Search

Triaminoborane-bridged diphosphorus ligands called TBDPhos can undergo cooperative ligand-centered reactions at the 1,8,10,9-triazaboradecalin (TBD) backbone while bound to metals, but the factors that control this reactivity are not well understood. Previous studies showed that TBDPhos reactivity is highly sensitive to phosphorus substituents, ancillary ligands, and metal coordination environment despite these changes being significantly removed from the reactive N–B bond. Here we describe how exchanging phenyl and ethyl substituents attached to phosphorus with methoxy turns on ligand-centered reactions in otherwise unreactive (TBDPhos)Pt(S2C6H4) and (TBDPhos)Mo(CO)4complexes. The synthesis and characterization of the complexes are described alongside comparative reactivity studies using MeOH as a simple but effective test substrate. Complementary density functional theory (DFT) calculations on an expanded series of (TBDPhos)Pt(S2C6H4) complexes corroborate the experimental results and show that both size and electronic properties of the phosphorus substituents can significantly influence the Gibbs free energy of reaction at the remote ligand site. These results demonstrate how seemingly ancillary ligand modifications can levy significant control over ligand-centered reactivity in TBDPhos complexes, which may be relevant when considering the design of other chemically reactive ligands with Lewis acidic functional groups.

We report on B←N coordination to support a single-crystal-to-single-crystal reaction in the solid state. A [2 + 2] photodimerization is achieved with face-to-face π-stacks of monotopic B←N adducts composed of a phenylboronic acid catechol ester and an alkene with a terminal thiophene group. The photoreaction generates a ditopic B-adduct involving a head-to-tail cyclobutane regio- and stereoselectively. The photodimerization is accompanied by an increase in the tetrahedral character of the B atom. The resulting boron enables channel confinement of chloroform upon recrystallization.

The 1:1 caffeine (CAF) and 3-nitrobenzoic acid (NBA) cocrystal (CAF:NBA) displays polymorphism. Each polymorph shares the same docking synthon that connects individual CAF and NBA molecules within the asymmetric unit; however, the extended intermolecular interactions are significantly different between the two polymorphic modifications. These alternative interaction topologies translate to distinct structural motifs, mechanical properties, and compaction performance. To assist our molecular interpretation of the structure–mechanics–performance relationships for these cocrystal polymorphs, we combine powder Brillouin light scattering (p-BLS) to determine the mechanical properties with energy frameworks calculations to identify potentially available slip systems that may facilitate plastic deformation. The previously reported Form 1 for CAF:NBA adopts a 2D-layered crystal structure with a conventional 3.4 Å layer-to-layer separation distance. For Form 2, a columnar structure of 1D-tapes is displayed with CAF:NBA dimers running parallel to the (110) crystallographic direction. Consistent with the layered crystal structure, the shear modulus for Form 1 is significantly reduced relative to Form 2, and moreover, our p-BLS spectra for Form 1 clearly display the presence of low-velocity shear modes, which support the expectation of a low-energy slip system available for facile plastic deformation. Our energy frameworks calculations confirm that Form 1 displays a favorable slip system for plastic deformation. Combining our experimental and computational data indicates that the structural organization in Form 1 of CAF:NBA improves the compressibility and plasticity of the material, and from our tabletability studies, each of these contributions confers superior tableting performance to that of Form 1. Overall, mechanical and energy framework data permit a clear interpretation of the functional performance of polymorphic solids. This could serve as a robust screening approach for early pharmaceutical solid form selection and development.

Principles of crystal engineering have been applied toward the construction of supramolecular assemblies between an acid-functionalized tetraphenylethylene derivative and three different bis(pyridine)s [4,4′-bis(pyridyl)ethylene, 4,4′-bis(pyridyl)ethane, and 4,4′-bipyridine]. Each assembly was structurally characterized, and charge transfer interactions within each sample were visually apparent. Quantum chemical calculations were used to determine crystal band structure and band gap magnitude, and electrical properties of the materials were measured using conducting probe atomic force microscopy (CP-AFM). The crystals displayed charge-carrier capability, and the magnitude of semiconductivity varied systematically as a function of conjugation in the bis(pyridine) component. Crystals incorporating 4,4′-bis(pyridyl)ethylene and 4,4′-bipyridine displayed conductivities comparable to those of established organic semiconductors (μeff= 0.38 and 1.7 × 10–2cm2/V·s, respectively).

A single-crystal-to-single-crystal (SCSC) photodimerization is achieved using Au(I) coordination and aurophilic interactions. The rigid Au2(dppbz)(CF3COO)2precursor (dppbz = 1,2-bis(diphenylphosphino)benzene) self-assembles with 1,2-trans-bis(4-pyridyl)ethylene (bpe) to afford a discrete [Au4(dppbz)2(bpe)2]4+macrocycle in the solid state. The alkene undergoes a [2 + 2] photocycloaddition reaction. The photoreaction proceeds via a rare SCSC transformation in quantitative yield that generates [Au4(dppbz)2(4,4′-tpcb)]4+(4,4′-tpcb = rctt-tetrakis(4-pyridyl)cyclobutane) stereoselectively. Mechanical strain induced by the photoreaction is evidenced by the formation of ramp features on single-crystal surfaces using scanning electron microscopy.

In an ongoing effort to study the environmental fate of endocrine-active steroid hormones, we report the formation of phenolic rearrangement products (3and 4) with a novel 6,5,8,5-ring system following aqueous photolysis of dienogest (1) and methyldienolone (2). The structures were established by analysis of 2D NMR and HRMS data, and that of 3was confirmed by X-ray diffraction analysis. These photoproducts exhibit progestogenic and androgenic activity, albeit with less potency than their parent compounds.

The ability of 2,4,6-trihalophenols (3X-phOH) (where X = F, Cl, or Br) to enable reactivity of 1,2-bis(4-pyridyl)ethylene (bpe) in the solid state via cocrystallization is reported. The trihalophenols display structure behavior defined by infinite face-to-face π···π contacts and hydrogen bonds as pure solids that we show can be transferred to binary cocrystals to organize bpeto undergo a solid-state photodimerization. Cocrystals based on Cl- and Br-halophenols undergo single-crystal-to-single-crystal photoreactions to afford rctt-tetrakis(4-pyridyl)cyclobutane (tpcb) stereoselectively and in near quantitative yield. The use of 3X-phOHto enable reactivity in the solid state is discussed in the context of long-range synthon Aufbau modules.

We report the discovery of three polymorphs of the very recently FDA-approved boron-containing active pharmaceutical ingredient, Crisaborole. Crisaborole displays polymorphism based on the syn(Form I) and anti(Form II) conformations of the hydroxyl group of the oxaborole ring as shown by single-crystal X-ray analysis. Forms I and II were discovered based on the availability from two different commercial suppliers, while Form III was obtained upon heating of Form I or II. A cocrystal based on 4,4′-bipyridine was also obtained.

Auxarthrones A–E (1–5), five new phenalenones, and two new naturally occurring cyclic tetrapeptides, auxarthrides A (7) and B (8), were obtained from three different solvent extracts of cultures of the coprophilous fungus Auxarthron pseudauxarthron. Auxarthrones C (3) and E (5) possess an unusual 7a,8-dihydrocyclopenta[a]phenalene-7,9-dione ring system that has not been previously observed in natural products. Formation of 1–5was found to be dependent on the solvent used for culture extraction. The structures of these new compounds were elucidated primarily by analysis of NMR and MS data. Auxarthrone A (1) was obtained as a mixture of chromatographically inseparable racemic diastereomers (1aand 1b) that cocrystallized, enabling confirmation of their structures by X-ray crystallography. The absolute configurations of 7and 8were assigned by analysis of their acid hydrolysates using Marfey’s method. Compound 1displayed moderate antifungal activity against Cryptococcus neoformansand Candida albicans, but did not affect human cancer cell lines.

Seven new polyketide metabolites (disseminins A–E, 1–5, and spiciferones D and E, 7and 8) were obtained from cultures of a fungicolous isolate of Pestalotiopsis disseminata(NRRL 62562), together with a related compound (6) previously known only as a semisynthetic product. Structures were determined mainly by analysis of HRMS and NMR data. Biogenetically related compounds 1and 2possess uncommon bis-tetrahydrofuran and dioxabicyclo[3.2.1]octane ring systems, respectively. X-ray crystallographic analysis of the p-bromobenzoate derivative of 1confirmed the structure and enabled assignment of its absolute configuration.

The ability of organoboronic acids to direct intermolecular [2 + 2] photodimerizations in the solid state is identified. The reactivity of 1,2-bis(4-pyridyl)ethylene (bpe) within cocrystals of discrete hydrogen-bonded molecular assemblies generates rctt-tetrakis(4-pyridyl)cyclobutane (tpcb) stereoselectively and in up to quantitative yield. Dry grinding of the boronic acids and excess bpereveal the acids to function as supramolecular catalysts.

AFM nanoindentationwas used to demonstrate that millimeter‐ and nanometer‐sized organic cocrystals exhibit changes in the mechanical properties before, during, and after a single‐crystal‐to‐single‐crystal [2+2] photodimerization of olefins. Millimeter‐sized crystals become 40 % softer, whereas nanocrystals of the same material become 40 % harder following the photoreaction.

Weiche Riesen, harte Zwerge: Mithilfe von AFM‐Nanoindentierung wurde demonstriert, dass sich die mechanischen Eigenschaften millimeter‐ und nanometergroßer organischer Cokristalle vor, während und nach einer Einkristall‐zu‐Einkristall‐[2+2]‐Photodimerisierung von Olefinen verändern; millimetergroße Kristalle werden infolge der Photoreaktion 40 % weicher, entsprechende Nanokristalle hingegen 40 % härter.

Hymenopsin A (1), hymenopsin B (2), and a new macrophorin analogue, 2′,3′-epoxy-13-hydroxy-4′-oxomacrophorin A (3), have been isolated from a fungicolous isolate of Hymenopsissp. (MYC-1703; NRRL 37638). The structures and relative configurations of these compounds were assigned on the basis of 2D NMR and MS data, and the identity of 1was confirmed by X-ray crystallographic analysis. The absolute configuration of 2was proposed on the basis of CD analysis using both empirical and computational methods. Compounds 2and 3showed antibacterial activity against Staphylococcus aureusand Bacillus subtilis. Compound 3was also active against Aspergillus flavusand Fusarium verticillioides.

No Abstract

No Abstract

Chaetochalasin A ( 1), a new bioactive fungal metabolite with a previously undescribed ring system, has been isolated from an EtOAc extract of Chaetomium brasiliense(NRRL 22999). The structure of 1was determined by NMR experiments and single-crystal X-ray diffraction analysis.

The genus Sphaerostilbellacomprises fungi that colonize basidiomata of wood-inhabiting fungi, including important forest pathogens. Studies of fermentation cultures of an isolate (TFC201724) collected on the foothills of Himalayas, and closely related to S. broomeanaisolates from Europe, led to the identification of a new cyclic octapeptide along with two closely related analogues (1–3) and four dioxopiperazines (4–7). The structure of the lead compound, broomeanamide A (1), was assigned mainly by analysis of 2D NMR and HRESIMS data. The structure consisted of one unit each of N-MeVal, Ala, N-MePhe, Pro, Val, and Ile and two N-MeLeu units. The amino acid sequence was determined on the basis of 2D NMR and HRESIMSMS data. NMR and HRMS data revealed that the other two new peptides have the same amino acid composition except that the Ile unit was replaced with Val in one instance (2) and the N-MeVal unit was replaced with Val in the other (3). The absolute configuration of 1was assigned by analysis of the acid hydrolysate by application of Marfey’s method using both C18and C3bonded-phase columns. Broomeanamide A (1) showed antifungal activity against Cryptococcus neoformansand Candida albicans, with MIC values of 8.0 and 64 μg/mL, respectively.

The structures of 4-chloro- and 4-bromotribenzoylbenzene, as well as a solid solution prepared from these two components, are isomorphous and dominated by C–XOC interactions, whereas type-II II interactions are important in the 4-iodo derivative.

C5Me5R2Ta2Cl4d2–d2 disproportionates under dinitrogen to C5Me4RTaCl22μ-N2 and the D3hcluster cation C5Me4R3Ta3μ-Cl6with anionic C5Me4RTaCl4−.

Base hydrolysis of BiOClO4 yields ClO4−salts of the novel nonabismuth polyoxo cation Bi9μ3-O8μ3-OH651; ethanolysis converts 1to the ethoxide Bi9μ3-O8μ3-OEt652.

()‐Tartaric acid, C4H6O6, crystallized from ethanol in space group P. The structure is characterized by five hydrogen bonds, including the formation of a centrosymmetric carbox­ylic acid dimer which forms infinite chains along the body diagonal. These chains form sheets viahydrogen bonding between α‐hydroxyl groups. The sheets are connected through a bifurcated hydrogen bond. Structural comparisons are made with homochiral (2R,3R)‐(+)‐tartaric acid.

Massarilactones A and B (1and 2) have been isolated from cultures of the freshwater aquatic fungus Massarina tunicata. The structures, including absolute stereochemistry, were determined by X-ray diffraction analysis of their bis(4-bromobenzoate) derivatives.

The crystal structure of hexa‐μ‐hydroxo‐do­deca­methylocta‐μ3‐oxo‐do­deca­gallium(III) bis­[tetra­kis­(penta­fluoro­phenyl)­borate(III)] chloro­benzene disolvate dihydrate, [Ga12(CH3)12(μ3‐O)8(μ‐OH)6](C24F20B)2·2C6H5Cl·2H2O, is reported. The gallium–oxo–hydroxide dication is located on an inversion center and adopts a cage structure composed of 12 fused Ga3O3rings and is associated with the hydrate mol­ecules and the [B(C6F5)4]−anions through hydrogen bonds and one O—H⃛π‐ring interaction. Disordered chloro­benzene solvent mol­ecules are also present in the crystal structure.

We have synthesized two isomeric di­deoxy­nucleosides. 4(S)‐(6‐Amino‐9H‐purin‐9‐yl)‐3‐methyl­ene‐2,3,4,5‐tetra­hydrofuran‐2(S)‐yl­methanol, C11H13N5O2, is an analogue of the anti‐HIV compound (S,S)‐isodi­deoxy­adenosine (isoDDA) with an exocyclic methyl­ene group and is found to be anti‐HIV inactive. The solid‐state comformation is very similar to that of isoDDA. 4(S)‐(6‐Amino‐3H‐purin‐3‐yl)‐3‐methyl­ene‐2,3,4,5‐tetra­hydro­furan‐2(S)‐ylmethanol, C11H13N5O2, has an isomeric arrangement of the carbohydrate and base moieties, as confirmed by the crystal structure analysis. The asymmetric unit contains two independent mol­ecules that differ in conformations at the sugar moiety.

We have synthesized a di­deoxy­dide­hydro­nucleoside derivative, 2(S)‐acetoxymethyl‐4‐[4‐amino‐2‐oxopyrimidin‐1(2H)‐yl]‐2,5‐di­hydro­furan, C11H13N3O4, which is an analogue of the potently anti‐HIV active compound, di­deoxy‐dide­hydro­cytidine (d4C). The target compound crystallizes with two mol­ecules in the asymmetric unit that differ primarily in the orientation of the C6′‐acetyl group. One mol­ecule has an extended conformation and the orientation of the acetyl group in the second mol­ecule gives an unusual hooked‐shaped conformation. The two conformers form A–Bdimers viaN—H⃛N hydrogen bonds. The dimers link viaN—H⃛O hydrogen bonds to form chains parallel to the bcell axis.

The title triene, C18H10F6, was prepared viathe Pd0coupling reaction of (E)‐(1,2‐di­fluoro‐1,2‐ethenediyl)­bis­(tri­butyl­stan­nane) with (Z)‐β‐iodo‐α,β‐di­fluoro­styrene in N,N′‐dimethylformamide/tetrahydrofuran. The crystal structure shows the product to be the 1E,3E,5Eisomer. Due to steric interactions between F atoms, the double bonds are not coplanar. The planes defined by the two terminal double bonds are almost perpendicular.

The title compound, [Hf(C7H7)3(C10H15)], adopts a monomeric three‐legged piano‐stool structure. One benzyl ligand is disordered between two sites (44:56%) related by a ∼30° rotation about an axis defined by the Hf atom and the ipso‐C atom of the benzyl ligand.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

For Abstract see ChemInform Abstract in Full Text.