Synthesis of acyclic nucleoside and nucleotide analogs derived from 6-amino-7H-purine-8(9H)-thione and 8-(methylsulfanyl)adenine

Article abstract of DOI:10.1135/cccc20001698

Reaction of 8-bromoadenine derivatives 1 with thiourea in ethanol or butanol was used for the synthesis of the corresponding N⁹-substituted 6-amino-7H-purine-8(9H)-thiones 2. 8-(Methylsulfanyl)adenine derivatives 3 were prepared by reaction of thiones 2 with iodomethane in 1 M sodium methoxide or in aqueous 1.5 M potassium hydroxide. Alkylation of 6-amino-7H-purine-8(9H)-thione (2a) proceeds preferentially on the sulfur atom. Under similar conditions, alkylation of 8-(methylsulfanyl)adenine (3a) with diverse alkylation agents afforded N⁹-substituted adenine derivatives 3 and 6, and N³-substituted adenine derivatives 5 and 7. 8,3′-S-Anhydro derivatives 9 were prepared in good yields by cyclization of 6-amino-7H-purine-8(9H)-thiones 2d and 2f under the Mitsunobu reaction conditions.

Full text of DOI:10.1135/cccc20001698

1698
Janeba, Holý, Masojídková:
SYNTHESIS OF ACYCLIC NUCLEOSIDE AND NUCLEOTIDE ANALOGS
DERIVED FROM 6-AMINO-7H-PURINE-8(9H)-THIONE AND
8-(METHYLSULFANYL)ADENINE
1,
2
Zlatko JANEBA *, Antonín HOLÝ and Milena MASOJÍDKOVÁ
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
1
2
166 10Prague 6, Czech Republic; e-mail: janeba@uochb.cas.cz, holy@uochb.cas.cz
Received October 18, 2000
Accepted Novem ber 10, 2000
Reaction of 8-brom oaden in e derivatives 1 with th iourea in eth an ol or butan ol was used for
th e syn th esis of th e correspon din g N9-substituted 6-am in o-7H-purin e-8(9H)-th ion es 2.
8-(Meth ylsulfan yl)aden in e derivatives 3 were prepared by reaction of th ion es 2 with
iodom eth an e in
1 M sodium m eth oxide or in aqueous 1.5 M potassium h ydroxide.
Alkylation of 6-am in o-7H-purin e-8(9H)-th ion e (2a) proceeds preferen tially on th e sulfur
atom . Un der sim ilar con dition s, alkylation of 8-(m eth ylsulfan yl)aden in e (3a) with diverse
alkylation agen ts afforded N9-substituted aden in e derivatives 3 an d 6, an d N3-substituted ade-
n in e derivatives 5 an d 7. 8,3′-S-An h ydro derivatives 9 were prepared in good yields by
cyclization of 6-am in o-7H-purin e-8(9H)-th ion es 2d an d 2f un der th e Mitsun obu reaction
con dition s.
Key w ord s: Purin es; Acyclic n ucleoside an d n ucleotide an alogues; Nucleosides; Nucleotides;
Alkylation ; Mitsun obu reaction ; An h ydro derivatives; Cyclization .
Th e im portan ce of 8-substituted purin e derivatives in n ucleoside an d n ucle-
otide ch em istry an d th eir poten cy as biologically active com poun ds is obvi-
ous. Th is work is a con tin uation of th e structure–biological activity
relation sh ip (SAR) studies in th e series of N-(2,3-dih ydroxypropyl) (DHP),
N-[2-(ph osph on om eth oxy)eth yl] (PME) an d (S)-N-[3-h ydroxy-2-(ph osph on o-
m eth oxy)propyl] (HPMP) derivatives of h eterocyclic bases1. Th e syn th esis
of th e DHP, PME an d HPMP derivatives with various substituen ts in posi-
tion 8 of aden in e was un dertaken in order to obtain in form ation about th e
effect of substitution in th is position on th e biological activity in th ese se-
ries. A recen t study2 was dedicated to 8-h ydroxyaden in e (6-am in o-
7H-purin e-8(9H)-on e) derivatives. An alogous com poun ds derived from
6-am in o-7H-purin e-8(9H)-th ion e an d 8-(m eth ylsulfan yl)aden in e are n ow of
our special in terest.
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Acyclic Nucleoside and Nucleotide Analogs
1699
Som e 8-sulfan yl or S-substituted 8-sulfan ylpurin e derivatives possess im -
portan t biological activities. For in stan ce, 8-(ben zylsulfan yl)purin es are
kn own as irreversible in h ibitors of xan th in e oxidase3, 8-th iocyan opurin e
derivatives as an tican cer agen ts4, an d 8-[(ph en oxyalkyl)sulfan yl]aden osin es
exh ibit h ypolipidem ic activity5. Also th e im portan ce of 6-sulfan ylpurin e as
a bacterial growth an tagon ist6 an d as an an titum or agen t7 is worth m en -
tion in g.
RESULTS AND DISCUSSION
Th e syn th esis of 6-am in o-7H-purin e-8(9H)-th ion e (8-m ercaptoaden in e) de-
rivatives was usually perform ed eith er by th e purin e rin g form ation from
suitably substituted pyrim idin es with th iourea or carbon disulfide8, or by
th e reaction of th e appropriate 8-brom opurin e derivatives with th iourea9,
h ydrogen sulfide10, sodium h ydrogen sulfide11, or n ewly with 2-(trim eth yl-
silyl)eth an e-1-th iol followed by th e deprotection of th e th ion e fun ction 12
.
Sim ilarly as in th e 8-oxo (8-h ydroxy) purin e series2, two prin cipal ap-
proach es were used in th is study for preparation of 8-substituted purin e
acyclic n ucleoside an d n ucleotide an alogues con tain in g 6-am in o-7H-pu-
rin e-8(9H)-th ion e or 8-(m eth ylsulfan yl)aden in e as a base: (i) m odification
of th e correspon din g acyclic n ucleoside or n ucleotide derivative in position
8 of th e purin e m oiety or, (ii) preparation of th e 8-substituted purin e base
an d its subsequen t alkylation .
Syn th esis of com poun ds con tain in g sulfan yl group in position 8 of th e
purin e m oiety (Sch em e 1) was perform ed by th e reaction of appropriate
NH2
NH2
NH2
H
N
N
N
(i)
(ii)
N
N
N
Br
S
SCH3
N
R
N
R
N
R
N
N
N
1
2
3
1-3 a, R = H
b, R = CH2CH2OCH2P(O)(OiPr)2
1, 2 d, R = (S)-CH2CH(CH2OH)OCH2P(O)(OiPr)2
(iii)
3g, R = (S)-CH2CH(CH2OH)OCH2P(O)(OMe)2
2, 3 c, R = CH2CH2OCH2P(O)(OH)2
(iii)
e, R = (S)-CH2CH(CH2OH)OCH2P(O)(OH)2
3f, R = (S)-CH2CH(CH2OH)OCH2P(O)(OH)(OMe)
(ia) thiourea, BuOH, reflux, 24 h; (i) thiourea, EtOH, reflux, 15 h;
(iia) CH3I, 2 M aq. KOH, (ii) CH3I, 1 M MeONa; (iii) TMSBr, CH3CN
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

1700
Janeba, Holý, Masojídková:
8-brom o com poun ds 1 (ref.2) with th iourea in eth an ol or butan ol9,13. Th us,
6-am in o-7H-purin e-8(9H)-th ion e (2a), PME derivative 2b an d, HPMP deriv-
ative 2d were syn th esized from com poun ds 1.
Th e tran sform ation of com poun ds 2 to th e 8-(m eth ylsulfan yl)purin e de-
rivatives 3 was perform ed by th e reaction of th e correspon din g 8-sulfan yl
derivative 2 with on e equivalen t of iodom eth an e in 1 M sodium m eth oxide
at room tem perature. In th e case of HPMP derivative a m ixture of two prod-
ucts was detected by TLC an d electroph oresis: dim eth yl ester 3g (accordin g
to MS spectrum ) an d m on oester. It was proved by 1H NMR an d 13C NMR
spectra to be a m on om eth yl ester 3f, wh ich eviden tly arises by tran s-
esterification of th e diisopropyl ester to dim eth yl ester 3g followed by par-
tial cleavage of th e protected ph osph on ate m oiety. Th e crude reaction
m ixture was directly treated with TMSBr to afford ph osph on ate 3e.
8-(Meth ylsulfan yl)purin e derivatives can also be obtain ed directly by th e re-
action of th e correspon din g 8-brom opurin e derivatives with sodium
m eth an eth iolate14
.
Alkylation of 6-am in o-7H-purin e-8(9H)-on e (8-h ydroxyaden in e) with di-
verse alkylation agen ts afforded N9-m on osubstituted an d N7,N9-di-
substituted derivatives2. Compared to oxygen atom, the sulfur atom in
6-am in o-7H-purin e-8(9H)-th ion e (2a) is an easy target for alkylation 5,15. Al-
kylation s of com poun d 2a with on e equivalen t of an alkylation agen t gave
th e correspon din g 8-(alkylsulfan yl) derivatives: 8-(m eth ylsulfan yl)aden in e
(3a, Sch em e 1) an d PME derivative 4a (Sch em e 2). Sim ilarly, th e literature5
describes alkylation of 6-am in o-7H-purin e-8(9H)-th ion e with ({[4-(eth oxy-
carbon yl)ph en yl]oxy}m eth yl)oxiran e catalyzed with 2,6-lutidin e un der th e
form ation of th e correspon din g 8-(alkylsulfan yl)aden in e derivative in 50%
yield.
NH2
NH2
H
N
N
(i)
N
N
S
SCH2CH2OCH2P(O)(OR)2
N
H
N
H
N
N
2a
4
4 a, R = iPr
b, R = H
(ii)
(i) ClCH2CH2OCH2P(O)(OiPr)2, NaH, DMF, reflux, 11 h; (ii) TMSBr, CH3CN
SCHEME 2
To avoid th e alkylation at th e sulfur atom , we h ave perform ed an alogous
alkylation s of 8-(m eth ylsulfan yl)aden in e (3a). Th e base 3a was prepared by
m eth ylation of com poun d 2a with iodom eth an e in aqueous 1.5 M potas-
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Acyclic Nucleoside and Nucleotide Analogs
1701
sium h ydroxide in 86% yield. Its alkylation gave rise to N9-alkyl derivatives
3 an d 6, an d N3-alkyl derivatives 5 an d 7 (Sch em e 3, ratio ca 1 : 1). Th e
N9-substituted derivative 3b is iden tical with an auth en tic com poun d pre-
pared by th e base m odification of com poun d 2b (Sch em e 1). In th e
alkylation with (S)-[(trityloxy)m eth yl]oxiran e ((S)-tritylglycidol), also th e
O-an h ydro derivative 8 was isolated as a m in or product arisin g from th e
in tram olecular cyclization of th e N9-regioisom er 6a un der th e Cs2CO3 catal-
ysis. On acid treatm en t, th e N3-substituted derivative 7a an d N9-substituted
derivative 6a were detritylated to give com poun ds 7b an d 6b, respectively
(Sch em e 3).
NH2
NH2
NH2
N
N
N
N
(i)
N
N
N
SCH3
SCH3
+
SCH3
N
H
N
R
N
N
N
R
3a
3
5
3, 5 b, R = CH2CH2OCH2P(O)(OiPr)2
c, R = CH2CH2OCH2P(O)(OH)2
h, R = CH3
(vi)
(ii)
NH2
N
NH2
NH2
N
N
N
N
N
N
N
N
SCH3
SCH3
+
+
O
N
N
N
OTr
OR
RO
7
6
8
OH
OH
6, 7 a, R = Tr
b, R = H
(iii)
(iv)-(v)
(i) ClCH2CH2OCH2P(O)(OiPr)2, NaH, DMF; (ih) MeOTs, DMF, NaH, (ii) (S)-tritylglycidol, DMF,
Cs2CO3; (iii) 80% aq. AcOH, reflux, 1 h; (iv) Me2NCH(OMe)2, DMF; (v) TsOCH2P(O)(OiPr)2,
THF, NaH; (vi) TMSBr, CH3CN
SCHEME 3
Th e attem pts to prepare HPMP derivatives from N6-[(dim eth yl-
am in o)m eth yliden e] derivatives of com poun ds 6a an d 7a (wh ich were
prepared by th eir reaction with dim eth ylform am ide dim eth yl acetal) were
un successful. Un der th e stan dard syn th etic procedure leadin g to th e
(S)-HPMP derivatives (treatm en t with NaH in THF followed by reaction
with diisopropyl [(tosyloxy)m eth yl]ph osph on ate16), th e protected N3-deriv-
ative did n ot react; th e un ch an ged startin g com poun d 7a was regen erated
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

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Janeba, Holý, Masojídková:
(75%) from th e reaction m ixture after (dim eth ylam in o)m eth yliden e
deprotection . Un der th e sam e con dition s, th e protected N9-derivative un -
derwen t cyclization to th e an h ydro derivative 8, iden tical with th e com -
poun d prepared by an oth er syn th etic approach in th e previous work2. Th is
in tram olecular n ucleoph ilic substitution in th e presen ce of Cs2CO3 or NaH
con firm s th at th e 8-SCH3 group can serve as a leavin g group.
Som e acyclic an alogs of 8-cyclon ucleosides an d 8-cyclon ucleotides with
th e O-an h ydro lin kage were prepared17. Also a cyclic HPMPA an alog was
obtain ed2. We h ave attem pted preparation of an an alogous com poun d con -
tain in g th e S-an h ydro lin kage. Th ere are several approach es available for
th e syn th esis of purin e S-cyclon ucleosides18. Gen erally, th e cyclization re-
action s usin g m esyl an d tosyl leavin g groups on th e sugar m oiety are ac-
com pan ied by cyclization to th e N3,5′-cyclon ucleosides19. Th erefore, th e
use of th e in tram olecular Mitsun obu reaction 20 seem ed to be th e reaction
of ch oice. It was successfully used for th e S-cyclon ucleoside syn th esis21.
Com poun d 2f was prepared by th e reaction of brom o derivative 1f (ref.22)
with th iourea in absolute eth an ol (Sch em e 4). Un der th e Mitsun obu reac-
tion con dition s, it cyclized to th e an h ydro derivative 9f in 90% yield. De-
spite in itial failure21b, th e acyclic an alog of S-cyclon ucleotide 9d was
syn th esized from com poun d 2d by an alogous cyclization in 92% yield.
NH2
NH2
NH2
H
N
N
N
N
N
(i)
(ii)
N
N
N
Br
S
S
N
N
N
N
OH
OH
R
1
9
2
R
R
1, 2, 9 f, R = H
d, R = OCH2P(O)(OiPr)2
e, R = OCH2P(O)(OH)2
(iii)
(i) thiourea, EtOH, reflux, 15 h; (ii) PPh3, DEAD, DMF; (iii) TMSBr, CH3CN
SCHEME 4
Th e O-an h ydro lin kage of purin e cyclon ucleoside is easily cleaved un der
m ild con dition s23. In con trast, purin e S-cyclon ucleosides in gen eral are re-
sistan t to m ild acid or alkalin e h ydrolysis, wh ile h ydrolysis with a stron g
acid or alkali leads to cleavage of th e glycosidic an d/or an h ydro lin kage or
even to destruction of th e purin e rin g24. Com poun d 9d resisted th e action
of 1 M HCl, as well of 1 M NaOH at room tem perature for 24 h . Th e altered
ch aracter of th e bon d between N-9 an d C-1′ atom s can be th e cause of th e
en h an ced stability to th e h ydrolysis.
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Acyclic Nucleoside and Nucleotide Analogs
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Stan dard treatm en t with brom otrim eth ylsilan e (TMSBr) in aceton itrile
followed by h ydrolysis was used for th e ultim ate cleavage of ph osph on ate
diesters 2b, 2d , 3b, m ixture of 3g an d 3f, 4a, 5b, an d 9d . Deion isation on
Dowex 50 (H+) followed by Dowex 1 (AcO–) ion -exch an ge ch rom atograph y
was used for isolation of th e free ph osph on ates 2c, 2e, 3c, 3e, 4b, 5c, an d
9e. Th e purified com poun ds were crystallized from water.
1
All n ew com poun ds were fully ch aracterized by H NMR (an d 13C NMR),
MS, an d HRMS or m icroan alysis. Th e structures of th e com poun ds prepared
by alkylation of startin g com poun d 3a were determ in ed on th e basis of
proton -coupled 13C NMR spectra: N9-alkyl derivatives of 8-(m eth yl-
sulfan yl)aden in e 3b , 3h , an d 6b are ch aracterized by doublet of C-2
(1J(C-2,H-2) = 199.2), by doublet of C-6 (3J(C-6,H-2) = 11.7), an d by triplet
of C-5 (3J(C-5,NH2) = 3.9) disappearin g after D2O addition . Th e sign al of
C-4 was splitted by H-2 an d H-1′ proton s (3J(C-4,H-2) = 12.7 an d
3J(C-4,H-1′) = 2.9) an d th at of C-8 by CH3-group proton s an d H-1′ (J = 3.9).
Th e alkylation in th e N-3 position of com poun ds 5b, 5c, 5h , an d 7b was
con firm ed by th e observation of ch aracteristic alkylation effects an d an al-
teration of sign al m ultiplicity of C-2 (upfield sh ift (–8 ppm ), 1J(C-2,H-2) =
3
3
209.0, J(C-2,H-1′) = 3.9), C-8 (down field sh ift (12 ppm ), J(C-8,CH3) = 3.9,
3
3
absen ce of J(C-8,H-1′)), C-6 (upfield sh ift (–2 ppm ), J(C-6,H-2) = 11.7), an d
3
C-5 (down field sh ift (2 ppm ), J(C-5,NH2) = 3.9). Th e ch em ical sh ift of C-4
in N3-alkyl derivatives was virtually th e sam e, on ly th e value of th e cou-
plin g con stan ts was ch an ged (3J(C-4,H-2) = 6.8 an d J(C-4,H-1′) = 3.9).
3
Com pared with correspon din g 8-(m eth ylsulfan yl)aden in e derivatives 3
an d 6, a con siderable down field sh ift of C-8 (δ 166 ppm ) an d splittin g of
C-4, C-5, an d C-8 by NH proton (3J(C-4,NH) = 5.9, 2J(C-5,NH) = 4.9,
2J(C-8,NH) = 5.9) were observed for N9-alkyl derivatives of 6-am in o-7H-
purin e-8(9H)-th ion e 2b an d 2d .
Th e structure of m odified purin e bases is un am biguously reflected in
th eir UV spectra. Th ey are an addition al eviden ce of th e substituen t type in
position
8 of th e purin e m oiety an d of th e correspon din g alkyl
regioisom ers. Th us, it is possible to distin guish between (average values of
λm ax an d εm ax are given , respectively): N9-alkyl derivatives of 8-sulfan yl-
adenine 2 (pH 2: 308 nm , 25 000 and 241 nm , 15 000; pH 12: 300 nm , 24 000
an d 228 n m , 22 000), th eir 8-(m eth ylsulfan yl)aden in e an alogues 3 (pH 2:
284 n m , 20 000; pH 12: 222 n m , 20 000 an d 280 n m , 20 000), an d N3-alkyl
derivatives of 8-(m eth ylsulfan yl)aden in e 5 (pH 2: 301 n m , 12 000 an d 235
n m , 10 000; pH 12: 305 n m , 18 000 an d 235 n m , 14 000).
Th e CD spectra of en an tiopure ch iral acyclic n ucleoside an d n ucleotide
an alogues 2e, 3e, 6b, an d 7b do n ot exh ibit con siderable Cotton effect,
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

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Janeba, Holý, Masojídková:
wh ich reflects th e flexible ch aracter of th e side aliph atic ch ain bearin g a
ch iral carbon atom . On th e con trary, th e CD spectrum of S-an h ydro deriva-
tive 9e, wh ich sh ows a sign ifican t n egative Cotton ban d aroun d 223 n m , is
an oth er eviden ce of th e rigid ch aracter of th is tricyclic system . Th is spec-
trum agrees qualitatively with th at of 8,5′-S-cycloaden osin e25
.
In con clusion , two in depen den t m eth ods were used for preparation of
acyclic n ucleoside an d n ucleotide derivatives derived from 6-am in o-7H-
purin e-8(9H)-th ion e (2a) an d 8-(m eth ylsulfan yl)aden in e (3a): (i) m odifica-
tion of 8-brom oaden in es in position 8, (ii) alkylation of th e both
8-substituted aden in e bases with diverse alkylation agen ts. Th e form er
m eth od is direct an d con ven ien t, affords good yields of products, an d is n ot
accom pan ied by an y side products except for th e tran sesterification an d
partial form ation of th e m on oester in th e case of HPMP derivatives. Th e lat-
ter m eth od, th e base alkylation , is suitable for 8-(m eth ylsulfan yl)aden in e
(3a) on ly. Th e yields are lower an d two regioisom ers are form ed as m ain
products in an approxim ately equim olar ratio: N3-alkyl derivatives 5 an d 7,
an d N9-alkyl derivatives 3 an d 6. Th e alkylation of 6-am in o-7H-pu-
rin e-8(9H)-th ion e (2a) is n ot con ven ien t for th e syn th esis of acyclic
n ucleoside an d n ucleotide an alogs, because th e reaction occurs preferen -
tially at th e sulfur atom in position 8. N9-substituted an alog 3b was pre-
pared by two in depen den t routes. Successful preparation of 8,3′-S-an h ydro
derivatives 9 was also perform ed. Biological activities of th e fin al com -
poun ds will be exam in ed.
EXPERIMENTAL
Un less oth erwise stated, solven ts were evaporated at 40 °C/2 kPa an d com poun ds were dried
at 2 kPa over P2O5. Meltin g poin ts were determ in ed on a Kofler block an d are un corrected.
An alytical TLC were perform ed on Silufol UV 254 plates (Kavalier Votice, Czech Republic)
in th e system s ch loroform –m eth an ol (9 : 1) (S1), ch loroform –m eth an ol (85 : 15) (S2),
ch loroform –m eth an ol (8 : 2) (S3), isopropyl alcoh ol–con cen trated aqueous am m on ia–water
(7 : 1 : 2) (S4), an d water–eth an ol–aceton –eth yl acetate (1 : 1 : 1 : 4) (S5). Preparative TLC
were carried out on 40 × 17 × 0.4 cm loose-layer plates of silica gel con tain in g UV in dicator
(m ade in th e Service Laboratory of th e In stitute). Paper electroph oresis was perform ed on a
Wh atm an No.
3
MM paper at 40 V/cm for
1
h
in 0.05
M
trieth ylam m on ium
h ydrogen carbon ate (TEAB) at pH 7.5; th e electroph oretical m obilities are referen ced to
uridin e 3′-ph osph ate. NMR spectra were m easured on a Varian Un ity 500 spectrom eter
(500 MHz for 1H an d 125.7 MHz for 13C NMR) in h exadeuteriodim eth yl sulfoxide
(DMSO-d6) referen ced to th e solven t sign als (2.5 for 1H an d 39.7 for 13C NMR), or in deute-
rium oxide con tain in g sodium deuteroxide with sodium 3-(trim eth ylsilyl)propan e-
1-sulfon ate as an in tern al stan dard for 1H NMR an d dioxan e as an extern al stan dard for
13C NMR (δ(dioxan e) 66.86 ppm ). Ch em ical sh ifts are given in ppm (δ-scale), couplin g
con stan ts (J) in Hz. Mass spectra were m easured on a ZAB-EQ (VG An alytical) spectrom eter
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Acyclic Nucleoside and Nucleotide Analogs
1705
usin g FAB (ion ization by Xe, acceleratin g voltage 8 kV, glycerol m atrix). UV absorption
spectra (λ in n m ) were m easured on a UV m in i-1240 Sh im adzu spectrom etr, CD spectra on a
Jobin Yvon Mark V in strum en t.
Startin g Materials an d Reagen ts
Brom otrim eth ylsilan e an d cesium carbon ate were purch ased from Fluka (Switzerlan d); DBU
was purch ased from Aldrich (Germ an y). Dim eth ylform am ide was distilled from P2O5 an d
stored over m olecular sieves (4 Å). Aceton itrile was refluxed with CaH2 an d distilled over
m olecular sieves (4.Å). Tetrah ydrofuran was distilled before use from sodium m etal.
6-Am in o-7H-purin e-8(9H)-th ion e (2a)
A m ixture of 8-brom oaden in e (1a ; 6 g, 28.0 m m ol), th iourea (17 g, 0.22 m ol), an d
butan -1-ol (140 m l) was refluxed for 28 h , evaporated in vacuo an d th e residue was sus-
pen ded in water (120 m l). Th e precipitate was filtered off an d wash ed successively with wa-
ter, aceton e, eth er, an d dried over ph osph orus pen toxide. Yellowish powder, m .p. >360 °C,
yield 3.9 g (96%), RF = 0.28 (S1). FAB MS, m/z (rel.%): 168 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 6.75 (brs, 2 H, NH2); 8.06 (s, 1 H, H-2); 12.04 (brs, 1 H, NH); 13.04 (brs, 1 H, NH).
13C NMR (125 MHz, DMSO-d6): 108.22 (C-5); 147.55 (C-6); 150.06 (C-4); 152.84 (C-2);
166.73 (C-8). IR (KBr): 3 439, 3 323, 3 169, 3 092 (NH2, NH); 2 587 (SH); 1 659 (NH2); 1 613,
1 486, 1 466, 1 419, 1 329 (rin g). Exact m ass (FAB HRMS) foun d: 168.0354; calculated for
C5H6N5S [M + H]: 168.0344.
Reaction of 8-Brom opurin e Derivatives 1 with Th iourea. Gen eral Procedure
A m ixture of th e correspon din g 8-brom o derivative 1 (5 m m ol) an d th iourea (40 m m ol) in
eth an ol (70 m l) was refluxed for 15 h an d evaporated in vacuo. Th e residue was suspen ded in
h ot ch loroform (100 m l), th iourea was filtered off an d wash ed with h ot ch loroform (250 m l).
Th e ch loroform solution was taken down in vacuo. Ch rom atograph y of th e residue on a
colum n of silica gel (60 g) in ch loroform –m eth an ol gradien t, followed by crystallization ,
afforded com poun ds 2.
6-Amino-9-{2-[(diisopropoxyphosphoryl)methoxy]ethyl}-7H-purine-8(9H)-thione (2b). Wh ite crystals,
m.p. 191 °C (ethanol), yield 81%, RF = 0.20 (S1). FAB MS, m/z (rel.%): 390 (100) [M + H]. 1H NMR
(500 MHz, DMSO-d6): 1.11 (d, 6 H, J(CH3,CH) = 6.1, CH3); 1.16 (d, 6 H, J(CH3,CH) = 6.1,
CH3); 3.79 (d, 2 H, J(P,CH) = 8.5, PCH2); 3.93 (t, 2 H, J(2′,1′) = 5.6, H-2′); 4.31 (t, 2 H, J(1′,2′) =
5.6, H-1′); 4.47 (m , 2 H, POCH); 6.85 (brs, 2 H, NH2); 8.14 (s, 1 H, H-2); 12.35 (brs, 1 H,
NH). For C14H24N5O4PS (389.4) calculated: 43.18% C, 6.21% H, 17.98% N, 7.95% P, 8.23% S;
foun d: 43.23% C, 6.26% H, 18.24% N, 8.13% P, 8.51% S.
6-Amino-9-{2-[(diisopropoxyphosphoryl)methoxy]-3-hydroxypropyl}-7H-purine-8(9H)-thione (2d ).
Wh ite crystals, m .p. 168 °C (eth an ol–eth er), yield 64%, RF = 0.38 (S2), RF = 0.70 (S5). FAB MS,
m/z (rel.%): 420 (100) [M + H]. 1H NMR (500 MHz, DMSO-d6): 1.09 (d, 3 H, J(CH3,CH) = 6.1,
CH3); 1.12 (d, 6 H, J(CH3,CH) = 6.1, CH3); 1.16 (d, 3 H, J(CH3,CH) = 6.1, CH3); 3.50 (dt, 1 H,
J(3′b,OH) = J(3′b,2′) = 4.8, J(gem ) = 12.0, H-3′b); 3.60 (dt, 1 H, J(3′a,OH) = J(3′a,2′) = 5.0,
J(gem ) = 12.0, H-3′a); 3.71 (dd, 1 H, J(P,CHb) = 9.8, J(gem ) = 13.4, PCHb); 3.89 (dd, 1 H,
J(P,CHa) = 8.4, J(gem ) = 13.4, PCHa); 4.06 (dd, 1 H, J(1′b,2′) = 4.6, J(gem ) = 13.7, H-1′b);
4.13 (m , 1 H, H-2′); 4.35 (dd, 1 H, J(1′a,2′) = 7.6, J(gem ) = 13.7, H-1′a); 4.45 (m , 2 H, POCH);
4.81 (t, 1 H, J(OH,3′) = 5.3, OH); 6.83 (brs, 2 H, NH2); 8.13 (s, 1 H, H-2); 12.35 (brs, 1 H,
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NH). 13C NMR (125 MHz, DMSO-d6): 23.68 (d, J(P,C) = 4.9, CH3); 23.78 (d, J(P,C) = 4.9,
CH3); 23.85 (d, J(P,C) = 3.9, CH3); 23.91 (d, J(P,C) = 3.9, CH3); 43.33 (C-1′); 61.13 (C-3′);
63.77 (d, J(C,P) = 164.4, PC); 70.24 (d, J(C,P) = 6.4, POC); 70.40 (d, J(C,P) = 6.4, POC); 78.80
(d, J(C,P) = 11.9, C-2′); 107.06 (C-5); 147.78 (C-6); 149.73 (C-4); 152.58 (C-2); 166.89 (C-8).
For C15H26N5O5PS (419.4) calculated: 42.95% C, 6.25% H, 16.70% N, 7.38% P, 7.64% S;
foun d: 42.92% C, 6.27% H, 16.68% N, 7.29% P, 7.98% S.
6-Amino-9-(3-hydroxypropyl)-7H-purine-8(9H)-thione (2f). Yellowish crystals, m .p. 266 °C
(eth an ol), yield 51%, RF = 0.35 (S2). FAB MS, m/z (rel.%): 226 (100) [M + H]. 1H NMR (500
MHz, DMSO-d6): 1.87 (br pen t, 2 H, H-2′); 3.44 (dt, 2 H, J(3′,OH) = 5.2, J(3′,2′) = 6.3, H-3′);
4.16 (t, 2 H, J(1′,2′) = 7.3, H-1′); 4.55 (t, 1 H, J(OH,3′) = 5.2, OH); 6.84 (brs, 2 H, NH2); 8.15
(s, 1 H, H-2); 12.30 (s, 1 H, NH). UV, λm ax (εm ax): (MeOH) 307 (23 900), 237 (14 400). For
C8H11N5OS (225.3) calculated: 42.65% C, 4.92% H, 31.09% N, 14.23% S; foun d: 42.44% C,
4.88% H, 30.89% N, 13.84% S.
8-(Meth ylsulfan yl)aden in e (3a)
A m ixture of 6-am in o-7H-purin e-8(9H)-th ion e (2a; 1.5 g, 9 m m ol), 1.5 M KOH (50 m l), an d
iodom eth an e (1.4 g, 10 m m ol) was stirred at 15 °C for 0.5 h in a closed flask. Th e m ixture
was n eutralized with acetic acid. Th e precipitated solid was filtered off an d wash ed succes-
sively with water, aceton e an d eth er to give 1.4 g (86%) of product 3a. Yellowish powder,
m .p. 274–275 °C, RF = 0.31 (S1). FAB MS, m/z (rel.%): 182 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 2.67 (s, 3 H, SCH3); 6.98 (brs, 2 H, NH2); 8.03 (s, 1 H, H-2); 12.99 (brs, 1 H, NH).
13C NMR (125 MHz, DMSO-d6): 13.94 (SCH3); 119.53 (C-5); 148.09 (C-8); 151.63 (C-2);
152.44 (C-4); 153.99 (C-6). Exact m ass (FAB HRMS) foun d: 182.0497; calculated for C6H8N5S
[M + H]: 182.0500.
8-(Meth ylsulfan yl)purin e Derivatives 3. Gen eral Procedure
A m ixture of th e correspon din g derivative 2 (5 m m ol), 1 M sodium m eth oxide (25 m l), an d
iodom eth an e (5.5 m m ol, 0.78 g) was stirred at room tem perature for 0.5 h . Th e m ixture was
n eutralized with acetic acid, extracted with ch loroform (3 × 25 m l), an d th e organ ic layer
was dried with an h ydrous MgSO4 an d evaporated in vacuo. Th e residue was ch rom ato-
graph ed on a colum n (250 m l) of silica gel (ch loroform –m eth an ol gradien t) an d/or crystal-
lized. In th e case of HPMPA derivative, a m ixture of dim eth yl ph osph on ate 3g (RF = 0.48
(S2), EUp = 0.05) an d m on om eth yl ph osph on ate 3f (RF = 0.00 (S2), EUp = 0.52) was detected
by TLC, electroph oresis, an d m ass spectrum . Th is m ixture was directly treated with TMSBr
un der stan dard con dition s (see com poun d 3e). An alytical sam ple of m on oester 3f was puri-
fied by stan dard tech n ique usin g Dowex 1 (AcO–).
9-{2-[(Diisopropoxyphosphoryl)methoxy]ethyl}-8-(methylsulfanyl)adenine (3b). Yellow crystals,
m .p. 106–108 °C (eth an ol–eth er), yield 92%, RF = 0.35 (S1). FAB MS, m/z (rel.%): 404 (100)
[M + H]. 1H NMR (500 MHz, DMSO-d6): 1.09 (d, 6 H, J(CH3,CH) = 6.1, CH3); 1.14 (d, 6 H,
J(CH3,CH) = 6.1, CH3); 2.70 (s, 3 H, SCH3); 3.75 (d, 2 H, J(P,CH) = 8.3, PCH2); 3.89 (t, 2 H,
J(2′,1′) = 5.4, H-2′); 4.23 (t, 2 H, J(1′,2′) = 5.4, H-1′); 4.45 (m , 2 H, POCH); 7.07 (brs, 2 H,
NH2); 8.07 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6): 14.60 (SCH3); 23.68 (d, 2 C, J(P,C) =
4.9, CH3); 23.86 (d, 2 C, J(P,C) = 3.9, CH3); 42.36 (C-1′); 64.90 (d, J(P,C) = 163.1, PC); 69.69
(d, J(P,C) = 11.2, C-2′); 70.32 (d, 2 C, J(P,C) = 6.3, POC); 119.04 (C-5); 149.16 (C-8); 151.73
(C-2); 151.85 (C-4); 154.20 (C-6). For C15H26N5O4PS (403.4) calculated: 44.66% C, 6.50% H,
17.36% N, 7.68% P, 7.95% S; foun d: 44.80% C, 6.40% H, 17.38% N, 7.93% P, 8.29% S.
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Acyclic Nucleoside and Nucleotide Analogs
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(S)-9-{2-[(Dimethoxyphosphoryl)methoxy]-3-hydroxypropyl}-8-(methylsulfanyl)adenine (3g).
FAB MS, m/z (rel.%): 378 (100) [M + H].
(S)-9-[3-Hydroxy-2-{[hydroxy(methoxy)phosphoryl]methoxy}propyl)-8-(methylsulfanyl)adenine
(3f). Wh ite crystals, m .p. 108–110 °C (eth an ol–eth er), EUp = 0.52. FAB MS, m/z (rel.%): 364
(100) [M + H]. 1H NMR (500 MHz, DMSO-d6): 2.70 (s, 3 H, SCH3); 3.41 (d, 3 H, J(P,OCH) =
10.6, POCH3); 3.48 (dd, 1 H, J(3′b,2′) = 4.9, J(gem ) = 12.0, H-3′b); 3.52 (dd, 1 H, J(3′a,2′) =
4.5, J(gem ) = 12.0, H-3′a); 3.59 (dd, 1 H, J(P,CHb) = 8.4, J(gem ) = 13.9, PCHb); 3.66 (dd, 1 H,
J(P,CHa) = 8.4, J(gem ) = 13.9, PCHa); 3.90 (m , 1 H, H-2′); 4.15 (d, 2 H, J(1′,2′) = 6.2, H-1′);
4.90 (br, 1 H, OH); 7.44 (brs, 2 H, NH2); 8.10 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6):
14.71 (SCH3); 44.28 (C-1′); 51.87 (d, J(P,C) = 5.9, POCH3); 60.80 (C-3′); 64.31 (d, J(P,C) =
160.2, PCH2); 79.97 (d, J(P,C) = 8.8, C-2′); 118.88 (C-5); 150.11 (C-2); 150.48 (C-8); 151.68
(C-4); 153.13 (C-6). For C11H18N5O5PS (363.3) calculated: 36.36% C, 4.99% H, 19.28% N,
8.53% P, 8.82% S; foun d: 36.15% C, 4.80% H, 17.23% N, 8.71% P, 9.03% S.
8-({2-[(Diisopropoxyph osph oryl)m eth oxy]eth yl}sulfan yl)aden in e (4a)
A m ixture of com poun d 2a (0.8 g, 4.8 m m ol) an d sodium h ydride (0.2 g of 60% dispersion ,
5 m m ol) in DMF (15 m l) was stirred at 110 °C for 0.5 h . Diisopropyl [(2-ch loroeth oxy)-
m eth yl]ph osph on ate (1.2 m l, 5 m m ol) was added an d th e m ixture was stirred for an oth er
4 h . Th e m ixture was evaporated in vacuo an d th e residue was codistilled with toluen e (2 ×
10 m l). Th e crystallization from eth yl acetate afforded 1.25 g (67%) of wh ite crystals, m .p.
93–95 °C, RF = 0.41 (S1). FAB MS, m/z (rel.%): 390 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 1.22 (d, 6 H, J(CH3,CH) = 6.3, CH3); 1.23 (d, 6 H, J(CH3,CH) = 6.3, CH3); 3.45 (t,
2 H, J(1′,2′) = 5.3, H-1′); 3.80 (d, 2 H, J(P,CH) = 8.2, PCH2); 3.81 (t, 2 H, J(2′,1′) = 5.3, H-2′);
4.58 (m , 2 H, POCH); 7.01 (brs, 2 H, NH2); 8.04 (s, 1 H, H-2); 13.00 (br, 1 H, NH). 13C NMR:
23.88 (d, 2 C, J(P,C) = 4.9, CH3); 23.99 (d, 2 C, J(P,C) = 3.9, CH3); 30.56 (C-1′); 64.83 (d,
J(P,C) = 165.0, PC); 70.36 (d, 2 C, J(P,C) = 5.9, POC); 71.17 (d, J(P,C) = 11.7, C-2′); 119.23
(C-5); 148.79 (C-8); 151.57 (C-2); 153.11 (C-4); 155.26 (C-6). Exact m ass (FAB HRMS) foun d:
390.1291; calculated for C14H25N5O4PS [M + H]: 390.1364.
Alkylation of 8-(Meth ylsulfan yl)aden in e (3a) with Meth yl Tosylate
A m ixture of com poun d 3a (0.5 g, 2.8 m m ol) an d sodium h ydride (0.12 g of 60% dispersion ,
3 m m ol) in DMF (15 m l) was stirred at 110 °C for 0.5 h . Meth yl tosylate (0.5 m l, 3 m m ol)
was added an d th e m ixture was stirred for an oth er 8 h at th is tem perature. Th e solven t was
evaporated an d th e preparative th in -layer ch rom atograph y on a silica gel in ch loroform –
m eth an ol m ixture (85 : 15) followed by crystallization from eth yl acetate afforded 233 m g
(43%) of com poun d 3h an d 140 m g (26%) of com poun d 5h .
9-Methyl-8-(methylsulfanyl)adenine (3h ). Yellowish crystals, m .p. 215 °C, RF = 0.52 (S2). FAB MS,
m/z (rel.%): 196 (100) [M + H]. 1H NMR (500 MHz, DMSO-d6): 2.71 (s, 3 H, SCH3); 3.56 (s, 3 H,
NCH3); 7.07 (brs, 2 H, NH2); 8.09 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6): 14.07
(SCH3); 28.60 (NCH3); 118.93 (C-5); 149.26 (C-8); 151.71 (C-2); 151.91 (C-4); 154.09 (C-6).
UV, λm ax (εm ax) (MeOH): 278 (18 800), 221 (23 300). Exact m ass (FAB HRMS) foun d:
196.0670; calculated for C7H10N5S [M + H]: 196.0657.
3-Methyl-8-(methylsulfanyl)adenine (5h ): Yellowish crystals, m .p. 269 °C, RF = 0.22 (S2). FAB MS,
m/z (rel.%): 196 (100) [M + H]. 1H NMR (500 MHz, DMSO-d6): 2.58 (s, 3 H, SCH3); 3.84 (s,
3 H, NCH3); 7.58 (brs, 2 H, NH2); 8.19 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6): 14.13
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(SCH3); 35.88 (NCH3); 121.67 (C-5); 142.60 (C-2); 151.84 (C-4); 152.12 (C-6); 161.65 (C-8).
UV, λm ax (εm ax) (MeOH): 307 (16 100). Exact m ass (FAB HRMS) foun d: 196.0632; calculated
for C7H10N5S [M + H]: 196.0657.
Alkylation of 8-(Meth ylsulfan yl)aden in e (3a) with Diisopropyl
[(2-Ch loroeth oxy)m eth yl]ph osph on ate
A m ixture of com poun d 3a (0.5 g, 2.8 m m ol) an d sodium h ydride (0.12 g of 60% disper-
sion , 3.1 m m ol) in DMF (15 m l) was stirred at 110 °C for 0.5 h . Diisopropyl [(2-ch loro-
eth oxy)m eth yl]ph osph on ate (0.7 m l, 3.1 m m ol) was added an d th e m ixture was stirred for
an oth er 15 h . Th e solven t was evaporated an d th e residue codistilled with toluen e (2 ×
15 m l). Preparative ch rom atograph y on a silica gel plate in ch loroform –m eth an ol m ixture
(9 : 1) followed by crystallization from eth an ol afforded 0.20 g (18%) of com poun d 3b an d
0.20 g (18%) of com poun d 5b.
9-{2-[(Diisopropoxyphosphoryl)methoxy]ethyl}-8-(methylsulfanyl)adenine (3b). Th e com poun d
is iden tical with th e auth en tic m aterial (accordin g to FAB MS, 1H NMR, an d 13C NMR spec-
tra) prepared by m odification at th e position 8. Wh ite crystals, m .p. 118 °C, RF = 0.35 (S1).
3-{2-[(Diisopropoxyphosphoryl)methoxy]ethyl}-8-(methylsulfanyl)adenine (5b). Wh ite crystals,
m .p. 156 °C, RF = 0.31 (S1). FAB MS, m/z (rel.%): 404 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 1.11 (d, 6 H, J(CH3,CH) = 6.1, CH3); 1.15 (d, 6 H, J(CH3,CH) = 6.1, CH3); 2.58 (s,
3 H, SCH3); 3.78 (d, 2 H, J(P,CH) = 8.5, PCH2); 3.94 (t, 2 H, J(2′,1′) = 4.9, H-2′); 4.43 (t, 2 H,
J(1′,2′) = 4.9, H-1′); 4.46 (m , 2 H, POCH); 7.64 (brs, 2 H, NH2); 8.14 (s, 1 H, H-2). 13C NMR
(125 MHz, DMSO-d6): 14.13 (SCH3); 23.73 (d, 2 C, J(P,C) = 4.9, CH3); 23.87 (d, 2 C, J(P,C) =
3.9, CH3); 48.67 (C-1′); 64.69 (d, J(P,C) = 164.1, PCH2); 69.31 (d, J(P,C) = 11.7, C-2′); 70.32
(d, 2 C, J(P,C) = 6.3, POC); 121.78 (C-5); 142.57 (C-2); 151.06 (C-4); 152.17 (C-6); 161.58
(C-8). For C15H26N5O4PS (403.4) calculated: 44.66% C, 6.50% H, 17.36% N, 7.68% P, 7.95% S;
foun d: 44.36% C, 6.34% H, 17.14% N, 7.66% P, 8.16% S.
Alkylation of 8-(Meth ylsulfan yl)aden in e (3a) with (S)-[(Trityloxy)m eth yl]oxiran e
A m ixture of 8-(m eth ylsulfan yl)aden in e (3a; 1.5 g, 8.3 m m ol), DMF (50 m l), (S)-[(trityloxy)-
m eth yl]oxiran e (2.9 g, 9.2 m m ol), an d cesium carbon ate (0.54 g, 1.7 m m ol) was stirred at
110 °C for 15 h . Th e wh ite solid was filtered off, wash ed with DMF (10 m l), m eth an ol (2 ×
10 m l) an d eth er (2 × 10 m l), an d dried to give 0.15 g (4%) of com poun d 8. Th e filtrate after
evaporation an d codistillation with toluen e (3 × 15 m l) afforded, by colum n ch rom atogra-
ph y on silica gel (ch loroform –m eth an ol), two products: 6a (1.45 g, 35%) an d 7a (1.6 g,
39%). Th e com poun ds 6a an d 7a were fully ch aracterized after detritylation .
(S)-7-[(Trityloxy)methyl]-7,8-dihydro[1,3]oxazolo[3,2-e]purine-4-amine (8). Wh ite crystals,
m .p. 281 °C, RF = 0.66 (S2). FAB MS, 1H NMR, an d 13C NMR spectra are iden tical with th e
previously described com poun d2. For C27H23N5O2 (449.5) calculated: 72.14% C, 5.16% H,
15.58% N; foun d: 71.84% C, 5.08% H, 15.41% N.
(S)-9-[2-Hydroxy-3-(trityloxy)propyl]-8-(methylsulfanyl)adenine (6a). Yellowish solid, RF = 0.40
(S1). FAB MS, m/z (rel.%): 498 (30) [M + H], 243 (100) [trityl].
(S)-3-[2-Hydroxy-3-(trityloxy)propyl]-8-(methylsulfanyl)adenine (7a). Wh ite solid, RF = 0.36
(S1). FAB MS, m/z (rel.%): 498 (35) [M + H], 243 (100) [trityl].
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Acyclic Nucleoside and Nucleotide Analogs
1709
Deprotection of th e Trityl Derivatives 6a an d 7a. Gen eral Procedure
Th e correspon din g trityl derivative (2 m m ol) was refluxed in a m ixture water–m eth an ol
(1 : 1, 50 m l) with Dowex 50 (H+ form , 20 m l) an d a trace of h ydroch loric acid for 0.5 h .
Th e resin was filtered off, wash ed with water (3 × 10 m l), eth er (3 × 10 m l) an d 5% am m o-
n ia in 50% aqueous m eth an ol. Th e am m on ia solution was evaporated an d th e residue crys-
tallized from water–eth an ol m ixture.
(S)-9-(2,3-Dihydroxypropyl)-8-(methylsulfanyl)adenine (6b). Wh ite crystals, m .p. 175 °C, yield
62%, RF = 0.20 (S1). FAB MS, m/z (rel.%): 256 (100) [M + H]. 1H NMR (500 MHz, DMSO-d6):
2.68 (s, 3 H, SCH3); 3.33 (brdt, 1 H, J(3′b,2′) = 5.5, J(3′b,OH) = 5.9, J(gem ) = 11.2, H-3′b);
3.39 (ddd, 1 H, J(3′a,2′) = 5.2, J(3′a,OH) = 5.9, J(gem ) = 11.2, H-3′a); 3.91 (m , 1 H, H-2′); 3.95
(dd, 1 H, J(1′b,2′) = 8.2, J(gem ) = 13.8, H-1′b); 4.12 (dd, 1 H, J(1′a,2′) = 3.9, J(gem ) = 13.8,
H-1′a); 4.83 (t, 1 H, J(OH,3′) = 5.9, OH); 5.04 (d, 1 H, J(OH,2′) = 5.1, OH); 7.07 (brs, 2 H,
NH2); 8.07 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6): 14.70 (SCH3); 46.61 (C-1′); 63.93
(C-3′); 69.59 (C-2′); 118.99 (C-5); 149.99 (C-8); 151.56 (C-2); 151.99 (C-4); 154.18 (C-6). UV,
λm ax (εm ax) (MeOH): 279 (22 500), 223 (26 900). CD, λ (∆ε) (MeOH): 279 (–0.60), 223 (1.16),
197 (–1.75). Exact m ass (FAB HRMS) foun d: 256.0818; calculated for C7H10N5S [M + H]:
256.0868.
(S)-3-(2,3-Dihydroxypropyl)-8-(methylsulfanyl)adenine (7b). Wh ite crystals, m .p. 189–190 °C,
yield 55%, RF = 0.20 (S1). FAB MS, m/z (rel.%): 256 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 2.58 (s, 3 H, SCH3); 3.29 (dd, 1 H, J(3′b,2′) = 6.4, J(gem ) = 11.2, H-3′b); 3.41 (dd,
1 H, J(3′a,2′) = 5.1, J(gem ) = 11.2, H-3′a); 3.95 (m , 1 H, H-2′); 4.06 (dd, 1 H, J(1′b,2′) = 8.3,
J(gem ) = 13.6, H-1′b); 4.42 (dd, 1 H, J(1′a,2′) = 3.3, J(gem ) = 13.6, H-1′a); 5.02 (brs, 1 H, OH);
5.20 (brs, 1 H, OH); 7.64 (brs, 2 H, NH2); 8.09 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6):
14.13 (SCH3); 52.58 (C-1′); 63.53 (C-3′); 68.67 (C-2′); 121.65 (C-5); 143.25 (C-2); 151.47
(C-4); 152.24 (C-6); 161.26 (C-8). UV, λm ax (εm ax) (MeOH): 306 (14 500). CD, λ (∆ε) (MeOH):
312 (–0.35), 278 (–0.80), 254 (–0.36), 198 (–5.72). Exact m ass (FAB HRMS) foun d: 256.0810;
calculated for C7H10N5S [M + H]: 256.0868.
Syn th esis of 8,3′-S-An h ydro Com poun ds 9 by Mitsun obu Reaction . Gen eral Procedure
A m ixture of th e correspon din g 6-am in o-7H-purin e-8(9H)-th ion e derivative 2f or 2d (1 mmol),
triph en ylph osph in e (1 m m ol), an d DMF (20 m l) was cooled to –10 °C an d dieth yl azo-
dicarboxylate (DEAD; 1 m m ol) was added. Th e m ixture was stirred at room tem perature
overn igh t. Th en an oth er part of triph en ylph osph in e (1 m m ol) was added, th e m ixture was
cooled to –10 °C an d DEAD (1 m m ol) was added. Th e stirrin g was con tin ued at room tem -
perature overn igh t. Th e solven t was evaporated in vacuo an d th e residue was codistilled with
toluen e (3 × 10 m l) an d eth an ol (2 × 10 m l). Th e residue was purified by preparative TLC
ch rom atograph y on silica gel an d crystallized.
8,9-Dihydro-7H-[1,3]thiazino[3,2-e]purine-4-amine (9f). Yellowish crystals, m .p. 289 °C (eth a-
n ol), yield 90%, RF = 0.54 (S2). FAB MS, m/z (rel.%): 208 (100) [M + H]. 1H NMR (500 MHz,
DMSO-d6): 2.29 (m , 2 H, H-2′); 3.29 (t, 2 H, J(3′,2′) = 5.6, H-3′); 4.14 (t, 2 H, J(1′,2′) = 6.0,
H-1′); 7.06 (brs, 2 H, NH2); 8.05 (s, 1 H, H-2). 13C NMR (125 MHz, DMSO-d6): 22.70 (C-2′);
25.42 (C-3′); 41.60 (C-1′); 118.33 (C-5); 143.82 (C-8); 150.92 (C-4); 151.22 (C-2); 154.02
(C-6). UV, λm ax (εm ax) (MeOH): 281 (18 500), 223 (18 400). For C8H9N5S (207.3) calculated:
46.36% C, 4.38% H, 33.79% N, 15.47% S; foun d: 46.38% C, 4.41% H, 33.51% N, 15.24% S.
Diisopropyl (S)-{[(4-amino-8,9-dihydro-7H-[1,3]thiazino[3,2-e]purin-8-yl)oxy]methyl}phosphonate
(9d ). Hygroscopic wh ite solid (eth er), yield 92%, RF = 0.51 (S5). FAB MS, m/z (rel.%): 402
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(100) [M + H]. 1H NMR (500 MHz, DMSO-d6): 1.11 (d, 3 H, J(CH3,CH) = 6.2, CH3); 1.14 (d, 3 H,
J(CH3,CH) = 6.2, CH3); 1.16 (d, 3 H, J(CH3,CH) = 6.2, CH3); 1.18 (d, 3 H, J(CH3,CH) = 6.2,
CH3); 3.49 (ddd, 1 H, J(3′b,P) = 1.5, J(3′b,2′) = 5.3, J(gem ) = 13.3, H-3′b); 3.55 (dd, 1 H,
J(3′a,2′) = 2.0, J(gem ) = 13.3, H-3′a); 3.88 (dd, 1 H, J(P,CHb) = 9.4, J(gem ) = 13.7, PCHb);
3.99 (dd, 1 H, J(P,CHa) = 8.9, J(gem ) = 13.7, PCHa); 4.12 (dd, 1 H, J(1′b,2′) = 2.8, J(gem ) =
13.6, H-1′b); 4.34 (ddd, 1 H, J(1′a,P) = 1.2, J(1′a,2′) = 3.8, J(gem ) = 13.6, H-1′a); 4.45 (m , 1 H,
H-2′); 4.53 (m , 2 H, POCH); 7.10 (brs, 2 H, NH2); 8.05 (s, 1 H, H-2). 13C NMR (125 MHz,
DMSO-d6): 23.68 (d, J(P,C) = 4.9, CH3); 23.76 (d, J(P,C) = 4.9, CH3); 23.92 (d, 2 C, J(P,C) =
3.9, CH3); 27.94 (C-3′); 45.04 (C-1′); 62.62 (d, J(P,C) = 164.1, PC); 68.92 (d, J(P,C) = 12.7,
C-2′); 70.53 (d, 2 C, J(P,C) = 5.9 (POC); 118.13 (C-5); 143.44 (C-8); 151.02 (C-2); 151.13
(C-4); 153.84 (C-6). UV, λm ax (εm ax) (MeOH): 281 (19 500), 223 (19 300). Exact m ass (FAB
HRMS) foun d: 402.1287; calculated for C15H25N5O4PS [M + H]: 402.1364.
Deprotection of Ph osph on ates with TMSBr. Gen eral Procedure
A m ixture of a ph osph on ate diester (1 m m ol), TMSBr (1 m l) an d aceton itrile (5 m l) was
stirred at am bien t tem perature overn igh t, th en evaporated an d codistilled with aceton itrile
(10 m l). Th e residue was dissolved in water an d alkalin ized with aqueous am m on ia. After
evaporation , th e residue was dissolved in water an d applied to a colum n of Dowex 50X8 (H+
form , 50 m l); th e colum n was wash ed with water an d eluted with 2.5% aqueous am m on ia.
After evaporation of th e UV absorbin g fraction , th e product was purified on a Dowex 1X2
(acetate) colum n by elution with lin ear gradien t of acetic acid (0–0.5 M, 1 l each ). Th e UV
absorbin g fraction s were evaporated in vacuo an d th e residue was crystallized from water.
6-Amino-9-[2-(phosphonomethoxy)ethyl]-7H-purine-8(9H)-thione (2c). Yellowish crystals, m .p.
>250 °C, yield 52%, EUp = 1.10, RF = 0.24 (S4). FAB MS, m/z (rel.%): 306 (100) [M + H].
1H NMR (500 MHz, D2O): 3.52 (d, 2 H, J(P,CH) = 8.3, PCH2); 3.93 (t, 2 H, J(2′,1′) = 6.2,
H-2′); 4.42 (t, 2 H, J(1′,2′) = 6.2, H-1′); 8.00 (s, 1 H, H-2). 13C NMR (125 MHz, D2O): 42.27
(C-1′); 69.00 (d, J(P,C) = 149.9, PC); 69.47 (d, J(P,C) = 9.8, C-2′); 118.03 (C-5); 149.30 (C-2);
150.45 an d 150.74 (C-4 an d C-6); 164.79 (C-8). UV, λm ax (εm ax): (pH 2) 308 (21 200), 241
(12 600); (pH 12) 300 (20 000), 229 (19 600). Exact m ass (FAB HRMS) foun d: 306.0387;
calculated for C8H13N5O4PS [M + H]: 306.0425.
6-Amino-9-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]-7H-purine-8(9H)-thione (2e). Yellowish
crystals, m .p. 319–320 °C, yield 45%, EUp = 1.07. FAB MS, m/z (rel.%): 336 (100) [M + H].
1H NMR (500 MHz, D2O): 3.50 (dd, 1 H, J(P,CHb) = 9.6, J(gem ) = 12.3, PCHb); 3.54 (dd, 1 H,
J(3′b,2′) = 5.6, J(gem ) = 12.8, H-3′b); 3.66 (dd, 1 H, J(P,CHa) = 8.5, J(gem ) = 12.3, PCHa);
3.70 (dd, 1 H, J(3′a,2′) = 2.7, J(gem ) = 12.8, H-3′a); 4.01 (m , 1 H, H-2′); 4.25 (dd, 1 H,
J(1′b,2′) = 7.8, J(gem ) = 14.0, H-1′b); 4.41 (dd, 1 H, J(1′a,2′) = 6.2, J(gem ) = 14.0, H-1′a); 8.01
(s, 1 H, H-2). 13C NMR (125 MHz, D2O): 43.63 (C-1′); 61.51 (C-3′); 69.03 (d, J(P,C) = 149.4,
PC); 80.45 (d, J(P,C) = 9.8, C-2′); 118.94 (C-5); 150.28 (C-2); 151.36 (C-4); 151.75 (C-6);
165.87 (C-8). UV, λm ax (εm ax): (pH 2) 308 (26 900), 241 (15 900); (pH 12) 300 (25 600), 229
(24 700). CD, λ (∆ε) (H2O): 298 (–0.45), 256 (0.25), 225 (–1.99), 214 (–0.22). Exact m ass (FAB
HRMS) foun d: 336.0583; calculated for C9H15N5O5PS [M + H]: 336.0532.
8-(Methylsulfanyl)-9-[2-(phosphonomethoxy)ethyl]adenine (3c). Wh ite crystals, m .p. 270 °C,
yield 73%, EUp = 0.73. FAB MS, m/z (rel.%): 320 (100) [M + H]. 1H NMR (500 MHz, D2O):
2.53 (s, 3 H, SCH3); 3.34 (d, 2 H, J(P,CH) = 8.2, PCH2); 3.70 (t, 2 H, J(2′,1′) = 6.0, H-2′); 4.00
(t, 2 H, J(1′,2′) = 6.0, H-1′); 7.81 (s, 1 H, H-2). 13C NMR (125 MHz, D2O): 14.62 (SCH3); 43.19
(C-1′); 69.79 (d, J(P,C) = 8.8, C-2′); 69.83 (d, J(P,C) = 149.4, PC); 118.85 (C-5); 151.05 (C-8);
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Acyclic Nucleoside and Nucleotide Analogs
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151.77 (C-2); 153.05 an d 153.44 (C-4 an d C-6). UV, λm ax (εm ax): (pH 2) 284 (20 600); (pH
12) 279 (20 000), 221 (21 800). Exact m ass (FAB HRMS) foun d: 320.0556; calculated for
C9H15N5O4PS [M + H]: 320.0582.
(S)-9-[3-Hydroxy-2-(phosphonomethoxy)propyl]-8-(methylsulfanyl)adenine (3e). Wh ite crystals,
m .p. 146–148 °C, yield 69%, EUp = 0.80. FAB MS, m/z (rel.%): 350 (100) [M + H]. 1H NMR
(500 MHz, DMSO-d6): 2.73 (s, 3 H, S-CH3); 3.37 (dd, 1 H, J(P,CHb) = 9.5, J(gem ) = 12.2,
PCHb); 3.53 (dd, 1 H, J(3′b,2′) = 5.6, J(gem ) = 12.4, H-3′b); 3.60 (dd, 1 H, J(P,CHa) = 8.2,
J(gem ) = 12.2, PCHa); 3.68 (dd, 1 H, J(3′a,2′) = 2.7, J(gem ) = 12.4, H-3′a); 3.85 (m , 1 H, H-2′);
4.09 (dd, 1 H, J(1′b,2′) = 6.4, J(gem ) = 14.8, H-1′b); 4.17 (dd, 1 H, J(1′a,2′) = 6.1, J(gem ) =
14.8, H-1′a); 8.06 (s, 1 H, H-2). UV, λm ax (εm ax): (pH 2) 284 (17 200); (pH 12) 280 (16 600),
222 (17 500). CD, λ (∆ε) (H2O): 303 (0.18), 258 (–0.22), 226 (0.64), 207 (–4.62).
8-{[2-(Phosphonomethoxy)ethyl]sulfanyl}adenine (4b). Wh ite crystals, m .p. 310 °C, yield 71%,
EUp = 0.79. FAB MS, m/z (rel.%): 306 (100) [M + H]. 1H NMR (500 MHz, D2O): 3.47 (t, 2 H,
J(1′,2′) = 5.5, H-1′); 3.59 (d, 2 H, J(P,CH) = 8.5, PCH2); 3.89 (t, 2 H, J(2′,1′) = 5.5, H-2′); 8.08
(s, 1 H, H-2). UV, λm ax (εm ax): (pH 2) 290 (17 400); (pH 12) 285 (17 800). For C8H12N5O4PS
(305.3) calculated: 31.48% C, 3.96% H, 22.94% N, 10.15% P, 10.50% S; foun d: 31.27% C,
3.87% H, 22.69% N, 10.22% P, 10.69% S.
8-(Methylsulfanyl)-3-[2-(phosphonomethoxy)ethyl]adenine (5c). Wh ite crystals, m .p. 279–280 °C,
yield 73%, EUp = 0.70. FAB MS, m/z (rel.%): 320 (100) [M + H]. 1H NMR (500 MHz, D2O):
2.63 (s, 3 H, SCH3); 3.47 (d, 2 H, J(P,CH) = 8.5, PCH2); 3.95 (t, 2 H, J(2′,1′) = 5.1, H-2′); 4.46
(t, 2 H, J(1′,2′) = 5.1, H-1′); 8.26 (s, 1 H, H-2). 13C NMR (125 MHz, D2O): 14.625 (SCH3);
50.505 (C-1′); 69.88 (d, J(P,C) = 10.7, C-2′); 69.89 (d, J(P,C) = 150.4, PC); 121.79 (C-5);
145.05 (C-2); 151.29 (C-4); 152.50 (C-6); 164.11 (C-8). UV, λm ax (εm ax): (pH 2) 301 (12 100),
236 (7 900); (pH 12) 305 (18 400). Exact m ass (FAB HRMS) foun d: 320.0508; calculated for
C9H15N5O4PS [M + H]: 320.0582.
(S)-{[(4-Amino-8,9-dihydro-7H-[1,3]thiazino[3,2-e]purin-8-yl)oxy]methyl}phosphonic acid (9e).
Wh ite crystals, m .p. 323–324 °C, yield 67%, EUp = 0.73. FAB MS, m/z (rel.%): 318 (100) [M + H].
1H NMR (500 MHz, D2O): 3.52 (brdd, 1 H, J(3′b,2′) = 5.8, J(gem ) = 13.4, H-3′b); 3.56 (dd, 1 H,
J(3′a,2′) = 3.0, J(gem ) = 13.4, H-3′a); 3.59 (dd, 1 H, J(P,CHb) = 9.0, J(gem ) = 12.6, PCHb);
3.71 (dd, 1 H, J(P,CHa) = 8.9, J(gem ) = 12.6, PCHa); 4.06 (dd, 1 H, J(1′b,2′) = 3.0, J(gem ) =
13.3, H-1′b); 4.25 (brdd, 1 H, J(1′a,2′) = 4.7, J(gem ) = 13.3, H-1′a); 4.55 (m , 1 H, H-2′); 7.92
(s, 1 H, H-2). UV, λm ax (εm ax): (pH 2) 284 (20 900); (pH 12) 282 (20 700), 222 (19 400). CD,
λ (∆ε) (H2O): 300 (–0.4), 280 (2.0), 239 (2.9), 223 (–11.4), 209 (2.3). For C9H12N5O4PS
(317.3) calculated: 34.07% C, 3.81% H, 22.07% N, 9.76% P, 10.11% S; foun d: 34.18% C,
4.00% H, 21.73% N, 9.52% P, 10.21% S.
This work was supported by the Grant Agency of the Czech Republic (grant No. 203/96/K001) and
by Gilead Sciences (Foster City (CA), U.S.A.). The authors’ thanks are due to Dr H. Votavová and
Dr P. Maloň for measurement of CD spectra, Dr P. Fiedler for measurement of IR spectra, and to the
staff of the Mass Spectrometry and Analytical Departments of this Institute.
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