J. Med. Chem. 1990, 33,97-101 at this temperature for 20 h. (The reaction progress was followed by taking from the mixture a sample which was treated with 2 M sodium hydroxide and extracted with diethyl ether. The extract was subjected to silica TLC with methylene chloride and methanol (lO:l).) The reaction mixture was allowed to cool to 120 "C and 2 M sodium hydroxide (650 mL) was added. The temperature was lowered to room temperature and the mixture stirred about 0.5-1 h and extracted with ether. After evaporation, the residue was distilled at 225 " C / l Torr. Compound 2b (5 g, 37%) was obtained by recrystallization from ligroin (100-140 "C), mp 186-187 OC (lit.29 mp 186 "C). 9-[(2-Methoxyp heny1)amino 1- 1,2,3,4-tetrahydroacridine (2c). Phosphorus pentoxide (1.8 mol, 256 g) was mixed with triethylamine hydrochloride (1.8mol, 448 g) in a flask fitted with a mechanical stirrer and a reflux condenser with a drying tube (calcium chloride) a t room temperature. 2-Methoxyaniline (1.8 mol, 222 g) was added dropwise while the mixture was heated in an oil bath to 60 "C (oil-bath temperature). The mixture was further heated to 160 "C until a homogeneous mixture was achieved (0.5 h). The oil-bath temperature was then lowered to 130 "C. Methyl anthranilate (0.3 mol, 45.4 g) and cyclohexanone (0.54 mol, 53.0 g) were added dropwise. The temperature was again increased to 160 "C and maintained a t that temperature for 15 min. The reaction mixture was allowed to cool to 110 OC and 2 M sodium hydroxide (4000 mL) was added. The aqueous suspension was extracted with 2 X 1500 mL of diethyl ether. The solvent was stripped off under reduced pressure. The residue was further evaporated at 0.1 mmHg to remove 2-methoxyaniline. A black solid formed and was recrystallized twice from ligroin (80-100 "C) to yield 2c (32.4 g, 36%) as white-yellow crystals: mp 131-132 "C; 'H NMR (CDC13/TMS) d/ppm 1.91 (m, 4 H), 2.79 (m, 2 H), 3.19 (m, 2 H), 4.02 (s, 3 H), 6.27 (s, NH), 6.10-8.20 (m, 8 H); '% NMR (CDCl,/TMS) b/ppm 25.09 (C-1),22.75 (C-2), 22.49 (C-3), 33.98 (C-4), 159.77 (C-4a), 128.60 (C-5) 128.41 (C-6), 124.84 (C-7), 123.08 (C-8), 123.67 (C-8a), 142.96 (C-9), 124.45 (C-ga), 147.24 (C-loa);MS m / e 304 (loo), 289 (13), 273 (ll),197 (ll),182 (11). Anal. (CzoHzoNzO)C, H, N.
97
9-[(4-Amino-2-methoxyphenyl)amino]-lf,3,4-tetrahydroacridine (4). A mixture of 3 (13 mmol, 4.6 g), tin (83mmol, 9.9 g), and 6 M hydrochloride acid (100 mL) was heated with stirring to 120 "C (oil-bath temperature) by which time the tetrahydro-
acridine had dissolved. The mixture was refluxed for 2 h and cooled. The precipitate was dissolved in water and, after addition of 2 M sodium hydroxide (50 mL), extracted into chloroform. The chloroform extract was evaporated and the residue was recrystallized from 50% ethanol to yield 4 (2.5 g, 56%), mp 155-156 " C. N-[4-[(1,2,3,4-Tetrahydro-9-acridinyl)amino]-3-methoxyphenyl]methanesulfonamide (2d). Compound 4 (7.5 mmol, 2.4 g) was dissolved in 25 mL of dry pyridine. Mesyl chloride (15 mmol, 1.16 mL) was added slowly at -5 "C and the mixture was stirred for 1 h. The mixture was evaporated under reduced pressure and dissolved in water (200 mL). Hydrochloric acid (4 M, 20 mL) was added to precipitate the hydrochloride, which was taken up in 200 mL of water. 10 mL of sodium hydrogen carbonate was added and the precipitate was rrystallized from ethanol (96%) to yield 2d (1.5 g, 50%),mp 248-249 "C (lit.% mp 243-245 "C. NMR Experiments. All DNA samples for NMR were made 5 mM in DNA phosphate by diluting with distilled water. This gave [Na+]/[P] ratios of 1.2. The NMR intercalator titrations were performed by adding successive aliquots (corresponding to r 0.005) of a drug stock solution directly to the DNA solution 0.05, the volume in the NMR tube. For titrations up to r increases by 10%. A control experiment, in which water alone was added up to 20% volume increase, showed that T1, within measuring uncertainties, was unchanged by such dilution. p H was measured to be 7 both before and after the addition of intercalators. =Na NMR spectra were recorded at 5.9 T on a Bruker AC 250 and obtained without lock. The inversion-recovery (180'-790"-acq) pulse sequence was used for the T,measurements with 15 different values of 7 for each experiment. The Tl values were obtained by a three-parameter linear least square fitting procedure. 9-[(4-Nitro-2-methoxyphenyl)amino]-1,2,3,4-tetrahydro- Each Tl value is the average of at least two measurements. The acridine (3). Compound 2c (20 mmol, 6.1 g) was dissolved in temperature for the NMR measurements was 27 "C. 13Cand 'H spectral data given were also obtained a t 5.9 T on acetic acid (99%, 80 mL). After addition of nitric acid (68%) at a Bruker AC 250 NMR instrument. 70 "C and stirring for 4 h, it was poured into ice (500 mL). When the ice had melted, 2 M sodium hydroxide (0.5 L) was added. A Registry No. 1,321-64-2;2a, 14807-16-0;2b,110245-49-3; 2c, yellow precipitate 6.5 g (ortho and paraisomer) was washed with 123333-18-6; 2d, 111232-55-4; 3, 123333-19-7; 4, 123333-20-0; water and dried in vacuum. Recrystallization twice from ethyl o-NH2C6H,C0,Me, 134-20-3;4-methylcyclohexanone, 589-92-4; acetate yielded 3 (2.4 g, 34%), mp 221-223 "C. Anal. (CzoH19cyclohexanone, 108-94-1;aniline, 62-53-3; 2-methoxyaniline, 90N303) C, H,N. 04-0. (29) Endicott, M.; Alden, B. W.; Sherrill, M. L. J.Am. Chem. SOC. 1946, 68, 1303.
-
-
(30) Yamato, M.; Takeuchi, Y.; Ikeda, Y. Heterocycles 1987, 26, 191.
Cyclization-Activated Prodrugs. Basic Carbamates of 4-Hydroxyanisole Walfred S. Saari,* J o h n
E. Schwering, Paulette A. Lyle, Steven J. Smith, and Edward L. Engelhardt
Merck Sharp & Dohme Research Laboratories, West Point, Pennsylvania 19486. Received January 18, 1989 A series of basic carbamates of 4-hydroxyanisole was prepared and evaluated as progenitors of this melanocytotoxic phenol. All of the carbamates were relatively stable a t low p H but released 4-hydroxyanisole cleanly a t pH 7.4 a t rates that were structure dependent. A detailed study of the N-methyl-N-[2-(methylamino)ethyl]carbamate showed that generation of the parent phenol followed first-order kinetics with tll2 = 36.3 min a t pH 7.4, 37 "C, and was accompanied by formation of N,N'-dimethylimidazolidinone. These basic carbamates are examples of cyclization-activated prodrugs in which generation of the active drug is not linked to enzymatic cleavage but rather depends solely upon a predictable, intramolecular cyclization-elimination reaction. Esterification of therapeutically active agents t o provide prodrugs with improved properties has become a familiar strategy for the circumvention of adverse physicochemical limitations. Ester prodrugs of alcohols and phenols are frequently explored t o improve solubility, absorption, and bioavailability a n d t o extend the duration of action of the parent drug.'S2 It is of course essential for the success of 0022-2623/90/1833-0097$02.50/0
this strategy that the ester progenitor be capable of delivering the parent d r u g at a practical rate i n vivo. Generally, ester prodrugs have depended u p o n chemical or (1) Stella, V. J.; Charman, W. N. A.; Naringrekar, V. H. Drugs.
19a5,29,455. (2) Leinweber, F.-J. Drug. Metab. Reu. 1987, 18, 379.
0 1989 American Chemical Society
98 Journal of Medicinal Chemistry, 1990, Vol. 33, No. 1
Saari et al.
Table I. Carbamates of 4-Hydroxyanisole. Chemical Properties and Half-Lives for Conversion to 4-Hydroxyanisole D0TN(cH2)"N,
B1
/R2 * H a R3
CH30 t l l z , min,
compd"
n
lab
2
lb IC Idd le
2 2 2 2 2
lfe
1gf lh
3 3
8
at 37 "C tllz at 37 "C pH 7.4 pH 6.8 pH 5.2 pH 4.2 36.3 f 1.3 140 f 5 57.8 f 1.9 h >15 days 56.OCf 1.4 CH3 CH3 CH3 153.0-154.5 39.6 f 0.7 CzHS CzHS H 149.0-150.0 118 f 2 CH, H H 152.5-154.5 304 f 1 H CH3 H 159.0-160.5 335 f 1 H H H 185.0-192.0 724 f 2 H H H 162.0-165.0 (softens at 110) 910 i 10 143.0-145.0 942 f 1 CH3 CH3 H 53.0-55.0
