Purification and identification of an impurity in bulk hydrochlorothiazide.
Hydrochlorothiazide (6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide 1,1-dioxide) (HCTZ) 1 is a widely used diuretic and anti-hypertensive. Recently, the Pharmeuropa recognized a new impurity initially thought to be an HCTZ dimer 6, which consists of the active drug (HCTZ) linked via the former beta-ring methylene to a known degradate, 5-chloro-2,4-disulfamylaniline 2. In an effort to meet a new requirement, an analytical high-pressure liquid chromatography method was developed that was selective and sensitive to the subject impurity. The impurity was concentrated and purified using a combination of solid phase extraction and reverse-phase high-pressure liquid chromatography. Subsequently, the impurity has been identified as a specific HCTZ-CH2-HCTZ isomer utilizing a variety of analytical techniques, including hydrolysis, ultraviolet spectroscopy, liquid chromatography/mass spectrometry, and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The data resulting from the application of these analytical techniques confirm the identity of the impurity as a methylene bridged pair of HCTZ molecules; however, a total of six possible isomers 7a-f exist because of the presence of three reactive amines/sulfonamides on each HCTZ molecule. One unique molecular structure (4-[[6-chloro-3,4,-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide]-methyl]-chloro-3-hydro-H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide) 7f was identified using two-dimensional COSY, NOESY, and TOCSY 1H NMR experiments.
Fang
X
X
Regulatory & Analytical Sciences, Merck & Co., Inc., WP38-3, West Point, PA 19486, USA. xueguang_fang@merck.com
Bibart
R T
RT
Mayr
S
S
Yin
W
W
Harmon
P A
PA
McCafferty
J F
JF
Tyrrell
R J
RJ
Reed
R A
RA
D000959:Antihypertensive Agents / Q000737:chemistry / Q000302:isolation & purification*; D004340:Drug Contamination; D006852:Hydrochlorothiazide / Q000737:chemistry / Q000302:isolation & purification*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods
D000959:Antihypertensive Agents; D006852:Hydrochlorothiazide