Four cocrystals of thymine with phenolic coformers: influence of the coformer on hydrogen bonding

Cocrystals are molecular solids composed of at least two types of neutral chemical species held together by noncovalent forces. Crystallization of thymine [systematic name: 5-methylpyrimidine-2,4(1H,3H)-dione] with four phenolic coformers resulted in cocrystal formation, viz. catechol (benzene-1,2-diol) giving thymine-catechol (1/1), C5H6N2O2·C6H6O2, (I), resorcinol (benzene-1,3-diol) giving thymine-resorcinol (2/1), 2C5H6N2O2·C6H6O2, (II), hydroquinone (benzene-1,4-diol) giving thymine-hydroquinone (2/1), 2C5H6N2O2·C6H6O2, (III), and pyrogallol (benzene-1,2,3-triol) giving thymine-pyrogallol (1/2), C5H6N2O2·2C6H6O3, (IV). The resorcinol molecule in (II) occupies a twofold axis, while the hydroquinone molecule in (III) is situated on a centre of inversion. Thymine-thymine base pairing is common across all four structures, albeit with different patterns. In (I)-(III), the base pair is propagated into an infinite one-dimensional ribbon, whereas it exists as a discrete dimeric unit in (IV). In (I)-(III), the two donor N atoms and one carbonyl acceptor O atom of thymine are involved in thymine-thymine base pairing and the remaining carbonyl O atom is hydrogen bonded to the coformer. In contrast, in (IV), just one donor N atom and one acceptor O atom are involved in base pairing, and the remaining donor N atom and acceptor O atom of thymine form hydrogen bonds to the coformer molecules. Thus, the utilization of the donor and acceptor atoms of thymine in the hydrogen bonding is influenced by the coformers.

Four oxoindole-linked α-alkoxy-β-amino acid derivatives

Four structures of oxoindolyl α-hydroxy-β-amino acid derivatives, namely, methyl 2-{3-[(tert-butoxycarbonyl)amino]-1-methyl-2-oxoindolin-3-yl}-2-methoxy-2-phenylacetate, C24H28N2O6, (I), methyl 2-{3-[(tert-butoxycarbonyl)amino]-1-methyl-2-oxoindolin-3-yl}-2-ethoxy-2-phenylacetate, C25H30N2O6, (II), methyl 2-{3-[(tert-butoxycarbonyl)amino]-1-methyl-2-oxoindolin-3-yl}-2-[(4-methoxybenzyl)oxy]-2-phenylacetate, C31H34N2O7, (III), and methyl 2-[(anthracen-9-yl)methoxy]-2-{3-[(tert-butoxycarbonyl)amino]-1-methyl-2-oxoindolin-3-yl}-2-phenylacetate, C38H36N2O6, (IV), have been determined. The diastereoselectivity of the chemical reaction involving α-diazoesters and isatin imines in the presence of benzyl alcohol is confirmed through the relative configuration of the two stereogenic centres. In esters (I) and (III), the amide group adopts an anti conformation, whereas the conformation is syn in esters (II) and (IV). Nevertheless, the amide group forms intramolecular N-H···O hydrogen bonds with the ester and ether O atoms in all four structures. The ether-linked substituents are in the extended conformation in all four structures. Ester (II) is dominated by intermolecular N-H···O hydrogen-bond interactions. In contrast, the remaining three structures are sustained by C-H···O hydrogen-bond interactions.

The first polymorph in the family of nucleobases: a second form of cytosine

A new polymorph of cytosine, C4H5N3O, is reported half a century after the report of its first known crystal structure [Barker & Marsh (1964).Acta Cryst.17, 1581–1587]. Cytosine thus provides the first polymorphic example in the category of parent nucleobases. The new form, denoted (Ib), was observed unexpectedly during an attempt to cocrystallize cytosine with catechol. Form (Ib) crystallizes in the orthorhombic centrosymmetric space groupPccnwith two molecules in the asymmetric unit. The previously known form, denoted (Ia), crystallizes in the orthorhombic noncentrosymmetric space groupP212121. The cytosine molecule is planar in both forms. Hydrogen-bonding interactions are also similar for both forms. Infinite one-dimensional ribbons composed of cytosine base-pair dimers inR22(8) arrangements are observed in both (Ia) and (Ib). However, the way that the ribbons are packed differs in (Ia) and (Ib). This appears to guide the centrosymmetricversusnoncentrosymmetric space-group selection through the formation of an inversion-related motif in polymorph (Ib) and a helical propagation in polymorph (Ia). A few selected polymorphic systems have been gathered from the Cambridge Structural Database to understand possible structural features responsible for achiral molecules adopting centro- and noncentrosymmetric space groups.

Folded conformations due to arene interactions in dissymmetric and symmetric butylidene-linker models based on pyrazolo[3,4-d]pyrimidine, purine and 7-deazapurine

The butylidene-linker models 1-[2-(2,6-dimethylsulfanyl-9H-purin-9-yl)-2-methylidenepropyl]-4,6-bis(methylsulfanyl)-1H-pyrazolo[3,4-d]pyrimidine, C18H20N8S4, (XI), 7,7'-(2-methylidenepropane-1,3-diyl)bis[3-methyl-2-methylsulfanyl-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one], C20H22N6O2S2, (XIV), and 7-[2-(4,6-dimethylsulfanyl-1H-pyrazolo[3,4-d]pyrimidin-1-yl)-2-methylidenepropyl]-3-methyl-2-methylsulfanyl-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one, C19H21N7OS3, (XV), show folded conformations in solution, as shown by (1)H NMR analysis. This folding carries over to the crystalline state. Intramolecular π-π interactions are observed in all three compounds, but only (XIV) shows additional intramolecular C-H···π interactions in the solid state. As far as can be established, this is the first report incorporating the pyrrolo[2,3-d]pyrimidine nucleus for such a study. In addition to the π-π interactions, the crystal structures are also stabilized by other weak intermolecular C-H···S/N/O and/or S···N/S interactions.

Understanding the amino ↔ imino tautomeric preference in (imidazole)imidazolidine-N-aryl(alkyl) systems: a case study of moxonidine drug and insights from the Cambridge structural database (CSD)

Moxonidine drug crystallizes exclusively as its imino tautomer. Conjugation plays a key role in the tautomer stability.

Tetra- and hexahydrates of bis(adeninium) zoledronate

The present paper reports the structures of bis(adeninium) zoledronate tetrahydrate {systematic name: bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate tetrahydrate}, 2C5H6N5+·C5H8N2O7P22−·4H2O, (I), and bis(adeninium) zoledronate hexahydrate {systematic name: a 1:1 cocrystal of bis(6-amino-7H-purin-1-ium) hydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)-1-phosphonatoethyl]phosphonate hexahydrate and 6-amino-7H-purin-1-ium 6-amino-7H-purine dihydrogen [1-hydroxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-diyl]diphosphonate hexahydrate}, 2C5H6N5+·C5H8N2O7P22−·6H2O, (II). One of the adenine molecules and one of the phosphonate groups of the zoledronate anion of (II) are protonated on a 50% basis. The zoledronate group displays its usual zwitterionic character, with a protonated imidazole ring; however, the ionization state of the phosphonate groups of the anion for (I) and (II) are different. In (I), the anion has both singly and doubly deprotonated phosphonate groups, while in (II), it has one singly deprotonated phosphonate group and a partially deprotonated phosphonate group. In (I), the cations form anR22(10) base pair, while in (II), they formR22(8) andR22(10) base pairs. Two water molecules in (I) and five water molecules in (II) are involved in water–water interactions. The presence of an additional two water molecules in the structure of (II) might influence the different ionization state of the anion as well as the different packing mode compared to (I).

Tosylate salts of the anticancer drug lapatinib

Two tosylate salts of an anticancer drug lapatinib, viz. a monotosylate [systematic name: ({5-[4-({3-chloro-4-[(3-fluorophenyl)methoxy]phenyl}amino)quinazolin-6-yl]furan-2-yl}methyl)[2-(methylsulfonyl)ethyl]azanium 4-methylbenzenesulfonate], C29H27ClFN4O4S(+)·C7H7O3S(-), (I), and a ditosylate [systematic name: 4-({3-chloro-4-[(3-fluorophenyl)methoxy]phenyl}amino)-6-]5-({[2-(methylsulfonyl)ethyl]azaniumyl}methyl)furan-2-yl[quinazolin-1-ium bis(4-methylbenzenesulfonate)], C29H28ClFN4O4S(2+)·2C7H7O3S(-), (II), were obtained during crystallization attempts for polymorphism. In both structures, the lapatinib cation is in a distorted U-like conformation and the tosylate anion is clamped between the aniline N atom and methylamine N atom through N-H···O hydrogen bonds, forming an R2(2)(15) ring motif. The 4-anilinoquinazoline ring system is essentially planar in (I), while it is twisted in (II), controlled by an intramolecular C-H···N interaction. In (I), alternating cations and anions are linked by N-H···O hydrogen bonds into C2(2)(6) chains. These chains are linked by cations in a helical manner. The presence of the additional tosylate anion in (II) results in the formation of one-dimensional tapes of fused hydrogen-bonded rings through N-H···O and C-H···O interactions. These studies augment our understanding of the role of nonbonded interactions in the solid state, which is useful for correlation to the physicochemical properties of drug products.

2-[(Ferrocen-1-yl)(hydroxy)methyl]prop-2-enenitrile

In the title ferrocene derivative, [Fe(C5H5)(C9H8NO)], the dihedral angle between the enenitrile group and the substituted cyclopentadienyl ring is 71.2 (1)°. The cyclopentadienyl rings of the ferrocene moiety are arranged in an eclipsed conformation. The hydroxy group, and the corresponding methine H atom, are disordered over two sets of sites with site-occupancy factors of 0.744 (4) and 0.256 (4). An intramolecular C—H...O close contact is observed. In the crystal, O—H...N hydrogen bonds form aC(6) chain along [100].

Zolmitriptan oxalate and zolmitriptan camphorsulfonate: the first structural study of salt complexes of the antimigraine drug zolmitriptan

Zolmitriptan hydrogen oxalate [(S)-dimethyl(2-{5-[(2-oxo-1,3-oxazolidin-4-yl)methyl]-1H-indol-3-yl}ethyl)azanium hydrogen oxalate], C16H22N3O2(+)·C2HO4(-), (I), and zolmitriptan camphorsulfonate [(S)-dimethyl(2-{5-[(2-oxo-1,3-oxazolidin-4-yl)methyl]-1H-indol-3-yl}ethyl)azanium (S,R)-{2-hydroxy-7,7-dimethylbicyclo[2.2.1]heptan-1-yl}methanesulfonate], C16H22N3O2(+)·C10H15O4S(-), (II), are the first reported salt complexes of the antimigraine drug zolmitriptan. Compound (I) crystallizes in the space group P2(1) with two molecules of protonated zolmitriptan and two oxalate monoanions in the asymmetric unit, while compound (II) crystallizes in the space group P2(1)2(1)2(1) with one protonated zolmitriptan molecule and one camphorsulfonate anion in the asymmetric unit. The orientations of the ethylamine side chain and the oxazolidinone ring with respect to the indole ring of the zolmitriptan cation are different for (I) and (II). In (I), they are oriented in opposite directions and the molecule adopts a step-like appearance, while in (II) the corresponding side chains are folded in the same direction, giving the molecule a cup-like appearance. The zolmitriptan molecules of (I) form an R2(2)(8) dimer, while in (II) they form a helical chain with a C(11) motif. The oxalate monoanions of (I) interact with the zolmitriptan cations and extend the dimer into a three-dimensional hydrogen-bonded network. In (II), the camphorsulfonate anion forms an R2(2)(15) ring motif with the zolmitriptan cation.

Solvent-mediated pseudo-quadruple hydrogen-bond motifs in three lamotrigine–carboxylic acid complexes

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion ofN,N-dimethylformamide (DMF) solvent,viz.lamotriginium [3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazin-2-ium] 4-iodobenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H4IO2−·C3H7NO, (I), lamotriginium 4-methylbenzoateN,N-dimethylformamide monosolvate, C9H7Cl2N5+·C8H8O2−·C3H7NO, (II), and lamotriginium 3,5-dinitro-2-hydroxybenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H3N2O7−·C3H7NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine–lamotrigine, lamotrigine–acid and lamotrigine–solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine–lamotrigine dimers into a pseudo-quadruple hydrogen-bonding motif.

Frovatriptan salts of aliphatic carboxylic acids

The interaction of the antimigraine pharmaceutical agent frovatriptan with acetic acid and succinic acid yields the salts (±)-6-carbamoyl-N-methyl-2,3,4,9-tetrahydro-1H-carbazol-3-aminium acetate, C14H18N3O(+)·C2H3O2(-), (I), (R)-(+)-6-carbamoyl-N-methyl-2,3,4,9-tetrahydro-1H-carbazol-3-aminium 3-carboxypropanoate monohydrate, C14H18N3O(+)·C4H5O4(-)·H2O, (II), and bis[(R)-(+)-6-carbamoyl-N-methyl-2,3,4,9-tetrahydro-1H-carbazol-3-aminium] succinate trihydrate, 2C14H18N3O(+)·C4H4O4(2-)·3H2O, (III). The methylazaniumyl substitutent is oriented differently in all three structures. Additionally, the amide group in (I) is in a different orientation. All the salts form three-dimensional hydrogen-bonded structures. In (I), the cations form head-to-head hydrogen-bonded amide-amide catemers through N-H···O interactions, while in (II) and (III) the cations form head-to-head amide-amide dimers. The cation catemers in (I) are extended into a three-dimensional network through further interactions with acetate anion acceptors. The presence of succinate anions and water molecules in (II) and (III) primarily governs the three-dimensional network through water-bridged cation-anion associations via O-H···O and N-H···O hydrogen bonds. The structures reported here shed some light on the possible mode of noncovalent interactions in the aggregation and interaction patterns of drug molecule adducts.

Structural and spectral characterization of a new non-centrosymmetric organic thiosulfate

Aqueous reaction of ammonium thiosulfate with ethylenediamine (en) results in the formation of the title compound (enH(2))[S(2)O(3)] (1) (enH(2)=ethylenediammonium) in good yields. Compound 1 was characterized by analytical data, IR, Raman and NMR spectra, X-ray powder pattern and its crystal structure was determined. The structure of 1 which crystallizes in the non-centrosymmetric orthorhombic space group P2(1)2(1)2(1), consists of two crystallographically independent (enH(2))(2+) dications and two unique thiosulfate anions, which are interlinked by three varieties of H-bonding interactions, namely N-H⋯O, N-H⋯S, and C-H⋯O. (1)H and (13)C NMR spectra reveal the purity of 1 while its transparent nature can be evidenced from the UV-Vis-NIR spectral data. In compound 1 which exhibits SHG property, the infrared and Raman spectra confirm the presence of the organic dication and the thiosulfate anion.

Three novel benzothiazine-fused triazoles as potential centrally acting muscle relaxants

The structures of the novel triazolobenzothiazines 2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thiazin-1-one (IDPH-791), C(9)H(7)N(3)OS, (I), a potential muscle relaxant, its benzoyl derivative, 2-(2-oxo-2-phenylethyl)-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thiazin-1-one, C(20)H(17)N(3)O(4)S, (II), and the β-keto ester derivative, ethyl 3-oxo-2-(1-oxo-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]thiazin-2-yl)-3-phenylpropanoate, C(17)H(13)N(3)O(2)S, (III), are the first examples of benzothiazine-fused triazoles in the crystallographic literature. The heterocyclic thiazine rings in all three structures adopt a distorted half-chair conformation. Compound (III) exists in the trans-β-diketo form. Other than N-H···O hydrogen bonds in (I) forming dimers, no formal intermolecular hydrogen bonds are involved in the crystal packing of any of the three structures, which is dominated by C-H···O/N and π-π stacking interactions.