United States Patent (19) (11) 4,092,315 Bianco 45) May 30, 1978 (54) NOVEL CRYSTALLINE FORMS OF PRAZOSN HYDROCHLORDE OTHER PUBLICATIONS Weissberger, A. Ed., "Technique of Organic Chem.", (75) Inventor: Ernest J. Bianco, Niantic, Conn. vol. III, Interscience N.Y., N.Y., (1950). 73 Assignee: Pfizer Inc., New York, N.Y. Primary Examiner-Alton D. Rollins Assistant Examiner-D. B. Springer (21) Appl. No.: 662,937 Attorney, Agent, or Firm-Connolly and Hutz 22 Filed: Mar. 1, 1976 57 ABSTRACT The invention relates to novel and valuable crystalline 51) Int. C.’............................................ CO7D 239/94 forms of the hypotensive agent prazosin hydrochloride. 52 U.S. C. .................................... 544/291; 424/251 The anhydrous a-form is preferred because it is rela 58 Field of Search .................. 260/256.4 Q; 424/251 tively non-hygroscopic and hence possesses important (56) References Cited advantages in handling and formulation. The polyhy drate form of prazosin hydrochloride is preferred be U.S. PATENT DOCUMENTS cause of its low, uniform rate of dissolution. 3,635,979 1/1972 Hess .............................. 260/256.4 Q 3,663,706 5/1972 Hess ..................................... 424/251 4 Claims, 6 Drawing Figures U.S. Patent May 30, 1978 Sheet 1 of 6 4,092,315 IIT III IIST s S s T TNs. - SETIN. S.22s) & ITIL || sTSS-1c S st | | | || || TST II SST Hills STT N SN ERT IIIs TTSEE N N O | | | | | | ls. E.e s SS C R55 s TTTFIIs S. TT SI ITT cy S || || || NIIT II ST N & NIT S-3se a Wy Y NT TTTM les SS S N S S S S & S (2a1a2.2, asaraut U. S. Patent May 30, 1978 Sheet 3 of 6 4,092,315 CG-Form, polyhydrate Š s SNS S. A-Form. Auydrate 2-F2rm Methartolate 5060A03M 2000 150 low" i "isazania: A 90 W W Aeyuency (CM) Arezzersy(60?-) 27, U. S. Patent May 30, 1978 Sheet 4 of 6 4,092,315 CC-Aranz A-72rm. A27z full-serfoll Morzozyazaze All----- Mezzzzzozze 446 73.910 Af 20 25 362 26 20 Zezee 26 U. S. Patent May 30, 1978 Sheet 5 of 6 4,092,315 QS(w//5u) 227057(famoufN 4,092,315 1. 2 NOVEL CRYSTALLINEHYDROCHLORIDE FORMS OF PRAZOSN weigh, weigh, weigh, BACKGROUND OF THE INVENTION 5 33 2: g 1. Field of the Invention 3. The invention pertains to the novel, relatively non- 612 846 11.90 hygroscopic, crystalline a-form of the valuable hypo- : S. tensive agent prazosin hydrochloride of the formula: 654 525 133 10 6.75 9.60 13.87 6,81 9.85 13.95 CHO 29: 10,02 14.82 3 N w n-N N-C HC 21 N v O So 1s Another object of this inventionv . 0 is to provide a new CHO crystalline anhydrous form of prazosin hydrochloride 3 NH, which is relatively non-hygroscopic and stable. Yet another object of the invention is to provide the and processes for preparing said crystalline ot-form, as novel crystalline hydrates of 2-4-(furoyl)piperazin-1- well as the novel, crystalline polyhydrate form of 20 yl)-4-amino-6,7-dimethoxyquinazoline hyrochloride prazosin hydrochloride which has a low, uniform rate characterized by the infrared spectrum in potassium of dissolution. bromide having the following absorption bands: 2. Description of the Prior Art U.S. Pat. Nos. 3,511,836, 3,635,979 and 3,663,706 Wavelength, Wavelength, Wavelength, disclose 2-4-(2-furoyl)piperazin-1-yl)-4-amino-6,7- 25 Microns Microns Microns dimethoxyquinazoline. The first of these U.S. Patents 2.98 7.80 10.15 3.14 7.95 10.66 specifically claims this compound and its acid addition 6.04 8.08 11.10 salts and U.S. Pat. No. 3,663,706 claims the use of the 6.14 8.27 11.31 compound and its pharmaceutically acceptable acid 6.30 8.40 11.70 30 6.53 8.75 11.90 addition salts as valuable hypotensive agents. Pharma 6.72 8.96 12.00 cological studies on 2-4-(2-furoyl)piperazin-1-yl)-4- 6.95 9.17 13.10 7.15 9.33 13.27 amino-6,7-dimethoxyquinazoline hydrochloride, here 7.21 9.85 13.57 inafter designated by its generic name, prazosin hydro 7.73 10.03 14.05 chloride, were reported by Scriabine et al., Experientia, 35 24, 1150(1968), and by Constantine et al., in "Hyperten and further characterized by containing from about 8 to sion: Mechanisms and Management”, Onesti et al., edi 15% by weight of water. tors, Grune and Stratton, Inc., 1973, p. 429-444. Prelim Still another object of the invention is to provide a inary clinical studies on prazosin hydrochloride were process for producing a hypotensive effect which com reported by Cohen, J. Clin. Pharmacol, 10, 408(1970). prises administering to a hypertensive host a hypoten Side effects due to initial doses of prazosin have been sive effective amount of said hydrate of prazosin hydro reported by Bendall et al., Brit. Med. Jour, 2, chloride. 727(1975). DETAILED DESCRIPTION OF THE DESCRIPTION OF THE DRAWINGS INVENTION FIG. I is the infrared spectrum of the a-form of 45 The present invention is based on the discovery of prazosin hydrochloride in KBr. two novel, crystalline forms of the valuable hypoten FIG. II is the infrared spectrum of prazosin hydro sive agent prazosin hydrochloride which have decided chloride polyhydrate in KBr. advantages over other forms of this drug. The first of FIG.III is representative infrared spectra of various so these novel crystalline forms of prazosin hydrochloride crystalline modifications of prazosin hydrochloride. is an anhydrous form herein designated as the "a-form'. FIG. IV is representative X-ray diffractograms of The ot-form has been found to be relatively non-hygro various crystalline modifications of prazosin hydrochlo scopic and stable. It thus possesses important advan ride. tages in handling, storing and formulation. Other crys FIG. V is the powder dissolution profile of various 55 talline, anhydrous, unsolvated forms of prazosin hydro crystalline modifications of prazosin hydrochloride in chloride disclosed herein are designated, for conve water at 25 C. nience, the "g-form', the "y-form' and "anhydrate'. FIG.VI is the powder dissolution profiles of prazosin Also disclosed is the solvate, prazosin hydrochloride hydrochloride, a-form and polyhydrate in simulated methanolate. gastric juice at 25 C. As used herein the term "relatively non-hygro SUMMARY scopic' means that a sample, initially containing not more than about 0.5% water, when exposed to a tem It is an object of this invention to provide a novel perature of about 37° C. and a relative humidity of crystalline polymorph of 2-4-(2-furoyl)piperazin-1-yl)- about 75% for a period of about 30 days, contains not 4-amino-6,7-dimethoxyquinazoline hydrochloride 65 materially in excess of 1.5% water. Prazosin hydrochlo herein designated as the ot-form of prazosin hydrochlo ride having up to but not materially in excess of about ride, characterized by the infrared spectrum in potas 1.5% water is considered to be anhydrous within the sium bromide having the following absorption bands: context of this invention. 4,092,315 3 4. The second novel crystalline form of prazosin hydro 2-methyl-3-pentanol, 4-methyl-1-pentanol, 2-methyl-3- chloride which has decided advantage over otherforms hexanol, 2-methyl-2-hexanol, cycloheptanol and the of this drug is herein designated as the "polyhydrate'. It like. Especially preferred for producing the a-form of has now been found that when any of the other forms of prazosin hydrochloride is isoamyl alcohol, also known prazosin hydrochloride are crystallized from an aque 5 as 3-methyl-1-butanol, because of its ready availability ous medium or mixtures of water and organic solvents, and efficiency in forming the desired crystalline poly followed by drying until the water content of the result morph of prazosin hydrochloride. For convenience, the ing crystals is in the range of about 8 to 15% by weight preferred temperature for formation of the a-form as determined by the well-known Karl Fischer method when isoamyl alcohol is employed is about 132 C. for determination of water, prazosin hydrochloride 10 which is the boiling point of this alcohol at atmospheric polyhydrate is obtained. At the lower end of this range pressure. of water content, that is at about 8% water by weight, In carrying out the process to prepare the a-form of the stiochiometry corresponds to a dihydrate of prazosin hydrochloride it is preferred to use an amount prazosin hydrochloride having about two moles of of alcoholic solvent sufficient to effect at least a partial water per mole of prazosin hydrochloride. Said dihy 15 solution of prazosin hydrochloride when the mixture is drate is within the scope and purview of this invention. heated to a temperature within the preferred range of Especially preferred, however, is prazosin hydrochlo temperature. Ordinarily, from about 4 to 25 ml. of such ride polyhydrate having from about 12 to 15% water by alcohol per gram of prazosin hydrochloride will suffice, weight because it is more readily obtained and has less although, more or less than this amount of alcohol may tendency to absorb water than other hydrates of 20 be employed in some instances with satisfactory results. prazosin hydrochloride. The heating time required to effect substantially con The polyhydrate may be prepared, for example, by plete formation of the a-form of prazosin hydrochloride crystallization of prazosin hydrochloride from hot by the above process can vary from as little as a few water or from mixtures of water and organic solvents minutes to about 6 hours or more.