Highly sensitive LC-MS method for stereochemical quality control of a pharmaceutical drug substance intermediate.

Stereochemical quality control for pharmaceutical drug substance intermediates is a daunting task, especially considering the need to separate multiple stereoisomers simultaneously with low ppm level sensitivity. To address these challenges, we have successfully implemented chiral column screening, and developed an ultrasensitive liquid chromatography-mass spectrometry (LC-MS) method to separate four stereoisomers including the API intermediate, its enantiomer, and two other diastereomers. Parameters such as mobile phase additives, MS fragmentor, and column temperature were optimized to achieve the desired selectivity and sensitivity. The method enabled stereoisomer detection with high sensitivity (2 ppm LOD and 5 ppm LOQ), good linearity, and desired spike recovery, and it has been successfully applied for stereoisomer quantitation in multiple large-scale batches and demonstrated chiral quality control of the drug substance intermediate.

A consortium-driven framework to guide the implementation of ICH M7 Option 4 control strategies.

The ICH M7 Option 4 control of (potentially) mutagenic impurities is based on the use of scientific principles in lieu of routine analytical testing. This approach can reduce the burden of analytical testing without compromising patient safety, provided a scientifically rigorous approach is taken which is backed up by sufficient theoretical and/or analytical data. This paper introduces a consortium-led initiative and offers a proposal on the supporting evidence that could be presented in regulatory submissions.

Evaluation of C18 monolithic columns for radiochemical purity measurement.

Speeding the analysis of reaction aliquots, high-performance liquid chromatography (HPLC) fractions and final products continue to be an area of great interest in the study of radiopharmaceuticals. Translating recently developed rapid HPLC and ultra high-performance liquid chromatography analysis approaches to radio-HPLC can sometimes be fraught with peril, owing to specific peculiarities of online radiochemical chromatographic detection (notably, a proportionally large system volume for the radio-HPLC detector). In this study, we investigate an alternate approach for rapid radio-HPLC analysis where a 150-cm C18 monolithic column is used with a 15-min run time. To ascertain this method's ability to distinguish between radiolabeled compounds with acceptable (≥97%) and unacceptable purity, the results were compared with results from a conventional HPLC 45-min method using a 25-cm C18 column, where a large radiodetector cell volume is of lower impact. Overall, for the 54 radiolabeled compounds assayed by the two methods, there were similar measured radiochemical purities, but cases were also found where there were significantly large differences between the results (>1%). A calculated confidence of ~85% was found for the 15-min monolithic method's ability to accurately reproduce the corresponding result from the 25-cm column method.

An extension of the BioAssay Ontology to include pharmacokinetic/pharmacodynamic terminology for the enrichment of scientific workflows.

With the capacity to produce and record data electronically, Scientific research and the data associated with it have grown at an unprecedented rate. However, despite a decent amount of data now existing in an electronic form, it is still common for scientific research to be recorded in an unstructured text format with inconsistent context (vocabularies) which vastly reduces the potential for direct intelligent analysis. Research has demonstrated that the use of semantic technologies such as ontologies to structure and enrich scientific data can greatly improve this potential. However, whilst there are many ontologies that can be used for this purpose, there is still a vast quantity of scientific terminology that does not have adequate semantic representation. A key area for expansion identified by the authors was the pharmacokinetic/pharmacodynamic (PK/PD) domain due to its high usage across many areas of Pharma. As such we have produced a set of these terms and other bioassay related terms to be incorporated into the BioAssay Ontology (BAO), which was identified as the most relevant ontology for this work. A number of use cases developed by experts in the field were used to demonstrate how these new ontology terms can be used, and to set the scene for the continuation of this work with a look to expanding this work out into further relevant domains. The work done in this paper was part of Phase 1 of the SEED project (Semantically Enriching electronic laboratory notebook (eLN) Data).

High throughput screening of active pharmaceutical ingredients by UPLC.

Ultra performance LC (UPLC) was evaluated as an efficient screening approach to facilitate method development for drug candidates. Three stationary phases were screened: C-18, phenyl, and Shield RP 18 with column dimensions of 150 mm x 2.1 mm, 1.7 microm, which should theoretically generate 35,000 plates or 175% of the typical column plate count of a conventional 250 mm x 4.6 mm, 5 microm particle column. Thirteen different active pharmaceutical ingredients (APIs) were screened using this column set with a standardized mobile-phase gradient. The UPLC method selectivity results were compared to those obtained for these compounds via methods developed through laborious trial and error screening experiments using numerous conventional HPLC mobile and stationary phases. Peak capacity was compared for columns packed with 5 microm particles and columns packed with 1.7 microm particles. The impurities screened by UPLC were confirmed by LC/MS. The results demonstrate that simple, high efficiency UPLC gradients are a feasible and productive alternative to more conventional multiparametric chromatographic screening approaches for many compounds in the early stages of drug development.

Efficient HPLC method development using structure-based database search, physico-chemical prediction and chromatographic simulation.

Development of a robust HPLC method for pharmaceutical analysis can be very challenging and time-consuming. In our laboratory, we have developed a new workflow leveraging ACD/Labs software tools to improve the performance of HPLC method development. First, we established ACD-based analytical method databases that can be searched by chemical structure similarity. By taking advantage of the existing knowledge of HPLC methods archived in the databases, one can find a good starting point for HPLC method development, or even reuse an existing method as is for a new project. Second, we used the software to predict compound physicochemical properties before running actual experiments to help select appropriate method conditions for targeted screening experiments. Finally, after selecting stationary and mobile phases, we used modeling software to simulate chromatographic separations for optimized temperature and gradient program. The optimized new method was then uploaded to internal databases as knowledge available to assist future method development efforts. Routine implementation of such standardized workflows has the potential to reduce the number of experiments required for method development and facilitate systematic and efficient development of faster, greener and more robust methods leading to greater productivity. In this article, we used Loratadine method development as an example to demonstrate efficient method development using this new workflow.

Gas chromatographic analysis of the thermally unstable dimethyl methylphosphonate carbanion via trimethylsilyl derivatization.

A sensitive gas chromatographic method was developed to monitor the reaction of lithium diisopropylamide (LDA) with dimethyl methylphosphonate (DMMP) to generate the phosphonate carbanion (DMMPA). Analysis of the DMMPA was complicated due to its thermal instability and lack of a chromophore. To overcome these problems, samples were derivatized with trimethylsilylchloride (TMSCI) to form DMMPA-TMS which was sufficiently volatile and thermally stable for GC analysis. Work-up of the derivatized solution with 10 vol.% 2-propanol in hexanes was necessary to quench residual TMSCI prior to GC analysis. The presence of DMMPA-TMS and other sample components was confirmed by GC-MS analysis. This method was utilized to profile the synthesis of DMMPA as DMMP was added to LDA and then aged at -78 degrees C. Method precision for DMMPA-TMS of less than 0.2% RSD was achieved for repeat injections after normalization of the response with n-dodecane contained in the sample. Due to the thermal instability of the DMMPA, subambient derivatization temperatures were essential to the stability, and consequently, accurate quantification. Under optimized conditions, this derivatization was successfully utilized as a process monitoring tool.

Determination of minor conformational changes of a doxorubicin-peptide conjugate under chromatographic conditions.

Thermodynamic analysis of the reversed-phase retention behavior of a doxorubicin-peptide conjugate demonstrated that the degree of non-linearity observed in Van't Hoff plots was impacted by mobile phase acetonitrile content over the 25-38% acetonitrile (v/v) range tested. Small decreases in the non-polar surface area of the doxorubicin-peptide conjugate as a function of temperature were estimated from these data using linear solvent strength relationships, suggesting that the retention behavior may be the result of minor analyte conformational changes during the chromatographic experiment. This hypothesis was supported via circular dichroism (CD), Raman and 1H NMR spectroscopic studies of the doxorubicin-peptide conjugate in selected chromatographic mobile phase compositions. The CD and Raman data indicated small changes to the apparent analyte microenvironment as a function of temperature and bulk solvent environment, while 1H NMR studies specifically demonstrated the environmental sensitivity of protons on three non-polar peptide residues and the proximal aromatic region of the analyte. Together, these data suggest that minor changes to the conformational order of the essentially random structure of the doxorubicin-peptide conjugate are sufficient to impact chromatographic performance.

Investigations into the chromatographic behavior of a doxorubicin-peptide conjugate.

HPLC impurity profile method development for a doxorubicin-heptapeptide conjugate included significant changes of the separation profile with diluent, eluent and pH. These separation variables were also temperature-dependent with a shift in retention from 35 to 45 degrees C. There was also a direct relationship of temperature with LC retention, and a pH minimum at 5.9. Atypical dependence of the impurity profile on diluent at a k' of 18 led to further investigation. A large change in retention by several minutes was a function of both the organic eluent composition and temperature between 15 and 30 degrees C. Several Van't Hoff temperature studies from 5 to 65 degrees C on several column types resulted in non-linear plots. Analysis of the molecular subunits suggested that the peptide portion of the analyte influenced the non-linear retention behavior. The stationary phase type was not a significant factor causing non-linearity. Circular dichroism-temperature studies indicated a notable transition in ellipticity for the amine regions (198-202 nm) that occurred between 39 and 44 degrees C. This transition temperature range coincided with the results of the Van't Hoff analysis, between 35 and 44 degrees C, to indicate that these effects were not primarily stationary phase induced.

In situ moisture determination of a cytotoxic compound during process optimization.

A simple and safe prototype apparatus was designed and adapted for the in situ determination of the moisture content of a cytotoxic compound (9-fluorenylmethyl-protected doxorubicin-peptide conjugate, or Fm-DPC) by near-infrared absorbance spectroscopy during optimization of the chemical isolation procedure. The cytotoxic nature of the compound restricts one's ability to safely sample such drying processes for more traditional means of moisture determination for fear of hazardous solids dusting, hence in situ sampling approaches are of great importance. These concerns also exist for the process development laboratory, where despite the smaller scale of operations, the volume of experiments (hence cytotoxic samples) required to define a chemical process is often more significant. In this application, partial least squares regression was used with Karl Fischer volumetric titration analysis to generate a calibration model. Although pronounced differences in cake density were observed as a function of the buffer selected for the isolation process, the model still achieved a standard error of calibration of 0.63% w/w and a standard error of prediction of 0.99% (w/w). These results demonstrated the versatility of the prototype apparatus/data processing approach to model Fm-DPC drying under extremely variable conditions, as inherently expected during the investigational laboratory development of a chemical process.

Employment of on-line FT-IR spectroscopy to monitor the deprotection of a 9-fluorenylmethyl protected carboxylic acid peptide conjugate of doxorubicin.

A method for accurately determining the end-point, >98% conversion, of the deprotection reaction of a highly toxic 9-fluorenylmethyl (Fm) ester 1b to its corresponding carboxylate 1d in real time by FT-IR spectroscopy is reported. Advantages of this method over analysis by conventional chromatographic means include real time determination of the end-point of a reaction that is time sensitive to by-product formation, and elimination of sampling a highly toxic reaction mixture. The FT-IR method is based on monitoring, in real time, the disappearance of the Fm ester carbonyl band for 1b at 1737 cm(-1), during deprotection by piperidine, and calibration models were established by Partial Least Squares (PLS) regression analysis with high performance liquid chromatography (HPLC) as reference. The best calibration model was built with 5 PLS factors in the spectral range of 1780-1730 and 1551-1441 cm(-1) and resulted in a standard error of cross validation (SECV) of 0.63 mM 1b and a standard error of prediction (SEP) of 0.51 mM 1b in the range of 0-25 mM. This error of prediction is approximately 0.8% of the initial concentration of 1b and is well within our specifications of <2% initial concentration.

High-efficiency sample preparation with dimethylformamide for multi-element determination in pharmaceutical materials by ICP-AES.

The pressure to reduce cycle times of sample analysis has made it increasingly important to improve sample throughput during pharmaceutical process development. For ICP-based analyses, sample preparation is often the bottleneck of the entire analytical scheme due to the tedious digestion procedure and lacking a universal diluent for organic compounds. In this work, N,N-dimethylformamide (DMF) was used as a "universal" organic diluent so that the sample preparation can be simplified as a "dilute-and-shoot" procedure. An optimized interface with a commercial membrane desolvation unit was implemented, which enabled the introduction of organic solvents into an ICP-AES without organic loading. Mixed standard solutions of 15 elements (Al, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pd, Pt, Rh, Ru, W, Zn, and Zr), which covered the majority of processing metals routinely monitored in pharmaceutical development, were prepared for the study and stability of each element in a multi-element DMF solution was investigated. It was found that the addition of a stabilizing agent (EDTA) was necessary to ensure that all the elements at concentrations of 0.10-0.50 microg/mL remained physically stable in solution (recovery better than 95%) for 2 weeks. It was also important to use an internal standard (yttrium) in order to compensate for signal drift and matrix effects from different sample matrices. A 2-10-fold increase of sensitivity (due to enhanced analyte transport efficiency) and acceptable levels of precision (RSD<3%) and recoveries (91-111%) were achieved. The LOQs of all 15 elements were less than 10 microg/L in the solution, which translates to less than 5 microg/g or microg/mL in pharmaceutical samples tested. This technique would minimize the effort required for sample preparation, thus reducing the cycle time by approximately 60-90% in the entire analytical scheme for samples that are difficult to be dissolved in nitric acid. This will provide opportunities for a new level of sample handling and automation for metal analysis in pharmaceutical process development.

Simultaneous enantioseparation of a basic active pharmaceutical ingredient compound and its neutral intermediate using reversed phase and normal phase liquid chromatography with a new type of polysaccharide stationary phase.

Simultaneous enantioseparation of a basic API compound, (R)-2-Amino-N-[2-[1,2-dihydro-1-(methylsulfonyl) spiro [3H-indole-3,4'-piperidin]-1'-yl]-2-oxo-1-[(phenylmethyloxy) ethyl]-2-methylpropanamide monomethanesulfonate (compound-A) and its neutral penultimate intermediate, (R)-2-BOC-Amino-N-[2-[1,2-dihydro-1-(methylsulfonyl) spiro [3H-indole-3,4'-piperidin]-1'-yl]-2-oxo-1-[(phenylmethyloxy) ethyl]-2-methylpropanamide monomethanesulfonate (compound-B) was investigated using reversed phase (RPLC) and normal phase liquid chromatography (NPLC). After an initial screening, a Sepapak-4 column, a new type of polysaccharide chiral stationary phase (CSP), was selected for further method development based on hits on separation selectivity for both compounds under RPLC and NPLC. After comparing the pros and cons, a method utilizing the Sepapak-4 chiral column (150 mm x 4.6 mm, 3 microm particle size) in RPLC mode was finally developed. Separations were performed in gradient elution mode starting at 50% A (10 mM, NH(4)COOH at pH 6.5)/50% B (50/50 EtOH/MeCN) to 25% A (10 mM, NH(4)COOH at pH 6.5)/75% B (50/50 EtOH/MeCN). The flow rate was 1.0 mL/min; the column temperature was 50 degrees C; the UV wavelength was 220nm and the mass spectrometric detection was APCI in the positive ionization mode. The reaction mixture sample was directly diluted in ethanol. Baseline enantioseparation were achieved for both compound-A and its intermediate simultaneously with resolution greater than 2.0. The method was validated in terms of injection precision, linearity, limit of detection (LOD), limit of quantitation (LOQ), accuracy, and ruggedness. The specificity of the method was further evaluated by spiking a mixture of enantiomers of compound-A and its intermediate into a reaction matrix containing all of the synthetic reagents. No matrix interference was observed across the elution windows of compound-A and its intermediate. Additionally, the peak purity of each enantiomer was evaluated by mass spectra, indicating the specificity of the method.

Development of LC chiral methods for neutral pharmaceutical related compounds using reversed phase and normal phase liquid chromatography with different types of polysaccharide stationary phases.

The enantioselectivity of a collection of neutral pharmaceutical compounds on six different types of polysaccharide chiral stationary phases (CSPs), Chiralpak AD (and AD-RH), Chiralcel OD (and OD-RH), Chiralpak OJ (and OJ-R), Chiralcel AS (and AS-RH), Sepapak-2 and Sepapak-4 are compared using reversed phase (RPLC) and normal phase liquid chromatography (NPLC). Screening strategies for maximizing the probability of achieving an initial chiral separation hit for neutral compounds using both RPLC and NPLC are described. Further method optimizations are demonstrated by modifying parameters such as organic modifier composition, eluent pH or CSP particle size. Several practical examples of the application of chiral methods for the study of synthetic reaction mixtures are presented. The most critical validation aspects, including limit of detection, specificity, and ruggedness, are also briefly presented.

Use of a quality-by-design approach to justify removal of the HPLC weight % assay from routine API stability testing protocols.

Due to the high method variability (typically > or = 0.5%, based on a literature survey and internal Merck experience) encountered in the HPLC weight percent (%) assays of various active pharmaceutical ingredients (APIs), it is proposed that the routine use of the test in stability studies should be discouraged on the basis that it is frequently not sufficiently precise to yield results that are stability-indicating. The high method variability of HPLC weight % methods is not consistent with the current ICH practice of reporting impurities/degradation products down to the 0.05% level, and it can lead to erroneous out-of-specification (OOS) results that are due to experimental error and are not attributable to API degradation. For the vast majority of cases, the HPLC impurity profile provides much better (earlier and more sensitive) detection of low-level degradation products. Based on these observations, a Quality-by-Design (QbD) approach is proposed to phase out the HPLC weight % assay from routine API stability testing protocols.