beauveriolides) are abundant, biologically active cyclodepsipeptides produced by many entomopathogenic fungi, including those that are used as biopesticides. Beauverolides act as cholesterol acyltransferase inhibitors in humans; thus, their mode of action has been the subject of pharmacological and clinical research. The cost‐effective analytical methods are needed for fast, routine laboratory analysis of beauverolides. We isolated beauverolides from the fungal strain Isaria fumosorosea PFR 97‐Apopka and opened the rings of the isolated beauverolides using a pyridine alkaline medium. We separated fractions of cyclic and linearized beauverolides by thin‐layer chromatography, and found the chloroform–acetate (9:1, v/v) and chloroform–acetonitrile–acetate (8:1:1, v/v/v) mobile phases, respectively, to be the most efficient. We examined all the fractions by liquid chromatography–mass spectrometry using ion trap and Orbitrap high resolution mass spectrometry. For rapid screening of the contents of cyclic, and, particularly, linearized beauverolides, we developed a novel analytical method that consisted of using capillary electrophoresis coupled with contactless conductivity detection. Furthermore, we improved the separation of the peptides by applying capillary micellar electrokinetic chromatography with the N‐cyclohexyl‐2‐aminoethanesulfonic acid:SDS:NaOH buffer, pH 9.8 as the background electrolyte. The described novel methods allow fast and cost‐effective separation of chemically related groups of beauverolides. [ABSTRACT FROM AUTHOR]

The potential of solid-state NMR techniques is demonstrated to study and determine the 3D structure of moderately sized spin systems at natural isotopic abundance. It is clear from experiments that skillful execution and careful interpretation of modern solid-state NMR techniques can lead to a complete structure, i.e. conformation and mutual orientation of crystallized molecules of simvastatin and other related compounds.

Beauverolides are hydrophobic cyclodepsipeptides that inhibit sterol O-acyltransferases and calmodulin, thereby reducing senile plaques in Alzheimer’s disease and preventing foam cell formation in atherosclerosis. Other sterol O-acyltransferase inhibitors suffer from low bioavailability, and evidence of the distribution of beauverolides in bodily fluids is lacking. We aimed to determine the optimal formulation of beauverolides for administration to experimental animals and to determine if the orally administered beauverolides could cross the gastrointestinal barrier and be secreted in urine. We found that beauverolides formed gels in aqueous solutions and we developed a formula for their peroral administration. Administration of the beauverolide gel pellets to experimental mice revealed that beauverolides cross the gastrointestinal barrier, circulate untouched in the blood, and are excreted in the urine. Using liquid chromatography-mass spectrometry analyses, we show that the administered beauverolides circulate in mouse blood and are excreted from the body 24 h after their administration. [ABSTRACT FROM AUTHOR]

Analysis of brown bullhead (Ameiurus nebulosus) bile by ultra performance liquid chromatography high-resolution mass spectrometry (UPLC/HRMS) revealed a series of bile acids similar to those found in humans. Accordingly, we chose this fish as a model organism to examine the metabolism of obeticholic acid, a bile acid used to treat a number of human liver diseases and the one that has the potential to occur as an environmental contaminant. The taurine and glycine conjugates of obeticholic acid and keto-obeticholic acid were identified, as well as the d-cysteinolic acid conjugate of obeticholic acid, likely a metabolite specific to fish. In addition, metabolites of obeticholic acid (sulphate and glucuronide) and several hydroxy-obeticholic acid derivatives were found, representing typical pathways of primary and secondary steroid metabolism. Brown bullhead exposed to obeticholic acid at a dose of 100 mg/kg gave no overt signs of distress or toxicity. [ABSTRACT FROM AUTHOR]

Uncertainties in the structure determination of peptide analogs of boronic acid, exacerbated by the many coordination modes of boron, represent an obstacle in understanding their role in living organisms and thus also in developing the next generation of anticancer drugs. For that reason, we present here a general experimental-computational strategy allowing structure determination of complex boronic acid derivatives with extensive conformational variability. We demonstrate successful solution of the crystal structures of two nonsolvated polymorphs of ixazomib citrate directly from synchrotron powder diffraction data, which is challenging because the two molecules in the asymmetric unit cell that exhibit 32 degrees of conformational freedom push the limits of current solution procedures. We used a novel two-step Rietveld refinement based on DFT-D restraints to improve information quality derived from powder diffraction data to be comparable with that of single-crystal solutions. NMR crystallography was applied to verify the crystal structures, and the high potential value of using 11B NMR parameters toward the solution of unknown structures was demonstrated. Evolution of 11B–11B double-quantum coherences allows probing of interatomic distances up to 7 Å. Overall, we present an integrated approach that applies several techniques in conjunction to provide otherwise unavailable structural information. [ABSTRACT FROM AUTHOR]

Enantiomeric purity of drugs is essential for their biological activity. In the present study, we investigate the performance of Raman optical activity (ROA) spectroscopy in distinguishing four possible stereoisomers of the synthetic precursor used for the production of taxol from baccatin III. Taxol is one of the best-selling medicaments used in the treatment of ovarian, lung, and breast cancers and Kaposi's sarcoma. In a low yield, it may be isolated from the bark of the Pacific yew tree (Taxus brevifolia); however, its industrial production is largely dependent on the precursor. It is shown that for reliable comparison of the experimental and computed Raman and ROA intensities a large number of conformers had to be averaged, to properly account for molecular flexibility in solution. In addition, if combined with the density functional theory computations, ROA spectra provide convenient and economic means of absolute configuration determination. [ABSTRACT FROM AUTHOR]

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Kinetic fluorescence imaging was used to set a new detection limit for plant exposure to low levels of destruxins – phytotoxins of Alternaria brassicae . A general experimental algorithm is presented that can be used to identify the combination of fluorescence parameters providing the highest contrast between the affected and unaffected plants or plant segments. Leaves of canola (Brassica napus ) and white mustard (Sinapis alba ) were exposed to various concentrations of destruxins and images of key fluorescence signals (F 0 , F M , F P , and of F S ) were captured in a single kinetic experiment. Contrast was quantified within these images between the leaf areas exposed to destruxins and the untreated areas. The highest contrast was found in the image constructed by pixel-to-pixel division of images F 0 by F P and F 0 by F M . Using the F 0 /F M ratio image, we were able to detect exposure to destruxin concentration as low as approximately 0.05 mg l-1 applied to canola leaf and approximately 10 mg l-1 when applied to mustard. The detection limits were significantly lower than those obtained by optical microscopy indicating that kinetic chlorophyll fluorescence imaging can be used as a diagnostic tool in screening for varieties with an enhanced resistance to destruxins of Alternaria brassicae. [ABSTRACT FROM AUTHOR]

The mass spectrometric sequence determination of amino acid residues in cyclosporins using fast atom bombardment, collisionally activated dissociations in the first field-free region and linked B/E scan is described. The general fragmentation scheme was derived from the spectra of cyclosporins A, B, C, D, F, G, L and [DH-MeBmt1]CS. The main fragmentation pathways start by primary splitting between amino acids 2-3, 1-11 and 5-6. The corresponding N-terminal b-type ions are common fragment types in the mass spectra. The 1-11 splitting can be enhanced by the introduction of a lactone group into the peptide ring by conversion of cyclosporins into isocyclosporins. The fragmentation scheme was used for amino acid sequence determination in four new natural cyclosporins, [MeLeu1]CS, [Leu4]CS, [Ile4]CS and [Leu5]CS. [ABSTRACT FROM AUTHOR]

Describes the crystal structure of the organic compound simvastatin. Isostructurality with lovastatin; Close relation of general conformational features with those of other reported crystal structures of statins; Facilitation of the formation of infinite chains of molecules along the b axis by the only hydrogen bond present.

An aminoborane side product from the nicergoline manufacture process was identified by single-crystal X-ray diffraction. As boranes of pharmaceutical molecules are quite rare, the binding potential of the BH3 group was investigated and compared with similar compounds using Cambridge Structural Database (CSD). Surprisingly, the packing was stabilized by a dihydrogen bond, which triggered a false alert for too-short contact of hydrogen atoms in IUCR checkCIF. As the dihydrogen bond concept is not widely known, such an alert might mislead crystallographers to force –CH3 optimal geometry to –BH3 groups. The B–H distances equal to or less than 1.0 Å (17% of the CSD structures) are substantially biased when analyzing the structures of aminoborane complexes in CSD. To conduct proper searching, B–H bond length normalization should be applied in the CSD search. [ABSTRACT FROM AUTHOR]

Discusses the crystal structure of pergolide mesylate form II. Ability to crystallize in the trigonal system; Difference from pergolide mesylate form I; Result of its differential thermal analysis thermogram; Hydrogen-bonding geometry.