A new and enantioselective liquid chromatographic method was developed for estimation of S-Linagliptin in Linagliptin (LINA) drug substances. The desired enantiomeric separation was achieved on Chiralpak AD-H (250*4.6 mm*5 μm) column with the mobile phase composition of ethanol, methanol and diethylamine in a ratio of 90:10:0.1 (v/v/v) with flow rate of 0.5 mL·min - 1 and column oven temperature 30°C and the eluted compounds were monitored at 225 nm. In the proposed chiral method, USP resolutions between both the enantiomers were more than 5.0. Limit of detection and Limit of quantitation of S-LINA was found to be 0.03 μg·mL -1 and 0.10 μg·mL -1 respectively. Linearity study was conducted from LOQ to 150% and correlation coefficient found to be 0.9997. Accuracy was within the range of 98.6% to 101.5%. To prove selectivity power of the method specificity study was conducted by subjecting drug substance to acid, base, hydrolysis, oxidation and photolysis and ensured the peak purity of analyte in degraded samples. Moreover, the method has been fully validated as per ICH guidelines. The proposed method is precise, accurate, linear, rugged, robust and suitable for accurate quantification of S-LINA in LINA drug substance.
LINA is chemically (R) 8-(3-aminopiperidin-1-yl)-7-(but-2-yn-1-yl)-3-methyl-1-[(4-methylquinazolin-2-yl) methyl]-3, 7-dihydro-1H-purine-2, 6-dione with molecular formula C25H28N8O2. Linagliptin is a xanthine based DPP-4 (Dipeptidyl peptidase-4) inhibitor, which can be orally taken for treatment of type-II diabetes, which is approved by US Food and Drug Administration.
Type 2 diabetes mellitus is a progressive disease, and it occurs with increasing prevalence in the elderly and those with other comorbidities. Blood glucose control presents a challenge that is magnified by these co-existing problems. To achieve glycemic targets, many patients need more than one antidiabetic drug, and additional medications are often required as glucose control deteriorates [
The dipeptidyl peptidase-4 inhibitors are one of the recently developed therapeutic classes for treatment of hyperglycemia in Type 2 diabetes mellitus. The various agents in the class have differing chemical structures, but all acts by inhibiting the DPP-4 enzyme, thus prolonging the life of incretin hormones, which in turn raise insulin levels and suppress glucagon secretion in a glucose-dependent manner. As a class, DPP-4 inhibitors have been shown to provide significant improvements in glycosylated hemoglobin (HbA1c), and to have a good safety profile. In addition, their glucose-dependent mechanism of action is associated with a low rate of hypoglycemic events [
High-throughput screening using an assay to detect inhibition of DPP-4 led to the discovery of linagliptin, a xanthine-based molecule with a high selectivity for DPP-4. The pharmacokinetics and pharmacodynamics of linagliptin have been reviewed in detail elsewhere [
The separation of chiral isomers can be carried out by using HPLC through direct and indirect methods. Indirect methods are based on adding a chiral additive to the mobile phase. The optical isomers react with the chiral additives, and then the derivatives are separated on an achiral stationary phase. Direct methods separate the isomers on a chiral stationary phase. But in recent development into the chiral separation technology the enantiomers can be separated directly over a chiral stationary phase, they must form short-lived diastereomeric molecular complexes of non-identical stability by interacting rapidly and reversibly [
The polysaccharides coated on silica are the most widely used synthetic polymer for preparation of stationary phase. The polysaccharide phase is comprised of derivatized cellulose or amylose coated on a silica support. Derivatization of the polysaccharide hydroxyl groups with various side chains gives different helical supramo- lecular structures. The curved groove of the helix is chiral, and can greatly favor the binding of one enantiomer over the other. The result is separation of the enantiomers. Interaction between analyte and synthetic polymer chiral stationary phases are based on both attractive interactions (H-bonding, pi-pi interaction, and/or dipole stacking) and inclusion complexes. Instead of a silica surface, inclusion complexes utilize cavities in which the analyte fits [
LINA is a chiral molecule, and exists as S-LINA and R-LINA mentioned in (
During through literature survey it is understood that there were few methods for single LINA estimation by spectrophotometry and HPLC [
and reproducible method for the quantification of S-LINA in LINA. Method was validation as per ICH guidelines. Specificity study also conducted to proven the selectivity power of the method.
Individual enantiomers of Linagliptin were prepared and provided by Dr. Reddys Laboratories Limited, IPDO, Hyderabad, India. Ethanol, Methanol and Diethyl amine was purchased from Merck Germany .
All experiments were carried out on a Waters e2695 separation module consisting of 2998 photodiode array detector and Agilent 1260 series ternary pump with variable wavelength detector. Empower 2 software was used for signal monitoring and data processing. The method was developed by using Chiralpak AD-H (250*4.6 mm*5 µm) column which contains Amylose Tris (3, 5-Dimethylphenylcarbamate) as stationary phase. Mobile phase consists of ethanol, methanol and diethylamine in a ratio of 90:10:0.1 (v/v/v) with a flow rate of 0.5 mL∙min−1, 5 µL injection volume, 30˚C column oven temperature and chromatographic signal was monitored at 225 nm. Chromatograms were summarized in (Figures 2(a)-(c)).
LINA samples are prepared in the methanol (1 mg∙mL−1). The system suitability was prepared by mixing equal portion of R-LINA and S-LINA at 0.2 mg∙mL−1 in methanol.
The main goal of method development was to achieve separation of S-LINA from R-LINA. As part of method development screened various chiral columns namely Chiralcel OD-H, Chiralcel OJ-H, Chiralpak-IA, Chiralpak-IB,
Chiralpak-IC and Chiralpak-IE manufactured by Diacel Japan were employed. A series of experiments were conducted to select the best stationary and mobile phase that would give optimum resolution for S-LINA from R-LINA. For this study mobile phase with different ratios of n-Hexane, 2-Propanol and Ethanol were used. As the Linagliptin contains basic functional group, Diethyl amine used as mobile phase modifier to improve the peak shape. It was observed that the usage of n-Hexane more than 50% in mobile phase is highly retaining the compound in stationary phase and decrease in % of n-Hexane in mobile phase provided no separation of enantiomers. Hence further trails were carried out by using Methanol, Acetonitrile and Ethanol in all above mentioned columns. No adequate separation was found with above columns.
After careful screening of columns and mobile phase compositions it was observed that Chiralpak AD-H provides better resolution between S-LINA and R-LINA using n-Hexane, Ethanol and diethylamine in the ratio of (10%:90%:0.1% v/v/v) as mobile phase. To improve the chromatographic efficiency and resolution between enantiomers further mobile phase composition was altered and prepared the mobile phase in the composition of ethanol, methanol and diethylamine in the ratio of (90:10:0.1 v/v/v). In this optimized method the typical retention times of S-LINA and R-LINA were approximately about 12.3 min. and about 17.2 min. respectively. Resolutions between two enantiomers are found more than 5 and total run time of method was within 35 minutes. The complete screening of chiral columns and mobile phase compositions were summarized in
Sr. No. | Column name and dimensions | Mobile phase composition (% v/v) | Observations and Retention time (min) | Resolution | Tailing factors of S-LINA and R-LINA |
---|---|---|---|---|---|
1 | Chiralpak OD-H (250 × 4.6 mm) | 90:10:0.1 n-Hex:EtoH:DEA | Peaks not eluted | NA | NA |
30:70:0.1 n-Hex:IPA:DEA | 25.21 and 33.44 | 1.2 | 1.2 and 1.3 | ||
100:0.1 IPA:DEA | Peaks not eluted | No Res | NA | ||
100:0.1 EtoH:DEA | 20.99 and 23.47 | 1.1 | 0.9 and 1.5 | ||
2 | Chiralpak OJ-H (250 × 4.6 mm) | 30:70:0.1 n-Hex:IPA:DEA | 10.63 | No Res | NA |
100:0.1 IPA:DEA | 16.24 | No Res | NA | ||
100:0.1 EtOH:DEA | 11.83 | No Res | NA | ||
3 | Chiralpak IC (250 × 4.6 mm) | 100:0.1 EtoH:DEA | Peaks not eluted | NA | NA |
50:50:0.1 MeoH:EtoH:DEA | Peaks not eluted | NA | NA | ||
50:50:0.1 EtoH:ACN:DEA | 26.01 and 27.97 | 0.9 | 1.0 and 2.1 | ||
4 | Chiralpak IE (250 × 4.6 mm) | 100:0.1 EtoH:DEA | 31.59 and 34.67 | 1.2 | 1.1 and 1.4 |
50:50:0.1 MeoH:EtoH:DEA | Peaks not eluted | No Res | NA | ||
5 | Chiralpak IA (250 × 4.6 mm) | 100:0.1 IPA:DEA | 11.43 | No Res | NA |
100:0.1 EtoH:DEA | 7.17 and 7.87 | 1.3 | 1.1 and 1.5 | ||
50:50:0.1 MeoH:EtoH:DEA | 9.10 and 10.59 | 1.5 | 1.5 | ||
6 | Chiralpak AD-H (250 × 4.6 mm) | 90:10:0.1 n-Hex:EtoH:DEA | Peaks not eluted | NA | NA |
30:70:0.1 n-Hex:IPA:DEA | 10.27 | No Res | NA | ||
10:90:0.1 n-Hex:EtoH:DEA | 13.72 and 15.41 | 2.2 | 1.3 and 1.2 | ||
100:0.1 EtoH:DEA | 14.25 and 17.68 | 3.8 | 1.3 and 1.2 | ||
90:10:0.1 EtoH:MeoH:DEA | 14.25 and 17.69 | 5.5 | 1.1 and 1.3 |
Note: n-Hex: n-Hexane; MeoH: Methanol; EtoH: Ethanol; DEA: Diethyl amine; IPA: Isopropyl alcohol; ACN: Acetonitrile; NA: Not applicable; No Res: No resolution.
The developed method was validated in terms of repeatability (Intra-day) and intermediate precision. Repeatability was established at four different levels (LOQ, 50%, 100%, and 150%) to the specification limit of 0.15% as per ICH guidelines. Performed the study by spiking the S-LINA in test sample at four different concentration as per above.
The same study has been repeated to generate intermediate precision for two consecutive days by using different instruments, different columns and different analyst. The intermediate precision and method repeatability are measured by calculating % relative standard deviation (% RSD) for area of S-LINA. The % RSD values for intra-day precision and inter-day precision were found less than 0.5%, these values indicate that developed method was precise.
Limit of detection (LOD) and limit of quantitation (LOQ) were established based on signal to noise ratio. LOD is the lowest analyte concentration that can be detected and LOQ is the lowest analyte concentration that can be quantified. LOD and LOQ values are established by injecting a series of diluted solutions of S-LINA and calculated signal to noise ratio (S/N ratio). The LOD and LOQ values achieved for S-LINA were 0.03 µg∙mL−1 and 0.10 µg∙mL−1 respectively.
Linearity is performed by injecting a series of diluted solutions of S-LINA ranging from LOQ to 150%. The linearity curve was plotted for peak area of S-LINA and concentration using least squares method. The correlation
coefficient between concentration and peak area was 0.9997. Slope, y-intercept and % y-intercept at 100% level were calculated.
The recovery studies were performed at LOQ, 50%, 100% and 150% to the specification level. Each concentration level was prepared in triplicate, and the recovery was calculated based on mentioned in Equation (1).
The accuracy values are in between 98.6% to 101.5%.
Establishing solution and mobile phase stability by keeping the system suitability solution, Reference solution, test solution and spiked solution separately in tightly closed volumetric flasks at room temperature for 48 hr. during which they were analysed at 12 hrs intervals. Stability of mobile phase was demonstrated by analysis of freshly prepared sample solution at 12 hrs intervals for 48 hrs and comparing the results with those obtained from freshly prepared reference solution. Mobile phase was kept constant during the study period. From the data it can be concluded that mobile phase and sample solutions were found to be stable for 48 hrs.
Robustness was studied by altering chromatographic conditions like flow rate and column oven temperature and found to be there is no significant change observed in resolution between S-LINA and R-LINA.
Validation parameters were summarized in Tables 2-4.
Parameter | S-LINA |
---|---|
Linearity | |
Correlation coeffient | 0.9997 |
Slope | 76,094,169.1 |
Y-Intercept | 1137.7 |
% Y-Intercept | 0.99 |
Accuracy (% Recovery) | |
LOQ (n = 3) | 98.6 |
50% (n = 3) | 101.5 |
100% (n = 3) | 100.3 |
150% (n = 3) | 99.8 |
Precision (% RSD) | |
LOQ (n = 6) | 1.53 |
50% (n = 6) | 0.42 |
100% (n = 6) | 0.35 |
Ruggedness; Different day and analyst (% RSD) | |
100% (n = 6) | 0.49 |
Robustness (Resolution) | |
Actual flow 0.5 mL/min | 5.5 |
Different flow 0.45 mL/min | 5.8 |
Different flow 0.55 mL/min | 5.0 |
Different Column Temperature 35˚C | 5.2 |
Different Column Temperature 25˚C | 5.6 |
Limit of Detection (Concentration in µg/mL) | 0.03 |
Limit of Quantification (Concentration in µg/mL) | 0.1 |
SUMMARY OUTPUT |
| ||||||
---|---|---|---|---|---|---|---|
Regression Statistics | |||||||
Multiple R | 0.999740884 | ||||||
R Square | 0.999481835 | ||||||
Adjusted R Square | 0.999378202 | ||||||
Standard Error | 1533.145899 | ||||||
Standard Error × 3 | 4599.437698 | ||||||
Observations | 7 | ||||||
ANOVA | |||||||
df | SS | MS | F | Significance F | |||
Regression | 1 | 22,669,609,164 | 22,669,609,164 | 9644.441 | 2.07553E-09 | ||
Residual | 5 | 11,752,681.75 | 2,350,536.349 | ||||
Total | 6 | 22,681,361,846 | |||||
Coefficients | Standard Error | t Stat | P-value | Lower 95% | |||
Intercept | 1137.723473 | 1049.036734 | 1.084541118 | 0.327627 | −1558.9113 | ||
X Variable 1 | 76,094,169.07 | 774,841.4559 | 98.20611494 | 2.08E-09 | 74,102,375.7 | ||
Upper 95% | Lower 95.0% | Upper 95.0% | |||||
3834.358245 | −1558.9113 | 3834.358245 | |||||
78,085,962.45 | 74,102,375.7 | 78,085,962.45 | |||||
RESIDUAL OUTPUT | |||||||
Observation | Predicted Y | Residuals | Standard Residuals | ||||
1 | 1898.665163 | 664.3348367 | 0.474672601 | ||||
2 | 30,053.50772 | −146.507721 | −0.104680949 | ||||
3 | 58,208.35028 | 405.6497212 | 0.289839999 | ||||
4 | 87,124.13453 | −832.1345272 | −0.594566834 | ||||
5 | 115,278.9771 | −50.97708498 | −0.036423539 | ||||
6 | 144,194.7613 | −2303.761333 | −1.64605606 | ||||
7 | 172,349.6039 | 2263.396109 | 1.617214781 |
Specificity is the ability of the method to measure the analyte in presence of degradation products. The specificity of developed method for LINA was performed in the presence of degradation products. Stress studies were performed at concentration of 1 mg∙mL−1 for LINA drug substance. Linagliptin was subjected to Thermal, photolytic, water, oxidation, Acid and Basic conditions were applied. Each degraded sample was injected as such and spiked with enantiomer. To evaluate the ability of proposed method to separate S-LINA from its degradation products, stressed samples were analyzed by using PDA detector and peak purities were calculated, and found that purity angle was within the purity threshold limit in all stressed samples which demonstrates the homogeneity of analyte peak. S-LINA content remains same in all stressed samples. Enantiomer was well separated from the obtained degradation products. Stress conditions for LINA and purity plot were summarized in
S. No | concentration | Actual concentration in mg/ml | S-LINA Area | |
---|---|---|---|---|
1 | LOQ | 0.00001 | 2563 | |
2 | 25% | 0.00038 | 29,907 | |
3 | 50% | 0.00075 | 58,614 | |
4 | 75% | 0.00113 | 86,292 | |
5 | 100% | 0.00150 | 115,228 | |
6 | 125% | 0.00188 | 141,891 | |
7 | 150% | 0.00225 | 174,613 | |
Correlation | 0.9997 | |||
Slope | 76,094,169.1 | ` | ||
y-intercept | 1137.7 | |||
% y-intercept | 0.99 |
A simple, precise, accurate and cost effective chiral method was developed and validated as per ICH guidelines.
Enantiomers were well separated from each other and the method validation data showed satisfactory results for all tested method parameters. All the degradation products formed during stress conditions were well separated from the S-LINA and purity angle was within the purity threshold limit in all stressed samples indicating that the developed liquid chromatographic method was specific. This simple HPLC method was precise, accurate, linear, robust, sensitive and rugged. Developed method can be used for routine testing in quality control laboratories for estimation of S-LINA in LINA drug substance.
The authors wish to thank the management of Dr. Reddy’s Laboratories Ltd. for supporting this work. Co-opera- tion from colleagues of Research & Development and Analytical Research & Development of Dr. Reddy’s Laboratories Ltd. is appreciated.
Cholleti Vijay Kumar,Pasula Aparna,Pavan Kumar Vasa,Y. Ravindra Kumar,Nitin Haridas Dhekale, (2016) A New and Enantioselective Chromatographic Method for Linagliptin on Amylose Coated Chiral Stationary Phase. American Journal of Analytical Chemistry,07,556-567. doi: 10.4236/ajac.2016.77051