Concise and efficient syntheses of preQ1 base, Q base, and (ent)-Q base

Article abstract of DOI:10.1039/c2ob26387d

To thoroughly study the functional role of prokaryotic t-RNA-guanine- transglycosylases which are essential in the pathogenesis of shigellosis, novel efficient, high-yielding synthetic approaches for preQ₁ base, Q base, as well as for (ent)-Q b

Full text of DOI:10.1039/c2ob26387d

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PAPER
Concise and efficient syntheses of preQ1 base, Q base, and (ent)-Q base†
Hans-Dieter Gerber and Gerhard Klebe*
Received 17th July 2012, Accepted 14th September 2012
DOI: 10.1039/c2ob26387d
To thoroughly study the functional role of prokaryotic t-RNA-guanine-transglycosylases which are
essential in the pathogenesis of shigellosis, novel efficient, high-yielding synthetic approaches for preQ1
base, Q base, as well as for (ent)-Q base mainly employing cheap and readily available starting materials
have been developed. Q base as well as (ent)-Q base are accessible starting from preQ1 base via
nucleophilic substitution reactions with appropriately decorated halocyclopentenyl synthons, prior to that
prepared from naturally occurring carbohydrates.
Introduction
t-RNA-guanine-transglycosylases (TGTs) are ubiquitously found
in all three kingdoms of life. They are involved in the modifi-
cation of tRNAs of numerous organisms including humans.
In eukaryotic TGTs, the nucleobase queuine, also referred to as
Q base (Fig. 1), is incorporated into cognate t-RNAs in the anti-
codon position 34 via a transglycosylation step.1,2 In contrast,
prokaryotic TGT, present in bacteria, is engaged in the hyper-
modification of t-RNAs that catalyze the base exchange reaction
of guanine34 by the base preQ1 (1) (Fig. 1), a precursor of
queuine (2), which represents the 7-deaza-7-aminomethyl deriva-
tive of guanine.3,4 Subsequently, in a biochemical pathway invol-
ving further enzymes, preQ1 is chemically modified to reveal
queuine.2,5–15 This important difference in substrate specificity
makes bacterial TGT an interesting drug target for the structure-
based drug design of e.g. novel antibiotics. The respective shi-
gella TGT enzyme was proven to play a crucial role in the regu-
lation of the bacterial virulence of shigellosis, the causative
agent of dysentery.16,17 This bacterial infection is still respon-
sible for more than one million deaths per year, especially affect-
ing children in the developing countries.18 Due to its essential
Fig. 1 Structures of preQ1 base (numbering according to the nucleo-
side nomenclature), Q base, and (ent)-Q base.
role in the pathogenesis of dysentery, we have embarked on
thorough investigations of this enzyme as a putative drug target.
To enable mutational studies of TGTs, in-depth enzyme-
In the literature a few synthetic routes for preQ1 base (1) as
well as for Q base (2) have been described as yet, including one
for (ent)-Q base (3), which follows the corresponding Q base
procedure described in the same paper.19
For preQ1 base (1) as well as for Q base (2), four synthetic
pathways have been reported so far, differing in length and syn-
thetic effort from each other.19–25
kinetic investigations, crystallization experiments with different
enzyme mutants as well as analysis of the distinct substrate
specificity of eukaryotic and prokaryotic TGTs, fairly large quan-
tities of the above-described, natively occurring nucleobases are
required.
A concise schematic overview (Schemes S1 and S2†) and dis-
cussion of the previously reported procedures for the synthesis
of preQ1 and Q bases can be found in the ESI.†
As all hitherto published syntheses for preQ1 base (1) as well
as Q base (2) are quite lengthy, low-yielding, or partially utilize
Institut für Pharmazeutische Chemie der Philipps-Universität Marburg,
Marbacher Weg 6, 35032 Marburg, Germany.
E-mail: klebe@mailer.uni-marburg.de; Fax: (+)49-06421-2828994;
Tel: (+)49-06421-2821313
†Electronic supplementary information (ESI) available: 1H- and
13C-NMR spectra of all compounds. See DOI: 10.1039/c2ob26387d
8660 | Org. Biomol. Chem., 2012, 10, 8660–8668
This journal is © The Royal Society of Chemistry 2012

rather expensive chemicals, we sought for a more cost-saving,
convenient approach aimed to mainly employ cheap and readily
available starting materials, avoid laborious work-up protocols,
and render the desired nucleobases in such amounts that would
allow easier handling of successive synthetic operations thus
offering access to other non-naturally occurring nucleobases
such as (ent)-Q base (3) or related structures from a common
intermediate.
As outlined in Scheme 1, for the synthesis of preQ1 base we
envisaged a Michael addition of the commercially available
building block 4 to nitroolefin 7, the latter designed as a functio-
nalized, protected synthon for the pyrrolo[2,3d]pyrimidine-4-one
formation as well as preQ1 base side chain implementation.
Synthon 7 was supposed to be conveniently accessible via a
Henry reaction from the likewise commercially available phthali-
midoacetaldehyde 5. Subsequent Nef reaction of the heterocyclic
Michael adduct, followed by intramolecular cyclization should
furnish, after final phthalimide deprotection, the desired preQ1
base (1) in large amounts merely utilizing readily available and
cheap material.
Taking the expected convenient availability of considerable
preQ1 base quantities into account, Q base as well as (ent)-Q
base were thought to be easily accessible from preQ1 base as
starting compound by applying just two additional steps invol-
ving an SN2 reaction with the stereochemically appropriately
decorated bromocyclopentene derivatives 13 and 16, respectively
Scheme 1 Retrosynthetic analysis of preQ1 base (systematically numbered), Q base, and (ent)-Q base.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8660–8668 | 8661

(Scheme 1). Both synthons were supposed to be accessible
via straightforward protocols starting from naturally occurring
D-(−)-ribose and D-(+)-mannose, respectively.
conditions present during the Nef reaction. Hence, this ring clea-
vage rendered the corresponding phthalamic acid derivative 9, as
indicated by 1H NMR analysis of the isolated product. This
finding prompted us to carry out removal of this altered N-pro-
tecting group under acidic reaction conditions utilizing aqueous
hydrochloric acid in the final step. As a consequence, deprotec-
tion according to the Ing-Manske procedure,28 which is usually
employed for cleavage of the phthalimido protecting group,
could be circumvented. The latter approach is frequently
accompanied by major difficulties in product isolation resulting
in tedious work-up procedures and quite often poor yields.
Instead, in our case the acidic cleavage with hydrochloric acid
performed excellently without any detectable side reaction
product. Refluxing a suspension of pyrrolo[2,3-d]pyrimidin-
4-one 9 in aqueous 6 M HCl led to neat truncation of the
N-phthalimido protecting group, completeness of which was just
indicated by a clear reaction solution usually obtained after
5–6 h of reflux. The ease of product isolation turned out to be a
further important advantage gained by this approach. Separation
of the resulting phthalic acid from the desired reaction product
was simply achieved by complete removal of the volatile hydro-
chloric acid in vacuo and subsequent trituration of the remaining
residue with diethyl ether which only dissolved the formed
phthalic acid whereas the desired deprotected, doubly protonated
product remained undissolved. Successive filtration, washing,
and thorough drying of the obtained microcrystalline solid gave
analytically pure preQ1 base (1) as its dihydrochloride salt in
almost quantitative yield.
Results and discussion
Synthesis of preQ1 base
Our synthesis of preQ1 base, outlined in Scheme 2, commenced
with commercially available phthalimidoacetaldehyde (5), which
was readily converted into racemic β-nitroalcohol 6 via a nitro-
aldol reaction (Henry reaction) in excellent yield. 6 was sub-
sequently dehydrated under mild conditions via an intermediate
hydroxyl group activation with trifluoroacetic anhydride, fol-
lowed by trifluoroacetate elimination utilizing N,N-diisopropyl-
1
ethylamine26 to yield nitroolefin 7 in good yield. The H NMR
spectrum of the raw product material revealed exclusive for-
mation of one stereoisomer. The observed coupling constants
(J = 13.5 Hz) indicated the presumed trans configuration of the
corresponding olefinic protons thus confirming the yield of the
E-isomer of 7. Analogous to a procedure developed by Taylor
et al.,27 in the following step a Michael addition of pyrimidinone
4 to nitroolefin 7 involving the unsubstituted, quite nucleophilic
position 5 of heterocycle 4 (Scheme 1) was easily performed by
just stirring the starting compounds at 60 °C in a solvent mixture
of THF–EtOAc–H2O to readily afford racemic nitroalkyl deriva-
tive 8 in high yield and analytical purity after separation of the
precipitated reaction product by simple filtration. The sub-
sequently applied Nef reaction with 8 led to intermediate for-
mation of aldehyde 18, which directly underwent intramolecular
cyclization thus forming the desired pyrrolo[2,3d]pyrimidine-
4-one scaffold. However, this step happened to be the only one
delivering a moderate product yield along the whole synthesis
sequence. Interestingly, even at the rather low reaction tempera-
tures (−5 °C to rt), semilateral hydrolysis of the phthalimido
moiety was observed, obviously due to the particular reaction
Synthesis of Q base
As mentioned before, for the synthesis of the nucleobase
queuine (2), preQ1 base served as a starting point. In order to
attach the required cyclopentenyl moiety to the aminomethyl
side chain of preQ1 base, an SN2 reaction with the stereochemi-
cally appropriately decorated halocyclopentenyl precursor 13 as
Scheme 2 Synthesis of preQ1 base-dihydrochloride (1) reagents and conditions: (a) CH3NO2, cat. KOtBu, THF/CH3OH, 0–20 °C, 18 h, 93%; (b)
TFAA, THF, −5 °C, 15 min, then TEA, THF, −10 °C, 5 min, 86%; (c) 4, THF/EtOAc/H2O, 60 °C, 4 h, 91%; (d) NaOH, H2O, 20 °C, 5 min, then
H3O+, H2O, −5 °C to rt, 18 h, 47%; (e) 6 M HCl, reflux, 6 h, 98%.
8662 | Org. Biomol. Chem., 2012, 10, 8660–8668
This journal is © The Royal Society of Chemistry 2012

Scheme 4 Synthesis of Q base-dihydrochloride 2 reagents and con-
ditions: (a) 13a, DBU, DMF, 65 °C, 5 h, 74%; 13b, DBU, DMF, 65 °C,
5 h, 69%; (b) employing 14a: 1.25 M HCl/MeOH, reflux, 5 h, 95%;
employing 14b: 1.25 M HCl/MeOH, reflux, 5 h, 91%.
Q base side chain attachment
As depicted in Scheme 4, the final substitution reaction of
bromocyclopentene 13a or b with preQ1 base-dihydrochloride
was successfully carried out in DMF at 65 °C in the presence of
DBU as a non-nucleophilic base. The crude product was sub-
jected to column chromatography delivering a mixture of pro-
tected Q base as well as the resulting DBU-hydrohalides.
Through trituration with chloroform and subsequent filtration of
the resulting suspension, the latter side products could be
removed rendering the desired protected Q base as mono-
hydrochloride (14a or b). Acidic deprotection with 1.25 M HCl/
MeOH finally rendered Q base (2) as dihydrochloride in 70%
yield over two steps from preQ1 base-dihydrochloride. For the
purpose of kinetic studies to be carried out with Q base, it was
very important to obtain a preQ1-free product. Therefore, in
these cases a moderate excess of 13a or b was applied in the
substitution reaction to ensure complete preQ1 base consump-
tion. A doubly-alkylated product, however, could not be
observed. In this respect it should also be noted that employment
of the cyclohexylidene-protected substrate 13b turned out to be
superior compared to the acetonide derivative 13a delivering a
particularly pure product.
Scheme 3 Synthesis of bromocyclopentene synthon 13 reagents and
conditions: (a) for 10a: 4 steps from D-(−) ribose, 23%,29 for 10b: 7
steps from D-(+)-mannose, 37%;32 (b) PNBA, TPP, DEAD, THF, 55 °C,
48 h, for 11a: 90%, for 11b: 79%; (c) NaOH, MeOH–H2O 5 : 1, 20 °C,
18 h, for 12a: 93%, for 12b: 96%; (d) Br2, TPP, imidazole, CH2Cl2,
−20 °C to rt, 1 h, for 13a: 84%, for 13b: 96%.
a substrate was envisioned, the synthesis of which is outlined in
Scheme 3. Cyclopentenol 10a was obtained in four steps with
good overall yield applying a known procedure starting from
naturally occurring D-(−)-ribose.29
According to a comparable literature protocol,30 subsequent
stereo inversion of the hydroxyl functionality of 10a was easily
accomplished via its conversion into 4-nitrophenylester 11a
under Mitsunobu conditions, saponification of which yielded the
inverted alcohol 12a in 84% over two steps. The following bro-
mination under mild reaction conditions following a procedure
of Diederich et al.31 rendered bromocyclopentene 13a in 84%
yield. The resulting reinversion of the stereo centre at C-4 now
provided the required configuration for the concluding SN2
reaction. Alternatively, synthesis of cyclohexylidene-protected
alcohol 10b from D-(+)-mannose gave for almost all of the fol-
lowing reaction steps increased yields of the respective inter-
mediates towards the synthesis of bromocyclopentene 13b when
compared to the corresponding acetonide-protected derivative
13a thus leading to an improved overall yield (27% versus 16%)
of this synthon.
Synthesis of (ent)-Q base
In a similar manner, the Q base enantiomer (ent)-queuine (3)
could also be synthesized (Scheme 6). The respective cyclopen-
tenol 15 was accessible from D-(+)-mannose in 20.5% overall
yield circumventing a Mitsunobu inversion at the hydroxyl func-
tion according to a high-yielding, straightforward literature pro-
tocol.33 Subsequent bromination of 15 as described for alcohol
12 (Scheme 3) gave directly access to the desired enantiomeric
bromocyclopentene 16 in 79% yield (Scheme 5).
Analogous to the synthesis of queuine, synthon 16 was
reacted with preQ1 base-dihydrochloride in the subsequent
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8660–8668 | 8663

overall yield (Scheme 4). This approach circumvents a separate
synthetic protocol for the heterocyclic core of Q base by apply-
ing an SN2 reaction of preQ1 base with the stereochemically
appropriately decorated bromocyclopentene building block 13a,
the latter obtainable either starting from D-(−)-ribose or
D-(+)-mannose (Scheme 3). Product yields for the building block
13 and consequently for Q base could further be improved
when a cyclohexylidene protection (compounds 10b–13b)
instead of the commonly employed acetonide protection (com-
pounds 10a–13a) was applied.
In a similar fashion, the stereochemically fully inverted deriva-
tive of Q base, (ent)-Q base (3), was also synthesized (Scheme 6).
The required corresponding enantiomeric bromocyclopentene 16
was prepared starting from D-(+)-mannose (Scheme 5).
In summary, the above reported strategies render the desired
title compounds in high and overall improved yields by straight-
forward, convenient and low-cost approaches thus offering facile
synthetic modifications at these nucleobases or other 7-deaza-7-
aminomethylguanine-related derivatives.
Scheme 5 Synthesis of enantiomeric bromocyclopentene 16 reagents
and conditions: (a) ref. 33; (b) Br2, TPP, imidazole, −20 °C to rt, 1 h,
79%.
Experimental section
General information
All proton and carbon NMR spectra were recorded on a JEOL
ECA-500 MHz spectrometer (1H NMR: 500.2 MHz, 13C NMR:
125.8 MHz) or a JEOL ECX-400 MHz spectrometer (1H NMR:
399.8 MHz, 13C NMR: 100.5 MHz). The data were processed
employing Delta NMR Processing and Control Software, version
4.3.6 or 5.0.0. Chemical shifts are stated in parts per million
1
(ppm) and were referenced to TMS at 0.00 ppm for H NMR
spectra or to the solvent residual peak at 4.79 ppm for spectra in
D2O. For 13C NMR spectra, references were adjusted to the fol-
lowing NMR solvent peaks: DMSO-d6 at 39.5 ppm, CD3OD at
49.0 ppm, CDCl3 at 77.0 ppm. For D2O spectra, CD3OD was
used as an internal reference and adjusted to 49.0 ppm. Abbrevi-
ations: bd = broad doublet, bs = broad singlet, d = doublet, dm =
doublet of multiplets, dq = doublet of quartets, dt = doublet of
triplets, m = multiplet, ps = pseudo, q = quartet, s = singlet, sm
= symmetric multiplet, t = triplet. Mass spectra were obtained
from a double-focussing sectorfield spectrometer type 7070 H
(Vacuum Generators) or of type VG-Auto-Spec (Micromass).
Combustion analyses were determined on a vario Micro cube
CHNS analyzer (Elementar Analysensysteme GmbH) or a CHN
autoanalyzer (Hewlett–Packard). Determination of chlorine was
accomplished manually according to the Schöniger method.
Optical rotations were obtained using a Jasco DIP-370 polari-
meter at room temperature. Melting points were obtained by
a melting point microscope HM-LUX (Leitz) and are uncor-
rected. Chromatography was performed using silica gel 60
(0.04–0.063 mm). TLC was carried out using 0.2 mm aluminium
plates coated with silica gel 60 F254 and the products were visu-
alized by UV detection or by utilization of phosphomolybdic
acid (“blue stain”). Solvents and reagents that are commercially
available were used in analytical quality without further purifi-
cation unless otherwise noted. Tetrahydrofuran was dried by dis-
tillation from sodium/benzophenone. All moisture-sensitive
reactions were carried out using oven-dried glassware under a
positive stream of argon.
Scheme 6 Synthesis of (ent)-Q base-dihydrochloride 3 reagents and
conditions: (a) 16, DBU, DMF, 65 °C, 5 h, 67%; (b) 1.25 M HCl/
MeOH, reflux, 5 h, 91%.
nucleophilic displacement rendering protected (ent)-Q base (17),
which, after acidic deprotection, provided the stereochemically
fully inverted isomer of Q base as dihydrochloride (3) in 61%
yield over two steps (Scheme 6).
Conclusion
We have developed a short and straightforward, high-yielding
synthetic pathway to preQ1 base (1) which allows the convenient
synthesis of this nucleobase on a gram-scale basis by a five-step
approach (Scheme 2). In comparison to all hitherto published
procedures, the overall yield (33.5% over five steps) could sig-
nificantly be improved. Moreover, the sequence is based on in-
expensive and readily available starting materials providing
preQ1 base in a highly favourable cost-benefit ratio.
In addition, we have worked out a strategy to readily syn-
thesize significant amounts (>300 mg) of Q base (2) in just two
additional steps from the starting compound preQ1 base in 70%
8664 | Org. Biomol. Chem., 2012, 10, 8660–8668
This journal is © The Royal Society of Chemistry 2012

(R,S)-2-(2-Hydroxy-3-nitropropyl)-1H-isoindole-1,3(2H)-dione
(6). To a stirred solution of phthalimidoacetaldehyde (5)34
(18.92 g, 100.0 mmol) in THF (80 mL), nitromethane (9.12 g,
8.0 mL, 149.0 mmol, 1.5 equiv.) was added at ambient tempera-
ture. After cooling to 0–5 °C, a solution of KOtBu (1.12 g,
10.0 mmol, 0.1 equiv.) in MeOH (30 mL) was added dropwise.
The mixture was stirred for 60 min at 0–5 °C and then for 15 h
at room temperature. After addition of 1 mL aq. HCl (32%), the
mixture was evaporated in vacuo and the resulting residue
thoroughly triturated with diethyl ether (250 mL). The precipitate
was separated by filtration, washed with water, subsequently
with diethyl ether, and dried in vacuo giving rise to analytically
pure 6 (23.2 g, 93%) as almost a white solid. Mp: 185–186 °C
(EtOAc–cyclohexane 2 : 1); 1H NMR (DMSO-d6, 400 MHz):
δ = 7.86 (sm, 4H), 5.77 (d, 1H, J = 5.3 Hz), 4.87 (psd, 1H, J =
10.1 Hz), 4.53–4.42 (m, 2H), 3.71 (dd, 1H, J = 14.0, 7.1 Hz),
3.60 (dd, 1H, J = 14.0, 5.3 Hz); 13C NMR (DMSO-d6,
100 MHz): δ = 167.9, 134.3, 131.8, 123.0, 79.2, 65.7, 40.8; MS
(ES+): m/z 273 (100, [M + Na]+); HRMS (ES+) m/z calcd for
C11H10N2O5Na: 273.0487, found: 273.0478; anal. calcd for
C11H10N2O5 (250.21): C, 52.8; H, 4.0; N, 11.2; found: C, 53.0;
H, 4.1; N, 11.4%.
precipitate was separated by filtration, thoroughly washed with
water, followed by EtOAc, and finally dried in vacuo to furnish
analytically pure 8 (4.99 g, 91%) as monohydrate. Mp:
220–222 °C (EtOAc/THF/H2O); 1H NMR (DMSO-d6,
500 MHz): δ = 9.84 (bs, 1H), 7.83 (sm, 4H), 6.05 (bs, 2H), 5.79
(bs, 2H), 5.21 (dd, 1H, J = 12.6, 9.2 Hz), 4.91 (dd, 1H, J = 13.2,
5.7 Hz), 3.96 (dd, 1H, J = 13.8, 7.1 Hz), 3.75 (dd, 1H, J = 13.8,
5.0 Hz), 3.59 (bs, 1H); 13C NMR (DMSO-d6, 125.8 MHz): δ =
168.1, 162.6, 162.3, 153.7, 134.2, 131.7, 122.9, 83.2, 75.8,
38.1, 34.8; MS (ES+) m/z 359 (20, [M + H]+); HRMS (ES+) m/z
calcd for C15H15N6O5 359.1104, found 359.1142; anal. calcd for
C15H16N6O6 (376.33): C, 47.9; H, 4.3; N, 22.3; found: C, 48.0;
H, 4.4; N, 22.7%.
2-({[(2-Amino-4-oxo-4,7-dihydro-3H-pyrrolo[2,3-d]pyrimidin-
5-yl)methyl]amino}carbonyl)benzoic acid dihydrate (9). Mono-
hydrate 8 (3.58 g, 9.50 mmol) was dissolved in 2 M NaOH
(30 mL, 60.0 mmol) and stirred for 5 min. The solution was
filtered and the filtrate carefully added at −5 °C to a solution of
2.5 M H2SO4 (40 mL, 100.0 mmol). After stirring for 1 h at
−5 °C, the reaction mixture was allowed to reach room tempera-
ture and stirred for additional 15 h. The resulting precipitate was
dissolved at 0–5 °C by addition of 2.5 M NaOH (approx.
70 mL, pH 12), the solution filtered, and the filtrate carefully
adjusted to pH 3 at 0–5 °C with 1 M HCl. The resulting precipi-
tate was separated by filtration, the residue thoroughly washed
with water, and dried in vacuo giving rise to dihydrate 9 (1.61 g,
47%) as a beige solid. Mp: > 240 °C (decomp.); 1H NMR
(DMSO-d6, 400 MHz): δ = 12.83 (bs, 1H), 10.84 (bs, 1H),
10.33 (bs, 1H), 8.81 (t, 1H, J = 5.5 Hz), 7.72 (dd, 1H, J = 7.6,
1.4 Hz), 7.58–7.44 (m, 3H), 7.50 (td, 1H, J = 7.6, 1.4 Hz), 7.50
(dd, 1H, J = 7.3, 1.4 Hz), 6.62 (m, 1H), 6.07 (bs, 2H), 4.48 (d,
2H, J = 5.3 Hz); 13C NMR (DMSO-d6, 125.8 MHz): δ = 168.3,
167.8, 159.8, 152.3, 151.6, 138.2, 131.4, 131.0, 129.3, 129.1,
127.5, 115.3, 113.9, 98.5, 35.9; MS (ES+) m/z 350 (100,
[M + Na]+); HRMS (ES+) m/z calcd for C15H14N5O4 328.1046,
found 328.1071; anal. calcd for C15H17N5O6 (363.33): C, 49.6;
H, 4.7; N, 19.3; found: C, 49.8; H, 4.5; N, 19.5%.
2-[(2E)-3-Nitroprop-2-en-1-yl]-1H-isoindole-1,3(2H)-dione (7).
To a stirred solution of 6 (7.50 g, 30.0 mmol) in dry THF
(200 mL), TFAA (7.35 g, 4.9 mL, 35.0 mmol, 1.2 equiv.) in
THF (5 mL) was carefully added at −5 °C under an argon atmos-
phere. After stirring for 15 min at this temperature, the mixture
was cooled to −10 °C. N-Ethyl-N,N-diisopropylamine (12.0 mL,
70.0 mmol, 2.3 equiv.) was added at once, the resulting yellow-
ish solution stirred for 5 min at −10 °C and then poured into
MTBE (200 mL). The mixture was washed with a 10%
NaH2PO4 solution (250 mL), and the aqueous layer was
extracted with MTBE (2 × 50 mL). The combined organic layers
were exhaustively washed with brine (3 × 100 mL), dried over
MgSO4, filtered, and concentrated under reduced pressure. The
crude product was recrystallized (BuOAc–cyclohexane 7 : 3)
yielding a first fraction of 7 (3.61 g, 52%) as pearly-coloured
crystals. The mother liquid was evaporated in vacuo, dissolved
in DMF (5 mL), and the solution was directly applied to a silica
gel column. Chromatography with iso-hexane–EtOAc 3 : 2 (Rf =
0.65) gave rise to an additional fraction (2.37 g, 34%) of 7. Mp:
131 °C (BuOAc–cyclohexane 7 : 3); 1H NMR (DMSO-d6,
500 MHz): δ = 7.87 (sm, 4H), 7.61 (dt, 1H, J = 13.5, 1.8 Hz),
7.36 (dt, 1H, J = 13.5, 5.0 Hz), 4.48 (dd, 2H, J = 5.0, 1.8 Hz);
13C NMR (DMSO-d6, 125.8 MHz): δ = 167.3, 140.6, 137.9,
134.2, 131.9, 123.0, 35.3; MS (ES+) m/z 255 (39, [M + Na]+);
HRMS (ES+) m/z calcd for C11H8N2O4Na 255.0381, found
255.0421; anal. calcd for C11H8N2O4 (232.20): C, 56.9; H, 3.5;
N, 12.1; found: C, 56.8; H, 3.7; N, 12.1%.
2-Amino-5-(aminomethyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyri-
midin-4-one dihydrochloride hydrate (1). A suspension of dihy-
drate 9 (1.64 g, 4.5 mmol) in 6 M HCl (120 mL, 720 mmol)
was refluxed until a clear solution was obtained (∼6 h). The hot
solution was stirred with charcoal, filtered, and the filtrate eva-
porated under reduced pressure to complete dryness. To the
remaining residue diethyl ether (500 mL) was added and the
resulting suspension triturated via sonication for 1 h, filtered,
the residue thoroughly washed with diethyl ether, and dried
in vacuo. The obtained microcrystalline product was finally
dried at 80 °C/0.01 mbar to constant mass (∼6 h) yielding light-
1
brownish 1 (1.19 g, 98%). Mp: >250 °C (decomp.); H NMR
(R,S)-2-[2-(2,4-Diamino-6-oxo-1,6-dihydropyrimidin-5-yl)-3-
nitropropyl]-1H-isoindole-1,3(2H)-dione hydrate (8). Nitro-
olefin 7 (3.39 g, 14.6 mmol) and 2,6-diamino-3H-pyrimidin-
4-one (4) (2.03 g, 16.1 mmol, 1.1 equiv.) were suspended in a
solvent mixture of EtOAc (110 mL), THF (40 mL), and water
(40 mL) and stirred at 60 °C. After 45 min, a beige-coloured pre-
cipitate started to form. The mixture was stirred for additional
3 h at 60 °C and then cooled to room temperature. The
(DMSO-d6, 500 MHz): δ = 11.58 (bs, 2H), 8.36 (bs, 3H), 6.86
(s, 1H), 5.44 (bs, 3H), 4.03 (d, 2H, J = 5.5 Hz); 1H NMR
1
(CD3OD, 500 MHz): δ = 6.97 (s, 1H), 4.21 (s, 2H); H NMR
(D2O, 400 MHz): δ = 6.92 (s, 1H), 4.21 (s, 1H); 13C NMR
(DMSO-d6, 125.8 MHz): δ = 158.6, 152.0, 145.0, 117.0, 111.2,
98.5, 34.7; 13C NMR (D2O, 125.8 MHz): δ = 160.6, 152.0,
142.8, 120.0, 111.7, 99.8, 36.0; MS (ES+) m/z 180 (90, [M + H]+);
HRMS (ES+) m/z calcd for C7H10N5O 180.0885, found
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8660–8668 | 8665

(3aR,4S,6aS)-2,2-Dimethyl-2H,3aH,4H,6aH-cyclopenta[d][1,3]-
dioxol-4-ol (12a). Cyclopentenol 12a was prepared according to
a slightly modified procedure of Seley et al.30 as following: nitro-
phenylester 11a (823 mg, 2.7 mmol) was added to a solution of
NaOH (1.00 g, 25.0 mmol, 9.3 equiv.) in 10 mL H2O and
50 mL MeOH and stirred for 18 h at 20 °C. The reaction
mixture was concentrated in vacuo and brine (20 mL) was added
subsequently. After extraction with ethyl ether (3 × 50 mL), the
combined organic layers were dried over MgSO4, filtered, and
the solvent removed in vacuo to afford spectroscopically pure
12a (390 mg, 93%) as a colourless oil, which was directly used
in the following reaction. Rf = 0.24 (EtOAc–iso-hexane 1 : 2);
1H NMR (CDCl3, 400 MHz): δ = 6.04 (dm, 1H, J = 5.7 Hz),
5.92 (dm, 1H, J = 5.7 Hz), 5.29 (dq, 1H, J = 5.7, 0.9 Hz), 4.80
(bd, 1H, J = 4.8 Hz), 4.53 (d, 1H, J = 5.5 Hz), 1.94 (d, 1H, J =
5.9 Hz), 1.40 (s, 3H), 1.35 (s, 3H); 13C NMR (CDCl3,
100 MHz): δ = 135.1, 134.7, 111.6, 85.8, 84.2, 80.6, 27.1, 25.6;
[α]2D0 +112° (c 0.92, CHCl3). All other analytical data were in
accordance with those given in the literature.35
180.0867; anal. calcd for C7H13Cl2N5O2 (270.12): C, 31.1; H,
4.85; N, 25.9; Cl, 26.25; found: C, 31.1; H, 4.6; N, 26.2; Cl,
26.0%.
(3′aR,4′R,6′aS)-4′,6′a-Dihydro-3′aH-spiro[cyclohexane-1,2′-
cyclopenta[d][1,3]dioxole]-4′-ol (10b). Cyclopentenol 10b was
prepared according to a literature procedure for the enantiomeric
1
form of the title compound.32 The following H NMR data of
the colourless oil obtained after the final step matched with those
1
of the enantiomer described in the literature. H NMR (CDCl3,
400 MHz): δ = 5.88 (m, 2H), 5.02 (dm, 1H, J = 5.50 Hz), 4.74
(t, 1H, J = 5.50 Hz), 4.55 (m, 1H), 2.79 (d, 1H, J = 9.9 Hz),
1.70–1.51 (m, 8H), 1.44–1.33 (m, 2H).
(3aS,4S,6aS)-2,2-Dimethyl-2H,3aH,4H,6aH-cyclopenta[d][1,3]-
dioxol-4-yl 4-nitrobenzoate (11a). 4-Nitrophenylester 11a was
prepared according to a slightly modified procedure of Seley
et al.30 as following: to a solution of 4-nitrobenzoic acid (1.00 g,
6.0 mmol, 2.0 equiv.) and triphenylphosphine (1.57 g,
6.0 mmol, 2.0 equiv.) in 20 mL THF, diethyl azodicarboxylate
(1.05 g, 6.0 mmol, 2.0 equiv.) in 5 mL THF was added dropwise
and stirred at 20 °C for 30 min. Subsequently, a solution of
cyclopentenol 10a29 (0.47 g, 3.0 mmol) in 5 mLTHF was added
and the mixture stirred at 55 °C for 48 h. The solvent was
removed under reduced pressure, and the oily residue was
purified by flash column chromatography on silica gel using
EtOAc–iso-hexane 1 : 10 (Rf = 0.16) yielding 4-nitrophenyl ester
11a (827 mg, 90%) as a colourless solid. Mp: 112–114 °C
(EtOAc–iso-hexane); 1H NMR (CDCl3, 400 MHz): δ = 8.29 (dt,
2H, J = 8.9, 2.1 Hz), 8.20 (dt, 2H, J = 8.9, 2.1 Hz), 6.24 (bd,
1H, J = 5.7 Hz), 6.03 (dm, 1H, J = 5.9 Hz), 5.88 (m, 1H), 5.35
(dq, 1H, J = 5.7, 0.9 Hz), 4.76 (d, 1H, J = 5.7 Hz), 1.47 (s, 3H),
1.39 (s, 3H); 13C NMR (CDCl3, 100 MHz): δ = 164.1, 150.6,
138.3, 135.1, 130.80, 130.75, 123.5, 112.5, 84.7, 83.9, 83.2,
27.2, 25.6; MS (ES+) m/z 328 (100, [M + Na]+); anal. calcd for
C15H15NO6 (305.29): C, 59.0; H, 4.95; N, 4.6; found: C, 59.0;
H, 5.2; N, 4.8%; [α]2D0 +234° (c 0.98, MeOH).
(3′aR,4′S,6′aS)-4′,6′a-Dihydro-3′aH-spiro[cyclohexane-1,2′-
cyclopenta[d][1,3]dioxole]-4′-ol (12b). 4-Nitrophenylester 11b
(3.21 g, 9.3 mmol) was stirred at 20 °C for 18 h in a solution of
NaOH (2.00 g, 50.0 mmol, 5.4 equiv) in 20 mL H2O and
160 mL MeOH. The reaction mixture was concentrated in vacuo
and brine (30 mL) was added to the solution. After extraction
with ethyl ether (3 × 50 mL), the combined organic layers were
dried over MgSO4 and the solvent removed in vacuo to afford
spectroscopically pure 12b (1.75 g, 96%) as a colourless oil,
which was directly used in the following reaction. Rf = 0.29
1
(EtOAc–cyclohexane 1 : 2); H NMR (CDCl3, 400 MHz): δ =
6.04 (bd, 1H, J = 5.7 Hz), 5.90 (ddt, 1H, J = 5.7, 2.3, 0.9 Hz),
5.29 (dm, 1H, J = 5.6 Hz), 4.81 (dm, 1H, J = 6.0 Hz), 4.51 (d,
1H, J = 5.3 Hz), 1.90 (d, 1H, J = 6.2 Hz), 1.69–1.50 (m, 8H),
1.46–1.32 (m, 2H); 13C NMR (CDCl3, 100 MHz): δ = 135.6,
134.6, 112.4, 85.5, 83.8, 81.1, 37.0, 35.1, 25.0, 24.0, 23.7; MS
(EI) m/z 196 (51 [M]+); HRMS (EI) m/z calcd for C11H16O3
196.1099, found 196.1105; [α]2D0 +132° (c 2.5, CH3OH).
(3a′S,4′S,6a′S)-4′,6a′-Dihydro-3a′H-spiro[cyclohexane-1,2′-
cyclopenta[d][1,3]dioxol]-4′-yl 4-nitrobenzoate (11b). To a solu-
tion of 4-nitrobenzoic acid (3.34 g, 20.0 mmol, 1.6 equiv) and
triphenylphosphine (5.25 g, 20.0 mmol, 1.6 equiv) in 60 mL
THF, diazodiethylcarboxylate (3.48 g, 20.0 mmol, 1.6 equiv) in
10 mLTHF was added dropwise and stirred at 20 °C for 30 min.
(3aS,4R,6aS)-4-Bromo-2,2-dimethyl-2H,3aH,4H,6aH-cyclopenta-
[d][1,3]dioxole (13a). Compound 13a was prepared according to
a slightly modified procedure of Diederich et al.31 as following:
to a stirred solution of triphenylphosphine (525 mg, 2.0 mmol,
1.1 equiv) in CH2Cl2 (20 mL), bromine (320 mg, 2.0 mmol,
1.1 equiv) in CH2Cl2 (2 mL) was added dropwise at −10 °C.
The resulting colourless solution was slowly added to a mixture
of cyclopentenol 12a (281 mg, 1.8 mmol) and imidazole
(136 mg, 2.0 mmol, 1.1 equiv) in CH2Cl2 (10 mL) at −10 °C,
the solution stirred for 45 min at −10 °C, and then allowed to
reach room temperature. The reaction mixture was poured into
TBME (50 mL), washed with water (2 × 20 mL), subsequently
with brine (20 mL), filtered, dried over CaCl2, and concentrated
in vacuo. The residue was redissolved in CH2Cl2 (2 mL) and the
solution subsequently added dropwise to iso-hexane (50 mL).
The precipitated TPPO was separated by filtration, thoroughly
washed with iso-hexane, and the filtrate was concentrated
in vacuo. Subsequent flash column chromatography of the oily
residue with iso-hexane–EtOAc 15 : 1 (Rf = 0.45) yielded 13a
Subsequently,
a solution of cyclopentenol 10b (2.50 g,
12.7 mmol) in 10 mL THF was added and the mixture stirred at
55 °C for 48 h. The solvent was removed under reduced
pressure, and the remaining oily residue was purified by flash
column chromatography on silica gel using EtOAc–iso-hexane
1 : 15 yielding 4-nitrophenyl ester 11b (3.45 g, 79%) as a colour-
less solid. Rf = 0.28 (EtOAc–cyclohexane 1 : 15); Mp: 66–71 °C
(iso-hexane); 1H NMR (CDCl3, 400 MHz): δ = 8.29 (dt, 2H, J =
8.9, 2.1 Hz), 8.20 (dt, 2H, J = 8.9, 2.1 Hz), 6.24 (d, 1H, J =
5.7 Hz), 6.02 (dm, 1H, J = 5.9 Hz), 5.88 (m, 1H), 5.35 (dq, 1H,
J = 5.7, 0.9 Hz), 4.77 (d, 1H, J = 5.7 Hz), 1.72–1.52 (m, 8H),
1.46–1.34 (m, 2H); 13C NMR (CDCl3, 100 MHz): δ = 164.1,
150.6, 138.6, 135.2, 130.8, 123.5, 113.3, 84.9, 83.6, 82.7, 37.0,
35.2, 25.0, 23.9, 23.7; MS (ES+) m/z 363 (100, [M + NH4]+);
HRMS (ES+) calcd for C18H19NO6Na 368.1110, found
368.1126; [α]2D0 +123° (c 0.48, CHCl3).
1
(331 mg, 84%) as a yellowish oil. H NMR (CDCl3, 500 MHz):
8666 | Org. Biomol. Chem., 2012, 10, 8660–8668
This journal is © The Royal Society of Chemistry 2012

δ = 5.98 (sm, 2H), 5.33 (sm, 1H), 4.97 (sm, 1H), 4.85 (sm, 1H),
1.39 (s, 3H), 1.35 (s, 3H); 13C NMR (CDCl3, 125.8 MHz): δ =
135.1, 134.2, 112.2, 86.0, 84.1, 54.5, 27.4, 26.3; MS (EI) m/z
205 (92, {M − CH3}+[81Br]), 203 (100, {M − CH3}+[79Br]);
HRMS (EI) calcd for C7H879BrO2 202.9708, found 202.9701;
[α]2D0 −346° (c 0.39, CHCl3).
3H), 1.36 (s, 3H); 13C NMR (CD3OD, 125.8 MHz): δ = 162.7,
154.5, 154.0, 141.0, 128.7, 119.4, 113.6, 109.6, 99.8, 85.6, 81.5,
69.2, 43.4, 27.4, 25.7; MS (ES+) m/z 318 (100, [M + H]+);
HRMS (ES+) m/z calcd for C15H20N5O3 318.1566, found
318.1561; [α]2D0 +88° (c 0.40, MeOH).
A small sample of the monohydrochloride 14a was stirred
with Na2CO3 in MeOH for 30 min, the suspension subsequently
filtered, and finally evaporated to yield the free base as a white
(3aS,4R,6aS)-4-Bromo-4,6a-dihydro-3aH-spiro[cyclohexane-
1,2-cyclopenta[d][1,3]dioxole (13b). To a stirred solution of tri-
phenylphosphine (1.44 g, 5.5 mmol, 1.1 equiv) in CH2Cl2
(50 mL) was added bromine (880 mg, 5.5 mmol, 1.1 equiv) in
CH2Cl2 (10 mL) at −10 °C. A mixture of cyclopentenol 12b
(981 mg, 5.0 mmol) and imidazole (408 mg, 6.0 mmol) was
then added at −10 °C and the solution stirred for 18 h at 20 °C.
The reaction mixture was poured into TBME (100 mL), washed
with water and subsequently with brine, dried over CaCl2, and
evaporated to dryness. The residue was redissolved in CH2Cl2
(20 mL), and the solution was added dropwise to iso-hexane
(100 mL). The resulting precipitate was separated by filtration,
thoroughly washed with iso-hexane, and the filtrate concentrated
in vacuo. Iso-hexane (30 mL) was added again and the solution
separated from residual traces of TPPO. After removal of the
solvent under reduced pressure and subsequent chromatography
on silica gel with EtOAc–cyclohexane (1 : 10), 13b (1.25 g,
96%) was obtained as a yellowish oil. Rf = 0.5 (EtOAc–cyclo-
1
solid. H NMR (CD3OD, 400 MHz): δ = 6.59 (s, 1H), 5.90 (dt,
1H, J = 5.7, 1.4 Hz), 5.85 (dm, 1H, J = 5.7 Hz), 5.25 (dm, 1H, J =
5.7 Hz), 4.58 (d, 2H, J = 5.7 Hz), 3.91 (d, 2H, J = 13.3 Hz), 3.76
(m, 1H), 3.75 (d, 2H, J = 13.3 Hz), 1.33 (s, 3H), 1.32 (s, 3H).19,24
5-({[(3′aR,4′S,6′aS)-4′,6′a-Dihydro-3′aH-spiro[cyclohexane-
1,2′-cyclopenta[d][1,3]dioxole]-4′-yl]amino}methyl)-2-amino-
3H,4H,7H-pyrrolo[2,3-d]pyrimidin-4-one hydrochloride (14b).
Following the procedure for the corresponding acetonide 14a,
reaction of 1 (540 mg, 2.0 mmol) with bromocyclopentene 13b
(490 mg, 2.5 mmol, 1.3 equiv) yielded 491 mg (69%) of 14b as
a white solid, which was further purified through recrystallization
from MeOH. Rf = 0.24 (EtOAc–MeOH–TEA 3 : 1 : 0.01); Mp:
>250 °C (MeOH, decomp.); 1H NMR (CD3OD, 400 MHz):
δ = 6.88 (s, 1H), 6.31 (dm, 1H, J = 5.7 Hz), 5.99 (dm, 1H, J =
4.8 Hz), 5.33 (dm, 1H, J = 5.0 Hz), 4.40 (d, 2H, J = 13.7 Hz),
4.33 (d, 2H, J = 13.5 Hz), 4.33 (m, 1H), 1.66–1.53 (m, 8H),
1
1
hexane 1 : 10); H NMR (CDCl3, 400 MHz): δ = 6.01–5.95 (m,
1.45–1.35 (m, 2H); H NMR (DMSO-d6, 400 MHz): δ = 11.28
2H), 5.33 (dm, 1H, J = 5.5 Hz), 4.96 (d, 1H, J = 5.5 Hz), 4.86
(t, 1H, J = 1.8 Hz), 1.62–1.52 (m, 8H), 1.43–1.33 (m, 2H);
13C NMR (CDCl3, 100 MHz): δ = 135.3, 134.1, 112.9, 85.5, 83.7,
54.8, 37.2, 35.7, 24.9, 23.9, 23.7; MS (EI) m/z 260 (14 {M}+[81Br]),
258 (18, {M}+[79Br]); HRMS (EI) m/z calcd for C11H1579Br O2
258.0256, found 258.0239; [α]2D0 −325° (c 1.5, CHCl3).
(bs, 1H), 10.79 (bs, 1H), 9.38 (bs, 1H), 6.84 (s, 1H), 6.35
(bs, 2H), 6.29 (d, 1H, J = 5.5 Hz), 5.98 (d, 1H, J = 4.8 Hz), 5.27
(d, 1H, J = 5.0 Hz), 4.84 (d, 1H, J = 5.7 Hz), 4.24 (m, 3H),
1.60–1.43 (m, 8H), 1.39–1.27 (m, 2H); 13C NMR (CD3OD,
100 MHz): δ = 162.5, 154.4, 153.8, 139.4, 130.6, 118.8, 113.8,
111.9, 99.9, 85.3, 82.0, 69.4, 43.7, 38.1, 36.0, 26.1, 25.0, 24.8; MS
(ES+) m/z 358 (100, [M + H]+); HRMS (ES+) m/z calcd for
C18H24N5O3 358.1879, found 358.1872; [α]2D0 +94° (c 0.4, MeOH).
The free base of 14b was obtained as described for the corres-
ponding acetonide derivative 14a. 1H NMR (CD3OD,
400 MHz): δ = 6.65 (s, 1H), 5.92 (dt, 1H, J = 5.7, 1.6 Hz), 5.84
(dm, 1H, J = 5.7 Hz), 5.23 (dq, 1H, J = 5.7, 0.7 Hz), 4.55 (d,
1H, J = 5.7 Hz), 3.92 (dd, 1H, J = 13.3, 0.7 Hz), 3.78 (dd, 1H,
J = 13.3, 0.7 Hz), 3.77 (m, 1H,), 1.62–1.50 (m, 8H), 1.44–1.32
(bs, 2H); [α]2D0 +105° (c 0.3, MeOH).
2-Amino-5({[(3a′R,4′S,6a′S)-2,2-dimethyl-4,6a′-dihydro-3a′H-
cyclopenta[d][1,3]dioxol-4-yl]amino}methyl)-3,7-dihydro-4H-
pyrrolo[2,3-d]pyrimidin-4-one hydrochloride (14a). To a sus-
pension of 1 (378 mg, 1.4 mmol) in DMF (5 mL), DBU (2 mL,
13.4 mmol, 9.6 equiv.) was added and the mixture stirred at
room temperature for 10 min. The resulting dark, clear solution
was heated to 50 °C, after which a solution of protected bromo-
cyclopentene 13a (438 mg, 2.0 mmol, 1.4 equiv.) in DMF
(1 mL) was added dropwise under an argon atmosphere. After
stirring for 5 h at 65 °C, the reaction mixture was concentrated
under reduced pressure. The residual dark brown oil was re-dis-
solved in MeOH (3 mL) and subjected to a silica gel column.
Less-polar impurities were eluted starting with EtOAc, followed
by a solvent mixture of EtOAc–MeOH–TEA 10 : 1 : 0.1. The
product-containing fractions, which also consisted of the result-
ing DBU-hydrohalide salts, were obtained eluting with EtOAc–
MeOH–TEA 3 : 1 : 0.01. Subsequent removal of the solvent gave
rise to 550 mg of a beige solid which was triturated with CHCl3
(150 mL) through stirring for 10 min. The suspension was
filtered, the residue thoroughly washed with CHCl3, and finally
dried in vacuo rendering 14a (367 mg, 74%) as almost a white
solid. Rf = 0.21 (EtOAc–MeOH–TEA 3 : 1 : 0.01); Mp: >250 °C
2-Amino-5({[(1S,4S,5R)-4,5-dihydroxycyclopent-2-en-1-yl]amino}-
methyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one dihydro-
chloride hydrate (2). Acetonide 14a (353 mg, 1.0 mmol) was
refluxed in a methanolic solution of 1.25 M HCl (60 mL) for
5 h. The solution was evaporated to complete dryness yielding 2
(349 mg, 95%) as almost a white solid. The corresponding
cyclohexylidene-protected derivative 14b yielded 334 mg (91%)
of 2 from a 1.0 mmol reaction. Mp: >250 °C (decomp.);
1H NMR (CD3OD, 400 MHz): δ = 6.97 (s, 1H), 6.25 (dt, 1H,
J = 6.2, 2.1 Hz), 6.06 (dd, 1H, J = 6.2, 1.6 Hz), 4.60 (dt, 1H, J =
5.7, 1.6 Hz), 4.55 (d, 1H, J = 13.8 Hz), 4.43 (d, 1H, J =
1
13.8 Hz), 4.31 (t, 1H, J = 5.7 Hz), 4.22 (sm, 1H); H NMR
(D2O, 400 MHz): δ = 6.98 (s, 1H), 6.24 (dt, 1H, J = 6.4,
2.1 Hz), 6.06 (dd, 1H, J = 6.3, 1.6 Hz), 4.65 (dm, 1H, J =
5.7 Hz), 4.47 (d, 1H, J = 13.7 Hz), 4.39 (d, 1H, J = 13.7 Hz),
4.36 (t, 1H, J = 5.7 Hz), 4.26 (sm, 1H); 13C NMR (CD3OD,
125.8 MHz): δ = 161.0, 153.4, 145.8, 139.7, 129.8, 120.7,
1
(MeOH, decomp.); H NMR (CD3OD, 400 MHz): δ = 6.88 (s,
1H), 6.30 (dt, 1H, J = 5.7, 1.4 Hz), 6.00 (dm, 1H, J = 5.7 Hz),
5.34 (dm, 1H, J = 5.7 Hz), 4.91 (d, 1H, J = 5.7 Hz), 4.39 (d, 1H,
J = 13.7 Hz), 4.33 (d, 1H, J = 13.1 Hz), 4.31 (m, 1H), 1.37 (s,
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 8660–8668 | 8667

110.6, 100.3, 75.2, 74.4, 68.5, 43.0; MS (ES+) m/z 278 (100,
[M + H]+); HRMS (ES+) m/z calcd for C12H16N5O3 278.1253,
found 278.1254; anal. calcd for C12H17Cl2N5O3*H2O (368.22):
C, 39.1; H, 5.2; N, 19.0; found: C, 39.3; H, 4.8; N, 19.1%;
[α]2D0 +117° (c 0.30, H2O).26
Acknowledgements
We thank Prof. Dr W. E. Diederich, Marburg, for many helpful
discussions supporting this work.
(3aS,4R,6aR)-2,2-Dimethyl-2H,3aH,4H,6aH-cyclopenta[d][1,3]-
dioxol-4-ol (15). Cyclopentenol 15 was prepared according to a
Notes and references
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1
literature procedure.33 Rf = 0.24 (EtOAc–iso-hexane 1 : 2); H
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(dm, 1H, J = 5.7 Hz), 5.29 (d, 1H, J = 5.5 Hz), 4.80 (bs, 1H),
4.53 (d, 1H, J = 5.7 Hz), 1.93 (d, 1H, J = 5.5 Hz), 1.40 (s, 3H),
1.35 (s, 3H); [α]2D0 −117° (c 0.98, CHCl3). All other analytical
data were in accordance with those given in the literature.
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(3aR,4S,6aR)-4-Bromo-2,2-dimethyl-2H,3aH,4H,6aH-cyclopenta-
[d][1,3]dioxole (16). Compound 16 was prepared according to
the previously described procedure for the enantiomeric bromo-
cyclopentene 13a. 312 mg (79%) of
a colourless oil
were obtained from a 1.8 mmol reaction. 1H NMR (CDCl3,
500 MHz): δ = 5.99 (sm, 2H), 5.33 (sm, 1H), 4.97 (sm, 1H),
4.85 (sm, 1H), 1.39 (s, 3H), 1.36 (s, 3H); MS (EI) m/z 205 (83,
{M − CH3}+[81Br]), 203 (89, {M − CH3}+[79Br]); HRMS (EI)
calcd for C7H879BrO2 202.9708, found 202.9708; [α]2D0 +349°
(c 0.96, CHCl3).
2-Amino-5({[(3a′S,4′R,6a′R)-2,2-dimethyl-4,6a′-dihydro-3a′H-
cyclopenta[d][1,3]dioxol-4-yl]amino}methyl)-3,7-dihydro-4H-
pyrrolo[2,3-d]pyrimidin-4-one hydrochloride (17). Acetonide 17
was prepared according to the procedure for 14a. 237 mg (67%)
were obtained from a 1.0 mmol reaction. Mp: >250 °C
(decomp.); 1H NMR (CD3OD, 400 MHz): δ = 6.89 (s, 1H), 6.30
(dt, 1H, J = 5.7, 1.6 Hz), 6.00 (dm, 1H, J = 5.7 Hz), 5.35 (dm,
1H, J = 5.7 Hz), 4.92 (d, 1H, J = 5.7 Hz), 4.40 (d, 1H, J =
13.8 Hz), 4.33 (d, 1H, J = 13.5 Hz), 4.32 (m, 1H), 1.37 (s, 3H),
1.36 (s, 3H); 13C NMR (CD3OD, 125.8 MHz): δ = 162.6, 154.5,
154.0, 141.0, 128.7, 119.4, 113.6, 109.6, 99.7, 85.6, 81.5, 69.1,
43.3, 27.4, 25.7; MS (ES+) m/z 318 (100, [M + H]+); HRMS
(ES+) m/z calcd for C15H20N5O3 318.1566, found 318.1561;
[α]2D0 −92° (c 0.40, MeOH).
2-Amino-5({[(1R,4R,5S)-4,5-dihydroxycyclopent-2-en-1-yl]-
amino}methyl)-3,7-dihydro-4H-pyrrolo[2,3-d]pyrimidin-4-one
dihydrochloride hydrate (3). Compound 3 was prepared accord-
ing to the procedure for 2. From a 0.5 mmol reaction, 3
(168 mg, 91%) was obtained as almost a white solid. Mp:
>250 °C (decomp.); 1H NMR (CD3OD, 400 MHz): δ = 6.98
(s, 1H), 6.25 (dt, 1H, J = 6.2, 2.1 Hz), 6.05 (dd, 1H, J = 6.4,
1.6 Hz), 4.61 (dm, 1H, J = 6.2 Hz), 4.52 (d, 1H, J = 14.0 Hz),
4.40 (d, 1H, J = 13.7 Hz), 4.30 (t, 1H, J = 5.7 Hz), 4.21 (sm,
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1
1H); H NMR (D2O, 400 MHz): δ = 6.98 (s, 1H), 6.24 (ddd,
1H, J = 6.3, 2.5, 2.1 Hz), 6.06 (dd, 1H, J = 6.2, 1.4 Hz), 4.65
(dm, 1H, J = 5.7 Hz), 4.47 (d, 1H, J = 14.0 Hz), 4.39 (d, 1H,
J = 14.2 Hz), 4.36 (t, 1H, J = 5.5 Hz), 4.26 (dq, 1H, 5.5,
1.6 Hz); 13C NMR (CD3OD, 125.8 MHz): δ = 161.2, 153.6,
139.8, 144.5, 129.8, 120.3, 110.6, 100.3, 75.5, 74.4, 68.5, 43.2;
13C NMR (D2O, 125.8 MHz): δ = 161.2, 152.6, 145.5, 138.8,
129.8, 120.9, 109.6, 99.8, 74.5, 73.9, 67.6, 42.6; MS (ES+) m/z
278 (100, [M + H]+); HRMS (ES+) m/z calcd for C12H16N5O3
278.1253, found 278.1281; [α]2D0 −111° (c 0.30, H2O).
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41–43, 82481 Mittenwald, Germany.
35 H. Ovaa, B. Lastdrager, J. D. C. Codee, G. A. van der Marel,
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8668 | Org. Biomol. Chem., 2012, 10, 8660–8668
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