Analysis of molecular interactions in solid dosage forms; challenge to molecular pharmaceutics

The molecular states of active pharmaceutical ingredients (APIs) in pharmaceutical dosage forms strongly affect the properties and quality of a drug. Various important fundamental physicochemical studies were reviewed from the standpoint of molecular pharmaceutics. Mechanochemical effects were evaluated in mixtures of APIs and pharmaceutical additives. Amorphization, complex formation and nanoparticle formation are observed after grinding process depending on the combination of APIs and pharmaceutical additives. Sealed-heating method and mesoporous materials have been used to investigate drug molecular interactions in dosage forms. Molecular states have been investigated using powder X-ray diffraction, thermal analysis, IR, solid state fluorometry, and NMR.     

Physico-chemical characterization of an active pharmaceutical ingredient

The physico-chemical properties and polymorphism of a new active pharmaceutical ingredient entity has been analyzed and the gain of knowledge during the chemical development of the substance is described. Initial crystallization revealed an anhydrous crystal form with good crystallinity and a single, sharp DSC melting peak at 171°C and a straightforward development of this crystal form seemed possible. However, during polymorphism screening, new crystalline forms were detected that were often analyzed as mixtures of crystal forms. The process of characterization and identification of the different crystalline forms and its thermodynamical relationship has been supported by a combination of experimental and computational work including determination of the three-dimensional structures of the crystal forms. The crystal structure of one polymorphic form was solved by single crystal X-ray structure analysis. Unfortunately, Mod B resisted in formation of suitable single crystals, but its structure could be solved by high resolution powder diffraction data analysis using synchrotron radiation. Calculation of the theoretical X-ray powder diffraction pattern from three dimensional crystal coordinates allowed an unambiguous identification of the different crystalline forms. Two polymorphic crystal forms of the API-CG3, named Mod A and Mod B, are enantiotropic whereas Mod B is the most stable polymorph at room temperature up to about 50°C and Mod A at temperatures above 50°C. The mechanism of the solid-solid transition can be explained by analyzing the molecular packing information gained from the single crystal structures. A third crystalline form with the highest melting peak turned out to be not a polymorphic or pseudopolymorphic crystal modification of our API-CG3 but a chemically different substance. This revised version was published online in July 2006 with corrections to the Cover Date.     

手性尼莫地平绝对构型的确定和关联

概述了手性1, 4-二氢吡啶类（1, 4-DHPs）钙拮抗剂的立体化学结构及其药效与绝对构型的关系,以及尼莫地平（nimodipine）的多晶型现象。采用单晶X射线衍射与固体和溶液圆二色（ECD）光谱直接关联的方法,对自发拆分获得的一对尼莫地平外消旋聚集体进行了绝对构型确定,首次获得了手性1, 4-DHPs类化合物的固体和溶液ECD光谱图。本方法对确认有机小分子的绝对构型,以及关联系列手性1, 4-DHP衍生物的绝对构型具有重要参考价值,同时提供了有别于常规非手性方法鉴别优势手性药物晶型的有效手段。     

The Richest Collection of Tautomeric Polymorphs: The Case of 2‐Thiobarbituric Acid

Five new polymorphs and one hydrated form of 2‐thiobarbituric acid have been isolated and characterised by solid‐state methods. In both the crystalline form II and in the hydrate form, the 2‐thiobarbituric molecules are present in the enol form, whereas only the keto isomer is present in crystalline forms I (reported in 1967 by Calas and Martinex), III , V and VI . In form IV , on the other hand, a 50:50 ordered mixture of enol/keto molecules is present. All new forms have been characterised by single‐crystal X‐ray diffraction, 1D and 2D (¹H, ¹³C, and ¹⁵N) solid‐state NMR spectroscopy, Raman spectroscopy and X‐ray powder diffraction at variable temperature. It has been possible to induce keto–enol conversion between the forms by mechanical methods. The role of hydrogen‐bond interactions in determining the relative stability of the polymorphs and as a driving force in the conversions has been ascertained. To the best of the authors’ knowledge, the 2‐thiobarbituric family of crystal forms represents the richest collection of examples of tautomeric polymorphism so far reported in the literature.     

Two Crystal Forms of a Hydrated 2:1 β-Cyclodextrin Fluconazole Complex: Single Crystal X-ray Structures,Dehydration Profiles,and Conditions for Their Individual Isolation

Inclusion complexes between cyclodextrins (CDs) and active pharmaceutical ingredients (APIs) have potential for pharmaceutical formulation. Since crystallization of a given complex may result in the isolation of multiple crystal forms, it is essential to characterize these forms with respect to their structures and physicochemical properties to optimize pharmaceutical candidate selection. Here, we report the preparation and characterization of two crystallographically distinct hydrated forms of an inclusion complex between β-cyclodextrin (β-CD) and the antifungal API fluconazole (FLU) as well as temperature–concentration conditions required for their individual isolation. Determination of crystal water contents was achieved using thermoanalytical methods. X-ray analyses revealed distinct structural differences between the triclinic (TBCDFLU, space group P1) and monoclinic (MBCDFLU, space group C2) crystal forms. Removal of the crystals from their mother liquors led to rapid dehydration of the MBCDFLU crystal, while the TBCDFLU crystal was stable, a result that could be reconciled with the distinct packing arrangements in the respective crystals. This study highlights (a) the importance of identifying possible multiple forms of a cyclodextrin API complex and controlling the crystallization conditions, and (b) the need to characterize such crystal forms to determine the extent to which their physicochemical properties may differ.     

Three polymorphic forms of the co-crystal 4,4'-bipyridine/pimelic acid and their structural, thermal, and spectroscopic characterization

Three crystal forms of the co-crystal 4,4'-bipy/pimelic acid (bipy: bipyridine), [NH(4)C(5)-C(5)H(4)N][HOOC(CH(2))(5)COOH], have been prepared and their relationship investigated by single-crystal X-ray diffraction, variable-temperature X-ray powder diffraction, differential scanning calorimetry and solid-state NMR spectroscopy. Both X-ray and NMR spectroscopic results indicate that no proton transfer takes place, that is, the three crystal forms are true co-crystals of neutral molecules. Forms I and II both convert into Form III at high temperature, Forms II and III being the thermodynamically stable forms at room and high temperature, respectively.     

Absolute Configuration of Pharmaceutical Research Compounds Determined by X‐ray Powder Diffraction

The absolute configuration of active pharmaceutical ingredients (APIs) was determined by generating salts of the active pharmaceutical ingredient (API) with counterions of known chirality, and determining the crystal structures by X‐ray powder diffraction. This approach avoids the (often tedious) growth of single crystals, and is successful with very limited quantities of material (less than 1 mg). The feasibility of the method is demonstrated on five examples, and its limitations are discussed as well.     

A synthetic tripeptide as a novel organo-gelator: a structural investigation

A self-associating synthetic tripeptide [Boc-Ala(1)-Aib(2)-β-Ala(3)-OMe (Aib: α-amino-isobutyric acid, β-Ala: β-alanine)] forms thermoreversible transparent gels in various organic solvents and this offers the first example of a peptide gelator whose molecular self-assembly afforded for gelation has been characterised by single-crystal X-ray diffraction and FT-IR and NMR spectroscopic studies. The crystal structure of an analogous synthetic non-gelator tripeptide [Boc-Ala(1)-Gly(2)-β-Ala(3)-OMe] is also discussed in light of the self-assembly of the gelator tripeptide.     

Bulk material vs. single crystal: powder diffraction to the rescue

The crystal structure of bulk microcrystalline material obtained by interaction of two rigid building blocks, namely dirhodium(ii) tetra(trifluoroacetate), [Rh2(O2CCF3)4], and bis(4'-pyridyl)diphenylsilane, (C6H5)2Si(C5H4N)2, has been solved ab initio using X-ray powder diffraction data. The title product of the 1 [ratio] 1 composition, [Rh2(O2CCF3)4.(mu2-(C6H5)2Si(C5H4N)2)], is a one-dimensional zigzag polymer built on axial Rh...N interactions averaged at 2.16 A. Its structural characterization complements the previously reported product of the 2:1 composition obtained from the same reaction, namely {[Rh2(O2CCF3)4]2.(mu4-(C6H5)2Si(C5H4N)2)}. The latter has a 2D layered network revealed by the single crystal diffraction study. A combination of powder and single crystal X-ray techniques is shown to be methodologically important and complementary for understanding of product assembling in the system.     

Kinetic and thermodynamic stability of cluster compounds under heating

A new polymorphic form of Norfloxacin has been identified and fully characterized by a variety of methods including powder X-ray diffraction, vibrational spectroscopy (IR and Raman), thermal analysis (DSC and TG), SEM and solid-state NMR spectroscopy. The relationship between the new form C and the previously known forms A and B have been studied. Moreover, the crystal structure of the known form A has been solved by single-crystal methods.     

A new liquid crystal compound based on an ionic imidazolium salt

The preparation of 1,3-bis-(4-dodecyloxy-phenyl)-3H-imidazol-1-ium trifluoro-methanesulfonate is described from the 4-dodecyloxy phenylamine derivative. This new imidazolium salt exhibits a lamellar liquid crystal mesophase between 119 and 172 °C. The Smectic A phase has been characterised by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. In addition the lamellar crystallographic structure obtained on single crystal is reported and corroborated the self-assembly of molecules in the mesomorphic state.     

含吡咯三齿席夫碱配体的单核铜(Ⅱ)配合物的合成、晶体结构和性质

合成和表征了两个类似的三齿席夫碱配体(L1)-和(L2)-的铜[Ⅱ]配合物[CuL1I](1)和[CuL2I](2)(HL1为2-(2-pyridyl)-N-[1-(1H-pyrrol-2-yl)ethylidene]ethanamine;HL2为N-[1-(1H-pyrrol-2-yl)ethylidene](2-pyridyl)methanamine),并用红外光谱、电喷雾质谱、紫外-可见光谱、单晶X-射线衍射和热重分析等手段对配合物进行了表征。对配合物1的X-射线晶体结构测定表明它是一个畸变的平面正方形单核铜[Ⅱ]配合物。晶体结构还表明,除了配体的柔性和空间限制外,分子间的相互作用也是影响铜[Ⅱ]配合物结构的因素。     

Quantification of flupirtine maleate polymorphs using X-ray powder diffraction

Flupirtine maleate,a pharmaceutical compound for treating psychotic disease in clinics,has seven polymorphs.Form A,with better crystal stability and bioavailability,has been widely used as the pharmaceutical crystal form.Unfortunately,it is usually found in a polymorphic mixture with form B.In this study,pure crystal forms of A and B were prepared and characterized by X-ray powder diffraction (XRPD),Fourier transform infrared spectroscopy (FT-IR) and thermal analysis.An XRPD-based method for the quantitative determination of the amount of the flupirtine maleate polymorphs form A and form B was also established through a systematic optimization of instrumental parameters.The results of the analytical methodology validation showed that the XPRD method had a broad quantitative range of 0-100%(w/w),good linear relationship,with R²=0.999,excellent repeatability and precision and low limits of detection (LoD) of 0.15%(w/w) and quantification (LoQ) of 0.5%(w/w).The results also showed that the single-peak method was not as good as the whole pattern in reducing the influence of the preferred orientation,but this can be compensated for by a systematic optimization of instrumental parameters and validating the analytical methodology to reduce errors and obtain a good,repeatable,sensitive,and accurate method.This XRPD method can be used to analyze mixtures of flupirtine maleate polymorphs (forms A and B) quantitatively and control the quality of the bulk drug.     

Synthesis and Crystal Structure of 1-（4-Fluorophenyl）-2-hexylthiobenzo[4,5]-furo[3,2-d]-1,2,4-triazolo[1,5-a]pyrimidin-5（1H）-one

The crystal structure of the title compound 1-(4-fluorophenyl) -2-hexylthio-benzo [4,5]furo[3,2-d]-1,2,4-triazolo[1,5-a]pyrimidin-5(1H) -one(C23H21FN4O2S,Mr = 436.5) has been prepared and determined by single-crystal X-ray diffraction. The crystal is of monoclinic,space group P21/n with a = 13.9854(3) ,b = 17.2678(4) ,c = 18.1828(5) ,β = 99.364(2) °,V = 4332.58(18) 3,Z = 4,Dc = 1.338,F(000) =1824,μ = 0.185 mm-1,MoKa radiation(λ = 0.71073) ,R = 0.0538 and wR = 0.1162 for 4728 observed reflections with I > 2σ(I) . X-ray diffraction analysis reveals the fused rings of benzo[4,5]furo[3,2-d]-1,2,4-triazolo[1,5-a] pyrimidin-5(1H) -one system are nearly coplanar. The crystal packing is mainly stabilized by weak intermolecular C-H···O hydrogen bond and π-π interactions.     

Identification and quantitative determination of atorvastatin calcium polymorph in tablets using FT-Raman spectroscopy

Atorvastatin calcium (ATC) is the active pharmaceutical ingredient (API) of the best selling lipid-lowering formulation Lipitor. Twelve ATC crystal forms are known and several pharmaceutical companies are developing or have developed generic drug formulations based on different ATC polymorphs. The strong overlap of the X-ray diffraction patterns (XRD) of the polymorphs with the respective patterns of the excipients, the presence of small API quantities in the tablet and the similarity of the crystal phase VIII XRD pattern used in the tablet examined in this work to that of phases IV and IX made identification difficult. Quantitative determination of ATC was attempted using Raman spectroscopy (RS), IR spectroscopy and X-ray powder diffraction. It was found that RS exhibited lower detection limit and a calibration model was constructed. Its application on commercial ATC tablets with 40mg strength yielded an error of 1.25%.     

Synthesis and Crystal Structure of 2（1-Phenyl-3-methyl-5-chloro-1H-pyrazol-4-yl）-3-（1-naphthoylamido）-4-thiazolidinone

1INTRODUCTIONManypyrazolederivativeshavebeenreportedtoshowvariousbiologicalactivitiestobeusedasbactericide[1],fungicide[2],herbicide[3],insecticide[4]andvirucide[5]agents.Inaddition,4-thiazolidinoneplaysavitalroleowingtoitswiderangeofbiologi-calactivities…     

Synthesis and Crystal Structure of Ethyl 3-（4-Chlorophenyl）-3,4-dihydro-6-methyl-4-oxo-2- （pyrrolidin-1-yl）furo[2,3-d]pyrimidine-5-carboxylate

The crystal structure of the title compound ethyl 3-（4-chlorophenyl）-3,4-dihydro-6- methyl-4-oxo-2-（pyrrolidin-1-yl）furo[2,3-d]pyrimidine-5-carboxylate （C20H20ClN3O4, Mr= 401.84） has been prepared and determined by single-crystal X-ray diffraction. The crystal is of monoclinic, space group P21/n with a = 20.6215（9）, b = 8.5311（4）, c = 21.6886（9） A^°, β = 91.607（1）°, V = 3814.0（3）A^°^3, Z = 8, Dc = 1.400 g/cm^3, F（000） = 1680, μ = 0.233 mm^-1, R = 0.0718 and wR = 0.1545 for 6717 observed reflections with I 〉 2σ（I）. X-ray diffraction analysis reveals two crystallographically independent molecules in the asymmetric unit.     

Azoimidazole Complexes of Manganese(II)-thiocyanate. X-ray Structures of 2-(p-tolylazo)imidazole and Bis-[1-methyl-2-(p-tolylazo)imidazole]- Di-thiocyanato-manganese(II)

The reaction of Mn(OAc)₂ · 4H₂O and 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/), Et (2/4/)] and NH₄NCS in MeOH in a 1:2:2 mole ratio afforded [Mn(RaaiR′)₂(NCS)₂] (3) and (4) complexes. They were characterized by different physicochemical methods and the structure has been confirmed by single crystal X-ray diffraction study for title compound. One of the primary ligands was also characterised by an X-ray diffraction study.     

Synthesis and Crystal Structure of （S）-Ethyl-2-（2-methoxy-phenylsulfenamido）-3-（1H-indol-3-yl）propanoate

With an aim to discover novel AHAS inhibitors,the title compound (S)-ethyl-2(2-methoxy-phenylsulfenamido)-3-(1H-indol-3-yl)propanoate (C 21 H 22 N 2 O 4 S,M r=398.47) has been synthesized and its crystal structure was determined by single-crystal X-ray diffraction analysis.The crystal belongs to orthorhombic,space group P2 1 2 1 2 1 with a=8.078(2),b=12.824(4),c=18.788(6),V=1946.2(10) 3,Z=4,F(000)=840,D c=1.360 mg/m 3,μ=0.197 mm-1,the final R=0.0433 and wR=0.1035 for 3075 observed reflections with I > 2σ(Ⅰ).The absolute structure Flack parameter X of this compound is 0.00(8).A total of 14375 reflections were collected,of which 3431 were independent (R int=0.0437).X-ray analysis reveals that the crystal structure involves two intermolecular N-H···O and one N-H···S intermolecular hydrogen bonds with the neighboring molecules.The crystal structure was compared with our previously reported (S)-methyl 2-(4-R-phenylsulfonamido)-3-(1H-indol-3-yl)propanoate (R=H(1) and Cl(2)),which provided some useful information of these compounds.     

Synthesis and structural characterisation of (aryl-BIAN)copper(I) complexes and their application as catalysts for the cycloaddition of azides and alkynes

A series of Ar-BIAN-based copper(I) complexes (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine) were synthesised and characterised by (1)H and (13)C NMR spectroscopies, FT-IR spectroscopy, MALDI-TOF-MS spectrometry, cyclic voltammetry and single crystal X-ray diffraction. The bis-chelated complexes of general formula [Cu(Ar-BIAN)(2)]BF(4) (where Ar = C(6)H(5) (1), 4-iPrC(6)H(4) (3), 2-iPrC(6)H(4) (4)) were prepared by reaction of [Cu(NCMe)(4)]BF(4) with two equivalents of the corresponding Ar-BIAN ligands, in dichloromethane, while the mono-chelated complexes of the type [Cu(Ar-BIAN)L(2)]BF(4) (where Ar = 2,6-iPr(2)C(6)H(3), L = PhCN (6); Ar = 4-iPrC(6)H(4), L = PPh(3) (7)) were readily accessible by treatment of [Cu(NCR)(4)]BF(4) (R = Me, Ph) with one equivalent of the corresponding Ar-BIAN ligands in the absence or presence of two equivalents of PPh(3), in the same solvent. The structures of complexes 3, 4, 6 and 7 were obtained by single crystal X-ray diffraction, showing distorted tetrahedral geometries around the copper centres in all cases. The electrochemical studies of these complexes and of the already reported [Cu(2,4,6-Me(3)C(6)H(2)-BIAN)(2)]BF(4) (2) and [Cu(2,6-iPr(2)C(6)H(3)-BIAN)(NCMe)(2)] (5), demonstrated that the bis-chelated complexes 1-4 undergo a reversible one-electron reduction or oxidation processes on copper, while the mono-chelated complexes 5-7 show a partially reversible oxidation and an irreversible reduction feature. Both kinds of (Ar-BIAN)copper(I) complexes are active catalysts for the copper(I)-catalysed azide-alkyne cycloaddition reaction (CuAAC). Complex 7, bearing PPh(3) ligands, exhibits the highest catalytic activity, which is comparable with that of the typical CuSO(4)-sodium ascorbate catalyst system.