Covalent analogues of DNA base-pairs and triplets VII.+ synthesis and cytostatic activity of bis(purin-6-yl)acetylene and -diacetylene nucleosides

Article abstract of DOI:10.1135/cccc20041955

The title bis(purin-6-yl)acetylene and -diacetylene nucleoside derivatives were prepared as covalent base-pair analogues starting from acyl-protected 6-ethynylpurine and 6-iodopurine nucleosides by the Sonogashira cross-coupling or oxidative alkyne-dimeri

Full text of DOI:10.1135/cccc20041955

Covalent Analogues of DNA Base-Pairs and Triplets
1955
COVALENT ANALOGUES OF DNA BASE-PAIRS AND TRIPLETS VII.+
SYNTHESIS AND CYTOSTATIC ACTIVITY OF BIS(PURIN-6-YL)ACETYLENE
AND -DIACETYLENE NUCLEOSIDES
1
2,
Petr NAUŠ, Ivan VOTRUBA and Michal HOCEK *
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
1
Flemingovo nám. 2, CZ-166 10 Prague, Czech Republic; e-mail: votruba@uochb.cas.cz,
2
hocek@uochb.cas.cz
Received August 28, 2004
Accepted Septem ber 9, 2004
Dedicated to Professor Miloslav Černý on the occasion of his 75th birthday.
Th e title bis(purin -6-yl)acetylen e an d -diacetylen e n ucleoside derivatives were prepared as
covalen t base-pair an alogues startin g from acyl-protected 6-eth yn ylpurin e an d 6-iodopurin e
n ucleosides by th e Son ogash ira cross-couplin g or oxidative alkyn e-dim erization reaction s
followed by deprotection . Th e key startin g acyl-protected 6-eth yn ylpurin e n ucleosides were
prepared by a sequen ce of cross-couplin g reaction s of protected 6-h alopurin e n ucleosides
with (trim eth ylsilyl)acetylen e followed by a m odified desilylation with TBAF in presen ce of
acetic acid. Surprisin gly, th e acyl-protected n ucleosides exh ibited sign ifican t cytostatic activ-
ity h igh er th an th e fully deprotected title com poun ds.
Keyw ord s: Purin es; Nucleobases; Nucleosides; Base-pairs; Alkyn es; Cross-couplin g reaction s;
Protectin g groups; Desilylation ; Oxidative dim erization ; Cytostatics.
Th e effect of m an y clin ically used an titum or agen ts is based on DNA
cross-lin kin g1 or on in tercalation 2 in to DNA. Num erous m odels an d an a-
logues of Watson –Crick base pairs con sistin g of an n elated3 or cross-lin ked4
purin e an d pyrim idin e h eterocycles or even m ore sim ple arom atic rin gs5,6
h ave been prepared. Such base-pairs an alogues m ay in teract with DNA (e.g.
by in tercalation ); if in corporated in to sin gle-stran ded DNA, th ey are com -
plem en tary to abasic site of a dam aged DNA stran d; or, altern atively, if in -
corporated in to duplex, th ey form perm an en t cross-lin ks.
+ Part VI, see lit.7
Collect. Czech. Chem. Commun. (Vol. 69) (2004)
doi:10.1135/cccc20041955

1956
Nauš, Votruba, Hocek:
Recen tly, we h ave design ed a n ew group of covalen t base-pair or triplet
an alogues (Ch art 1) based on con jugates of two or th ree purin e an d/or
pyrim idin e bases con n ected with diverse carbon lin kages7. Such carbon
lin kers con n ected to carbon atom s of th e h eterocycles were expected to
be stable towards en zym atic degradation . Tran sition m etal-catalyzed
cross-couplin g reaction s or cyclom erization s were th e key syn th etic m eth -
odology8 for th e con struction of th e C-C bon ds in carbon -lin kages.
Tris(purin -6-yl)- an d tris(pyrim idin -5-yl)ben zen es were prepared9,10 as trip-
let an alogues by cyclotrim erization of 6-eth yn ylpurin es or 6-eth yn yl-
pyrim idin es. Bis(purin -6-yl)ben zen es as well as (purin -6-yl)(pyrim idin -5-yl)-
ben zen es were prepared by double cross-couplin g of ph en ylen ebis-
(stan n an es)11. Purin e dim ers lin ked th rough position s 6 an d 6′ with acety-
len e, diacetylen e, vin ylen e an d eth ylen e lin kers were prepared12,13 by
Son ogash ira cross-couplin g reaction s of 6-eth yn ylpurin es with 6-h alo-
purin es or 5-iodopyrim idin es or by oxidative dim erization s of eth yn yl-
purin es. Sim ilar acetylen e couplin gs were in depen den tly used by Matsuda14
an d Marsh 15 an d altern ative Heck couplin gs by Sessler16 for th e preparation
of oth er types of n ucleobase dim ers or covalen t din ucleotides th at were
used for self-assem bly or artificial receptor studies.
N
N
N
N
N
N
N
linker
O
linker
N
N
N
N
N
O
N
N
R
R
R
linker
=
CH2 CH2
H
H
H
H
CHART 1
Cytostatic activity screen in g of th e covalen t base-pair an alogues (Ch art 1)
revealed a sign ifican t an tiproliferative effect of som e bis(purin -6-yl)-
acetylen es an d diacetylen es12, wh ile th e partly an d fully saturated deriva-
tives, as well as th e ph en ylen e-lin ked an alogues were en tirely in active. Th e
activity of th ese com poun ds was som ewh at surprisin g sin ce th ese base-pair
an alogues were just m odel com poun ds bearin g sim ple alkyl substituen ts
in position 9 of purin e rin gs. Apparen tly, m ajor drawback of th ese m odel
com poun ds was th eir extrem ely low solubility in water. In order to im prove
th e water solubility an d bioavailability, as well as for poten tial in corpora-
tion in to n ucleic acids, th e logical con tin uation of th is project is to prepare
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

Covalent Analogues of DNA Base-Pairs and Triplets
1957
n ucleoside derivatives of th ese com poun ds. Th is paper reports on th e prep-
aration of n ucleosides derivatives of th e m ost active bis(purin -6-yl)-
acetylen es an d -diacetylen es.
RESULTS AND DISCUSSION
Chemistry
Th e first task was to prepare suitably protected 6-eth yn ylpurin e n ucleosides
as key buildin g blocks for th e acetylen ic couplin gs an d dim erization s. From
our previous experien ces17 with purin e n ucleosides bearin g C-substituen ts
in position 6 we kn ew th at th e best protectin g groups for th e glycon part
are acyl groups easily cleavable un der m ild basic con dition s (usually cata-
lytic am oun t of NaOMe in m eth an ol). On th e oth er h an d, acidolabile
groups are n ot suitable due to h igh acidolability of n ucleosidic bon ds in
th ese com poun ds. In troduction of th e acetylen e groups was perform ed by
th e stan dard Son ogash ira reaction s of acyl-protected 6-ch loropurin e n u-
cleosides 1a an d 1b with (trim eth ylsilyl)acetylen e in th e presen ce of
[PdCl2(PPh 3)2], CuI an d Et3N in DMF to give th e 6-[(trim eth ylsilyl)eth yn yl]-
purin e n ucleosides 2a an d 2b in good yields (Sch em e 1). Attem pted
protodesilylation s of 2a un der stan dard con dition s (TBAF·3H2O/THF,
NH3/MeOH, K2CO3/MeOH) led to con com itan t partial de-O-acetylation an d
resulted in com plex in separable m ixtures of partly an d fully deprotected
products. To overcom e th e problem of basicity/n ucleoph ilicity of th e re-
agen t, th e deprotection of TMS group was con ducted with TBAF·3H2O in
TMS
Cl
N
TMS
Pd(PPh3)2Cl2, CuI
N
N
N
N
N
N
TBAF, AcOH
THF
N
N
N
NEt3, DMF
N
N
R
R
R
1a, 1b
2a, 87%
2b, 83%
3a, 98%
3b, 97%
TolO
AcO
1a, 2a, 3a R=
O
O
1b, 2b, 3b R=
TolO
Tol = 4-methylbenzoyl
AcO
OAc
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

1958
Nauš, Votruba, Hocek:
th e presen ce of acetic acid (a sim ilar procedure h as been used18 for proto-
desilylation of S-acylben zen eth iols) providin g desired per-O-acetylated
6-eth yn ylpurin e riboside 1a in excellen t yield of 98%. An alogously, th e cor-
respon din g per-O-(4-m eth ylben zoyl)-6-eth yn ylpurin e 2-deoxyriboside 3b
was prepared in th e sam e way from 2b in 97% yield. No tran sesterification
with acetic acid h as been observed un der th ese con dition s.
For th e preparation of bis(purin -6-yl)acetylen e din ucleosides th e
Son ogash ira reaction between 6-eth yn ylpurin e 3 an d 6-iodopurin e n ucleo-
sides 4 was th e m eth od of ch oice (Sch em e 2). As it was previously dem on -
strated13 in 9-alkyl-6-eth yn ylpurin es, stan dard con dition s ([Pd(PPh 3)4], CuI,
Et3N in DMF) do n ot give th e expected bis(purin -6-yl)eth yn es but (E)-bis-
(purin -6-yl)eth en es as a result of reductive addition . For th e preparation of
th e desired bis(purin -6-yl)eth yn es, altern ative protocol based on th e reac-
tion in th e presen ce of TBAF as base in THF was foun d to be suitable an d
was also used h ere. Th us th e treatem en t of equim olar am oun ts of protected
6-eth yn ylpurin e 3a an d 6-iodopurin e ribon ucleosides 4a in th e presen ce of
TBAF (2 equivalen ts) as base, CuI (20%) an d [PdCl2(PPh 3)2] (10%) in THF at
R1
R2
N
N
N
N
R
N
I
N
N
N
N
N
N
Pd(PPh3)2Cl2, CuI
TBAF, THF
MeONa
MeOH
N
N
R1
N
N
N
R1
N
N
N
N
R1
N
N
R2
N
N
2, 3
4
5
7
R1
R2
Yield of 5
Yield of 7
AcO
HO
O
O
O
52% (R= H)
37%
a
b
a
b
42% (R= TMS)
AcO
OAc
HO
HO
OH
TolO
HO
O
39% (R= H)
42%
42% (R= TMS)
TolO
SCHEME 2
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

Covalent Analogues of DNA Base-Pairs and Triplets
1959
room tem perature afforded th e desired per-O-acetylated acetylen ic di-
n ucleoside 5a in an acceptable yield of 52% (Sch em e 2). It sh ould be n oted
th at th is reaction failed wh en 6-ch loro derivative 1a was used in stead of
6-iodopurin e 4a, as well as in th e absen ce of CuI.
Th e Son ogash ira reaction gen erally works19 also directly with (TMS-
eth yn yl)arom atics in stead of term in al acetylen es. Th e cross-couplin g of
6-(TMS-eth yn yl)purin e derivatives with con com itan t desilylation was ex-
em plified by th e reaction of TMS-alkyn e 2a with iodopurin e riboside 4a un -
der th e sam e con dition s as for term in al acetylen es (TBAF/THF) it afforded
th e desired com poun d 5a in 42% yield. Sim ilarly, protected 2-deoxyribo-
n ucleoside dim er 5b was prepared in 42% yield wh en 6-iodopurin e
2-deoxyriboside 4b was reacted with 6-(TMS-eth yn yl)purin e 2-deoxy-
riboside 2b an d in 39% yield from 6-eth yn ylpurin e 3b. Th ough th e yields
were som ewh at lower (presum ably due to partial deacylation ), th is direct
couplin g saves on e deprotection step an d th us it is syn th etically useful.
An advan tage of th is Son ogash ira couplin g approach is th e possibility of
syn th esis of un sym m etrically disubstituted acetylen es. Th is is im portan t for
th e syn th esis of bis(purin -6-yl)acetylen e m on on ucleosides or orth ogon ally
protected din ucleosides for in corporation in to oligon ucleotides or du-
plexes. It was exem plified by th e reaction s of THP-protected 6-iodopurin e
4c with 6-eth yn ylpurin e 3a or 6-(TMS-eth yn yl)purin e ribon ucleosides 2a
un der above m en tion ed con dition s, wh ich provided un sym m etrical acetyl-
en ic m on on ucleoside 5c in 34 an d 37% yield, respectively (Sch em e 3).
THP
H
N
N
N
N
N
N
N
N
N
N
R
N
I
N
N
Pd(PPh3)2Cl2, CuI
TBAF, THF
N
N
TFA
N
N
N
N
N
N
MeOH
N
N
N
THP
AcO
AcO
AcO
O
O
O
4c
AcO
OAc
AcO
5c
OAc
AcO
OAc
2a, R = TMS
3a, R = H
7c, 30%
37% (R= TMS)
34% (R= H)
SCHEME 3
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

1960
Nauš, Votruba, Hocek:
An alogously, we h ave also prepared sym m etrical bis-THP protected bis-
(purin -6-yl)acetylen e 5d as poten tial precursor of correspon din g free base
by th e reaction of 9-THP-6-(TMS-eth yn yl)purin e 2c an d iodide 4c in 66%
yield (Sch em e 4).
THP
N
H
N
TMS
N
N
N
N
N
N
I
N
N
PdCl2(PPh3)2, CuI
TBAF, THF
N
N
N
N
TFA
N
N
MeOH
N
N
N
N
N
THP
THP
N
H
N
N
THP
2c
4c
5d, 66%
7d, 50%
SCHEME 4
For th e preparation of bis(purin -6-yl)diacetylen e din ucleoside dim ers,
oxidative dim erization s of protected 6-eth yn ylpurin e n ucleosides 3a an d
3b were perform ed (Sch em e 5). Th us th e addition of 6-eth yn yl riboside 3a
to a stirred solution of a catalytic am oun t of CuCl an d TMEDA in aceton e
in air provided protected diyn e din ucleoside dim er 6a in 68% yield. Corre-
spon din g deoxyribon ucleoside dim er 6b was prepared sim ilarly by oxida-
tive h om ocouplin g of 3b in 82% yield.
R1
R2
N
N
N
N
N
N
N
N
O2, CuCl, TMEDA
acetone
NaCN
MeOH
N
N
R1
N
N
N
N
R1
N
N
R2
N
N
3a, 3b
N
N
6a, 6b
8a, 8b
R1
R2
Yield of 6
Yield of 8
AcO
HO
O
O
O
68%
48%
a
a
AcO
OAc
HO
OH
TolO
HO
O
82%
decomposition
b
b
TolO
HO
SCHEME 5
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

Covalent Analogues of DNA Base-Pairs and Triplets
1961
As for th e deprotection step, all prepared acetylen ic com poun ds were
foun d sen sitive to basic con dition s used for th e cleavage of ester protectin g
groups (MeONa/MeOH, NEt3/MeOH, NH3/EtOH, NaCN/MeOH) an d we
h ave observed th e form ation of in soluble red colored tarry (polym eric) de-
posits un der such con dition s. Th e deprotection s sh ould be perform ed un -
der strictly con trolled con dition s an d th e course of th e reaction sh ould be
carefully m on itored an d th e reaction quen ch ed as soon as th e deprotection
is com pleted. Protected eth yn e dim ers 5a an d 5b provided free n ucleosides
7a an d 7b on treatm en t with a catalytic am oun t of NaOMe in m eth an ol in
m oderate yields of 37–42% after colum n ch rom atograph y (Sch em e 2). Bis-
(purin -6-yl)eth yn e 7d was prepared by th e action of trifluoroacetic acid on
THP-protected derivative 5d (Sch em e 4) an d th e sam e acid treatm en t was
also used for partial deprotection of th e m ixed acetylen e m on on ucleoside
5c to give 7c (Sch em e 3). Th e deprotection of diacetylen ic dim ers 6a an d
6b was even m ore problem atic th an with th e acetylen e din ucleosides due
to m ore pron oun ced sen sitivity of th e diacetylen e m oiety to basic con di-
tion s. Th e cleavage of th e acyl groups was carried out un der m ilder con di-
tion s m akin g use of NaCN 20 in MeOH. In th e case of th e acetyl-protected
din ucleoside 6a, th e desired product 8a was obtain ed in 42% yield after col-
um n ch rom atograph y, wh ile in th e case of th e toluoyl-protected deoxyribo-
n ucleoside 6b th e cleavage of th e acyl groups was m uch slower th an side
reaction s of th e diacetylen e an d th erefore th e free diacetylen e deoxyribo-
n ucleoside 8b could n ot be obtain ed (Sch em e 5).
Biological Activity
Th e title covalen t din ucleosides 5a, 5b, 6a, 6b, 7a, 7b an d 8a, as well as
m on on ucleoside 5c an d base-pair 5d were tested for th eir cytostatic activity
– in h ibition of cell growth of th e followin g cell cultures: m ouse leukem ia
L1210 cells (ATCC CCL 219), h um an prom yelocytic leukem ia HL60 cells
(ATCC CCL 240), h um an cervix carcin om a HeLaS3 cells (ATCC CCL 2.2)
an d h um an T lym ph oblastoid CCRF-CEM cell lin e (ATCC CCL 119). For ex-
perim en tal details of th e cytostatic activity screen in g see17a. Most of th e
com poun ds exh ibited a cytostatic effect in m icrom olar ran ge, sim ilarly to
th e paren t alkyl substituted m odel com poun ds12. Also an alogously to th e
previous results, cytostatic poten cy of th ese com poun ds towards differen t
cell lin es decreased in th e order CCRF-CEM > HL60 > L1210 > HeLaS3. In
gen eral, th e m ore h ydroph obic acyl-protected derivatives were surprisin gly
m ore active th an th e h ydroph ilic free n ucleosides. It m ay be, h owever, due
to th eir better tran sport th rough th e cell m em bran e. Th e activity of th is
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

1962
Nauš, Votruba, Hocek:
class of com poun ds m ay be in relation to th e recen tly reported cytostatic
activity of sim ple (arylalkyn yl)purin es21.
Conclusions
In con clusion , th e bis(purin -6-yl)acetylen e an d -diacetylen e din ucleosides
could be prepared in m oderate yields by th e Son ogash ira cross-couplin g re-
action s of acyl-protected 6-eth yn yl- or 6-[(trim eth ylsilyl)eth yn yl]purin e n u-
cleosides with 6-iodopurin e n ucleosides or by oxidative dim erization of th e
form er on es. Th e startin g protected 6-eth yn ylpurin e n ucleosides prepared
by a m odified procedure m ay fin d application s in som e oth er reaction s
(cycloaddition s, h eterocyclization s, etc.). Cleavage of th e acyl-protective
groups is problem atic due to side reaction s of th e acetylen e or diacetylen e
m oiety un der basic con dition s. Due to th e h igh sen sitivity of th ese system s,
in corporation s in to oligon ucleotides does n ot seem to be realistic. Never-
th eless, th ese com poun ds, in particular th e protected lipoph ilic on es, dis-
play in terestin g cytostatic activity an d th erefore furth er research in th is
field is desirable.
TABLE I
Cytostatic activity of th e title covalen t din ucleosides or base-pairs
IC50, µm ol l–1a
Com poun d
CCRF-CEM
HL60
L1210
HeLa S3
5a
5b
5c
5d
6a
6b
7a
7b
7c
7d
8a
10.9 (±0.90)
3.5 (±0.20)
1.6 (±0.16)
0.42 (±0.028)
1.8 (±0.17)
NA
–
NA
NA
NA
NA
NA
12.8 (±1.0)
2.0 (±0.12)
7.2 (±0.63)
NA
22.7 (±1.6)
6.3 (±0.54)
21 (±2.2)
NA
NA
4.6 (±0.30)
NA
NA
3.0 (±0.21)
NA
3.3 (±0.27)
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
11.5 (±0.98)
NA
NA
NA
NA
NA
NA
a
NA, n ot active (in h ibition of cell growth at c = 10 µm ol l–1 was lower th an 20%).
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

Covalent Analogues of DNA Base-Pairs and Triplets
1963
EXPERIMENTAL
Un less oth erwise stated, solven ts were evaporated at 40 °C/2 kPa an d com poun ds were dried
at 60 °C/2 kPa. Meltin g poin ts were determ in ed on a Kofler block an d are un corrected. Opti-
cal rotation s were m easured at 25 °C on an Autopol IV (Rudolph Research An alytical) polari-
m eter, [α]D values are given in 10–1 deg cm 2 g–1. NMR spectra were recorded on a Bruker
Avan ce 400 MHz spectrom eter (1H at 400 MHz, 13C at 100.6 MHz) an d on a Bruker Avan ce
(1H at 500 MHz, 13C at 125.8 MHz). Ch em ical sh ifts (in ppm , δ-scale) were referen ced to
TMS as in tern al stan dard. Mass spectra were m easured on a ZAB-EQ (VG An alytical) spec-
trom eter usin g FAB (ion ization by Xe, acceleratin g voltage 8 kV, glycerol m atrix) or EI ion -
ization . IR spectra were recorded on a Nicolet 750 FT-IR an d waven um bers are given in
cm –1. DMF was distilled from P2O5, degassed in vacuo an d stored over m olecular sieves un -
der argon . THF was refluxed with Na an d ben zoph en on e un der argon an d fresh ly distilled
prior to use. Startin g 6-ch loro-9-(2,3,5-tri-O-acetyl-β-D-ribofuran osyl)purin e22, 6-ch loro-
9-[2-deoxy-3,5-bis-O-(4-m eth ylben zoyl)-β-D-erythro-pen tofuran osyl]purin e23 an d 9-(tetra-
h ydropyran -2-yl)-6-[(trim eth ylsilyl)eth yn yl]purin e10 were prepared by kn own procedures.
Cytostatic activity tests were perform ed as described in 17a
.
9-(2,3,5-Tri-O-acetyl-β-D-ribofuran osyl)-6-[(trim eth ylsilyl)eth yn yl]purin e (2a)
Trieth ylam in e (1 m l) an d DMF (4 m l) were added to an argon purged m ixture of 6-ch loro-
purin e 1a (413 m g, 1 m m ol), CuI (10 m g, 0.05 m m ol), [PdCl2(PPh 2)2] (14 m g, 0.02 m m ol),
(trim eth ylsilyl)acetylen e (0.24 m l, 1.7 m m ol) an d th e m ixture was stirred at 60 °C for 6 h .
Volatiles were evaporated un der reduced pressure an d th e residue was ch rom atograph ed on
silica (h exan e/AcOEt 2:1 th en 1:1) affordin g product 2a as yellowish oil, wh ich after
co-evaporation with dieth yl eth er form s foam (413 m g, 87%). [α]D –34.9 (c 0.2, CHCl3).
1H NMR (400 MHz, CDCl3): 0.34 (s, 9 H, CH3-TMS); 2.08, 2.12, 2.16 (3 × s, 3 × 3 H,
CH3CO); 4.43 (m , 3 H, H-5′, H-4′); 5.67 (ddd, 1 H, J(H-3′,H-5′) = 0.4, J(H-3′,H-4′) = 4.5,
J(H-3′,H-2′) = 5.6, H-3′); 5.96 (t, 1 H, J(H-2′,H-1′) = 5.4, J(H-2′,H-3′) = 5.6, H-2′); 6.24 (d, 1 H,
J(H-1′,H-2′) = 5.4, H-1′); 8.28 (s, 1 H, H-8); 8.94 (s, 1 H, H-2). 13C NMR (100.6 MHz, CDCl3):
–0.47 ((CH3)3Si); 20.31, 20.49 an d 20.71 (3 × CH3); 62.94 (CH2-5′); 70.56 (CH-3′); 73.01
(CH-2′); 80.48 (CH-4′); 86.44 (CH-1′); 98.14 (-C≡C-TMS); 106.18 (TMS-C≡C-); 134.89 (C-5);
141.78 (C-6); 143.68 (C-8); 151.25 (C-4); 152.75 (C-2); 169.26, 169.50 an d 170.22 (C=O).
FAB MS, m/z (rel.%): 475 (62) [M + H], 243 (33), 217 (100). IR (CCl4): 1757, 1580, 1251,
1216, 856, 848. For C21H26N4O7Si (474.2) calculated: 53.15% C, 5.52% H, 11.81% N; foun d:
52.88% C, 5.49% H, 11.63% N.
9-[2-Deoxy-3,5-bis-O-(4-m eth ylben zoyl)-β-D-erythro-pen tofuran osyl]-
6-[(trim eth ylsilyl)eth yn yl]purin e (2b)
Th is com poun d was prepared from 6-ch loropurin e 1b accordin g to th e procedure for th e
preparation of com poun d 2a in 83% yield after colum n ch rom atograph y on silica (h exan e/
AcOEt 2:1). Yellowish foam after co-evaporation with dieth yl eth er. [α]D –61.0 (c 0.1,
CHCl3). 1H NMR (400 MHz, CDCl3): 0.35 (s, 9 H, CH3-TMS); 2.41 an d 2.45 (2 × s, 2 × 3 H,
CH3-Tol); 2.87 (ddd, 1 H, Jgem = 14.2, J2′b1′ = 5.8, J2′b3′ = 2.2, H-2′b); 3.18 (ddd, 1 H, Jgem
14.2, J2′a1′ = 8.3, J2′a3′ = 6.3, H-2′a); 4.63–4.68 (m , 2 H, H-5′b an d H-4′); 4.78 (dd, 1 H, Jgem
=
=
13.3, J5′a4′ = 5.1, H-5′a); 5.84 (dt, 1 H, J3′2′a = 6.3, J3′4′ = 2.2, J3′2′b = 2.2, H-3′); 6.58 (dd, 1 H,
J1′2′a = 8.3, J1′2′b = 5.8, H-1′); 7.22 an d 7.29 (2 × m , 2 × 2 H, H-m-Tol); 7.87 an d 7.97 (2 × m ,
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1964
Nauš, Votruba, Hocek:
2 × 2 H, H-o-Tol); 8.29 (s, 1 H, H-8); 8.85 (s, 1 H, H-2). 13C NMR (100.6 MHz, CDCl3): –0.43
(CH3-TMS); 21.69 an d 21.75 (CH3-Tol); 37.83 (CH2-2′); 63.82 (CH2-5′); 75.03 (CH-3′); 83.23
(CH-4′); 85.01 (CH-1′); 98.28 (-C≡C-TMS); 105.75 (-C≡C-TMS); 126.32 an d 126.54 (C-i-Tol);
129.29 (CH-m-Tol); 129.58 an d 129.80 (CH-o-Tol); 134.87 (C-5); 141.50 (C-6); 143.62
(CH-8); 144.21 an d 144.58 (C-p-Tol); 151.17 (C-4); 152.51 (CH-2); 165.92 an d 166.10 (CO).
IR (CCl4): 1727, 1578, 1266, 1251, 1100, 856, 847. HR MS (FAB), calculated for
C
31H33N4O5Si [M + H]: 569.2220; foun d: 569.2245.
9-(2,3,5-Tri-O-acetyl-β-D-ribofuran osyl)-6-eth yn ylpurin e (3a)
A 1 M solution of TBAF·3H2O in THF (1 m l, 1 m m ol) was dropwise added to a stirred m ix-
ture of 6-[(trim eth ylsilyl)eth yn yl]purin e n ucleoside 2a (475 m g, 1 m m ol), acetic acid (69 µl,
1.2 m m ol) in THF (5 m l) at –10 °C. TLC in dicated th e disappearan ce of startin g TMS deriva-
tive 2a im m ediately after th e addition of TBAF solution . Th e m ixture was diluted with
AcOEt (15 m l) an d wash ed with saturated aqueous am m on ium ch loride solution (3 × 15 m l).
Th e organ ic ph ase was dried over MgSO4 an d evaporated in vacuo. Th e residue was passed
th rough a sh ort colum n of silica (h exan e/AcOEt 1:1 th en 1:2) affordin g product 3a (394 m g,
98%) as yellowish foam after co-evaporation with dieth yl eth er. [α]D –29.2 (c 0.2, CHCl3).
1H NMR (500 MHz, CDCl3): 2.09, 2.12 an d 2.16 (3 × s, 3 × 3 H, CH3CO); 3.75 (s, 1 H,
HC≡C-); 4.39 (dd, 1 H, J(H-5′b,H-4′) = 4.0, Jgem = 11.9, H-5′b); 4.46 (dd, 1 H, J(H5′a,H4′) =
3.3, Jgem = 11.9, H-5′a); 4.48 (dt, 1 H, J(H-4′,H-5′a) = 3.3, J(H-4′,H-5′b) = 4.0, J(H-4′,H-3′) =
4.3, H-4′); 5.66 (dd, 1 H, J(H-3′,H-4′) = 4.3, J(H-3′,H-2′) = 5.6, H-3′); 5.97 (t, 1 H, J(H-2′,H-3′) =
5.6, J(H-2′,H-1′) = 5.6, H-2′); 6.25 (d, 1 H, J(H-1′,H-2′) = 5.6, H-1′); 8.31 (s, 1 H, H-8); 8.97 (s,
1 H, H-2). 13C NMR (125.7 MHz, CDCl3): 20.29, 20.45 an d 20.66 (3 × CH3); 62.88 (CH2-5′);
70.51 (CH-3′); 73.08 (CH-2′); 77.74 (-C≡CH); 80.50 (CH-4′); 86.52 (HC≡C-); 86.59 (CH-1′);
135.52 (C-5); 141.23 (C-6); 143.92 (C-8); 151.22 (C-4); 152.78 (C-2); 169.24, 169.46 an d
170.16 (C=O). FAB MS, m/z (rel.%): 403 (55) [M + H], 278 (34), 259 (50), 243 (55), 231 (61),
145 (50), 109 (100). IR (KBr): 2113, 1749, 1581, 1232, 1095, 1049. HR MS (FAB), calculated
for C18H19N4O7 [M + H]: 403.1254; foun d: 403.1261.
9-[2-Deoxy-3,5-bis-O-(4-m eth ylben zoyl)-β-D-erythro-pen tofuran osyl]-
6-eth yn ylpurin e (3b)
Th is com poun d was prepared from 6-[(2-trim eth ylsilyl)eth yn yl]purin e n ucleoside 2b accord-
in g to th e procedure for th e preparation of com poun d 3a in 97% yield. Yellowish foam after
co-evaporation with dieth yl eth er. [α]D –66.9 (c 0.2, CHCl3). 1H NMR (500 MHz, CDCl3):
2.41 an d 2.45 (2 × s, 2 × 3 H, CH3-Tol); 2.88 (ddd, 1 H, Jgem = 14.2, J2′b1′ = 5.8, J2′b3′ = 2.2,
H-2′b); 3.18 (ddd, 1 H, Jgem = 14.2, J2′a1′ = 8.2, J2′a3′ = 6.3, H-2′a); 3.72 (s, 1 H, HC≡C);
4.64–4.69 (m , 2 H, H-5′b an d H-4′); 4.80 (dd, 1 H, Jgem = 13.3, J5′a4′ = 5.1, H-5′a); 5.84 (dt,
1 H, J3′2′a = 6.3, J3′4′ = 2.5, J3′2′b = 2.2, H-3′); 6.60 (dd, 1 H, J1′2′a = 8.2, J1′2′b = 5.8, H-1′); 7.22
an d 7.29 (2 × m , 2 × 2 H, H-m-Tol); 7.88 an d 7.98 (2 × m , 2 × 2 H, H-o-Tol); 8.30 (s, 1 H,
H-8); 8.88 (s, 1 H, H-2). 13C NMR (125.8 MHz, CDCl3): 21.68 an d 21.74 (CH3-Tol); 37.91
(CH2-2′); 63.80 (CH2-5′); 75.02 (CH-3′); 77.79 (-C≡CH); 83.31 (CH-4′); 85.04 (CH-1′); 86.28
(-C≡CH); 126.30 an d 126.51 (C-i-Tol); 129.30 (CH-m-Tol); 129.56 an d 129.81 (CH-o-Tol);
135.50 (C-5); 140.92 (C-6); 143.85 (CH-8); 144.26 an d 144.61 (C-p-Tol); 151.10 (C-4); 152.55
(CH-2); 165.92 an d 166.10 (CO). FAB MS, m/z (rel.%): 497 (100) [M + H], 433 (40), 303 (42),
289 (77), 263 (44). IR (CHCl3): 2120, 1721, 1583, 1268, 1179, 1102. HR MS (FAB), calculated
for C28H25N4O5 [M + H]: 497.1825; foun d: 497.1842.
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Covalent Analogues of DNA Base-Pairs and Triplets
1965
Gen eral Procedure for th e Preparation of Protected Bis(purin -6-yl)eth yn es 5
A 1 M solution of TBAF·3H2O in THF (2 m l, 2 m m ol) was dropwise added to an argon
purged stirred m ixture of protected 6-eth yn ylpurin e 3 (1 m m ol) or 6-(2-TMS-eth yn yl)purin e
2 (1 m m ol), protected 6-iodopurin e 4 (1 m m ol), CuI (38 m g, 0.2 m m ol), [PdCl2(PPh 3)2]
(70 m g, 0.1 m m ol) in THF (6 m l). Th e m ixture was stirred at am bien t tem perature for 4 h .
Th e solven t was rem oved in vacuo an d th e residue was ch rom atograph ed on a silica colum n
(AcOEt/h exan e 1:1 to 1:0 for 5a, 5c, 5d or AcOEt/h exan e 1:1 to 2:1 for com poun d 5b).
Bis[9-(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purin-6-yl]ethyne (5a). Yield 52% from 3a an d 4a
or 42% from 2a an d 4a. Brown ish solid. M.p. 92–93 °C. [α]D –60.9 (c 0.2, CHCl3). 1H NMR
(400 MHz, CDCl3): 2.10, 2.14 an d 2.17 (3 × s, 3 × 6 H, CH3CO); 4.38–4.52 (m , 6 H, H-5′ an d
H-4′); 5.67 (dd, 2 H, J3′2′ = 5.5, J3′4′ = 4.3, H-3′); 5.95 (t, 2 H, J2′3′ = 5.5, J2′1′ = 5.5, H-2′); 6.28
(d, 2 H, J1′2′ = 5.5, H-1′); 8.42 (bs, 2 H, H-8); 9.06 (s, 2 H, H-2). 13C NMR (100.6 MHz,
CDCl3): 20.34, 20.52 an d 20.78 (CH3); 62.94 (CH2-5′); 70.58 (CH-3′); 73.01 (CH-2′); 80.61
(CH-4′); 86.54 (CH-1′); 90.95 (C-alkyn e); 135.53 (C-5); 140.54 (C-6); 144.65 (CH-8); 151.40
(C-4); 152.94 (CH-2); 169.28, 169.52 an d 170.26 (CO). FAB MS, m/z (rel.%): 801 (35) [M +
Na], 779 (100) [M + H], 521 (86), 325 (66). IR (CHCl3): 1751, 1584, 1228. HR MS (FAB),
calculated for C34H35N8O14 [M + H]: 779.2273; foun d: 779.2288.
Bis{9-[2-deoxy-3,5-bis-O-(4-methylbenzoyl)-β-D-erythro-pentofuranosyl]purin-6-yl}ethyne (5b ).
Yield 42% from 3b an d 4b or 39% from 2b an d 4b. Wh ite solid. M.p. 159–160 °C. [α]D
–109.4 (c 0.3, CHCl3). 1H NMR (500 MHz, CDCl3): 2.40 an d 2.44 (2 × s, 2 × 6 H, CH3-Tol);
2.90 (ddd, 2 H, Jgem = 14.2, J2′b1′ = 5.9, J2′b3′ = 2.2, H-2′b); 3.20 (ddd, 2 H, Jgem = 14.2, J2′a1′
8.3, J2′a3′ = 6.4, H-2′a); 4.65–4.70 (m , 4 H, H-5′b an d H-4′); 4.79 (dd, 2 H, Jgem = 13.3, J5′a4′
=
=
5.2, H-5′a); 5.85 (ddt, 2 H, J3′2′a = 6.4, J3′4′ = 2.5, J3′2′b = 2.2, J3′5′b = 0.5, H-3′); 6.61 (dd, 2 H,
J1′2′a = 8.3, J1′2′b = 5.9, H-1′); 7.22 an d 7.29 (2 × m , 2 × 4 H, H-m-Tol); 7.88 an d 7.98 (2 × m ,
2 × 4 H, H-o-Tol); 8.35 (s, 2 H, H-8); 8.95 (s, 2 H, H-2). 13C NMR (125.8 MHz, CDCl3): 21.64
an d 21.70 (CH3-Tol); 37.89 (CH2-2′); 63.82 (CH2-5′); 75.07 (CH-3′); 83.33 (CH-4′); 85.13
(CH-1′); 90.74 (C-alkyn e); 126.41 an d 126.58 (C-i-Tol); 129.29 an d 129.30 (CH-m-Tol);
129.58 an d 129.81 (CH-o-Tol); 135.66 (C-5); 140.43 (C-6); 144.21 (CH-8); 144.23 an d 144.54
(C-p-Tol); 151.37 (C-4); 152.59 (CH-2); 165.90 an d 166.11 (CO). FAB MS, m/z (rel.%): 989
(78) [M + Na], 967 (100) [M + H], 615 (66). IR (CHCl3): 1721, 1612, 1585, 1269, 1179, 1102.
For C54H46N8O10 (966.3) calculated: 67.07% C, 4.79% H, 11.59% N; foun d: 66.95% C, 4.75% H,
11.43% N.
1-[9-(Tetrahydropyran-2-yl)purin-6-yl]-2-[(2,3,5-tri-O-acetyl-β-D-ribofuranosyl)purin-6-yl]ethyne
(5c). Yield 34% from 3a an d 4c or 37% from 2a an d 4c. Beige solid. M.p. 109–110 °C. [α]D
–35.6 (c 0.2, CHCl3). 1H NMR (400 MHz, CDCl3): 1.65–1.88 an d 2.04–2.30 (m , 6 H,
CH2-THP); 2.10, 2.14 an d 2.17 (3 × s, 3 × 3 H, CH3CO); 3.81 (dt, 1 H, J = 11.5 an d 2.6,
bCH2-O-THP); 4.20 (ddt, 1 H, J = 11.5, 4.0 an d 2.3, aCH2-O-THP); 4.37–4.52 (m , 3 H, H-5′
an d H-4′); 5.67 (dd, 1 H, J3′2′ = 5.5, J3′4′ = 4.3, H-3′); 5.84 (dd, 1 H, J = 10.3 an d 2.7,
CH-O-THP); 5.99 (t, 1 H, J2′3′ = 5.5, J2′1′ = 5.4, H-2′); 6.28 (d, 1 H, J1′2′ = 5.4, H-1′); 8.41 an d
8.45 (2 × bs, 2 × 1 H, H-8); 9.04 an d 9.06 (2 × s, 2 × 1 H, H-2). 13C NMR (100.6 MHz,
CDCl3): 20.35, 20.53 an d 20.78 (CH3); 22.65, 24.78 an d 31.80 (CH2-THP); 62.95 (CH2-5′);
68.87 (CH2-O-THP); 70.59 (CH-3′); 73.02 (CH-2′); 80.61 (CH-4′); 82.26 (CH-O-THP); 86.50
(CH-1′); 90.48 an d 91.33 (C-alkyn e); 135.08 an d 135.51 (C-5); 139.97 an d 140.74 (C-6);
144.53 an d 144.95 (CH-8); 151.09 an d 151.38 (C-4); 152.65 an d 152.94 (CH-2); 169.28,
169.53 an d 170.27 (CO). FAB MS, m/z (rel.%): 605 (21) [M + H], 521 (100) [M + H – THP].
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1966
Nauš, Votruba, Hocek:
IR (CHCl3): 1751, 1585, 1229. HR MS (FAB), calculated for C28H29N8O8 [M + H]: 605.2108;
foun d: 605.2118.
Bis[9-(tetrahydropyran-2-yl)purin-6-yl]ethyne (5d ). Yield 66% from 2c an d 4c. Beige solid.
M.p. > 315 °C (dec). 1H NMR (400 MHz, CDCl3): 1.65–1.89 an d 2.03–2.23 (m , 12 H,
CH2-THP); 3.81 (dt, 2 H, J = 11.6 an d 2.6, bCH2-O-THP); 4.20 (ddt, 2 H, J = 11.6, 4.2 an d
1.8, aCH2-O-THP); 5.83 (dd, 2 H, J = 10.3 an d 2.7, CH-O-THP); 8.40 (s, 2 H, H-8); 9.03 (s,
2
H, H-2). 13C NMR (100.6 MHz, CDCl3): 22.64, 24.77 an d 31.77 (CH2-THP); 68.83
(CH2-O-THP); 82.17 (CH-O-THP); 90.73 (C-alkyn e); 135.11 (C-5); 140.16 (C-6); 143.87
(CH-8); 151.08 (C-4); 152.56 (CH-2). FAB MS, m/z (rel.%): 431 (55) [M + H], 371 (24), 347
(100) [M + H – THP], 309 (80). IR (CHCl3): 1585, 1495, 1447, 1334, 1322, 1087, 1046, 990.
HR MS (FAB), calculated for C22H23N8O2 [M + H]: 431.1944; foun d: 431.1946.
1,4-Bis[9-(2,3,5-tri-O-acetyl-β-D-ribofuran osyl)purin -6-yl]butadiyn e (6a)
Th e 6-eth yn ylpurin e 3a (403 m g, 1 m m ol) dissolved in aceton e (8 m l) was dropwise added
to a stirred solution of CuCl (20 m g, 0.20 m m ol) an d TMEDA (38 µl, 0.25 m m ol) in aceton e
(2 m l). Th e m ixture was stirred in air at room tem perature for 1 h . Solven t was evaporated
in vacuo an d th e residue dissolved in AcOEt (20 m l). Th e organ ic ph ase was wash ed with
saturated aqueous am m on ium ch loride solution (2 × 20 m l), saturated aqueous Na2EDTA
solution (20 m l) an d brin e (20 m l), dried over an h ydrous MgSO4, evaporated in vacuo, an d
th e residue purified by colum n ch rom atograph y on silica (AcOEt) affordin g dim er 6a as
yellowish foam after co-evaporation with dieth yl eth er (273 m g, 68%). M.p. 85–86 °C. [α]D
–77.2 (c 0.2, CHCl3). 1H NMR (400 MHz, CDCl3): 2.10, 2.14 an d 2.17 (3 × s, 3 × 3 H,
CH3CO); 4.40 (dd, 1 H, J(H-5′b,H-4′) = 4.3, Jgem = 12.1, H-5′b); 4.46 (dd, 1 H, J(H-5′a,H-4′) =
3.2, Jgem = 12.1, H-5′a); 4.49 (dt, 1 H, J(H-4′,H-5′a) = 3.2, J(H-4′,H-5′b) = 4.3, J(H-4′,H-3′) =
4.4, H-4′); 5.66 (dd, 1 H, J(H-3′,H-4′) = 4.4, J(H-3′,H-2′) = 5.5, H-3′); 5.97 (t, 1 H, J(H-2′,H-1′) =
5.3, J(H-2′,H-3′) = 5.5, H-2′); 6.27 (d, 1 H, J(H-1′,H-2′) = 5.3, H-1′); 8.35 (s, 1 H, H-8); 9.00 (s,
1 H, H-2). 13C NMR (100.6 MHz, CDCl3): 20.33, 20.48 an d 20.72 (CH3); 62.88 (CH2-5′);
70.48 (CH-3′); 73.03 (CH-2′); 78.44 (Pur-C≡C-); 80.52 (CH-4′); 80.87 (-C≡C-Pur); 86.54
(CH-1′); 136.18 (C-5); 140.08 (C-6); 144.36 (C-8); 151.41 (C-4); 152.85 (C-2); 169.27, 169.50
an d 170.22 (CO). FAB MS, m/z (rel.%): 803 (100) [M + H], 663 (16), 545 (28). IR (CHCl3):
2157, 1752, 1577, 1227. HR MS (FAB), calculated for C36H35N8O14 [M + H]: 803.2273; foun d:
803.2249.
1,4-Bis{9-[2-deoxy-3,5-bis-O-(4-m eth ylben zoyl)-β-D-erythro-pen tofuran osyl]-
purin -6-yl}butadiyn e (6b)
Th e 6-eth yn ylpurin e 3b (497 m g, 1 m m ol) dissolved in aceton e (8 m l) was dropwise added
to a stirred solution of CuCl (20 m g, 0.20 m m ol) an d TMEDA (38 µl, 0.25 m m ol) in aceton e
(2 m l). Th e m ixture was stirred in air at room tem perature for 1 h after wh ich th e product
precipitated as a gel. Saturated aqueous am m on ium ch loride solution (25 m l) an d saturated
aqueous Na2EDTA (25 m l) were added an d th e resultin g m ixture was th orough ly sh aken .
Crude solid product was collected by suction on a Büch n er fun n el an d wash ed repeatedly
with saturated aqueous am m on ium ch loride solution (3 × 10 m l) an d water (3 × 10 m l). Th e
wet solid was dissolved in CHCl3 (50 m l) an d th e solution was dried over an h ydrous MgSO4.
After evaporation of CHCl3 th e product was passed th rough a sh ort colum n of silica (AcOEt)
affordin g product 6b as brown ish solid (408 m g, 82%). M.p. 114–115 °C. [α]D –132.7 (c 0.3,
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Covalent Analogues of DNA Base-Pairs and Triplets
1967
CHCl3). 1H NMR (400 MHz, CDCl3): 2.42 an d 2.45 (2 × s, 2 × 6 H, CH3-Tol); 2.90 (ddd, 2 H,
Jgem = 14.3, J2′b1′ = 5.9, J2′b3′ = 2.3, H-2′b); 3.18 (ddd, 2 H, Jgem = 14.3, J2′a1′ = 8.1, J2′a3′ = 6.3,
H-2′a); 4.64–4.71 (m , 4 H, H-5′b an d H-4′); 4.80 (dd, 2 H, Jgem = 13.2, J5′a4′ = 4.9, H-5′a); 5.85
(dt, 2 H, J3′2′a = 6.3, J3′4′ = 2.7, J3′2′b = 2.3, H-3′); 6.60 (dd, 2 H, J1′2′a = 8.1, J1′2′b = 5.9, H-1′);
7.22 an d 7.29 (2 × m , 2 × 4 H, H-m-Tol); 7.92 an d 7.98 (2 × m , 2 × 4 H, H-o-Tol); 8.34 (s,
2 H, H-8); 8.90 (s, 2 H, H-2). 13C NMR (100.7 MHz, CDCl3): 21.70 an d 21.73 (CH3-Tol);
37.91 (CH2-2′); 63.76 (CH2-5′); 75.02 (CH-3′); 78.48 an d 80.71 (C-alkyn e); 83.39 (CH-4′);
85.15 (CH-1′); 126.30 an d 126.46 (C-i-Tol); 129.30 (CH-m-Tol); 129.55 an d 129.80
(CH-o-Tol); 136.19 (C-5); 139.81 (C-6); 144.27 (CH-8); 144.31 an d 144.60 (C-p-Tol); 151.28
(C-4); 152.60 (CH-2); 165.92 an d 166.10 (CO). ESI MS, m/z: 991 [M + H], 1013 [M + Na].
IR (CHCl3): 2156, 1721, 1612, 1576, 1268, 1179, 1121, 1102.
Bis[9-(β-D-ribofuran osyl)purin -6-yl]eth yn e (7a)
Com poun d 5a (160 m g, 0.21 m m ol) in m eth an ol (2 m l) was treated with 1 M m eth an olic so-
dium m eth oxide (40 µl, 0.040 m m ol) at room tem perature for 1 h . Th e m ixture was evapo-
rated with silica gel an d ch rom atograph ed on a silica colum n (AcOEt/MeOH 10:1) affordin g
product 7a as yellow solid (40 m g, 37%). M.p. 155–156 °C. [α]D –72.2 (c 0.2, DMSO).
1H NMR (400 MHz, DMSO-d6): 3.61 (ddd, 2 H, Jgem = 11.7, J5′bOH = 5.5, J5′b4′ = 4.0, H-5′b);
3.72 (dd, 2 H, Jgem = 11.7, J5′aOH = 5.5, J5′a4′ = 4.1, H-5′a); 4.01 (q, 2 H, J4′5′a = 4.1, J4′3′ = 4.0,
J4′5′b = 4.0, H-4′); 4.22 (q, 2 H, J3′OH = 5.2, J3′2′ = 5.1, J3′4′ = 4.0, H-3′); 4.64 (q, 2 H, J2′OH
=
5.8, J2′1′ = 5.3, J2′3′ = 5.1, H-2′); 5.13 (t, 2 H, JOH5′ = 5.5); 5.28 (d, 2 H, JOH3′ = 5.2); 5.61 (d,
2 H, JOH2′ = 5.8); 6.09 (d, 2 H, J1′2′ = 5.3, H-1′); 9.03 (s, 2 H, H-8); 9.07 (s, 2 H, H-2).
13C NMR (100.6 MHz, DMSO-d6): 61.26 (CH2-5′); 70.31 (CH-3′); 74.07 (CH-2′); 85.91
(CH-4′); 88.11 (CH-1′); 90.24 (C-alkyn e); 135.30 (C-5); 138.56 (C-6); 146.88 (CH-8); 152.02
(C-4); 152.51 (CH-2). FAB MS, m/z (rel.%): 527 (91) [M + H], 465 (100), 417 (73). IR (KBr):
1590, 1332, 1211, 1099, 1061, 1032. HR MS (FAB), calculated for C22H23N8O8 [M + H]:
527.1639; foun d: 527.1650.
Bis[9-(2-deoxy-β-D-erythro-pen tofuran osyl)purin -6-yl]eth yn e (7b)
Com poun d 5b (245 m g, 0.25 m m ol) in m eth an ol (2 m l) an d THF (8 m l) was treated with
1
M m eth an olic sodium m eth oxide (40 µl, 0.040 m m ol) at room tem perature for 5 h . Th e
m ixture was evaporated with silica gel an d ch rom atograph ed on silica (AcOEt/MeOH 10:1)
affordin g product 7b as pin k solid (53 m g, 42%). M.p. 153–154 °C. [α]D –43.2 (c 0.2, DMSO).
1H NMR (400 MHz, CD3OD): 2.54 (ddd, 1 H, Jgem = 10.1, J2′b1′ = 6.4, J2′b3′ = 3.8, H-2′b); 2.90
(dt, 1 H, Jgem = 10.1, J2′a1′ = 6.8, J2′a3′ = 5.8, H-2′a); 3.77 (dd, 1 H, Jgem = 12.1, J5′b4′ = 4.1,
H-5′a); 3.85 (dd, 1 H, Jgem = 12.1, J5′a4′ = 3.5, H-5′a); 4.07 (q, 1 H, J4′5′b = 4.1, J4′5′a = 3.5,
J4′3′ = 3.4, H-4′); 4.63 (dt, 1 H, J3′2′a = 5.8, J3′2′b = 3.8, J3′4′ = 3.4, H-3′); 6.62 (t, 1 H, J1′2′a
=
6.8, J1′2′b = 6.4, H-1′); 8.87 (s, 1 H, H-8); 8.99 (s, 1 H, H-2). 13C NMR (100.6 MHz, CD3OD):
41.40 (CH2-2′); 63.12 (CH2-5′); 72.52 (CH-3′); 86.59 (CH-1′); 89.69 (CH-4′); 91.17 (C≡C);
136.48 (C-5); 140.33 (C-6); 147.96 (CH-8); 152.94 (C-4); 153.35 (CH-2). FAB MS, m/z (rel.%):
495 (25) [M + H], 443 (28), 413 (41), 355 (38), 309 (32), 278 (64), 263 (100), 231 (86).
IR (KBr): 1584, 1444, 1402, 1328, 1212, 1090, 1062. HR MS (FAB), calculated for C22H23N8O6
[M + H]: 495.1741; foun d: 495.1735.
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

1968
Nauš, Votruba, Hocek:
1-(Purin -6-yl)-2-[9-(2,3,5-tri-O-acetyl-β-D-ribofuran osyl)purin -6-yl]eth yn e (7c)
To a solution of 5c (205 mg, 0.34 mmol) in MeOH (3 ml), trifluoroacetic acid (130 µl, 1.69 mmol)
was added. Th e m ixture was stirred at am bien t tem perature for 1 h , solid NaHCO3 (145 m g)
was added an d th e m ixture was stirred for 5 m in . Th e solid was filtered off, wash ed with
m eth an ol an d th e filtrate was evaporated. Th e colum n ch rom atograph y of th e residue on
silica (AcOEt/MeOH) afforded product 7c as am orph ous yellow solid (53 m g, 30%). 1H NMR
(500 MHz, CD3OD): 2.07, 2.09 an d 2.16 (3 × s, 3 × 3 H, CH3CO); 4.42 (dd, 1 H, Jgem = 12.1,
J5′b4′ = 4.8, H-5′b); 4.48 (dd, 1 H, Jgem = 12.1, J5′a4′ = 3.5, H-5′a); 4.51 (td, 1 H, J4′3′ = 4.9,
J4′5′b = 4.8, J4′5′a = 3.5, H-4′); 5.77 (t, 1 H, J3′2′ = 5.8, J3′4′ = 4.9, H-3′); 6.12 (dd, 1 H, J2′3′ = 5.8,
J2′1′ = 4.9, H-2′); 6.40 (d, 1 H, J1′2′ = 4.9, H-1′); 8.73 (brs, 1 H, H-8-PurH); 8.82 (s, 1 H,
H-8-PurRf); 8.99 (brs, 1 H, H-2-PurH); 9.04 (s, 1 H, H-2-PurRf). 13C NMR (125.8 MHz,
CD3OD): 20.28, 20.44 an d 20.66 (CH3); 64.08 (CH2-5′); 71.86 (CH-3′); 74.29 (CH-2′); 81.84
(CH-4′); 88.70 (CH-1′); 90.66 an d 91.16 (C-alkyn e); 136.24 (C-5-PurRf); 140.40 (C-6-PurRf);
148.35 (CH-8-PurRf); 149.41 (CH-8-PurH); 152.89 (C-4-PurRf); 153.62 (CH-2-PurH); 153.88
(CH-2-PurRf); 171.24, 171.40 an d 172.22 (CO). Note: Quatern ary carbon s of free purin e m oi-
ety are n ot observable due to tautom erism . CH-8-PurH visible in C,H-HSQC spectrum .
IR (KBr): 1745, 1684, 1595, 1211. FAB MS, m/z (rel.%): 521 (25) [M + H], 433 (27), 391 (36),
373 (55), 355 (100). HR MS (FAB), calculated for C23H21N8O7 [M + H]: 521.1533; foun d:
521.1549.
Bis(purin -6-yl)eth yn e (7d )
To a solution of 5d (100 m g, 0.33 m m ol) in CHCl3 (2 m l), MeOH (0.25 m l) an d TFA (0.25 m l)
were added. Th e m ixture was stirred at am bien t tem perature for 1 h . Precipitated solid was
collected by suction an d wash ed with ch loroform (5 × 2 m l) affordin g product 7d as beige
solid (44 m g, 50%). M.p. > 300 °C (dec). 1H NMR (400 MHz, DMSO-d6): 8.77 (s, 2 H, H-8);
9.01 (s, 2 H, H-2). We were n ot able to record 13C NMR spectrum of com poun d 7d due to
tautom erism , wh ich results in m issin g quatern ary carbon s in 13C NMR spectrum . It could
n ot be observed even usin g C,H-HMBC experim en t due to poor solubility of 7d in com m on
NMR solven ts. EI MS, m/z (rel.%): 262 (32) [M+], 129 (100). IR (KBr): 3196, 3086, 3048,
1599, 1397, 1319. HR MS (EI), calculated for C12H6N8 [M+]: 262.0715; foun d: 262.0706.
1,4-Bis[9-(β-D-ribofuran osyl)purin -6-yl]butadiyn e (8a)
Dim er 6a (250 m g, 0.31 m m ol) was treated with NaCN (15 m g, 0.31 m m ol) in dry MeOH
(10 m l) at room tem perature for 25 m in . Th e m ixture was evaporated with silica gel an d
ch rom atograph ed on silica (AcOEt/MeOH 10:1) affordin g product 8a as redish solid (82 m g,
48%). M.p. > 300 °C (dec). [α]D –51.3 (c 0.2, DMSO). 1H NMR (400 MHz, DMSO-d6): 3.60
(ddd, 2 H, Jgem = 12.0, J5′bOH = 5.5, J5′b4′ = 4.0, H-5′b); 3.71 (ddd, 2 H, Jgem = 12.0, J5′aOH
=
5.5, J5′a4′ = 5.0, H-5′a); 4.00 (q, 2 H, J4′5′a = 5.0, J4′3′ = 4.3, J4′5′b = 4.0, H-4′); 4.21 (q, 2 H,
J3′OH = 5.1, J3′2′ = 4.6, J3′4′ = 4.3, H-3′); 4.62 (q, 2 H, J2′OH = 5.8, J2′1′ = 5.3, J2′3′ = 4.6, H-2′);
5.16 (t, 2 H, JOH5′ = 5.5, 5′-OH); 5.28 (d, 2 H, JOH3′ = 5.1, 3′-OH); 5.61 (d, 2 H, JOH2′ = 5.8,
2′-OH); 6.08 (d, 2 H, J1′2′ = 5.3, H-1′); 9.04 (s, 4 H, H-8 an d H-2). 13C NMR (100.6 MHz,
DMSO-d6): 61.21 (CH2-5′); 70.28 (CH-3′); 74.11 (CH-2′); 78.51 an d 79.20 (C-alkyn e); 85.82
(CH-4′); 88.15 (CH-1′); 136.19 (C-5); 137.58 (C-6); 147.21 (CH-8); 151.95 (C-4); 152.53
(CH-2). FAB MS, m/z (rel.%): 573 (73) [M + Na], 551 (100) [M + H], 482 (42), 460 (64),
Collect. Czech. Chem. Commun. (Vol. 69) (2004)

Covalent Analogues of DNA Base-Pairs and Triplets
1969
419 (67). IR (KBr): 2154, 1578, 1333, 1057. HR MS (FAB), calculated for C24H23N8O8 [M + H]:
551.1639; foun d: 551.1660.
This work is a part of a research project Z4 055 905, supported by Sumika Fine Chemicals Co Ltd.
(Osaka, Japan). The NMR spectra were measured and interpreted by Dr R. Pohl and IR spectra by
Dr P. Fiedler (both from this Institute). The contribution of these colleagues is gratefully acknowl-
edged. The authors’ thanks are also due to Ms K. Havlíčková for excellent technical assistance and to
the staff of the mass spectrometry and analytical departments of the Institute.
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