ANALYTICAL STUDY FOR TADALAFIL (Cialis ) AND EQUIVALENT COMPOUNDS

ANALYTICAL STUDY FOR TADALAFIL (Cialis ) AND EQUIVALENT COMPOUNDS Thesis Presented for the Partial Fulfillment of Master Degree in Pharmaceutical Sciences "Analytical Chemistry" By Moataz Abdalla Yehia (B. Pharm, Sci. 2001, October 6 th University) Under the Supervision of Prof. Dr. Mohamed Abdel Kawy Ibrahim Professor of Analytical Chemistry Faculty of Pharmacy Cairo University Dr. Mohamed AbdallaEl-Sayed Ass. Prof. of Analytical Chemistry Faculty of Pharmacy Cairo University Dr. MamdouhRedaRezkAss. Prof. of Analytical Chemistry Faculty of PharmacyCairo University Department ofanalytical Chemistry Faculty of Pharmacy Cairo University 2015

Acknowledgment I am grateful to ALLAHˮ by the grace of whom this work was accomplished. Itis my great pleasure to express my sincere thanks and feeling of gratitude to ProfessorDr. Abdel Aziz El-Bayoumi, Professor of Analytical Chemistry, Faculty of Pharmacy, Cairo University, for suggesting the point, his kind and expert supervision, continuous encouragement, patience, beneficial discussion, fruitful suggestions and helpful advise that allowed this work to take its real form. My deep appreciation and thanks also go to Prof.Dr.Mohamed Abdel Kawy Ibrahim,Professor of Analytical Chemistry, Faculty of Pharmacy,Cairo University, for his valuable assistance, guidance and sincere help. I wish to convey my deep appreciation and thanks to Dr. Mohamed A. El-SayedAss. Prof. of Analytical Chemistry anddr.mamdouh R. Rezk, Ass. Prof. of Analytical Chemistry, Faculty of Pharmacy, Cairo University, for their sincere help and assistance, expert advises and guidance, continuous support and valuable contribution in the work. My deep cordial thanks to my family and my friends for their immense love, care and support which were transformed into essential sources of energy, enthusiasm and persistence required for completing the thesis. Finally, I would like to extend my deep thanks to all my professors and colleagues in Analytical Chemistry Department, for their friendly cooperation and encouragement. Moataz A. Yehia 2015

APPROVAL SHEET This thesis has been approved on April 7, 2015 by the committee in charge: Prof. Dr.Mohamed Abdel Kawy Ibrahim Professor of Analytical Chemistry Faculty of Pharmacy Cairo University. Ass. Prof. Dr. Nouruddin Wageh Sayed Ass.Professor of Analytical Chemistry Faculty of Pharmacy Beni-Suef University... Ass. Prof. Dr. Hala EL Said Zaa'zaa Ass. Professor of Analytical Chemistry Faculty of Pharmacy Cairo University...

Contents List of Contents List of Tables.. List of Figures. I X XVI List of Abbreviations.. XX Preface... XXII English summary....... XXIII PART I General introduction on piperazine ring containing drugs I.1. Structure and properties.. 1 I.2. Origin and naming.. 1 I.3. Drugs containing piperazine ring... 1 I.4. Role of some piperazine derivatives as drugs. 2 PART II Determination of tadalafil Section A General introduction and literature review of tadalafil. II.A. Tadalafil.. 3 II.A.1. Structure.. 3 II.A.2. Properties... 3 II.A.3. Physiology of erection.... 4 II.A.4. Tadalafil and Erectile dysfunction (mechanism of action)... 4 II.A.5. Dosage.... 5 II.A.6. Storage.... 5

II.A.7. Reported methods of analysis... 5 II.A.7.1. Spectroscopic methods... 5 II.A.7.2. Chromatographic methods. 6 II.A.7.3. Micellar electrokinetic capillary chromatography 11 II.A.7.4. Miscellaneous methods...... 11 Section B Stability indicating methods for determination of tadalafil Section B1 Spectrophotometric methods. II.B.1.1. Introduction. 12 II.B.1.2. Experimental.. 12 II.B.1.2.1. Material... 12 II.B.1.2.2. Apparatus... 13 II.B.1.2.3. Reagents.. 13 II.B.1.2.4. Standard solutions. 13 II.B.1.2.5. Procedures. 14 II.B.1.2.5.1. Preparation of the degradation product of tadalafil 14 II.B.1.2.5.2. Spectral characteristics of tadalafil and its degradation product.. 14 II.B.1.2.6. Fourth derivative spectroscopy for determination of tadalafil.... 14 II.B.1.2.7. Derivative ratio spectrophotometric method.. 17 II.B.1.3. Results and discussion.. 19 Section B2 Chromatographic methods A- TLC- densitometric method II.B.2.1. Introduction... 39

II.B.2.2. Experimental.. 39 II.B.2.2.1. Material.. 39 II.B.2.2.2. Apparatus. 39 II.B.2.2.3. Reagents.. 39 II.B.2.2.4. Standard solutions. 39 II.B.2.2.5. Procedures. 40 II.B.2.2.5.1. Preparation of the degradation product of 40 tadalafil. II.B.2.2.5.2. Densitometric method...... 40 II.B.2.2.5.3. Methodvalidation.. 40 II.B.2.3. Results and discussion... 42 B- High performance liquid chromatographic method II.B.3.1. Introduction... 53 II.B.3.2. Experimental. 53 II.B.3.2.1. Material... 53 II.B.3.2.2. Apparatus.... 53 II.B.3.2.3. Reagents and chromatographic conditions. 54 II.B.3.2.4. Standard solutions.. 54 II.B.3.2.5. Procedures. 54 II.B.3.2.5.1 Preparation of the degradation product of 54 tadalafil. II.B.3.2.5.2. Methods validation.... 54 II.B.3.3. Results and discussion.. 57 PART III Determination of sildenafil Section A General introduction and literature review of sildenafil. III.A. Sildenafil. 68

III.A.1. Structure.. 68 III.A.2. Properties... 68 III.A.3. Sildenafil and Erectile dysfunction (mechanism of action)..... 69 III.A.4. Dosage.... 69 III.A.5. Storage.... 70 III.A.6. Reported methods of analysis.... 70 III.A.6.1. Spectroscopic methods... 70 III.A.6.2. Chromatographic methods. 70 Section B Stability indicating methods for determination of sildenafil Section B1 Spectrophotometric methods III.B.1.1. Experimental... 75 III.B.1.2. Material... 75 III.B.1.2.1. Apparatus... 75 III.B.1.2.2. Reagents.. 75 III.B.1.2.3. Standard solutions.. 75 III.B.1.2.4. Procedures... 76 III.B.1.2.4.1. Preparation of the degradation product of sildenafil.. 76 III.B.1.2.4.2. Spectral characteristics of sildenafil and its degradation product.. 76 III.B.1.2.5. Fourth derivative spectroscopy for determination of sildenafil.... 76 III.B.1.2.6. Derivative ratio spectrophotometric method.. 78 III.B.1.3. Results and discussion... 81

Section B2 Chromatographic methods A-TLC- densitometric method III.B.2.1. Experimental.. 100 III.B.2.2.1. Material... 100 III.B.2.2.2. Apparatus.. 100 III.B.2.2.3. Reagents.. 100 III.B.2.2.4. Standard solutions.. 100 III.B.2.2.5. Procedures. 100 III.B.2.2.5.1. Preparation of the degradation product of sildenafil citrate. 100 III.B.2.2.5.2. Densitometric method... 100 III.B.2.2.5.3. Methodvalidation.. 101 III.B.2.3. Results and discussion.. 103 B- High performance liquid chromatographic method III.B.3.1. Experimental... 113 III.B.3.2.1. Material.. 113 III.B.3.2.2. Apparatus... 113 III.B.3.2.3. Reagents and chromatographic conditions... 113 III.B.3.2.4. Standard solutions. 113 III.B.3.2.5. Procedures... 113 III.B.3.2.5.1. Preparation of the degradation product of sildenafil.. 113 III.B.3.2.5.2. Methodvalidation.. 114 III.B.3.3. Results and discussion.. 116 PART IV Determination of terazosin Section A

General introduction and literature review of terazosin. IV.A.1. Introduction. 127 IV.A.2. Principal classes of antihypertensive drugs. 127 IV.A.3. Drugs acting on the sympathetic nervous system. 127 IV.A.3.1. Adrenoceptor antagonists (α 1 blockers).. 127 IV.A.3.2. Centrally acting α 2 -adrenoceptor agonists.. ١28 IV.A.3.3. β- Adrenoceptor antagonists (β-blockers). ١28 IV.A.3.4. Ganglion blockers and postganglionic adrenergic neuron blockers.. ١28 IV.A.4. Terazosin hydrochloride. 130 IV.A.4.1. Structure.. 130 IV.A.4.2. Properties... 130 IV.A.4.3. Action and uses. 130 IV.A.4.4. Reported methods of analysis... 131 IV.A.4.4.1. Pharmacopoeia method. 131 IV.A.4.4.2. Spectroscopic methods. 131 IV.A.4.4.3. Electrochemical methods... 132 IV.A.4.4.4. Chromatographic methods. 133 Section B Stability indicating methods for determination of terazosin. Section B1 Spectrophotometric methods IV.B.1.1. Experimental.. 135 IV.B.1.2. Material.. 135 IV.B.1.2.1. Apparatus. 135 IV.B.1.2.2. Reagents.. 135 IV.B.1.2.3. Standard solutions. 135 IV.B.1.2.4. Procedures.. 136

IV.B.1.2.4.1. Preparation of the degradation product of terazosin.. 136 IV.B.1.2.4.2. Spectral characteristics of terazosin and its degradation product. 136 IV.B.1.2.5. The fourth derivative spectroscopy for determination of terazosin.. 136 IV.B.1.2.6. Derivative ratio spectrophotometric method.. 139 IV.B.1.3. Results and discussion. 141 Section B2 Chromatographic methods A-TLC- densitometric method IV.B.2.1. Experimental... 161 IV.B.2.2. Material.. 161 IV.B.2.2.1. Apparatus. 161 IV.B.2.2.2. Reagents.. 161 IV.B.2.2.3. Standard solutions.. 161 IV.B.2.2.4. Procedures. 161 IV.B.2.2.4.1. Preparation of the degradation product of terazosin hydrochloride. 161 IV.B.2.2.4.2. Densitometric method... 161 IV.B.2.2.4.3. Methodvalidation.. 162 IV.B.2.3. Results and discussion. 164 B- High performance liquid chromatographic method IV.B.3.1. Experimental... 174 IV.B.3.2.1. Material.. 174 IV.B.3.2.2. Apparatus. 174 IV.B.3.2.3. Reagents and chromatographic conditions... 174 IV.B.3.2.4. Standard solutions... 174

IV.B.3.2.5. Procedures. 175 IV.B.3.2.5.1. Preparation of the degradation product of terazosin hydrochloride.. 175 IV.B.3.2.5.2. Methodvalidation.... 175 IV.B.3.3. Results and discussion...... 177 PART V Conclusion..... 189 REFERENCES SUMMARY IN ARABIC

(Abstract) Four different stability indicating assay methods were developed and validated for the determination of (tadalafil, sildenafil and terazosin) in the presence of its degradation product. The first and second method was based on the derivative and derivative ratio spectrophotometric technique using acetonitrile: water mixture 1:1 for tadalafil and methanol as a solvent for both sildenafil and terazosin. In the third method, we used TLC-densitometric technique using high performance thin-layer chromatography plates with a developing system consisting of {chloroform: acetone: ammonia (9:1:0.1, by volume) }, {chloroform: toluene: ethanol: acetic acid (3:3:4:0.1, by volume)} and {chloroform: acetone: ammonia (6:4:0.1, by volumes)}. The fourth method was a high performance liquid chromatography. Separation of sildenafil from its degradate using C 18 column and a mobile phase consisting of {water: acetonitrile: methanol in the ratio of (45:35:20)}, {acetonitrile: methanol: 0.05 M potassium di-hydrogen phosphate (v/v, ph 5.8): tri-ethyl amine, in the ratio of (45: 25: 30: 0.2, by volumes)} and { acetonitrile: methanol: water: tri-ethyl amine (v/v ph 5.6), in the ratio of (45: 45: 10: 0.2, by volume)} at ambient temperature was achieved. The developed methods were successfully applied to the analysis of pharmaceutical formulations containing tadalafil, sildenafil and terazosin with excellent recoveries.

Summary This thesis is composed of four parts. PART I: General introduction on drugs containing piperazine ring. This part contains, a general overview on piperazine ring containing drugs and the role of piperazine ring in different drugs. PART II: Determination of tadalafil. Section (A):General Introduction and Literature Review of Tadalafil In this part, pharmacological action of tadalafil as well as its chemical structure and properties were discussed. A brief review of the different methods reported in the literature for the determination of tadalafil in pure form, and in biological fluids. Section (B): Stability indicating methods for the determination of Tadalafil. This part is divided into three sections: S e c t i o n ( B 1 ) : Stability indicating method for the determination of Tadalafil by derivative and Derivative ratio spectrophotometry. In this section, the conditions required for the degradation of tadalafil were studied, then the degradation product was isolated and its structure wasconfirmed using mass spectroscopy. This was followed by the development of two spectrophotometric stability-indicating methods for the determination of tadalafil. The first methodutilized fourth derivative spectrophotometry where the peak amplitude at 285.7 nm was used for the determination of the intactdrug. The second method was the derivative ratiospectrophotometricmethod, where tadalafil was determined by dividing the spectra of the prepared solutions of tadalafil by the spectrum of 7.5 µgml -1 of its degradation product then obtaining the first derivative of the ratio spectra ( 1 DD) and measuring

the peak amplitudes at 263.6 nm to the corresponding concentrations of tadalafil. Statistical analysis was done showing no significant difference in comparison with the reported method. Section (B2 ):Stability indicating TLC densitometric method for determination of Tadalafil. In this section, TLC-densitometric technique was used for the determination oftadalafilin presence of its degradation product without previous separation using chloroform: acetone: ammonia (9:1:0.1, by volume) as adeveloping system. Spots were scanned at 291nm in the range of 0.75 10µgspot -1 fortadalafil. The proposed TLC-densitometric method was applied for the determination of tadalafil in its pure powdered form, in laboratory prepared solutions and in its dosage form. Section (B3 ): Stability indicating High-Performance Liquid Chromatographic method for determination of Tadalafil. This section was concerned with application of HPLC for the determination of tadalafil in presence of its degradation product. The mobile phase was formed ofwater: acetonitrile: methanolin the ratio of (45:35:20 by volume), detection was at 225 nm using a UV detector. The proposed procedure was successfully applied for the determination of tadalafil in its pure powdered form, in laboratory prepared solutions and in its dosage form. PART III: Determination of sildenafil. Section (A): General Introduction and Literature Review of Sildenafil citrate. In this part, pharmacological action of sildenafil citrate as well as its chemical structure and properties were discussed. A brief review of the different methods reported in the literature for the determination

of sildenafil citrate in pure form, pharmaceutical formulations and biological fluids. Section (B ): Stability indicating methods for determination of Sildenafil citrate. This part is divided into three sections: S e c t i o n ( B 1 ) : Stability indicating methods for the determination of Sildenafil citrateby derivative and Derivative ratio spectrophotometry. In this section, the conditions required for the degradation of sildenafil citrate were studied, then the degradation product was isolated and its structure wasconfirmed. This is followed by the development of two spectrophotometric stability-indicating methods for the determination of sildenafil citrate. The first methodutilized fourth derivative spectrophotometry where the peak amplitude at 292.4nm was used for the determination of the parent drug. The second method was the derivative ratiospectrophotometricmethod, where sildenafil citrate was determined by dividing the zero order spectra of the prepared solutions by the spectrum of 10 µgml -1 of the corresponding degradation product then obtaining the first derivative of the ratio spectra ( 1 DD) and measuring the peak amplitudes at 305.4 nm to the corresponding concentrations of sildenafil citrate. Statistical analysis was done showing no significant difference in comparison with the reported method. Section ( B2): Stability indicating TLC densitometric method for determination of Sildenafil citrate. In this section, TLC-densitometric technique was used for the determination ofsildenafil citrate in presence of its degradation product without previous separation chloroform: toluene: ethanol:acetic acid (3:3:4:0.1, by volume) as adeveloping system. Spots were

scanned at 292 nm in the range of 0.5 8µg spot -1 for sildenafil citrate. The proposed TLC-densitometric method was applied for the determination of sildenafil in its pure powdered form, in laboratory prepared solutions and in its dosage form. Section (B3 ): Stability Indicating High-Performance Liquid Chromatographic Method for Determination of Sildenafil Citrate. This section was concerned with application of HPLC for the determination of sildenafilcitrate in presence of its degradation product. The mobile phase was formed ofacetonitrile: methanol: phosphate buffer (ph 5.8)and tri-ethanol amine in the ratio of (45:25:30:0.2 by volume), detection was at 225 nm using a UV detector. The proposed procedure was successfully applied for the determination of sildenafil in its pure powder form, in laboratory prepared solutions and in its dosage form. PART IV: Determination of terazosin hydrochloride. Section (A): General Introduction and literature review. In this part, the pharmacological action of terazosin hydrochloride as well as its chemical structure and properties were discussed. A brief review of the different methods reported in the literature for the determination of the drug in pure form, pharmaceutical formulations and biological fluids. Section (B ):Stability indicating methods for the Determination of Terazosin hydrochloride. This part is divided into three sections: S e c t i o n ( B 1 ) : Stability indicating methods for the determination of Terazosin hydrochloride by derivative and Derivative ratio spectrophotometry. In this section, the conditions required for the degradation of terazosin hydrochloride were studied, then the degradation

product was isolated and its structure was. This is followed by the development of two spectrophotometric stability-indicating methods for the determination of terazosin hydrochloride. The first methodutilized fourth derivative spectrophotometry where the peak amplitude at 329.2 nm was used for the determination of the parent drug. The second method was the derivative ratiospectrophotometricmethod, where terazosin hydrochloride was determined by dividing the zero order spectra of the prepared solutions by the spectrum of 8 µgml -1 of the corresponding degradation product then obtaining the first derivative of the ratio spectra ( 1 DD) and measuring the peak amplitudes at 310.6 nm to the corresponding concentrations of terazosin hydrochloride. Statistical studies were done showing no significant difference in comparison with the compendial method. Section (B2 ): Stability indicating TLC-Densitometric method for determination of Terazosin hydrochloride. In this section, TLC-densitometric technique was used for the determination ofterazosin hydrochloride in presence of its degradation product without previous separation using chloroform: acetone: ammonia (6:4:0.1, by volumes) as adeveloping system. Spots were scanned at 342nm in the range of 0.5 8 µg spot - 1 ofterazosin hydrochloride. The proposed TLCdensitometric method was applied for the determination of terazosin hydrochloride in its pure powder form, in laboratory prepared solutions and in its dosage form.

Section (B3 ): Stability Indicating High-Performance Liquid Chromatographic Method for Determination of Terazosin Hydrochloride. This section was concerned with application of HPLC for the determination ofterazosin hydrochloride in presence of its degradation product. The mobile phase was formed ofacetonitrile: methanol: water: tri-ethyl amine in the ratio of (45:45:10:0.2 by volume)detection was at 225 nm using a UV detector. The proposed procedure was successfully applied for thedetermination of terazosin hydrochloride in its pure powdered form, in laboratory prepared solutions and in its dosage form.