242 Journal of Medicinal Chemistry, 1974, Vol. 17, N o . 2
Tolman. et a/.
Synthesis and Anti-Deoxyribonucleic Acid Virus Activity of Certain 9-~-~-Arabinofuranosyl-2-substituted Adenine Derivatives Kenji Miyai, Lois B. Allen, John H . Huffman, Robert W. Sidwell.* and Richard L 'I'olman* IC" Pharmaceuticals Inc. , ,Vucleic Acid Research Institute 1rLine Calijornra YLhb-4 K e t v i i r d Juli 30, 1973
Several 2-substituted ara-A derivatives (2-methosy, 2-methylthio. ?-benzyloxy) were prepared hy nucleophilic displacement of chloride from 9-P-~-arabinofuranosyl-2-chloroadenine or 9-(~.3,~-1ri-~-henzyl-P-o-arabinofuranosyl)2-chloroadenine and debenzylation when appropriate. In citro anti-DNA virus evaluation revealed 2-chloro-arn-A to have activity comparable to ara-A. In side-hy-side examinations, ara-A proved to be more effective than 2chloro-ara-A in the treatment of herpes or vaccinia virus-induced encephalitis in mice. Topical treatment of type 1 herpes simplex virus infections in hamsters with ara-A and 2-chloro-ara-A also indicated ara-A to be more efficacious in increasing the mean survival time T h e antiviral activity of 9-P-D-arabinofuranosyladenine Scheme I (ara-A) against DNA viruses in vitro and in uivo is well KH, documented.l-s It was t h e purpose of this investigation to determine the effect of 2-substitution of purine in ara-A upon the antiviral activity. During the course of our investigation, the synthesis of two 2-substituted ara-A derivatives (%hydroxy and 2-amino) was reportedg and the compounds were stated to possess anti-DNA virus properties. Treatment of 9-(2,3,5-tri-0-benzyl-P-~-arabinofuranosyl)-2-chloroadenine (1)'O with NaOMe-MeOH gave the RO KO benzylated 2-methoxy-ara-A derivative 3 which was de1 R = CH,Ph 3.Y = OCH,; R = CHLPh benzylated in good yield by hydrogenation over a palladi2.R=H 4 , Y = OCHJ;R = H um catalyst to furnish 9-$-~-arabinofuranosyl-2-methoxy5 . Y = SCH,; R = H adenine ( 4 ) . A similar displacement of chloride from 1 with 6. Y = OCH>Ph;R=H sodium benzyl oxide in benzyl alcohol gave the benzylated cells was exposed to 320 CCIDso per ml of' virus and con2-benzyloxy-ara-A intermediate. The carbohydrate benzyl centrations of each compound ranging from 1000 to 0.01 ethers were found to be selectively removed by hydrogenaNgjml were added within 15 min after the virus. Antiviral tion with 10% palladium on charcoal in a hydrogen atmoactivity was determined by observing inhibition of the sphere leaving the benzyl ether of the 2-hydroxyadenine viral cytopathic effect (CPE) after a 72-hr incubation a t derivative 6 unaffected. Acidic hydrolysis of 6 and chro37". The degree of CPE inhibition and cytotoxicity exhibmatographic analysis of the mixture confirmed t h e presited by each compound was given a numerical virus rating ence of D-arabinose and the absence of a hydrolysis prod(VR) as described previously.12 A VR of 0.5 or greater was uct with t h e properties of an arabinose monobenzyl ether. indicative of significant antiviral activity. The viruses thereby substantiating the structure of 6 as 9-6-D-arabinoused in the study included types 1 and 2 herpes simplex furanosyl-2-benzyloxyadenine. virus. pseudorabies virus. vaccinia virus. myxoma virus, Displacement of chloride from g-$-D-arabinofuranosyItype 3 adenovirus (DNA viruses), type 3 parainfluenza 2-chloroadenine1' (2, 2-chloro-ara-A) with XaSMe in virus, and type 13 rhinovirus (RXA viruses). For comparMeOH proceeded in excellent yield to furnish 2-methylative purposes, ara-A was included in each experiment as thio-ara-A ( 5 ) . Preparation of 5 from the benzylated intera known active control. 2-Chloro-ara-A was significantly mediate 1 was avoided due t o possible difficulties in efeffective against herpes simplex and vaccinia viruses. with fecting debenzylation after introduction of the 2-methyl the degree of activity approximately equal t o that seen thio group (Scheme I ) . using ara-A (Table I). The other compounds tested were Antiviral Evaluation. In cztro antiviral studies were a t best only weakly to moderately active against DNA virun in disposable plastic microplates.12 In this system. an ruses in these experiments. Each of the compounds had 18-24-hr monolayer of human carcinoma of the nasopharapproximately the same degree of' toxicity for KB and ynx IKB) or continuous passaged rabbit kidney (RK-13) Table I. Comparative Ln vLtro Antiviral Activity' of 2-Chloro-ara-A, 2-Methylthio-ura-A, 2-Methoxy-ara-A, 2-Benzyloxy-ara-A, and ara-A . _____ __ _ _ ___ - 2-Chloro2-Methylthio2-Methoxy2-BenzyloxyVirus ara-A ara-A ura-A ara-A -
___
-~
Type 1 herpes simplex Type 2 herpes simplex Pseudorabies Vaccinia Myxoma Type 3 adeno Type 3 parainfluenza Type 13 rhino
____
-
___-
0 9 0 6 0 1
0 9 0 1
0 0 0 2 0 0 __
0 1 0 4 0 1 0 3 0 4 0 0 0 0 0 0
.
0 1 0 4
0 9 0 7
(J 4 0 L
0 5 0 0 0 1
(1
(I 0
i ('
0 0 0 0
0 6 0 8 0 8 0 0 0'' 0 1
\)
-
ara-A
~
0 4 0 2 (I 1
__
-
0
u
~
-
Antiviral activity was evaluated by the vnu5 rating I V R method'? In which C P E development is compared in drugtreated cells T) and virus control cells (C). I n this method, the CPE value 0-4 assigned to T for each drug level was subtracted from t h a t of C, and t h e differences iC - T) weie totaled. If partial toxicity was evident at any drug level, the C - T of that level was divided by 2. The sum of all C - T values was then divided by ten times the number of test cups used per drug lek el. "Average virus rating (VR) of two or more experimeiitq
Journal of Medicinal Chemistry, 1974, Vol. 17, No. 2 243
9-,!?-o-Arabinofuranosyl-2-substituted Adenine Derivatives
Table 11. Effect of a Single Intracerebral Injection of 2-Chloro-aru-A or ara-A on Virus-Induced Encephalitis in Mice
Compound
-
Dosage,a mg/k
2-Chloro-am-A ara-A Placebo
1.6 2.4
2-Chloro-am-A ara-A Placebo
1.6 2.4
Survivor increase, Survivors/total
P b
Mean survival time,c days
Mean survival increase, Pd
13.1 18.3 10.0
>o. 10
