J o u r n a l of Medicinal Chemistry, 1975, Vol. 18, No. 5
Notes (6) E. F. Godefroi, H. J. J. Loozen, and J. Th. J. Luderer-Platje, Recl. Trau. Chim. Pays-Bas, 91,1383 (1972). (7) B. Tertov, U. V. Burykin, and I. D. Sadekov, Khim. Geterotsikl. Soedin., 520 (1969); Chem. Abstr., 71,1243284, (1969).
533
(8) L. A. M. Bastiaansen and H. M. J. M. van As, unpublished results. For a related but independent study of this reaction, see D. S. Noyce, G. T. Stowe, and W. Wong, J. Org. Chem., 39, 2301 (1974).
Preparation of [ 18F]Haloperidol C. S. Kook, M. F. Reed, a n d G. A. Digenis*' Divisions of Medicinal Chemistry and Nuclear Medicine, Colleges of Pharmacy and Medicine, Uniuersity of Kentucky, Lexington, Kentucky 40506. Received March 18,1974 A procedure is described that permits the preparation of [18F]haloperidolin 140 min a t specific activities ranging from 4-5 WCi mg-'. A key step in the synthetic route involves the incorporation of 18Finto the molecule through a Schiemann-type reaction, which involves the pyrolysis of the diazonium tetrafluoroborate salt of 4-[4-(p-chlorophenyl)-4-hydroxypiperidino]-4'-aminobutyrophenone.
In vivo tissue distribution studies with 14C-labeled compounds require serial sacrifice of essentially identical isogenic animals followed by laborious analytical assessment of changes in 14C activity in organs as a function of time after administration. T h e d a t a obtained from such studies are n o t only inapplicable t o man b u t also are of limited use in any large mammal where colonies of identical isogenic subjects are unavailable.2 H u m a n studies with compounds labeled with "short-lived," y-emitting radionuclides can produce much valuable diagnostic information, such as t h e organ visualization a n d function studies of nuclear medicine. Such studies also provide t h e opportunity t o perform tissue distribution determinations a n d pharmacokinetics in m a n in a nondestructive manner. One of t h e more useful radionuclides for bone scanning is ISF which is now in routine use in many medical centers, including our own, in t h e form of the simple inorganic fluoride.3a ISF is a pure positron emitter (0.635 MeV, p+) a n d t h e resulting 511 keV annihilation radiation is easily detected with conventional nuclear medicine instrumentation. Its short physical half-life (110 min) results in a low radiation dose to t h e patient. lsF-Labeled amino acids such as 4 - f l ~ o r o p h e n y l a l a n i n ea~n~d ~6 - f l u ~ r o t r y p t o p h a n have ~ been prepared a n d evaluated as specific pancreas scanning agents4s6 Recently a method for t h e preparation of fluorine-18 labeled metal fluorides a n d organic diazonium tetrafluoroborates has been d e ~ c r i b e d .This ~ method has been applied in the synthesis of I8F-labeled amino acids. T h e synthesis of [1sF]-5-fluorouracils a n d [18F]-5-fluoroDopagJo has also been reported. T h e former has been prepared as a potential tumor localizing agents a n d t h e latter as a brain ~ c a n n e r .It~ is interesting t o note t h a t a signific a n t loading dose effect on t h e localization of both [lSF]-4fluorophenylalanine a n d [ISF]-6-fluorotryptophan has been observed in animals."J* T h u s , t h e pancreas t o liver ratio increases with decreasing amounts of 18F-labeled amino acids administered. These observations strongly suggest t h e necessity for development of synthetic methods which can result in carrier-free products of very high specific activity. I t is hoped t h a t t h e availability of such radiopharmaceuticals would permit studies dealing with organ localization of these agents as a function of their loading dose. Our interest in obtaining d a t a on tissue distribution a n d pharmacokinetics of t h e neuroleptic drug haloperidol (7) (the chemistry,13 p h a r m a ~ o l o g y , ' ~distribution, excretion, a n d metabolism in rats15 of t h e drug have been studied) by external scintigraphic techniques has led us t o devise a synthetic route (Scheme I) for its rapid preparation in t h e ISF isotopically labeled form. According to this sequence
t h e incorporation of 18Finto t h e molecule occurs a t t h e last step (6 t o 7) through a Schiemann-type reaction which involves the pyrolysis of t h e diazonium tetrafluoroborate salt
6.
Scheme I 0
0
C H 3 ! N H a
7 NCI. as, + ClCCH,CH,CH,Cl II n
L
1
0
0
+
3 1. PhCH,,
KI, A
+
2. 10% NaOH
HN%Cl
in EtOH.
4
5 0
-
I
I/
\ I
c1 7 0
8
,534 .lo:rmal
oj'
Medicinn/ Chemistry, 1975, Vol. 18, No. .5
T h e production of haloperidol (7) was favored (37.8% yield from 5 ) when the pyrolysis of salt 6 was conducted at 14.5' for 4 min in a xylene-dioxane9 (3:l) mixture. U n d e r such conditions olefin 8 was found t o b e t h e minor product of t h e reaction. In contrast, however, a t t e m p t s to r u n t h e pyrolysis of 6 for longer periods of time (30 min), or in t h e absence of a solvent, favored the production of the olefin 8. T h e procedure described below permits the preparation of ['PF]haloperidol in about 140 min (ca. 1.5 half-lives of t h e radionuclide) at specific activities ranging from 4 t o 5 gCi/mg.
unequivocally proven by mixture melting point (mp 149') and comparative spectroscopic determinations (ir, uv, and mass spectra) with authentic haloperidol. Preparation of ['*F]Haloperidol (7). I8F was produced by the "Neid,a)lsF nuclear reactionla at the end of which the glass target insert was washed with 7.5 ml of distilled HzO. The volume of the Hz0 was reduced to about 1 ml by heating at 110" and by blowing Nz into the solution. To the aqueous solution, containing 11.34 mCi of I8F, diazonium salt 6 (prepared from 1 g of 5 as described above) and 2.0 ml of acetone3 were added. After standing for 5 min (to enhance the incorporation of 18F into the tetrafluoroboratr moiety3 of 6) the mixture was dried by heating at 50' under N:> and by subjecting it to high vacuum for 5 min. The dried residue was subsequently pyrolyzed in xylene-dioxane (3:l) as described Experimental Section above. The pyrolysis product was chromatographed on neutral alumina first with CHC13 and subsequently with 2% MeOH in CHC13 Melting points were determined on a Fisher-Johns (hot stage) as eluent. The white crystalline residue, obtained from the evapoapparatus and are uncorrected. Where analyses are indicated by ration of 2% MeOH-CHC13 eluent fractions, was washed with 2 X 2 the symbols of the elements, analytical values were within &0.3% ml of Et20 to yield 0.37 g (1.76 mCi) of [lsF]haloperidol. The idenof the calculated values. Compounds gave satisfactory uv, ir, tity of the product was substantiated by two-dimensional T L C NMK, and mass spectral data obtained respectively on Cary 15, (see details above). A radioscan of the thin-layer plate showed all Heckman IR-8, Varian Associates A-60A, and Hitachi RMU-7 the activity coincident with the spot of authentic haloperidol. The ctrometers. Chemical shifts are downfield from the stanpercent yield of incorporation of 18F into the final product 7 w a s 4Si. For TLC, precoated silica gel plates (Quanta-Gram, calculated to be 35.5%. The present method permits the produc Quantum Industries, Fairfield, N.J.) were used. Compounds 7 and tion of [18F]haloperidol at specific activities of about 4-5 fiCi/mg in 8 were detected by first spraying the plates with a fluorescein soluabout 140 min. tion l 6 followed by visualization under a long-wave ultraviolet 4-[ 4-(p-Chlorophenyl)-2,5,6-trihydropyridino]-4'-fluor~lamp. The radionuclidic purity of the 18F was assured by y specbutyrophenone (8). 5 (1.1 g, 2.8 mmol) was converted LO its diazotrometry (Packard 4096 channel analyzer, Model 45) with a Ge(Li) nium salt 6 as described under the preparation of haloperidol. Salt r (Nuclear Diodes, Inc.). The absence of long-lived @-emit6 was then pyrolyzed in a mixture of xylene-dioxane (3:119at 150' ters was shown by liquid scintillation counting (Packard Model for 30 min. The xylene-dioxane mixture was then separated from X310) after the complete decay of lSF. the resulting brown residue. The latter was extracted with three 4'-(4-Chlorobutyryl)acetanilide(3)." To a mixture of acetan15-ml portions of CHC13, and the extracts were combined with thp ilide (1, 10 g. 0.07 mol), AlC13 (40 g), and 40 ml of CS2, a solution of xylene-dioxane mixture and evaporated to dryness. (Only trace 4-chlorobutyroyl chloride (2, 30 g, 0.21 mol) in 30 ml of CS2 was amounts of haloperidol could be detected when a small sampie added dropwise to 0'. The reaction mixture was then heated at 50' from the residue was examined by TLC, as described above.) The for 2 hr and the supernatant layer of CS2 discarded. The oily resiresidue was subsequently chromatographed on 10 g of neutral aludue \%asthen poured over a mixture of ice-water and the amormina (Fisher, activity I). Elution with CHC13 gave 0.54 f: (1.5 phous precipitate filtered and recrystallized from 95% EtOH to mmol, 50.5% yield) of olefin 8 (mle 357) as a white crystalline give 9.3 g (0.038 mol, 57% yield) of 3: mp 148-150' (lit. mp 147product. Recrystallization from 95% EtOH yielded the pure prod15'L".17a 15i-lj'3",17b 162-164°17C);m/e239 (M . ) . I- [ 4-(g-Chlorophenyl)-4-hydroxypiperidino]-4'-~mino- uct, mp 95'. Anal. (C21H2IClFNO) C, H, N.The NMR of the olefin exhibited a peak at 6 6.05 assigned to the olefinic proton. butyrophenone ( 5 ) . Product 3 (4.80 g, 0.02 mol) was heated in a sealed tube with 9.0 g (0.04 mol) of 4-(p-chlorophenyl)-4-hydroxypiperidine (4, mp 1 4 5 O , Aldrich, Milwaukee, Wis.), 0.05 g of KI, References and Notes and 75 ml of distilled toluene at 110-115' for 48 hr. Upon cooling the solid phase of the reaction was separated and washed succesAddress correspondence to this author at the College of Pharsively with HzO, CHClH, and EtzO. To an ethanolic (95% EtOH) macy, University of Kentucky. mixture of the product, which was refluxed for 1 hr, 7 5 ml of 10% M. B. Winstead, J . F. Lamb, and H. S. Winchell. J . N u d Med., 14, 747 (1973). NaOH was added and the reflux continued for 40 min. Upon cooling and the addition of 100 ml of HzO, 5.47 g (0.014 mol, 70% yield (a) R. W. Goulding and A. J. Palmer, Int. J . A p p l . Radial. Isot., 23, 133 (1973), and references cited therein: (b) R. M. from 3 ) of 5 was obtained. The buff crystals were recrystallized Hoyte, S. S. Lin, D. R. Christman, H. L. Atkins, W. Hauser. from 95% EtOH: mp 175'; mlp 372 (M+).Anal. (Cz1Hz&lNzOz) C, H. Cl. N. and A. P. Wolf, J . Nucl. Med., 12,280 (1971). M. F. Cottrall, D. M. Taylor, and T. J. McElwain, Hi- d. H f r Synthesis of Haloperidol ( 7 ) . To 1 g (2.6 mmol) of 5 , 1 ml of diol., 46, 277 (1973). concentrated HCI and '7 ml of Hz0 were added and the mixture ' . LiHF4 (1.2 g) in 2.4 ml of HzO, cooled to 5', was was cooled to 5 R. M. Hoyte, S. S. Lin, H. L. Atkins, D. R. Christman, W. Hauser, J. F. Klopper, and A. P. Wolf, J . Nucl. Med , 12, 367 then added dropwise. To this 3 ml of aqueous 10% NaN02 was (1971). added slowly and stirred vigorously for 15 min. The aqueous porD. M. Taylor and M. F. Cottrall, "New Developments in Ration of the reaction mixture was decanted and the brown solid (presumably the diazonium fluoroborate salt 6) washed with cold diopharmaceuticals and Labeled Compounds". Copenhagen. Water (5'). followed by 5 ml of aqueous 5% LiBF4 ( 5 O ) , and freeze1973, IAEA/SM-171. J. C. Clark, R. W. Goulding, M. Roman, and A. J . Palmer. Hadried. The dried salt 6 was subsequently pyrolyzed in a mixture of diochem. Radioanal. Lett., 1412,101 (1973). xylene-dioxaneY (3:l)at 145' for 4 min. The dark brown pyrolysate was then extracted with three 4-ml portions of CHC13. The xyJ . S. Fowler, R. D. Finn, R. M. Lamhrecht, and A. P. LVoIt', J lene--dioxane mixture and the extracts were combined and evapoNucl. Med., 14,63 (1973). G. Firnau, C. Nahmias, and S. Garnett, Int. J . Appl. K a d i a t . rated to dryness under 3 2 to yield 0.49 g of a light yellow residue. LVhen a sample from this residue was examined by two dimensionIsot., 24, 182 (1973). al TLC' [silica gel; solvent 1, CHC13-MeOH-concentrated NH40H G. Firnau, C. Nahmias, and S.Garnett, J . Med. Chem., 16, 196:4:1);solvent 2, 2-propanol-4 hr NH4OH (80:20)] it exhibited a 416 (1973). major spot with identical R f values (0.6 and 0.82, respectively) with H. L. Atkins, D. R. Christman, J. S. Fowler, W. Hauser, K. M. that of authentic haloperidol. A minor spot exhibiting Rf values Hoyte, J . F. Klopper, S. S.Lin, and A. P. Wolf, J . Nucl. Med.. 13,713 (1972). (0.7,j and 0.95, respectively) identical with those of olefin 8 was also detected. The residue was then chromatographed on 21 g of A. P. Wolf, D. R. Christman, J . S. Fowler, and R. M. L a n neutral alumina (Fisher, activity I). Five-milliliter fractions were brecht in ref 6. collected. Elution with CHC13 gave 0.10 g (11%yield from 5 ) of a P. A. J. Janssen, C. Van de Westeringh, A. H. M. ,Jageneau, P. white crystalline product which was shown, after one recrystallizaJ. A. Demoen, B. K. F. Hermans, G. H. P. Van Daele, K. H. L. tion f'rom 95% EtOH, by mixture melting point (mp 92O) and mass Schellekens, C. A. M. Van der Eyeken, and C. J. E. Niemegeers, J . Med. Pharm. Chem., 1,281 (1959). spectrometry to he identical with a sample of olefin 8, synthesized as described below. Elution with 2% MeOH in CHCl3 yielded 0.37 P. A. J. Janssen, Neuro-Psychopharmaco1., Proc. Meet. ('(ill. Int. Neuro-Psychopharmacol.,3rd, 1.962, 331 (1964). g t:l7.8% yield from 51 of haloperidol (7), the identity of which was
Journal of Medicinal Chemistry, 1975, V d . 18, No. 5
Notes
(15) (a) W. Soudijn, I. Van Wijngaarden, and F. Allewijn, Eur. J . Pharmacol., 1,47 (1967); (b) G. A. Braun, G. I. Poos, and W. Soudijn, Eur. J. Pharmacol., 1,58 (1957). (16) K. G. Krebs, D. Heusser, and H. Wimmer, "Thin Layer Chromatography", 2nd ed, E. Stahl, Ed., Springer-Verlag, New York, N.Y., 1969, p 878. (17) (a) P. Adriaan and J. Janssen, British Patent Application
535
881893 (1961) [Chem. Abstr., 57,2198~(1962)l; (b) C. Van de Westeringh, B. Hermans, F. Raeymalkers, and C. Van der Eycken, Ind. Chim. Belge, 25, 1073 (1960) [Chem. Abstr., 55, 6428g (1961)l; (c) May and Baker Co., British Patent Application 943739 (1959) [Chem.Abstr., 60,5522h (1964)l. (18) P. V. Harper, N. Lembares, and H. Krizek, J. Nucl. M e d , 12, 362 (1971).
Analogs of Campto thecin J a m e s A. Bristol, Daniel L. Comins, Richard W. Davenport, Michael J. Kane, Robert E. Lyle,* J o h n R. Maloney, David E. Portlock, Department of Chemistry, Parsons Hall, liniuersity of N e u Hampshire, D u r h a m , Neu, Hampshire 09824
a n d Susan B. Horwitz Department O / Pharmacology, Albert Einstein College of Medicine of Yeshim 'nicersity, B r o n x , N e ! ( ,York 1Od61 Receiivd Jul>,29,197-1
Several compounds having portions of the camptothecin ring system were prepared. These compounds were screened against L1210 lymphoid leukemia with negative results. T w o of the analogs which contained the pyridine and hydroxylactone D and E rings were also screened for inhibition of DNA and R N A syntheses in HeLa cells. Each o f these analogs had decreased activity as compared with camptothecin and there was no degradation of' DNA in the HeLa cells. This suggests that the D and E rings are not a sufficient requirement for camptothecin-like activity. T h e early animal tests showed t h e alkaloid camptothecin
(1) t o be a potent antineoplastic agent;' however, t h e toxic effects a n d lack of activity against gastrointestinal cancer showed 1 t o be ineffective as a chemotherapeutic agent.? The effectiveness of camptothecin against leukemia in experimental animals a n d t h e unusual effects it has o n macromolecular synthesis:' have caused an interest in determining t h e structural features of camptothecin associated with this activity. I8
camptothecin (1) Previous studies have indicated t h a t t h e functional groups of the hydroxylactone ring E must be present t o maintain t h e activity of camptothecin. T h u s substitution of t h e hydroxyl group a t C-20 by halogen,.l acetoxy,-l ethyl,5 or hydroxymethyl" gives compounds showing reduced or lack
0
8.
4
2, R = R = H
3, R-CH,;
R'=n-C,H,
&
N\
C1 6
'
Results and Discussion
0
I
of cytotoxicity in animals. Replacement of t h e hydroxyl group by hydrogen gave a desoxy compound inactive against tumors' b u t showing inhibition of DNA-RNA synthesis. Reduction of t h e c - 2 1 carbonyl group also caused a loss of activity.-' T h e activity of camptothecin is maintained if t h e lactone ring is opened t o t h e alkali metal salt or amide.' These d a t a suggest t h a t t h e D and E rings of camptothecin are necessary for activity. Only limited information about t h e biological activity of simple analogs of camptothecin is available; however, t h e report t h a t 2 has only 0.01 t h e activity of camptothecin; a n d t h e weak inhibition of R N A synthesis of 3" suggested t h a t t h e D a n d E rings were a necessary b u t not a sufficient requirement for activity.
0 5
I n a n a t t e m p t t o determine t h e structural requirements required for activity, several series of analogs were prepared, three of which (4,5, a n d 6) contain t h e D a n d E ring systems comparable t o camptothecin (1). T h e syntheses were described previously.x T h e analog 4 contains t h e same number of cyclic atoms as camptothecin; however, t h e nitrogen a t position l is replaced by carbon a n d t h e C-2-3 bond is not closed. This very close analog was inactive in t h e L1210 leukemia screen (Table I) a n d was less active t h a n camptothecin as a n inhibitor of nucleic acid synthesis in HeLa cells.'' Replacement of t h e 6-naphthylmethyl group on nitrogen by a benzyl group ( 5 ) gave a marked d e crease in inhibition of macromolecular synthesis. Neither of these analogs caused degradation of DNA, a property possibly related t o t h e suppression of tumor growth, a n d t h u s t h e inactivity in t h e L1210 screen was expected. Table I lists additional compounds related in structure t o camptothecin ( 1 ) whose syntheses have been reported."' 7 contains t h e atoms of D a n d E rings a n d 8 has all t h e atoms of camptothecin without closure of t h e lactone ring. 6 has t h e D a n d E ring with t h e carbonyl group of t h e pyridone replaced by chlorine.x T h e s e compounds, as well as t h e analogs with t h e B a n d D rings (type I), t h e A, B, a n d D rings (type 11), and t h e B, C, a n d D rings (type III),lo were inactive in t h e L1210 leukemia screen.
