Technetium-99m Labeled pAminohippuric Acid Analogues: Renal Function Agents

ZHUANGYU ZtiAIJG, KULDEEP K. BHARGAVA, S A M B. C H U N , M. DONALD BLAUFOX, AND L. RAO CHlERVU

Received Jul 29, 1988, from the Department of Nuclear Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 1&. Accepted for publication February 21, 1989.

~~~

Abstract 0 A number of paminohippuric acid analogues were synthe- sized in order to develop clinically useful 99"Tc-labeled radiopharma- ceuticals for evaluation of renal function measurements. Stable 99mT~- labeled complexes were formed at pH 5.7 using a Sn(ll) reduction method with all derivatives. The newly synthesized complexes were screened utilizing biodistribution studies in small animals. All complexes were excreted via the GU tract within 60 min post iv administration, with no significant activity in GI tract and liver. The [99mTc]methyl-PAHIDA complex showed optimal biodistribution among these analogues. Further investigation is needed to determine if these derivatives may be used to replace [I3' I]moduhippuric acid for the evaluation of renal function.

~ ~~ ~~ ~~ _ ~ _ _

['311]o-Iodo.hippurate (['311101H) has been used for radio- nuclidic evaluation of renal tubular function for the past 20 years. Among the many limitations of its application are the poor imaging characteristics of 13'1 and large absorbed radi- ation dose even with the limited amount of radioactivity administered during each study.1.2 Current availability of ['231]01H overc80mes many of these problems, imparting a lower radiation dose besides favorable radiation characteris- tics of 1231 for imaging with the gamma camera.

Technetium-99m has ideal physical properties for imaging, by virtue of its short half-life and nearly ideal radiation characteristics. Davison and co-workers3.4 investigated a new class of chelating agent, Nfl-bis(mercaptoacetamido)ethyl- enediamine, based on amide nitrogen and thiolate sulfur donor groups, 'l'c(V) ON2S2. With the object of finding a 99mTc-labelecl radiopharmaceutical that would replace OIH, Fritzberg and co-worke.rs5~6 studied [g9mTc]N2S2 and [99"rclN,S complexes. The ZggmTc]N2S, complexes have not shown favorable renal excr'etory characteristics and they also have shown diEerences in biological behavior of the 99n'Tc- labeled complexes formedl with the optical isomers. The [99mTclMAG, complex, representative of [99mTclN,S com- plexes, was shown to have potential clinical utility for application as al renal function agent.7

p-Aminohippmic acid (PAH), a well-established agent se- creted by renal tubules, forms very strong 99mTc-labeled complexes when coupled with IDA (PAHIDA, see structure). The [99"TclPAHIDA complex has been shown to be rapidly excreted in mice and rats; however, its renal clearance is slower than thlat of OIH in rats and Two more derivatives of aminohippuric acid, OAHIDA and MAHIDA, were prepared and their 99'nTc-labeled complexes were stud- ied in mice and rats.10 Relatively larger renal fixation and GI excretion for these two derivatives compared with PAHIDA suggested that the para derivative has optimal renal excre- tory characteric-t' r> 1cs.

As part of our continuing investigation of the PAHIDA derivatives, various substituents have been introduced on the ring of PAHIDA for complexing with 99mTc in order to evaluate the effect of difkrent substituents on the renal

clearance and to determine their potential for evaluating renal function. This paper presents the results of animal studies evaluating this new group of 99mTc-labeled analogues.

CONHCW,COOH FONHCH ,COOH

@ NHCOCH,N(CH,COOH),

AHCOCH,N(CH,COOH),

P A H I D A M A H IDA

CONH CH,COOH

NHCOCH,N(CH~COOH)~

O A H I D A

Results and Discussion The PAHIDA derivatives described here were prepared by

established procedures from substituted p-nitrobenzoic acids (Scheme I). In general, the carboxylic acids were treated with thionylchloride in benzene to form acid chlorides which in turn were reacted with glycine in the presence of sodium carbonate. The yields of the substituted p-nitrohippuric acids were 6545%. The reduction of the nitro group to an amino group using hydrogen and palladium charcoal proceeded with good yield (80-90%1. The generated substituted aminohip- puric acids were reacted with nitrilotriacetic acid anhydride (NTAA) in a suitable solvent and the resulting PAHIDA derivatives, purified by cryetallization, were isolated in 50- 65% yield.

The 99mTc-labeled complexes of these derivatives were stable when formulated a t pH 5.7 under the conditions described in the Experimental Section. The analysis ITLC with solvent A (CH,CN:H,O, 3:l) resulted in an Rfvalue of 1 for the complex and for pertechnetate, and an Rf value of 0 for the hydrolyzed form. In the solvent B system (CHC13:EtOH, 3:1j, the RfvaLlues were 0 and 1.0, respectively, for the 99mTc-labeled complex and free pertechnetate. Radio- chemical purity of the complexes was >95% even 6 h after preparation. When the coirnplex was incubated with rat plasma at 37 "C, even after 4 h, free technetium was unde- tectable as shown by ITLC and HPLC.

0022-3549/89//'1000-0829$01.00/0 0 1989, American Pharmaceutical Association

Journal of Pharmaceutical Sciences I 829 Vol. 78, No. 10, October 1989

FOOH ?ONHCH,COOH

4 . R = 2-CI

5 . R : 3 - F

6 . R = 3 - O M e

8 . R = 2 -CI

9 . R z 3 - F

10. R - 3 - O M e

7 . R Z 3-Me 11. R = 3 - M e

FONHCH2COOH .c CONH CH &OOH

I NHCOCH,N(CH,COOH)~ NH*

16. R z 2 -CI

17. R = 3 - F

18. R 3-OMe

19. R = 3 - M e

12. R : 2-

13. R : 3 -

14 . R : 3 -

1 5 . R z 3-

CI

F

o m e

Me

Scheme I

The biological results for the [99mTc]PAHIDA derivatives tested are given in Tables I and 11. Biodistribution of the complexes was evaluated in mice and rats at 15,60, and 240 min post injection. Rapid renal excretion was apparent a t the 15-min time period for all complexes. At 60 min post injection, all four complexes showed a high specificity for renal elimi- nation. The most promising agent was 3-methyl-PAHIDA, as shown in Table 11. The fractional dose in blood and kidney was found to be almost half of the PAHIDA complex. The activity in the liver and GI tract was also not significant. The methyl derivative which has significant urinary excretion with lim- ited activity in all other tissue offers further scope for improvement of the renal agents. Detailed structure-activity relationships with substitution with other groups in the aromatic ring might indicate the grouping which will result in optimal renal excretory behavior.

In conclusion, the PAHIDA analogues reported all form very stable complexes with 99mTc. The labeled complexes

Table I-Biodistribution of [99mT~]R-PAHIDA in Mice'

require no HPLC purification for biodistribution studies. Currently reported PAHIDA derivatives will serve as the skeleton for the future design of 99mTc-labeled renal radio- pharmaceuticals which might have renal secretory charac- teristics comparable if not superior to those of the parent PAH moiety.

Experimental Section Melting points were determined on an electrothermal melting

point apparatus and are uncorrected. The NMR spectra were obtained with a Varian XL-200 spectrometer locked on internal tetramethyl silane. F'recoated plates (Silica gel GF 250 pm; Analtech, Newark, DE) were used for ascending TLC in the following solvent system: Et0Ac:MeOH (1:2). Elemental microanalyses were performed by Schwarzkoff Microanalytical Laboratory, New York. 2-Chloro-4-nitrohippuric Acid @)--A suspension of 8.54 g (40

mM) of 2-chloro-4-nitrobenzoic acid, in 40 mL of benzene, and 6.5 g (55 mM) of thionyl chloride was refluxed for 5 h. Benzene was flash evaporated. The resulting yellow liquid was added in a dropwise manner to a mixture of glycine (3.75 g, 50 mM) and sodium carbonate (5.3 g, 50 mM) in 40 mL of H,O. The mixture was stirred at room temperature for 5 h. The solution was filtered and the filtrate was acidified using conc. HC1. The resulting solid was filtered and crystallized from ethyl acetate:pentane to yield 7.02 g (65%); mp 172-174 "C; NMR (Me,SO): 3.90 (d, ZH, CH,), 7.68-8.35 (m, 3H, ArH), and 8.92 ppm (t, lH, NH).

Anal.-Calc. for C,H,ClN,O,: C, 41.80, H, 2.73, N, 10.83. Found: C, 41.78, H, 2.66, N, 10.77.

4-Amino-2-chlorohippuric Acid (12)-A solution of 2-chloro- 4-nitrohippuric acid 5.0 g (19.3 mM) in 150 mL of ethyl alcohol was hydrogenated using a Parr apparatus at 30 psi pressure over 300 mg of 10% PdC. After 4 h, the catalyst was removed by filtration, the filtrate was evaporated, and the residue was crystallized from ethyl alcoho1:ethyl acetate to yield 3.6 g (81%) of 12; mp 187-188 "C; NMR (Me,SO): 3.86 (d, 2H, CH,), 5.60(b, 2H, NH,), 6.65-7.85 (m, 3H, ArH), and 8.70 ppm (t, lH, NH).

Anal.-Calc. for C,H,ClN,O,: C, 47.28, H, 3.96, N, 12.25. Found C, 46.98, H, 4.23, N, 12.05. 4-(Biscarboxymethyl)aminomethylcarboxyamino-2-chloro-

hippuric Acid ( 1 6 t A mixture of 3.42 g (15 mM) of 4-amino- 2-chlorohippuric acid (12) and 2.64 g (15.3 mM) of freshly prepared NTAA11 in 40 mL of DMF was stirred at 100 "C for 3 h. After cooling, the solvent was flash evaporated. Then 1 M NaOH was added to the residue (pH 11) which was treated with charcoal and filtered. The filtrate was acidified to pH 3 using conc. HC1. A solid separated upon cooling and was filtered off. Crystallization from acetone:H,O yielded 1.72 g (28%) of 16; mp 243-245 "C; NMR (Me,SO): 3.37 (s, 2H,

-CONHCH,COOH), 7.67-7.82 (m, 3H, ArH), and 8.56 ppm (t, lH, NH).

-NHOCCH,N), 3.47 (s, 4H, -N(CH&OOH)Z), 3.92 (d, 2H,

Percent Dose/Organb - Time. H -

min Blood GI Tract (Stomach & Intestines) Liver Kidney

3-F 15 60

240 2-CI 15

60 240

3-OMe 15 60

240 3-Me 15

60 240

HC 15 60

240

4.36 f 0.65 0.70 & 0.15 0.25 f 0.05 3.86 f 0.26 0.78 * 0.1 1 0.52 f 0.23 4.54 f 0.48 0.40 t 0.07 0.24 t 0.1 1 3.36 2 0.55 0.40 ? 0.14 0.20 * 0.07 3.30 f 0.50 0.60 2 0.20 0.30 & 0.10

1.02 2 0.06 0.58 2 0.04 0.65 +- 0.04 1.12 t 0.07 0.74 2 0.1 1 1.10 + 0.13 1.12 +- 0.10 0.38 t 0.04 0.46 t 0.10 0.94 +- 0.13 0.64 % 0.12 0.62 t 0.06 1.40 i; 0.50 1.70 * 0.10 1.60 +- 0.40

0.96 2 0.22 0.63 * 0.27 0.20 f 0.00 0.94 2 0.09 0.46 t 0.08 0.50 f 0.10 1.08 + 0.27 0.28 f 0.04 0.18 f 0.08 0.84 f 0.1 1 0.35 ? 0.06 0.1 8 f 0.04 0.90 2 0.20 0.40 f 0.10 0.30 f 0.10

2.28 f 0.83 0.88 t 0.34 0.20 f 0.06 3.20 t 0.86 1.08 ? 0.77 0.84 2 0.55 4.62 f 1.86 1.22 f 0.73 0.44 2 0.27 2.60 f 0.79 0.67 t 0.31 0.48 t 0.47 2.10 + 0.20 0.80 2 0.20 0.80 f 0.20

__ ~~~

a Six animals for each time interval. Mean value + 1 SD. PAHIDA.

830 / Journal of Pharmaceutical Sciences Vol. 78, No. 70, October 1989

Table 11-Biodlstribution of [ggmTc]R-PAHIDA In Rats' -

Percent Dose/Organ* Time, - min R Liver Kidney GI Tract

Blood (Stomach & Intestines)

1.25 f 0.22 5.05 2 1.68 15 9.71 2 1.03 1.53f 0.10 3-F 0.55 2 0.16 1.65 f 0.36 60 2.42 2 0.68 1.07 2 0.16

0.90 2 0.14 15 9.12? 1.16 1.80 t 0.1 5 1.50 t 0.33 4.20 f 0.39 2-CI 60 1.72 ? 0.08 1.20 2 0.20 0.54 ? 0.09 1.84 f 0.09

2.52 f 0.23 240 0.80 f 0.07 2.02 f 0.40 0.30 f 0.07 15 8.78 f 0.55 1.88 f 0.08 1.32 f 0.15 4.34 +- 0.61 3-OMe 1.36 f 0.09 60 1.60 * 0.07 1.26 f 0.23 0.46 2 0.1 1

1.42 2 0.1 5 240 0.44 2 0.05 1.40 f 0.24 0.20 f 0.00 3-Me 15 8.16 f 0.89 2.28 f 0.13 1 .oo t 0.22 5.89 2 0.84

60 1.30 f 0.35 1.06 f 0.09 0.36 f 0.09 1.10 f 0.24 0.70 t 0.07 0.20 '' 0.00 1.64 ? 0.39 0.10 f 0.00

- 1 80 2 0.40 4.10 f 0.40 9.20 f 1.10 3.20 t 0.40 - 0.70 f 0.10 2.50 2 0.60

- 0.40 k 0.10 3.50 f 7.00 240 1.20 '' 0.20

240 0.74 f 0.12 1.14 f 0.17 0.20 f 0.00

240 HC 15

60

a Six animals for each time interval. * Mean value ? 1 SD. PAHIDA.

And-Calc. for C,,HL6C1Ns0,: C, 44.84, H, 4.01, N, 10.46. Found C, 44.98, H, 3.92, N, 10.31

3-Fluoro-4-mitrohippuric Acid (9)-3-Fluoro-4-nitrobenzoic acid 5.5 g (30 mM) was refluxed in 30 mL of benzene with 4.89 g of thionylchloride for 4 h. The :solvent was evaporated under reduced pressure and the resulting yellow liquid was added in a dropwise manner to a solution of glycine (2.812 g, 37.5 mM) and sodium carbonate (3.97 g, 37.5 mM) in 30 mL of H,O. The mixture was stirred at room temperature for 4 h. The solution was filtered and the filtrate was acidified with conc. HCl. The solid was filtered, dried, and crystallized from ethyl acetate:pentane to yield 4.44 g (61%); mp 137-138°C; NMR (Me,SO): 3.98 (d, 2H, CH,), 7.92-8.32 (m, 3H, ArH), 9.30 (t, lH, NH), and 112.62 ppm (b, lH, COOH).

And-Calc. for C,H,FN,OI,: C, 44.64, H, 2.91, N, 11.57. Found C, 44.58, H, 2.79, N, 11.44.

4-Amino-3-rRuorohippuric Acid (13)-Compound 13 was prepared in 80% yield using exactly the same procedure as that for 12; mp 196-197 "C; PJMR (Me,SO): 3.91 (d, 2H, CH,), 5.72 (b, 2H, NH,), 6.72-7.52 (m, 3H, ArH), 8.53 (t, lH, NH), and 12.50 ppm (b, lH, COOH).

Anal.-Calc:. for C,HgFN,O~,: C, 50.95, H, 4.28, N, 13.20. Found: C,

4-(Biscarboxgmethyl)aminomethylcarboxyaminoj-3-fluorohip- puric Acid ( l7)cTo a solu.tion of 0.424 g (2 mM) of 4-amino- 3-fluorohippuric acid (13) in 25 mL of acetonitrile, 0.519 g (3 mM) of freshly prepared NTAA in 5 mL of acetonitrile was added. After 2 h of refluxing, the reaction mixture was cooled and the solid that separated was filtered off. Crystallization from H,O:acetone yielded 0.51 g (65%) of 17; mp 111.-112"C; NMR (Me,SO): 3.52 (s, 2H,

-CONHCH,COO), 7.70-8.40 (m, 3H, ArH), 8.89 (t, lH, NH), 10.26 (b, lH, COOH), and 12.54 ppm (b, 2H, 2 x COOH).

AnaLCalc . for C,,H,,FN,O,: C, 46.76, H, 4.19, N, 10.91. Found: C, 46.46, H, 4.29, N, 11.09. 3-Methoxy-4-nitrohippuric Acid (lO)-As in the preparation of 9,

6 was converted to 10 in 82%7 yield; mp 145-147 "C; NMR (Me,SO): 3.95 (6, 3H, OCHr,), 4.05 (d, 2H, CH,), 7.52-8.0 (m, 3H, ArH), 9.15 (t, lH, NH), and 12.70 ppm (b, lH, COOH).

AmL-Calc. for Cl,HloN,O,: C, 47.26, H, 3.57, N, 11.02. Found: C, 47.27, H, 3.8i!, Pi, 10.86.

4-Amino-3-methoxyhippuiric Acid (14)-As in the preparation of 12, 10 was converted to 1 4 in 96% yield; mp 173-174°C; NMR (Me,SO): 3.80 (s!, 3H, OCH,), 3.87 (d, 2H, CH,), 5.30 (b, 2H, NH,), 6.60-7.40 (m, 3:H, ArH), 8.4.2 (t, lH, NH), and 12.40 ppm (b, lH, COOH).

Anal.-Calc. for C,&,,N,O,: C, 53.57, H, 5.39, N, 12.49. Found: C, 53.48, H, 5.43, N, 12.35.

4-(Biscarboxymethyl jaminomethylcarboxyamino)-3-methoxy- hippuric Acid (18)-0n the basis ofthe method described for 17,4.08 g (51% yieldl) was prepared from 4.48 g (20 mM) of 4-amino- 3-methoxyhippuric acid (14). The product was crystallized from H,O:acetone; imp 139-1410 "C; NMR (Me,SO): 3.48 (s, 2H,

50.61, H, 4.381, PI[, 12.96.

-NHOCH,N), 3.59 (8, 4H, -N(CH,COOH),), 3.92 (d, 2H,

NHOCCH,N), 3.58 (s, 4H, -IT (CH,COOH),, 3.88 (s, 3H, OCH,), 3.97 (d, 2H, -CONHCH,COO:I, 7.47-8.35 (m, 3H, ArH), 8.78 (t, lH, NH), 10.00 (s, lH, COOH), and 12.60 ppm (b, 2H, 2 x COOH).

And-Calc. for C,,H,,N,O,: C, 48.37, H, 4.82, N, 10.58. Found: C, 48.25, H, 4.79, N, 10.61.

3-Methyl-4-nitrohippuric Acid (11)-Compound 11 was prepared in 86% yield by the method used for the preparation of 9; mp 111-113°C; NMR (Me,SO): 2.55 (s, 3H, CH,), 3.90 (d, 2H, CH,), 7.82-8.10 (m, 3H, ArH), and 9.10 ppm (t, lH, NH).

And-Calc. for CloH,,N,O,: C, 50.40, H, 4.23, N, 11.76. Found: C, 50.49, H, 4.14, N., 11.67.

4-Amino-3-methylhippuric Acid (15bAccording to the same method as used for 12, l .g g (91% yield) of 15 was prepared from 2.38 g of 11; mp 168-170 "C; NMR (Me,SO): 2.80 (s, 3H, CH,), 3.92 (d, 2H, CH,), 5.40 (b, 2H, NH,), 6.50-7.50 (m, 3H, ArH), and 8.30 ppm (t, IH, NH).

And-Calc. for C,,H,,N,O,: C, 57.68, H, 5.81, N, 13.45. Found: C, 57.53, H, 5.83, N, 13.20.

4-(Biscarboxymethyl)ami1~omethylcarboxyaminoj-3-methyl- hippuric Acid (19)-The desired compound was obtained as a white solid in 98% yield by following the procedure for the synthesis of 17; mp 179-180 "C; NMR (Me,SO): 2.35 (6 , 3H, CHJ, 3.43 (s, 2H,

-CONHCH,COO), 7.67-8.72 (m, 3H, ArH), 8.72 (t, lH, NH), 10.0 (s, lH, COOH), and 12.60 ppm (b, 2H, 2 x COOH).

And-Calc. for C,,H,,N,O,: C, 50.39, H, 5.02, N, 11.02. Found: C, 50.43, H, 5.53, N, 10.80.

99mTc-Labeled Complex Formation-A solution of 10 mg of the hippuric acid analogue in 0.5 niL of 0.1 M NaOH was adjusted to pH 7 with 0.05 M HC1 and saturated with nitrogen. Then, SnCl,.2H2O (0.25 mg) in 10 pL was added and the pH was adjusted to 5.7. The solution was filtered through a1 0.22-pm Millipore filter and 3 mL of [99mTc]pertechnetate (200-300 pCi) in saline (Technetium Tc-99m Generator from Dupont) was afdded to form the corresponding 99mTc- labeled complexes.

Determination of Radiochemical Purity-Two ITLC solvent sys- tems were developed to determine radiochemical purity: solvent A, CH,CN:H,O (7:3) and solvent B, CHC1,:EtOH (3:l). The strips (ITLC-SG) were spotted with 1 pL of sample and immediately developed for -9 cm. The strips were then air dried and 1-cm cuts were counted in a well counter to determine the complex, free pertechnetate, and reduced-hydrolyzed technetium. Reversed-phase HPLC was performed on a Dupont model 850 liquid chromatography unit using an ODS column, with eluant fractions monitored for radioactivity with a NaI(T1) detector. The system was run in an isocratic mode at 8 0 6 aqueous CH,CN for analysis of the complexes. An aliquot (2-25 pL) containing 1 pCi of the preparation of complex was injected, 1-mL eluate fractions were collected, and the activity in each fraction was measured in a gamma counter. Mice urine aliquots (5-10 4) containing the excreted activity were also similarly analyzed by ITLC and HPLC.

Stability Studies of Complex-The stability of the complexes was

-NHOCCH,N), 3.60 (s, 4H, -N(CH,COOH),), 3.93 (d, 2H,

Journal of Pharmaceutical Sciences / 831 Vol. 78, No. 70, October 1989

determined by incubating an aliquot of complex (8 pCi) with rat plasma (0.5 mL) at 37 "C and then determining the free technetium in this mixture a t different time intervals up to 4 h post formulation using ITLC and HPLC methods.

Animal Biodistribution-For biodistribution studies, male mice (CD-1,25-30 g) were used and 0.1 mL ofthe complex preparation ( 2 3 pCi) was injected into the tail vein. For rat biodistribution studies, Sprague-Dawley male rats (200-225 g ) were used and they were also injected with 0.2 mL (5-7 pCi) of the preparation via the tail vein. The animals were sacrificed at different time intervals, and tissues were recovered, weighed, and counted. The % doselorgan was determined by comparison of tissue radioactivity with suitable diluted aliquot8 of the injected dose.

1. 2.

3.

4. 5.

References and Notes Chervu, L. R.; Blaufox, M. D. Sem. Nucl. Med. 1984,12,224. Britton, K. D. Radionuclides in the Investigation of Renal Dis- euses; Blackwell Scientific: London, U.K., 1979; p 270. Davison, A.; Jones, A. G.; Orvig, C.; Sohn, M. Inorg. Chem. 1981, 6, 1629-1632. Davison, A.; Sohn, M, Orvig, G. J . Nucl. Med. 1979,20,641-645. Fritzberg, A. R.; Klingensmith, W. C.; Whitney, W. P.; Kuni,

C. C. J . Nucl. Med. 1981.22. 258-266 6. Fritzberg, A. R.; Kasina,'S.; Eshima, D.; Johnson, D. L. J . Nucl.

7. Taylor, A.; Eshima D.; Alazraki, N. Eur. J . Nucl. Med. 1987,12,

8. Chervu, R. L.; Sundoro, B. M.; Blaufox, M. D. J . Nucl Med. 1984,

Med. 1986,27, 111-116.

510-515.

25,1111-1115. 9. Summerville, D. A.; Packard, A. B.; Bartynski, B.; Lim, K. S.;

Chervu, L. R.; Treves, S. T. J. Nud. Med. 1987,28, 907-910. 10. Bhargava, K. K.; Zhang, Z.; Chun, S. B.; Chervu, L. R.; Blaufox,

M. D. J . Labelled Compd. Radiopharm. 1988,9, 943-948. 11. Burns, H. D.; Sowa, D. T.; Marzilli, L. G. J . Pharm. Sci. 1978,67,

1434-1437.

Acknowledgments This aper is dedicated to the memory of Professor L. Rao Chervu,

Ph.D. 8 e was instrumental in organizin the Central Lab of Nuclear Medicine at Albert Einstein College of dedicine and was its director for the past 18 years. His professional contributions were of highest standards and he strove continuously for excellence in the care of patients. The personal dedication of Dr. Chervu will long be cherished by all scientists in the field of radiopharmaceuticals.

This work was supported by NIH Grant no. 5 R01 DK 34251 02.

832 I Journal of Pharmaceutical Sciences Vol. 78, No. 10, October 1989