HPLC SEPARATION OF PIDOTIMOD ENANTIOMERS USING BETA-CYCLODEXTRIN BASED CHIRAL STATIONARY PHASE

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1 Page6182 Indo American Journal of Pharmaceutical Research, 2016 ISSN NO: HPLC SEPARATION OF PIDOTIMOD ENANTIOMERS USING BETA-CYCLODEXTRIN BASED CHIRAL STATIONARY PHASE Madhuri Baghel, Sadhana J. Rajput* Quality Assurance Laboratory, Centre of Relevance and Excellence in Novel Drug Delivery Systems, Faculty of Pharmacy, Shri G.H. Patel Building, Donor s Plaza, The Maharaja Sayajirao University of Baroda, Fatehgunj,Vadodara , Gujarat, India. ARTICLE INFO Article history Received 13/07/2016 Available online 30/07/2016 Keywords Enantiomer, Pidotimod, ICH Guideline, Immunomodulator. Corresponding author Sadhana J. Rajput Quality Assurance Laboratory, Centre of Relevance and Excellence in Novel Drug Delivery Systems, Faculty of Pharmacy, Shri G.H. Patel Building, Donor s plaza, The Maharaja Sayajirao University of Baroda, Fatehgunj, Vadodara , Gujarat, India. sjrajput@gmail.com ABSTRACT A simple, sensitive, specific, precise, and rapid isocratic chiral RP-HPLC method was developed and validated for estimation of R and S enantiomers of Pidotimod, a potent dipeptide immunomodulator. The separation was achieved with LICHROCART CHIRADEX ( mm, 5µm) column at wavelength of 215 nm. The mobile phase was ammonium acetate buffer and methanol in the ration of 85:15 at flow rate of 0.8 ml/ min. The developed method was validated as per ICH guideline which was linear over the range of μg/ml with LOD and LOQ of and respectively. The %RSD for repeatability and Intermediate precision was found to be less than 2. The elution of enantiomeric peaks of Pidotimod was further confirmed by LC-MS/MS analysis. The developed method could be utilized for estimation of pidotimod enantiomers. Please cite this article in press as Sadhana J. Rajput et al. HPLC Separation of Pidotimod Enantiomers Using Beta-Cyclodextrin Based Chiral Stationary Phase.Indo American Journal of Pharmaceutical Research.2016:6(07). Copy right 2016 This is an Open Access article distributed under the terms of the Indo American journal of Pharmaceutical Research, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 Page6183 INTRODUCTION Pidotimod (PDM), (R)-3-[(S)-(5-oxo-2-pyrrolidinyl) carbonyl]-thiazolidine- 4-carboxylic acid (Figure 1), is a biological response modifier with dipeptide structure, which can stimulate both primary and acquired immune response to virus and bacteria [1,2]. Studies demonstrated that PDM itself does not have antibacterial activity, but along with other antibacterial agents, can improve clinical symptoms of patients, promoting recovery and limiting hospital stay. It is often used in the treatment of repeated infections of the respiratory, urogenital, ear, nose, and throat systems. PDM therapy is a reliable, simple, and safe approach to treat children with recurrent respiratory infection. It has few adverse effects and demonstrates good safety and tolerability [3]. O H N O HOOC N S Figure 1 Structure of Pidotimod (PDM). An extensive literature survey revealed that, few analytical methods have been reported for the quantification of PDM including HPLC-UV [4], HPLC MS [5], HPLC-MS/MS [6], and HILIC-MS/MS [7]. There is one published report for the determination of residual organic solvents in PDM by GC [8]. Chiral separation of PDM by polysaccharide stationary phase has been reported by Zhang Lu Xing [9] so the aim of present study was to separate R and S enantiomers of Pidotimod on beta cyclodextrin based chiral stationary phase. MATERIALS AND METHODS Reagents and Chemicals The drug was purchased from Manas aktiva, Ahmedabad, India. HPLC grade Methanol (MeOH), Acetonitrile (ACN) was purchased from Spectrochem Pvt. Ltd. Mumbai, India. Glacial acetic acid and ammonium acetate were purchased from Merck, Darmstadt, Germany. Instrumentation and Chromatographic Conditions LC analysis was performed on a Waters Acquity HPLC (Waters Corporation, Milford, MA, USA) equipped with a photodiode array detector (PDA) at 215 nm using Empower-2 software (Waters Corporation, Milford, MA, USA). Separation was achieved on a LICHROCART CHIRADEX column ( mm, 5 µm). The mobile phase comprised of a mixture of 10 mm Ammonium acetate buffer, ph adjusted to 5.8 with glacial acetic acid and MeOH in the ratio 85:15, v/v at a flow-rate of 0.8 ml min 1 with isocratic elution. The column temperature was maintained at ambient temperature, and the injection volume was 20 µl. The mobile phase was filtered through 0.2 µm disposable filters (Ultipore, PALL lifesciences, 40 mm) and degassed by ultrasonic vibrations prior to use. Preparation of standard solution The stock solutions containing 1 mg/ml of R form of PDM were prepared in double distilled water and were stored in lightresistant containers. Aliquots of μg/ml of PDM with respect to R-enantiomer were prepared in the mobile phase for HPLC analysis. Preparation of sample solution The powder equivalent to 5 mg of of PDM from synthetic mixture was accurately weighed and transferred into a 5 ml volumetric flask. To this 5 ml of mobile phase was added and sonicated for 10 minutes. The solution was made up to 5 ml with mobile phase and filtered using 0.2 µ membrane filter. The solutions (standard and sample) were analyzed by the optimized chromatographic condition and chromatograms were recorded. Preparation of laboratory synthetic mixture The formulation (tablet) of PDM is not available in Indian market, so laboratory mixture was prepared using the excipients mentioned in the patent [10]. The prescribed formula used to prepare laboratory synthetic mixture is shown in Table 1. Table 1: Preparation of Laboratory synthetic mixture. Excipient Quantity (%) Pidotimod MCC PVP 4.55 Mannitol 4.00 Mag. Stearate 1.00

3 Page6184 Selection of Analytical wavelength The UV spectrum of PDM and its chiral form were extracted in PDA from nm and are shown in figure 2. Both the forms show sufficient absorbance at 215 nm so was taken for estimation. Method Validation The developed method was validated as per ICH guideline [11]. Figure 2: UV spectrum of PDM (R) and PDM (S). RESULT AND DISCUSSION Selection and Optimization of chromatographic condition The effect of different chromatographic variables such as ph of mobile phase, composition of mobile phase, flow rate and column oven temperature were studied to optimize the chromatographic condition. The resulting chromatograms were recorded and the chromatographic parameters (resolution, asymmetric factor, and theoretical plates) were calculated. The ph was crucial with respect to peak symmetry, resolution and retention time. Lower ph increases the retention time while higher ph causes peak tailing. Organic ratio specially effected the retention time and resolution. Higher ratio of buffer was used to resolve the peak due to polar nature of drug that has Pka value Column oven temperature had least effect so was kept ambient. Mobile phase flow rate effected retention time and resolution. The conditions that gave the best resolution, theoretical plate and peak symmetry were selected for estimation and are presented in Table 2. Table 2: Optimized Chromatographic condition for estimation of Pidotimod. Method Parameter Optimized condition Stationary Phase CHIRADEX (150 mm x 4.6 mm, 5 μm) Mobile Phase Ammonium Acetate buffer 10 mm: methanol ( ratio 85:15 Retention time 4.82 minutes for R form and 5.80 for S form Detection wavelength 215nm Flow rate 0.8 ml/min Temperature Ambient LC-MS/MS study of PDM and its enantiomers The LC-MS/MS was taken on positive ESI mode to confirm the entiomeric peak of PDM. The mass spectrum and fragmentation pattern of PDM at retention time 4.86 confirms the structure of PDM. The ESI-MS spectrum at RT 5.86 did not show protonated ions, but the [M+H]+ ion at 245 confirms the enantiomeric forms of PDM. The resolved chromatogram and mass spectra of both enantiomers are shown in figure 3 and 4.

4 Page6185 Figure 3: Chromatogram of PDM and its enantiomer. Figure 4: ESI-MS/MS spectra of PDM enantiomers. Method Validation Linearity and Range The calibration curve was constructed with respect to R-PDM and was linear over the concentration range of μg ml- 1. The correlation co-efficient was with regression equation y = 23000x The overlain chromatogram and calibration curve is shown in figure 5. The linearity data is shown in table 3.

5 Page6186 Table 3: Linearity data for PDM (R-enantiomer). PDM (R enantiomer) S.No. Peak Area (mv.s) Conc.( µg ml-1) (Mean±%RSD) ± ± ± ± ± *Average of three determinants. Figure5: Overlain chromatogram of PDM (R) and PDM (S) and calibration curve. Precision For intra-day precision, the experiment was repeated 3 times in a day and for inter-day precision on 3 different days. The average % RSD of intra-day and inter-day experiments for determination of PDM (R) was found to be and respectively. The low value of %RSD obtained confirms the precision of the developed method. LOD and LOQ The LOD and LOQ of the developed chromatographic method were found to be and Accuracy Accuracy of the method was confirmed by recovery study from laboratory prepared synthetic mixture at 3 level of standard addition (80 %, 100% and 120 %). The results are shown in table 4. Recovery greater than 98 % with low SD justifies the accuracy of the developed method. Table 4: Recovery from synthetic mixture. Excess drug added to analyte (%) Theoretical Content (µg ml -1 ) *Amount Found (µg ml -1 ) Recovery (%) ± S.D ± ± ± ± *Average of three determinants. Robustness For robustness study few parameters were deliberately varied, these are variation of mobile phase composition, flow rate and ph of buffer. The low average value of % RSD for determination of PDM less than 2 % revealed the robustness of the developed method (Table 5).

6 Page6187 Table 5: Robustness of HPLC method. Factor Level Retention time Mobile Phase composition (Ratio of MeOH) Mean ± % RSD 4.871± Flow Rate Mean ± % RSD 4.77± ph Mean ± % RSD 4.74± Specificity As illustrated in figure 3 the developed method is specific since complete separation of PDM and, its enantiomer was observed. The peaks of PDM and its enantiomer were well resolved. The resolution factor for the separating peak was greater than 1.5 from the nearest resolving peak. Also it was justified by peak purity plots as shown in figure 6. The peak purity studies of resolved peaks are presented in table 6. Figure 6: Peak purity plot of PDM (R) and PDM (S). Table 6: Peak purity studies of resolved peaks of PDM. S. No. Peaks RT Peak purity Angle Peak purity Threshold 1. PDM (R) PDM (S) Stability in sample solutions Solutions containing different concentrations of PDM were prepared from standard stock solution and stored at room temperature for 24hrs. No additional peaks were found in chromatogram indicating the stability of PDM in the sample solution. System Suitability Parameters (SST) System suitability test was carried out on freshly prepared standard solutions (n=6) containing PDM. SST parameters obtained with 100μl injection volumes are summarized in Table 7.

7 Page6188 Table 7: System Suitability Parameters for PDM. Parameter Data Obtained PDM (R) PDM (S) Retention time (min) ± SD Theoretical plate ± SD Tailing factor ± SD Resolution ±SD *Data shown is the average of six replicates. SD= Standard Deviation Applicability of the developed method The Developed method was successfully applied for the estimation of PDM (R) and PDM (S) in its Synthetic mixture. The percentage assay value of ± 0.10 indicates that the developed method could be applied successfully for estimation of R and S enantiomers of PDM. CONCLUSION A simple, precise, accurate and sensitive method based on chiral stationary phase has been developed and validated for analysis of enantiomer of pidotimod. The enantiomeric peak was confirmed by LC/MS-MS analysis. The good sample recovery and percentage assay suggested non-interference of formulation expients in estimation. The method requires very less run time. The method could be applied for estimation of R and S Pidotimod in formulation, and could also be utilized for determination of enantiomeric impurity of pidotimod. ACKNOWLEDGEMENTS The authors express their sincere thanks to SICART, vallabh vidyanagar, Anand for providing LC-MS/MS facility.

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