Investigation of Solid Dosage Form Components Interaction Using Orthogonal Techniques- Discovery of New Forms of Sodium Stearyl Fumarate.

Physical or chemical interactions between drug product (DP) components can occur during manufacturing and/or upon storage; and may alter DP shelf life and performance. In this work a new Powder X-ray Diffraction (PXRD) peak was observed in DP under accelerated storage conditions. Due to the complex drug product matrix (including API, polymer, fillers, super disintegrant and lubricant), it was challenging to pinpoint the component(s) responsible for the new peak. In addition to PXRD, other orthogonal techniques including Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA), dynamic vapor sorption (DVS), Solid State Nuclear Magnetic Resonance (SSNMR) and Infrared (IR) spectroscopy were employed in this investigation to understand the root cause mechanistically. Specifically, multi nuclei SSNMR (1H, 23Na, 13C) was instrumental in delineating the components of the matrix. We identified the root cause to be an acid base reaction occurring in the DP, whereby sodium ion in sodium stearyl fumarate (SSF) is replaced by proton leading to SSF form conversion. We also identified commercially available SSF to be a hydrate that can dehydrate to an anhydrous form upon heating. In general, the same techniques can be used to investigate interactions of any multi component solid dosage forms.

Solid-state NMR analysis of a complex crystalline phase of ronacaleret hydrochloride.

A crystalline phase of the pharmaceutical compound ronacaleret hydrochloride is studied by solid-state nuclear magnetic resonance (SSNMR) spectroscopy and single-crystal X-ray diffraction. The crystal structure is determined to contain two independent cationic molecules and chloride anions in the asymmetric unit, which combine with the covalent structure of the molecule to yield complex SSNMR spectra. Experimental approaches based on dipolar correlation, chemical shift tensor analysis, and quadrupolar interaction analysis are employed to obtain detailed information about this phase. Density functional theory (DFT) calculations are used to predict chemical shielding and electric field gradient (EFG) parameters for comparison with experiment. (1)H SSNMR experiments performed at 16.4 T using magic-angle spinning (MAS) and homonuclear dipolar decoupling provide information about hydrogen bonding and molecular connectivity that can be related to the crystal structure. (19)F and (13)C assignments for the Z' = 2 structure are obtained using DFT calculations, (19)F homonuclear dipolar correlation, and (13)C-(19)F heteronuclear dipolar correlation experiments. (35)Cl MAS experiments at 16.4 T observe two chlorine sites that are assigned using calculated chemical shielding and EFG parameters. SSNMR dipolar correlation experiments are used to extract (1)H-(13)C, (1)H-(15)N, (1)H-(19)F, (13)C-(19)F, and (1)H-(35)Cl through-space connectivity information for many positions of interest. The results allow for the evaluation of the performance of a suite of SSNMR experiments and computational approaches as applied to a complex but typical pharmaceutical solid phase.

Confocal UV and resonance Raman microscopic imaging of pharmaceutical products.

Chemical imaging using confocal Raman microscopy is a useful analytical tool in drug development because of its ability to spatially image active ingredients and excipients in dosage forms and relate their distribution to product performance. While Raman spectra are highly specific for individual components of a formulation, most Raman microscopic mapping experiments require extensive experimental time. Laser wavelengths in the near-infrared range are used to suppress fluorescence but reduce sensitivity because of the inverse quadratic dependence of Raman scattering on laser wavelength. Compact, simple ultraviolet (UV) laser designs now allow for confocal UV Raman microscopy to be performed using a versatile instrument also capable of conventional Raman microscopy and epifluorescence imaging analyses. This study presents the results of UV Raman microscopy analyses using 266 nm laser irradiation of four pharmaceutical compositions of interest, including two types of tablets containing low doses of active ingredients (in the 0.2% w/w range), an amorphous dispersion containing 1% w/w of a small molecule drug, and an enteric coated layered peptide formulation. Resonance Raman enhancements are observed for four of the active ingredients studied in these formulations. The spectroscopic properties of the materials used in this study are also assessed by diffuse reflectance UV-visible spectroscopy, fluorescence spectroscopy, and conventional bulk Fourier transform Raman spectroscopy using 1064 nm laser irradiation. Confocal UV Raman microscopy was found to offer good sensitivity and allowed for rapid microscopic mapping of drugs and excipients at low concentrations in pharmaceutical formulations.

2D solid-state NMR analysis of inclusion in drug-cyclodextrin complexes.

The solubility of drug molecules can often be improved through preparation and delivery of cyclodextrin (CD) inclusion complexes. These drug-oligosaccharide complexes can be prepared in solution and converted to the solid state via methods such as lyophilization and spray-drying, or they can be prepared directly from solids by a variety of methods. The development of drug-CD complexes as solids allows for potential advantages in dosage form design, such as the preparation of layered formulations, and it also can yield improvements in chemical and physical stability. 2D solid-state NMR (SSNMR) methods provide a direct way to probe drug-CD interactions in solid complexes through dipolar interactions between nuclei within the drug and CD molecules. In this study, 2D heteronuclear and homonuclear correlation SSNMR experiments involving (1)H, (13)C, (19)F, and (31)P nuclei are used to demonstrate the inclusion of drug within the CD cavity in a variety of powder samples. To illustrate the general applicability of the SSNMR approach presented, examples are shown for the drugs diflunisal, adefovir dipivoxil, voriconazole, dexamethasone, and prednisolone in complexes with α-CD, ß-CD, and sulfobutylether-substituted ß-CD. The quantitative analysis of included and free drug fractions in a solid drug-CD complex using SSNMR is also demonstrated. On the basis of these results, general approaches to the characterization of these materials using SSNMR are proposed.

Solid-state NMR studies of form I of atorvastatin calcium.

Solid-state (13)C, (19)F, and (15)N magic angle spinning NMR studies of Form I of atorvastatin calcium are reported, including chemical shift tensors of all resolvable carbon sites and fluorine sites. The complete (13)C and (19)F chemical shift assignments are given based on an extensive analysis of (13)C-(1)H HETCOR and (13)C-(19)F HETCOR results. The solid-state NMR data indicate that the asymmetric unit of this material contains two atorvastatin molecules. A possible structure of Form I of atorvastatin calcium (ATC-I), derived from solid-state NMR data and density functional theory calculations of various structures, is proposed for this important active pharmaceutical ingredient (API).

Analysis of amorphous solid dispersions using 2D solid-state NMR and (1)H T(1) relaxation measurements.

Solid-state NMR (SSNMR) can provide detailed structural information about amorphous solid dispersions of pharmaceutical small molecules. In this study, the ability of SSNMR experiments based on dipolar correlation, spin diffusion, and relaxation measurements to characterize the structure of solid dispersions is explored. Observation of spin diffusion effects using the 2D (1)H-(13)C cross-polarization heteronuclear correlation (CP-HETCOR) experiment is shown to be a useful probe of association between the amorphous drug and polymer that is capable of directly proving glass solution formation. Dispersions of acetaminophen and indomethacin in different polymers are examined using this approach, as well as (1)H double-quantum correlation experiments to probe additional structural features. (1)H-(19)F CP-HETCOR serves a similar role for fluorinated drug molecules such as diflunisal in dispersions, providing a rapid means to prove the formation of a glass solution. Phase separation is detected using (13)C, (19)F, and (23)Na-detected (1)H T(1) experiments in crystalline and amorphous solid dispersions that contain small domains. (1)H T(1) measurements of amorphous nanosuspensions of trehalose and dextran illustrate the ability of SSNMR to detect domain size effects in dispersions that are not glass solutions via spin diffusion effects. Two previously unreported amorphous solid dispersions involving up to three components and containing voriconazole and telithromycin are analyzed using these experiments to demonstrate the general applicability of the approach.

Solid-state 13C NMR investigations of 4,7-dihydro-1H-tricyclopenta[def,jkl,pqr]triphenylene (sumanene) and indeno[1,2,3-cd]fluoranthene: Buckminsterfullerene moieties.

4,7-Dihydro-1H-tricyclopenta[def,jkl,pqr]triphenylene (sumanene) and indeno[1,2,3-cd]fluoranthene (indenofluoranthene) are structural moieties related to Buckminsterfullerene (C(60)). As such, understanding their structural characteristics is of great interest because of the insight they shed upon C(60). Hence, solid-state NMR (ssNMR) and ab initio quantum mechanical calculations with Gaussian03 are used in order to understand and to better characterize the molecular conformation and properties of sumanene and indenofluoranthene. Sumanene has bowl shaped curvature in its natural conformation and indenofluoranthene is planar in its natural conformation, which led us to examine how altering the curvature affects the chemical shifts in relation to those of C(60). Using X-ray structures of both sumanene and indenofluoranthene as our starting model, we calculate the energy and chemical shielding tensors and compare these data with those collected utilizing the (13)C ssNMR FIREMAT experiment. We define curvature of sumanene and indenofluoranthene using the pi-orbital axis vector (POAV) pyramidalization angle (theta(p)). We calculate the energy of varying conformations of indenofluoranthene versus their theta(p) associated with each deformed conformation.

Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H-13C correlation data.

The (1)H-(13)C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by (13)C-(13)C correlations and therefore allows shorter average analysis times in natural abundance materials. The (1)H-(13)C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc)(2) phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc)(2) phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites.

Solid-state NMR spectra and long intradimer bonds in the pi-[TCNE]22- dianion.

The principal (13)C chemical-shift values for the pi-[TCNE](2)(2-) dimer anion within an array of counterions have been measured to understand better the electronic structure of these atypical chemical species in several related TCNE-based structures. The structure of pi-[TCNE](2)(2-) is unusual as it contains two very long C-C bond lengths (ca. 2.9 Angstroms) between the two monomeric units and has been found to exist as a singlet state, suggestive of a (1)A(1g) (b(2u)(2)b(1g)(0)) electronic configuration. A systematic study of several oxidation states of [TCNE](n) (n = 0, 1-, 2-) was conducted to determine how the NMR chemical-shift tensor values change as a function of electronic structure and to understand the interactions that lead to spin-pairing of the monomer units. The density functional theory (DFT) calculated nuclear shielding tensors are correlated with the experimentally determined principal chemical-shift values. Such theoretical methods provide information on the tensor magnitudes and orientations of their principal tensor components with respect to the molecular frame. Both theoretical and experimental ethylenic chemical-shielding tensors reveal high sensitivity in the component, delta(perpendicular), lying in the monomer molecular plane and perpendicular to the pi-electron plane. This largest shift dependence on charge density is observed to be about -111 ppm/e(-) for delta(perpendicular). The component in the molecular plane but parallel to the central C=C bond, delta(parallel), exhibits a sensitivity of approximately -43 ppm/e(-). However, the out-of-plane component delta'(perpendicular) shows a minimal dependence of -2.6 ppm/e(-) on the oxidation state (n) of [TCNE](n). These relative values support the claim that it is changes within the ethylenic pi-electrons and not the sigma-electrons that best account for the dramatic variations in bonding and shift tensors in this series of compounds. Concerning the intraion bonding, relatively weak Wiberg bond orders between the two monomeric components of the dimer correlate with the long bonds linking the two [TCNE(*)](-) monomers. The chemical-shift tensors for the cyano group, compared to the ethylene shifts, exhibit a reduced sensitivity on the TCNE oxidation state. The experimental principal chemical-shift components agree (within typical errors) with the calculated quantum mechanical shieldings used to correlate the bonding. The embedded ion model (EIM) was used to investigate the typically large electrostatic lattice potential in these ionic materials. Chemical-shielding principal values calculated with the EIM model differ from experiment by +/-3.82 ppm on average, whereas in the absence of an electrostatic field model, the experimental and theoretical results agree by +/-4.42 ppm, which is only a modest increase in error considering the overall ionic magnitudes associated with the tensor variations. Apparently, the effects of the sizable long-range electrostatic fields cancel when the shifts are computed because of lattice symmetry.

A new sensitive isotropic-anisotropic separation experiment-SPEED MAS.

A new sensitive 2D isotropic-anisotropic separation experiment that utilizes stroboscopic phase encoding in the evolution dimension (SPEED) under magic angle sample spinning is presented. This 2D experiment consists of a train of 2N - 1 pi pulses that are applied over 2N rotor periods. The pi pulse train effectively reduces the apparent spinning speed in the evolution dimension by a factor of 1 / (2N) from the mechanical spinning speed. Thus, problems commonly associated with magic angle turning such as stable slow spinning, different matching and TPPM proton decoupling conditions are avoided. Data replication similar to the five pi replicated magic angle turning (FIREMAT) and pseudo 2D sideband suppression (P2DSS) experiments transfers resolution from the acquisition dimension to the evolution dimension. Hence, large spectral windows with good digital resolution are obtained with a few evolution increments. Here, slow spinning sideband patterns are extracted from the replicated 2D dataset with TIGER processing. Nevertheless, 2D Fourier transformation is also applicable. The extracted sideband patterns are identical to magic angle turning sideband pattern allowing for easy extraction of principal shift components. Accurate (13)C principal shift components are obtained for 3-methylglutaric acid using SPEED and FIREMAT experiments to validate the method. Furthermore, SPEED spectra for calcium acetate and alpha santonin are reported to show the wide applicability of this new experiment.

Experimental and theoretical investigation of the 13C and 15N chemical shift tensors in melanostatin-exploring the chemical shift tensor as a structural probe.

The determination of backbone conformations in powdered peptides using 13C and 15N shift tensor information is explored. The 13C and 15N principal shift values in natural abundance 13C and 15N melanostatin (L-Pro-L-Leu-Gly amide) are measured using the FIREMAT technique. Furthermore, the orientation of the C-N bond in the 13C shift principal axis system for the backbone carbons is obtained from the presence of the 13C-14N dipolar coupling. The Ramachandran angles for the title compound are obtained from solid-state NMR data by comparing the experimentally determined shift tensor information to systematic theoretical shielding calculations on N-formyl-L-amino acid-amide models. The effects of geometry optimization and neglect of intermolecular interactions on the theoretical shielding values in the model compounds are investigated. The sets of NMR derived Ramachandran angles are assembled in a set of test structures that are compared to the available single-crystal X-ray structure. Shift tensor calculations on the test structures and the X-ray structure are used to further assess the importance of intermolecular interactions when the shift tensor is used as a structural probe in powdered peptides.

Accurate (13)C and (15)N Chemical Shift and (14)N Quadrupolar Coupling Constant Calculations in Amino Acid Crystals: Zwitterionic, Hydrogen-Bonded Systems.

EIM (embedded ion method), cluster, combined EIM/cluster, and isolated molecule (13)C and (15)N chemical shielding and quadrupolar coupling constant (QCC) calculations at the B3LYP level with D95**, D95++**, 6-311G**, and 6-311+G** basis sets were done on the amino acids l-alanine, l-asparagine monohydrate, and l-histidine monohydrate monohydrochloride and on the two polymorphs α and γ glycine. The intermolecular interactions that are present in the amino acid crystals are accounted for in the EIM calculations by a finite array of point charges calculated from Ewald lattice sums and in the cluster calculations by a shell of neighboring molecules or molecular fragments. The combined EIM/cluster calculations utilize a cluster of molecules inside an EIM point charge array. The theoretical (13)C and (15)N principal shielding values for the amino acids studied are compared to the experimental principal shift values. In addition, theoretical CN bond orientations in the chemical shift principal axis system (PAS) are compared to the experimental orientations obtained from (13)C-(14)N dipolar couplings. The theoretical QCC at the nitrogen positions are compared to experimental (14)N QCC principal values reported in the literature. The carbon and nitrogen theoretical chemical shielding, the C-N orientations, and the QCCs from the ab initio calculations show improved agreement with the experimental values when the intermolecular interactions are accounted for by EIM or cluster calculations. The EIM (13)C shielding calculations are found to give better agreement with the experimental values than cluster (13)C shielding calculations. However, to achieve good agreement between the theoretical (14)N QCC and the (15)N principal shielding values with the respective experimental values, both intermolecular electrostatic and covalent interactions have to be included explicitly in the EIM/cluster calculations.

Obtaining molecular and structural information from 13C-14N systems with 13C FIREMAT experiments.

The effect of dipolar coupling to 14N on 13C FIREMAT (five pi replicated magic angle turning) experiments is investigated. A method is developed for fitting the 13C FIREMAT FID employing the full theory to extract the 13C-14N dipolar and 13C chemical shift tensor information. The analysis requires prior knowledge of the electric field gradient (EFG) tensor at the 14N nucleus. In order to validate the method the analysis is done for the amino acids alpha-glycine, gamma-glycine, l-alanine, l-asparagine, and l-histidine on FIREMAT FIDs recorded at 13C frequencies of 50 and 100 MHz. The dipolar and chemical shift data obtained with this analysis are in very good agreement with the previous single-crystal 13C NMR results and neutron diffraction data on alpha-glycine, l-alanine, and l-asparagine. The values for gamma-glycine and l-histidine obtained with this new method are reported for the first time. The uncertainties in the EFG tensor on the resultant 13C chemical shift and dipolar tensor values are assessed.