Synthesis and biological activity of carbocyclic derivatives of the potent antiviral agent 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG)

Bioorgadc & MedicinalChemistry Lelters, Vo1.2,No.7, pp. 685-690.1992 Printedin Great&it&n

0960-894X/92$5.00+ .OO 0 1992Peqpmon PressLtd

SYNTHESIS AND BIOLOGICAL ACTIVITY OF CABBOCYCLIC DERIVATIVES OF THE POTENT ANTIVIRAL AGENT 9-1%(PHOSPHONOMBTHOXY)ETHYLJGUANINE (PMEG)’ Joanne J. Bronson,* Louis M. Ferrara, John C. Martin,2 and Muzammil M. Mansuri ~rjsfor-~y~s Squibb Company, P~nr~aceufical Research ~~sfifufe, 5 Research Parkway, Wallingford, CT 06492-7660 (Received 28 Aprii 1992)

Abstract: Carbocyclic analogues of the potent nucleotide analogue 9-12~(phosphonomethoxy)ethyllguanine (PMEG) were prepared and evaluated for antiviral activity against herpes simplex virus type 2 and human immunodeficiency virus.

The nucleotide

analogue

9-J24phosphonomethoxy)ethyllguanine

(1, PMEG) is an

exceptionally

potent antiviral agent which has demonstrated in vitro activity against both herpesviruses and retroviruses. 314 In vivo, PMEG has been shown to have activity against herpes simplex virus types 1 and 2 at doses as low as 0.1 mg/kg/day; however, toxicity is observed at doses higher than 5 mg/kg/day, giving PMEG a limited margin of selectivity.4 AS part of our efforts to improve upon the selectivity of PMEG> we have prepared related guanine derivatives 2 - 5. in which the acyclic chain connecting the phosphonomethoxy group and guanine base is replaced with a carbocyclic ring. An important feature of this approach is that incorporation of the ring into the PMEG skeleton provides conformational constraints which are not present in the acyclic system. Furthermore, there is ample precedent in the nucleoside area that introduction of a carbocyclic ring offers a viable strategy for generating nucleoside cyclopentane of antiviral activity. 6 The 1,2-substituted

mimics with a broad spectrum

derivatives 1 and 3 were chosen as synthetic targets in order to explore the orientation 0

2:

warts-isomer

3: cis- isomer

9: saturated B unsaturated

685

J. J. BRONSON et al.

686

requirements

of the phosphonomethoxy group relative to the base without altering the chain cyclopentane derivative & the guanine length between these key groups. In the 1,3-substituted and phosphonate groups are oriented in the same relative configuration as the base and phosphate

substituents

in naturally-occuring guanosine nucleotides. The related unsaturated 7 This phosphonate derivative is an isosteric, isoelectronic 5 was also prepared. analogue which has of the monophosphate of carbovir,s a carbocyclic nucleoside

derivative analogue received

much attention

The synthesis

as an anti-human

of the 1,2-substituted

Scheme 1. The ring-opening benzylguanine

provided

reaction

cyclopentane

of cyclopentane

the Ng-alkylated

of the more polar NT-isomer.

immunodeficiency

Introduction

virus agent. derivatives

epoxide

fruns-alcohol

2. and 2 is outlined

(4) with the lithium

2 in 43%,yield,

of the phosphonomethoxy

in

salt of 6-Q

along with a 22% yield

group on the secondary

Scheme I OCH,Ph 0

0

NH,

a

C

-P

b

NH,

d,e

fsg

‘NA~/ANH

““Y--P

MMTr = monomethoxytrityl,

2

b,c,d,e

NH,

(E-OMe-C6H4)Ph2C-

(a) 6Qbenzylguanine/LiH, DMF, 60 oC (43% N9-isomer, 22% N7-isomer); (b) Et3N, @-MeOC6H4lPh2CC1, 4_dimethylaminopyridine, CH2Cl2, rt (98%); (cl 2 equiv NaH, DMF, 80 oC, then 1.5 equiv (EtOl2P(OlCH20Ts, rt (72%); (d) 20% Pd(OHh-C, I:1 ethanol/cyclohexene, then 80% CH3C02H, 60 oC (90%); (el 10 equiv (CH3)3SiBr, DMF, rt (66%); (0 PhCO2H, Ph3P, diethylazodicarboxylate, THF (98%); (gl K2CO3, MeOH (98%).

687

Derivativesof the antiviral agent PMEG

hydroxyl required initial protection of the free amine in order to prevent the formation of significant amounts of bis-alkylated chloride and triethylamine

material.

Thus, reaction of 2 with monomethoxytrityl

gave the protected guanine derivative

&in quantitative

yield.

Generation of the sodium alkoxide of B, followed by addition of diethyl @-toluenesulfonyloxy)methylphosphonate,9

then provided phosphonate 2 in 72% yield. Sequential deprotection of

the guanine base and the phosphonic acid moiety gave trans-cyclopentane Access to the cis-isomer Mitsunobu conditions.

derivative

2.10

3 was achieved by inversion of the hydroxyl group in 2 under Basic hydrolysis of the intermediate benzoate afforded the cis-alcohol

J_f,l,which was converted to 310 as described for transformation of 2 to 2. Yields for each step were similar to those obtained in the tram series. The key step in the preparation of the 1,3-cyclopentane derivatives 4 and 5. involved the palladium-catalyzed benzylguanine

ring opening 11 of cyclopentadiene

epoxide f.JJ) in the presence of 6-Q-

(Scheme 2). This reaction proceeded with high regio- and stereoselectivity

provide the cyclopentene

derivative u

to

in which the guanine base was introduced in a 1,4-

relationship cis to the hydroxyl group. In addition, only the N9-alkylated guanine isomer was obtained.

Introduction

of the phosphonomethoxy

described to provide intermediate n.

group was carried out as previously

Hydrogenolysis of u in the presence of acetic acid gave a

Scheme2

0

0

NH2

d,e

f,e

NH2

-xl-

B

(a) 6-Q-benzylguanine, Pd(PPh& PPh3, DMF. 80 OC (77%, N9-isomer only); (b) EtsN, DMAP, @-MeO-C6H4)Ph$Xl, CH2C12, rt (92%); (c) 2 equiv NaH, DMF, 80 OC, then 1.5 equiv (EtO)$‘(O)CH20Ts, rt (57%); (d) 20% Pd(OH)z-C, 1:l ethanol/cyclohexene, CHsCOzH, reflux (80%); (e) 10 equiv (CH&SiBr, DMF, rt (80-90%); (f) 80% CH$Z@H, 60 OC (90%).

I. J. BRONSON et al

688

saturated

cyclopentane

provide

phosphonic

was achieved

intermediate,

by treatment

followed by subsequent Compounds

both

significant

for antiviral

immunodeficiency

virus

(IC50) for PMEG is 0.7 ug/mL at concentrations

l’- and

2’-methyl

anti-HSV

respectively),

2 activity

indicating

and the guanine

base is tolerated

onto the PMEG skeleton

relative

configuration versus

nucleoside modest It should

potency

against

will be responsible

derivative

series.5

the 50% inhibitory derivatives

groups

prefer

been

of 3 and

group

introduction

of

decrease

in activity

against

3 showed

moderate

activity

This result

indicates

that the

is important,

series, the unsaturated

at least in terms of

saturated

as in natural

derivative derivative

5 displayed

4 was inactive.

2 - 5 are racemic, and it is likely that only one enantiomer effect.

5 and found

In fact, we have prepared

that the isomer having

HIV, while its enantiomer

the active enantiomer

corresponds

is devoid

to the configuration

both enantiomers

the (lR,4S)-configuration

of activity.‘*

of the has an

The configuration

of naturally-occuring

nucleosides

to the active isomer of carbovir.8

Table

HSV-2 (vero cells1

HIV (CEM cells)

2 9

>lOO >I00

>I00 20

4.

>lOO

>loo

5

>lOO

66

0.7

0.2

1 @‘MEG)

to retain

11-25 ug/mL,

to be cis to one another

the corresponding

of

surprising

shown

Apparently,

isomer

2 was inactive.

IC.50 of 26 uM against

Comuound

groups,

the phosphonomethoxy

in a cumulative

and phosphonate

HIV, although

for the antiviral

(IC50 values

cyclopentane

In the 1,3-cyclopentyl

be noted that compounds

cyclopentene

results

HIV, and that the key groups

derivatives.

of PMEG have

to PMEG

while the frans-derivative of the guanine

Whereas

This result was somewhat

in the acyclic nucleotide

HIV, the cis-1,2-substituted

activity

1).

on the chain connecting

HSV 2. Against

protecting

$0

activity against herpes simplex virus type 2

(HIV) (Table

derivatives

both substituents UC50 = 20 ug/mL),

of the guanine

to

derivative

against HSV-2, all of the carbocyclic

relative

that branching

cyclopentene

ester.

up to 100 ug/mL.

substituted

with bromotrimethylsilane

to the unsaturated

of the phosphonic

2 - 5 were evaluated

PMEG were inactive since

was then treated

of u

with acetic acid to effect removal

deprotection

(HSV-2) and human concentration

which

acid g.10 Conversion

of and

689

Derivatives of the antiviral agent PMEG

An explanation that

most

for the diminished

nucleoside

corresponding

and

nucleotide

triphosphate

the monophosphate

analogue

analogues

to inhibit skeleton

analogues

the viral enzyme.

here bypass

Taken together,

ring results

Acknowledgement.

We thank the members

metabolized

to the

the target viral polymerase.

Although

analogue.13

or to an inability

our results indicate

of the carbocyclic

compound

References

be sequentially

by the fact

the need for the first phosphorylation

phosphorylation

relative to the parent

for the biological

is complicated

by cellular kinases to the triphosphate

may be due to inefficient

by introduction

must

in order to inhibit

described

step, they must still be converted lack of activity

activity of these compounds

that modification

in a significant

such that no increase in selectivity

of the Bristol-Myers

Thus, the

of the triphosphate of the PMEG

reduction

in activity

is realized.

Squibb Virology

Department

testing results.

and Notes

1. Presented

in part at the 200th American

Chemical

Nucleosides

and Nucleotides:

and Biochemistry,

Chemistry

Society National

Meeting,

Washington,

Symposium

DC, August,

on 1990;

Abstract No. CARB-20. 2. Present address:

Gilead Sciences, 344 Lakeside Drive, Foster City, CA 94404. I.; Holy, A. Antiviral

3. De Clercq, E.; Sakuma, T.; Baba, M.; Pauwels, R.; Balzarini, J.; Rosenberg, Res. 1987,8,261. 4.

Bronson,

J.J.; Kim, C.U.; Ghazzouli,

“Nucleotide

Analogues

as Antiviral

Washington,

D.C., 1989;Symposium

I.; Hitchcock,

Agents”;

Martin,

M.J.M.; Kern,

E.R.; Martin,

J.C., Ed.; American

Chemical

J.C. in Society:

Series 401, p. 88..

5. (a) Kim, C.U.; Luh, B.Y.; Misco, P.F.; Bronson,

J.J.; Hitchcock,

M.J.M.; Ghazzouli,

I.; Martin,

J.C. 1. Med. Chem. 1990,33,1207; (b) Bronson, J.J.; Yu, K.L.; Kim, C.U.; Yang, H.; Brankovan, Hitchcock, 6.

M.J.M.; Martin,

(al Marquez,

Antiviral

V.;

J.C. Antiviral Res. Suppl. 2,1990, 54.

V.E.; Lim, M-I. Medicinal

Research Reviews 1986,6, 1; (b) Montgomery,

J.A.

Res. 1989,12, 113.

7. A synthesis

of 5 similar

S.A.; Peel, M.R.; Roberts,

to ours has recently S.M.; Storer,

been reported:

Coe, D.M.; Hilpert,

R. I. Chem. Sot., Chem. Commun.

H.; Noble,

1991, 312. The

J. I. BRoNsoNet al.

690

corresponding biological

diphosphate

ester of 5 was also described

8. Vince, R.; Hua, M.; Brownell, Weislow,

Kluge,

Commun.

A.F. Org. 1982,47,

however,

no

Biophys.

W.M.; Lavelle, G.C.; Qualls, J.;

P.; Schultz, R.H.; Narayanan, Res. Commun.

1988,156,

Synth. 1986, 64, 80.; (b) Holy,

V.L.; Mayo, J.G.; Shoemaker,

1046.

A.; Rosenberg,

I. Co1Zect. Czech.

Chem.

3447.

10. All new compounds consistent

J.; Daluge, S.; Lee, F.; Shannon,

O.S.; Kiser, R.; Canonico,

R.H.; Boyd, M.R. Biochem. 9.

in this communication,

activity was reported.

gave satisfactory

with the assigned

data (IH and I3C NMR, UV, MS, combustion

11. Trost, B.M.; Kuo, G.H.; Benneche,

T. 1. Am. Chem. Sot. 1988,720,

12. Bronson, J.J.; Ferrara, L.M.; Martin, J.C., manuscript 13. For recent studies

analysis)

structure.

on the enzymes

responsible

621.

in preparation.

for phosphorylation

of a related nucleotide

analogue, 9-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine (HPMPA), see: a) Balzarini, J.; Hao, Z.; Herdewijn, P.; Johns, D.G.; De Clercq, E. Proc. AM. Ad. Sci. U.S.A. 1991,88, 1499; b) Balzarini, J.; De Clercq, E. J. Biol. Chem.. 1991,266, 8686