Synthesis of a xylo-puromycin analogue

Article abstract of DOI:10.1055/s-2008-1078025

N⁶-Bis-demethylated xylo-puromycin analogue 2 was synthesized over six steps in 56% yield from adenosine 3, involving a Mattocks bromoacetylation, a regio- and stereoselective ribo-epoxide ring opening with sodium azide and an efficient Staudin

Full text of DOI:10.1055/s-2008-1078025

LETTER
2461
Synthesis of a xylo-Puromycin Analogue
Synthesis of
a
xy
e
nin Analogueoît Y. Michel, Kollappillil S. Krishnakumar, Peter Strazewski*
Laboratoire de Synthèse de Biomolécules, CNRS, Institut de Chimie et Biochimie Moléculaires et Supramoléculaires (UMR 5246),
Université Claude Bernard Lyon 1, F-69622 Villeurbanne Cedex, France
E-mail: strazewski@univ-lyon1.fr
Received 12 June 2008
NMe2
Abstract: N6-Bis-demethylated xylo-puromycin analogue 2 was
N
N
OMe
NH2
N
synthesized over six steps in 56% yield from adenosine 3, involving
a Mattocks bromoacetylation, a regio- and stereoselective ribo-ep-
oxide ring opening with sodium azide and an efficient Staudinger–
Vilarrasa reaction to couple the amino acid to an azide precursor.
H2N
O
HO
N
O
N
N
N
N
NH
HO
NH OH
Key words: coupling, epoxides, nucleosides, amides, malaria
O
O
OH
OMe
H2N
The natural antibiotic nucleoside puromycin (1) first iso-
lated from Streptomyces alboniger1 has been used to ap-
proach and to clear up the understanding of the
mechanism of protein biosynthesis.2 Its structural similar-
ity to the 3¢-terminal 3¢-O-aminoacyl adenylate moiety of
aminoacyl-tRNA explains its activity in the ribosomal A
site causing the inhibition of the protein synthesis by
transferring the ribosomal nascent polypeptide chain to
puromycin’s a-amino group.3
2
1
Figure 1 Puromycin (1) and N6-bis-demethylated xylo-analogue 2
der mildly acidic aqueous conditions5z to yield the xylo-
azido alcohol 6 which was coupled to an N-protected L-
amino acid oxybenzotriazolyl ester via the Staudinger–
Vilarrasa reaction. Various azide reducing conditions us-
ing the commercial phosphines PMe2Ph, PMePh2, PBu3
and PMe3 were tested for the efficiency and practicality of
the coupling reaction. We justify our preferred use of
PMe3 (1 M in THF) by the weakest steric hindrance of the
corresponding in situ formed iminophosphorane and the
practical volatility of trimethylphosphine oxide. This alle-
viated possible co-migration problems upon chromatogra-
phy over silica and therefore led to the best isolated yields
of pure amide.
Besides, it has been demonstrated that some puromycin
analogues presented promising antitrypanosomal and an-
timalarial activities.4 Numerous syntheses of puromycin
analogues5 and similar nucleosides6 have been reported
that differ from 1, for example, by the configuration of a
substituent, thus, ara-puromycin5a and L,L-puromycin5e
analogues were synthesized. However, an inversion of the
configuration of the carbon atom carrying the amino acid
chain has never been envisaged. Hence, in order to test
whether the stereochemistry of the N-aminoacyl chain
could play a significant role in the antimalarial activity,
we decided to synthesize the N6-bis-demethylated xylo-
puromycin (2; Figure 1).
A comparative study of the difference in reactivity be-
tween this iminophosphorane and the nucleobase’s ami-
dine function towards the activated ester is likewise
depicted in Scheme 1. The Staudinger–Vilarrasa coupling
proved more efficient for the azide 7, where the N6-ami-
dine function was protected as a dibutylformamidine
(dbf),10a than for the less protected azido amidine 9 (83%
versus 60% optimized and isolated yields). The main as-
sets of the dbf protection are the facile and efficient prep-
aration and cleavage10 and, most importantly, it can be
used in the presence of numerous groups, such as hydrox-
yl, azido as well as many usual organic functions, contrary
to a number of other common amino protecting groups.11
Target compound 2 has been obtained in six steps from
adenosine (3; Scheme 1) beginning with the Moffatt
methodology7 for the stereospecific synthesis of the ribo-
epoxide 5 via vicinal trans-bromoacetate intermediates
obtained by a Mattocks bromoacetylation reaction.8 This
approach involves, in addition, a regio- and stereoselec-
tive epoxide ring opening and finally, as a key step in this
reaction sequence, an efficient Staudinger–Vilarrasa ami-
no acid coupling5x for which the conditions have been fur-
ther optimized.
Finally, both coupled products 8 and 9 were completely
deprotected with methyl amine followed in situ by a warm
NH4F treatment in THF.12 The use of TBAF for desilyla-
tion led after chromatography over silica to contamination
of the final polar product with the tetrabutylammonium
cation.
We started with adenosine (3) from which ribo-epoxide 4
was generated (Scheme 1).7 The primary alcohol group
was protected with a bulky silyl group.9,5u Epoxide 5 was
regio- and stereoselectively opened with sodium azide un-
In view of the shortness of this synthetic route we envis-
aged synthesizing the N6-bis-demethylated naturally con-
SYNLETT 2008, No. 16, pp 2461–2464
Advanced online publication: 10.09.2008
x
x
.x
x
.2
0
0
8
DOI: 10.1055/s-2008-1078025; Art ID: G21008ST
© Georg Thieme Verlag Stuttgart · New York

2462
B. Y. Michel et al.
LETTER
NH2
NH2
N
NH2
N
O
N
N
N
N
N
N
Br
O
HO
HO
TBDPSO
N
N
N
N
O
O
O
O
O
O
i) a)
, MeCN/H2O
ii) TBDPSCl
py., 100%
b) DOWEX HO–, 91%
OH OH
NBu2
3
4
5
N
NH2
N
N
N
N
N
N3
TBDPSO
N
N3
TBDPSO
N
iii) NaN3, NH4Cl, DMF/H2O,
N
N
iv)
O
O
MeO OMe
MeOH, r.t., 1 h, 98%
78–80 °C, 80%
OH
OH
6
7
vii) a) Fmoc-Tyr(Me)-OH, HOBt,
DIC, 0 °C
v) a) Fmoc-Tyr(Me)-OH,
HOBt, DIC, 0 °C
b) 7, PMe3, THF, r.t.,
overnight, 83%
b) 6, PMe3, THF, r.t., overnight,
55–60%
FmocHN
FmocHN
O
H2N
OMe
NH2
OMe
Ndbf
OMe
NH2
O
O
N
N
N
N
N
N
N
N
NH
NH
NH
viii) a) MeNH2, EtOH, r.t., overnight
vi) a) MeNH2, EtOH, r.t., overnight
TBDPSO
TBDPSO
HO
N
N
N
N
O
O
O
b) NH4F, THF, 55 °C, 4 h, 98%
b) NH4F, THF, 55 °C, 4 h, 95%
8
9
2
OH
OH
OH
Scheme 1 Mattocks–Moffatt bromoacetylation (ia), Moffatt epoxidation (ib), regio- and stereoselective epoxide ring opening with azide (iii)
and chemoselective Staudinger–Vilarrasa coupling (v and vii) as the key steps of the synthesis of 2
NH2
NH2
N
N
N
N
N
TBDPSO
TBDPSO
N
N
Me2BBr, Et3N,
CH2Cl2, –78 °C, 1 h
N
Br
O
O
O
96%
OH
5
10
Scheme 2 Epoxide ring opening according to Samano and Robins9
figured puromycin analogue. Thus, following to the Supporting Information for this article is available online at
approach of Samano and Robins,9,5u ribo-epoxide 5 was http://www.thieme-connect.com/ejournals/toc/synlett.
regio- and stereoselectively opened with Me2BBr to af-
ford the xylo-bromo alcohol 10 (Scheme 2). We then at-
tempted to carry out an SN2 reaction with sodium azide in
Acknowledgment
We gratefully acknowledge D. Bouchu and C. Duchamp for mass
spectrometry results, and, B. Fenet and C. Gilbert for NMR analy-
ses. B. Y. Michel and Krishnakumar K. S. are thankful to the Mini-
stère de la Recherche and the European Union consortium of
position 2¢. Not too surprisingly, we obtained, alas, azide
6 in 79% isolated yield which formed from epoxide 5 that
was reformed in situ in DMF at 75 °C despite the presence
of excess NaN3.
SynthCells (FP6-2005-NEST-Pathfinder STREP #043359: http://
www.synthcells.org) for their graduate fellowships.
To conclude, this synthesis is a combination of the Mof-
fatt’s approach, to obtain the ribo-epoxide, and our own
coupling protocol, the Staudinger–Vilarrasa coupling re-
action, linked through a regio- and stereoselective epoxide
ring opening procedure.13 It is hitherto the shortest and
highest yielding synthesis of a 6-N,N-bis-demethyl puro-
mycin analogue which was obtained in 56% or 39–43%
overall yield over six or five steps, respectively, from
adenosine. This route could be used for a series of similar
derivatives if 2 were shown to present some interesting bi-
ological activity.
References and Notes
(1) Porter, J. N.; Hewitt, R. I.; Hesseltine, C. W.; Krupka, G.;
Lowery, J. A.; Wallace, W. S.; Bohonos, N.; Williams, J. H.
Antibiot. Chemother. 1952, 2, 409.
(2) (a) Suhadolnik, R. J. Nucleoside Antibiotics; Wiley-
Interscience: New York, 1970, 1–50. (b) Suhadolnik, R. J.
Nucleosides as Biological Probes; Wiley: New York, 1979,
96–102.
Synlett 2008, No. 16, 2461–2464 © Thieme Stuttgart · New York

LETTER
Synthesis of a xylo-Puromycin Analogue
2463
(3) (a) Yarmolinski, M. B.; De la Haba, G. L. Proc. Natl. Acad.
Sci. U.S.A. 1959, 45, 1721. (b) Allen, D. W.; Zamecnik,
P. C. Biochim. Biophys. Acta 1962, 55, 865. (c) Nathans,
D.; Neidle, A. Nature (London) 1963, 197, 1076.
(7) (a) Greenberg, S.; Moffatt, J. G. J. Am. Chem. Soc. 1973, 95,
4016. (b) Russell, A. F.; Greenberg, S.; Moffatt, J. G. J. Am.
Chem. Soc. 1973, 95, 4025.
(8) (a) Mattocks, A. R. J. Chem. Soc. 1964, 1918.
(d) Gilbert, W. J. Mol. Biol. 1963, 6, 389. (e) Symons,
R. H.; Harris, R. J.; Clarke, L. P.; Wheldrake, J. F.; Elliott,
W. H. Biochim. Biophys. Acta 1969, 179, 248.
(b) Mattocks, A. R. J. Chem. Soc. 1964, 4840.
(9) Samano, M. C.; Robins, M. J. Tetrahedron Lett. 1989, 30,
2329.
(4) (a) Bohonos, N.; Williams, J. H. Antibiot. Chemother. 1952,
2, 409. (b) Hewitt, R. I.; Wallace, W. S.; Gumble, A.; White,
E.; Williams, J. H. Am. J. Trop. Hyg. 1954, 3, 225.
(c) Vince, R.; Lee, H.; Narang, A. S.; Shirota, F. N. J. Med.
Chem. 1981, 24, 1511. (d) Vara, J. A.; Portela, A.; Jiménez,
A. Nucleic Acids Res. 1986, 14, 4617. (e) De La Luna, S.;
Soria, I.; Pulido, D.; Ortin, J.; Jiménez, A. Gene 1988, 62,
121. (f) Ekong, R. M.; Kirby, G. C.; Patel, G.; Phillipson,
J. D.; Warhurst, D. C. Biochem. Pharmacol. 1990, 40, 297.
(g) Mielke, C.; Tummler, J.; Bode, J. Trends Genet. 1995,
11, 258.
(5) (a) Baker, B. R.; Joseph, J. P.; Williams, J. H. J. Am. Chem.
Soc. 1955, 77, 1. (b) Baker, B. R.; Schaub, R. E.; Williams,
J. H. J. Am. Chem. Soc. 1955, 77, 7. (c) Baker, B. R.;
Schaub, R. E.; Joseph, J. P.; Williams, J. H. J. Am. Chem.
Soc. 1955, 77, 12. (d) Baker, B. R.; Schaub, R. E.; Kissman,
H. M. J. Am. Chem. Soc. 1955, 77, 5911. (e) Gerber, N. N.;
Lechevalier, H. A. J. Org. Chem. 1962, 27, 1731.
(10) (a) Froehler, B. C.; Matteucci, M. D. Nucleic Acids Res.
1983, 11, 8031. (b) McBride, L. J.; Kierzek, R.; Beaucage,
S. L.; Caruthers, M. H. J. Am. Chem. Soc. 1986, 108, 2040.
(11) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; John Wiley & Sons, Inc.: New York,
1999.
(12) Zhang, W.; Robins, M. J. Tetrahedron Lett. 1992, 33, 1177.
(13) 9-(3¢-Azido-5¢-O-tert-butyldiphenylsilyl-3¢-deoxy-b-D-
xylofuranos-1-yl)adenine (6): To a stirred solution of 5 (52
mg, 0.11 mmol) in DMF (1 mL), were added NaN3 (42 mg,
0.69 mmol) and H2O (0.3 mL). The reaction mixture was
precisely warmed to 78–80 °C for 20 h, then quenched with
sat. NaHCO3 solution and diluted with EtOAc. The layers
were separated and the aqueous portion was washed with
EtOAc (3 ×). The combined organic extracts were washed
with 10% aq LiCl (3 ×) to remove the residual DMF, washed
once with brine, dried over anhyd MgSO4, filtered and
concentrated in vacuo. The resulting residue was purified by
silica gel column chromatography (EtOAc–toluene, 1:1, 3:1,
5:1, 7:1; EtOAc–toluene–MeOH, 7:1:0.5) to afford 6 as a
white solid (47 mg, 80%); mp 181 °C (uncorrected); Rf 0.40
(EtOAc–toluene, 4:1). 1H NMR (300 MHz, DMSO-d6): d =
0.99 (s, 9 H, Si-t-Bu), 3.88 (dd, 1 H, 2J = 11.0 Hz, 3J = 4.5
Hz, HA5¢), 4.00 (dd, 1 H, 2J = 11.0 Hz, 3J = 3.9 Hz, HB5¢),
4.46 (m, 1 H, H3¢), 4.48 (m, 1 H, H4¢), 4.82 (q ‘ddd’, 1 H,
3J = 3.9, 4.5 Hz, H2¢), 5.91 (d, 1 H, 3J = 4.5 Hz, H1¢), 6.36
(d, 1 H, 3J = 5.1 Hz, OH), 7.33 (br s, 2 H, NH2), 7.36–7.46
(m, 6 H, H-m-Ar, H-p-Ar), 7.61–7.66 (m, 4 H, H-o-Ar), 8.13
(s, 1 H, H8), 8.15 (s, 1 H, H2). 13C NMR (75 MHz, DMSO-
d6): d = 18.8 (SiCMe3), 26.6 [3 × C, SiCMe3], 63.0 (C5¢),
66.0 (C3¢), 77.0 (C2¢), 79.3 (C4¢), 87.6 (C1¢), 118.9 (C5),
127.9, 128.0 (4 × C, C-m-SiPh), 130.0 (2 × C, C-p-SiPh),
132.5, 132.8 (2 × C, C-i-SiPh), 135.0, 135.1 (4 × C, C-o-
SiPh), 138.9 (C8), 149.4 (C4), 152.8 (C2), 156.0 (C6).
HRMS (ESI+): m/z [M + H]+ calcd for C26H30N8O3Si
(530.65): 531.2288; found: 531.2285.
(f) Guarino, A. J.; Kredich, N. M. Biochim. Biophys. Acta
1963, 68, 317. (g) Sowa, W. Can. J. Chem. 1968, 46, 1586.
(h) Fisher, L. V.; Lee, W. W.; Goodman, L. J. Med. Chem.
1970, 13, 775. (i) Mengel, R.; Wiedner, H. Chem. Ber. 1976,
109, 433. (j) Okruszek, A.; Verkade, J. G. J. Med. Chem.
1979, 22, 882. (k) Ozols, A. M.; Azhayev, A. V.; Dyatkina,
N. B.; Krayevsky, A. A. Synthesis 1980, 557. (l) Ozols,
A. M.; Azhayev, A. V.; Krayevsky, A. A.; Ushakov, A. S.;
Gnuchev, N. V.; Gottikh, B. P. Synthesis 1980, 559.
(m) Saneyoshi, M.; Nishizaka, H.; Katoh, N. Chem. Pharm.
Bull. 1981, 29, 2769. (n) Vince, R.; Lee, H.; Narang, A. S.;
Shirota, F. N. J. Med. Chem. 1981, 24, 1511. (o) Lee, H.;
Fong, K.-L.; Vince, R. J. Med. Chem. 1981, 24, 304.
(p) Visser, G. M.; Schattenkerk, C.; Van Boom, J. H. Recl.
Trav. Chim. Pays-Bas 1984, 103, 165. (q) Vince, R.;
Daluge, S.; Brownwell, J. J. Med. Chem. 1986, 29, 2400.
(r) Motawia, M. S.; Meldal, M.; Sofan, M.; Stein, P.;
Pedersen, E. B.; Nielsen, C. Synthesis 1995, 265.
(s) McDonald, F. E.; Gleason, M. M. J. Am. Chem. Soc.
1996, 118, 6648. (t) Botta, O.; Strazewski, P. Nucleosides
Nucleotides 1999, 18, 721. (u) Robins, M. J.; Miles, R. W.;
Samano, M. C.; Kaspar, R. L. J. Org. Chem. 2001, 66, 8204.
(v) Nguyen-Trung, N. Q.; Botta, O.; Terenzi, S.; Strazewski,
P. J. Org. Chem. 2003, 68, 2038. (w) Gilbert, C. L. K.;
Lisek, C. R.; White, R. L.; Gumina, G. Tetrahedron 2005,
61, 8339. (x) Chapuis, H.; Strazewski, P. Tetrahedron 2006,
62, 12108. (y) Takatsuki, K.; Ohgushi, S.; Kohmoto, S.;
Kishikawa, K.; Yamamoto, M. Nucleosides, Nucleotides
Nucleic Acids 2006, 25, 719. (z) Charafeddine, A.; Dayoub,
W.; Chapuis, H.; Strazewski, P. Chem. Eur. J. 2007, 13,
5566.
9-(3¢-Azido-5¢-O-tert-butyldiphenylsilyl-3¢-deoxy-b-D-
xylofuranos-1-yl)-6-N-(di-n-butylamino)methylene-
adenine (7): Beforehand co-evaporated with toluene (3 × 2
mL), the azido compound 6 (243 mg, 0.46 mmol) was
dissolved in anhyd MeOH (1.2 mL). N,N-Di-n-
butylformamide dimethylacetal5z (196 mg, 0.96 mmol) was
added and the reaction mixture was slightly warmed for a
few seconds with a heat gun every 15 min and stirred for 1
h. The volatiles were removed under reduced pressure and
the residue was purified by silica gel column
chromatography (EtOAc–cyclohexanes, 1:1, 2:1, 3:1, 4:1,
5:1) to yield 7 (301 mg, 98%) as a colorless oil; Rf 0.63
(EtOAc–cyclohexanes, 5:1). 1H NMR (300 MHz, CDCl3): d
= 0.94–0.97 [m, 6 H, N(CH2CH2CH2CH3)2], 0.96 (s, 9 H, Si-
t-Bu), 1.30–1.46 [m, 4 H, N(CH2CH2CH2CH3)2], 1.59–1.72
[m, 4 H, N(CH2CH2CH2CH3)2], 3.40 [t, 2 H, 3J = 7.4 Hz,
N(CH2CH2CH2CH3)2], 3.61–3.79 [m, 2 H,
(6) (a) De Koning-Ward, T. F.; Waters, A. P.; Crabb, B. S. Mol.
Biochem. Parasit. 2001, 117, 155. (b) Kicska, G. A.; Tyler,
P. C.; Evans, G. B.; Furneaux, R. H. J. Biol. Chem. 2002,
277, 3219. (c) Kicska, G. A.; Tyler, P. C.; Evans, G. B.;
Furneaux, R. H. J. Biol. Chem. 2002, 277, 3226.
N(CH2CH2CH2CH3)2], 3.87 (dd, 1 H, 2J = 10.8 Hz, 3J = 4.8
Hz, HA5¢), 3.94 (dd, 1 H, 2J = 10.8 Hz, 3J = 5.4 Hz, HB5¢),
4.37 (dd, 1 H, 3J = 4.7, 5.1 Hz, H3′), 4.54 (pseudo q ‘ddd’, 1
H, 3J = 4.8, 5.1, 5.4 Hz, H4¢), 4.81 (pseudo t, 1 H, 3J = 4.1,
4.7 Hz, H2¢), 5.91 (d, 1 H, 3J = 4.1 Hz, H1¢), 6.46 (br s, 1 H,
OH), 7.32–7.42 (m, 6 H, H-m-Ar, H-p-Ar), 7.62–7.65 (m, 4
H, H-o-Ar), 8.05 (s, 1 H, H8), 8.41 (s, 1 H, H2), 9.01 (s, 1 H,
(d) Weisman, J. L.; Liou, A. P.; Shelat, A. A.; Cohen, F. E.;
Guy, R. K.; DeRisi, J. L. Chem. Biol. Drug. Des. 2006, 67,
409. (e) Herforth, C.; Wiesner, J.; Heidler, P.; Sanderbrand,
S.; Van Calenbergh, S.; Jomaa, H.; Link, A. Bioorg. Med.
Chem. 2004, 12, 755. (f) Hirsch, A. K. H.; Diederich, A. F.
Chimia 2008, 62, 226.
Synlett 2008, No. 16, 2461–2464 © Thieme Stuttgart · New York

2464
B. Y. Michel et al.
LETTER
19.0 [SiCMe3], 19.7, 20.2 [2 × C, N(CH2CH2CH2CH3)2],
N=CHNBu2). 13C NMR (75 MHz, CDCl3): d = 13.6, 13.9 [2
× C, N(CH2CH2CH2CH3)2], 19.0 (SiCMe3), 19.7, 20.1 [2 ×
C, N(CH2CH2CH2CH3)2], 26.7 (3 × C, SiCMe3), 29.2, 30.9
[2 × C, N(CH2CH2CH2CH3)2], 45.3, 52.0 [2 × C,
N(CH2CH2CH2CH3)2], 62.1 (C5¢), 66.2 (C3¢), 79.5 (C2¢),
81.3 (C4¢), 90.9 (C1¢), 125.8 (C5), 127.7 (4 × C, C-m-SiPh),
129.8 (2 × C, C-p-SiPh), 132.7 (2 × C, C-i-SiPh), 135.5 (4 ×
C, C-o-SiPh), 139.5 (C8), 150.4 (C4), 152.0 (C2), 158.8
(N=CHNBu2), 159.9 (C6). HRMS (ESI+): m/z [M + H]+
calcd for C35H47N9O3Si (669.89): 670.3644; found:
26.7 (3 × C, SiCMe3), 29.2, 30.9 [2 × C, N(CH2CH2CH2CH3)2],
38.4 (Cb), 45.4 [N(CH2CH2CH2CH3)2], 47.1 (CH aliph. Fl.),
52.0 [N(CH2CH2CH2CH3)2], 55.0 (OMe), 56.7 (C3¢), 57.2
(Ca), 62.6 (C5¢), 66.9 (CH2Fl.), 80.3 (C2¢), 80.3 (C4¢), 91.6
(C1¢), 113.8 [2 × C, C-o-Ph(OMe)], 119.9 (2 × C, C-m4-Fl.),
125.0 (2 × C, C-o1-Fl.), 126.7 (C5), 127.0 (2 × C, C-m2-Fl.),
127.6 (2 × C, C-p3-Fl.), 127.7 (4 × C, C-m-SiPh), 127.8 [C-
p-Ph(OMe)], 129.8 (2 × C, C-p-SiPh), 130.3 [2 × C, C-m-
Ph(OMe)], 132.6, 132.7 (2 × C, C-i-SiPh), 135.5 (4 × C, C-
o-SiPh), 141.2 (2 × C, C8), 141.2 (2 × C, C-o5-Fl.), 143.7,
(2 × C, C-i-Fl.), 150.0 (C2), 151.9 (C4), 155.6
670.3649.
9-[5¢-O-tert-Butyldiphenylsilyl-3¢-N-(a-N-fluorenyl-
methoxycarbonyl-p-methoxy-L-phenylalanyl)amido-3¢-
deoxy-b-D-xylofuranos-1-yl]-6-N-(di-n-butyl-
(N=CHNBu2), 158.4 (C6), 158.5 [C-i-Ph(OMe)], 162.3
[RC(O)OCH2Fl.], 171.4 [3¢-NHC(O)R¢]. HRMS (ESI+): m/z
[M + H]+ calcd for C60H70N8O7Si (1043.36): 1043.5215;
found: 1043.5211.
amino)methyleneadenine (8): N-Fmoc-O-Me-L-Tyr (114
mg, 0.282 mmol) and HOBt (45 mg, 0.282 mmol) were co-
evaporated from anhyd THF (3 × 3 mL). The mixture was
dissolved in anhyd THF (2 mL) and the solution was cooled
to 0 °C under N2 for 10 min. Then, DIC (38.3 mL, 0.242
mmol) was added and the reaction mixture was stirred for 10
min at the same temperature. PMe3 (1 M in THF, 303 mL,
0.303 mmol) was added to a solution of 7 (135 mg, 0.202
mmol) in THF (2 mL), and the mixture was stirred for 1 min
at r.t. The amino acid solution was warmed to r.t. during 1
min, and then added to the iminophosphorane solution. The
reaction mixture was stirred at r.t. overnight, concentrated
under reduced pressure and co-evaporated from CHCl3 (2 ×
3 mL), then dissolved in EtOAc (30 mL) and quenched with
sat. NaHCO3 (15 mL). The organic layer was extracted with
EtOAc (2 ×) and washed with H2O (2 × 10 mL), dried over
anhyd MgSO4, filtered and evaporated under reduced
pressure. The residue was purified by silica gel column
chromatography (EtOAc–toluene, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1,
EtOAc–toluene–MeOH, 3:1:0.25) to yield 8 (175 mg, 83%).
1H NMR (300 MHz, CDCl3): d = 0.92 (s, 9 H, Si-t-Bu), 0.96
[t, 6 H, 3J = 6.9 Hz, N(CH2CH2CH2CH3)2], 1.31–1.47 [m, 4
H, N(CH2CH2CH2CH3)2], 1.60–1.73 [m, 4 H,
N(CH2CH2CH2CH3)2], 2.81–2.98 (m, 2 H, Hb), 3.41 [t, 2 H,
3J = 7.2 Hz, N(CH2CH2CH2CH3)2], 3.61 (s, 3 H, OMe),
3.65–3.81 [m, 3 H, N(CH2CH2CH2CH3)2, HA5¢], 3.92 (dd, 1
H, 2J = 11.3 Hz, 3J = 4.1 Hz, HB5¢), 4.15 (pseudo t, 1 H, 3J =
6.0, 6.9 Hz, H aliph. Fl.), 4.24–4.30 (m, 2 H, Ha, CH2Fl.),
4.38–4.47 (m, 3 H, H4¢, H2¢, CH2Fl.), 4.71–4.77 (m, 1 H,
H3¢), 5.43 (d, 1 H, 3J = 6.9 Hz, NHFmoc), 5.43 (br s, 1 H,
OH), 5.74 (d, 1 H, 3J = 3.6 Hz, H1¢), 6.63 [d, 2 H, 3J = 8.1
Hz, H-o-Ph(OMe)], 6.99 [d, 2 H, 3J = 8.1 Hz, H-m-
Ph(OMe)], 7.20–7.30 (m, 8 H, H-m2-Fl., H-m-SiPh, H-p-
SiPh), 7.32–7.40 (m, 2 H, H-p3-Fl.), 7.48–7.55 (m, 6 H, H-
o1-Fl., H-o-SiPh), 7.73 (t ‘2×d’, 2 H, 3J = 7.2, 7.5 Hz, H-m4-
Fl.), 7.97 (s, 1 H, H8), 8.46 (s, 1 H, H2), 8.54 (d, 1 H, 3J =
7.8 Hz, 3¢-NH), 9.02 (s, 1 H, N=CHNBu2). 13C NMR (75
MHz, CDCl3): d = 13.7, 13.9 [2 × C, N(CH2CH2CH2CH3)2],
9-[3¢-Deoxy-3¢-N-(p-methoxy-L-phenylalanyl)amido-b-D-
xylofuranos-1-yl]adenine (2): Compound 9 (25 mg, 0.027
mmol) (or 8) was dissolved in 33% MeNH2–EtOH (5 mL).
The reaction mixture was stirred at r.t. overnight in a closed
vessel. The solution was concentrated under reduced
pressure and co-evaporated from CHCl3 (2 × 4 mL). The oily
residue was dissolved in MeOH (1 mL) and then ammonium
fluoride (5.2 mg, 0.138 mmol) was added to the solution.
The reaction mixture was warmed to 50–55 °C for 4 h, and
monitored by TLC. The volatiles were removed under
reduced pressure. The residue was purified by silica gel
column chromatography (EtOAc–MeOH–H2O, 14:1:0.5,
12:1: 0.5, 10:1:0.5, 8:1:0.5, 6:1:0.5, 4:1:0.5) to yield after
evaporation the target compound 2 as a fluffy white solid (12
mg, 98% from 9). 1H NMR (300 MHz, CD3OD): d = 2.90
(dd, 1 H, 2J = 13.5 Hz, 3J = 6.3 Hz, Hb1), 2.97 (dd, 1 H, 2J =
13.5 Hz, 3J = 7.5 Hz, Hb2), 3.53 (dd, 1 H, 2J = 12.6 Hz, 3J =
4.2 Hz, HA5¢), 3.64 (s, 3 H, OMe), 3.68–3.70 (m, 1 H, Ha),
3.75 (dd, 1 H, 2J = 12.6 Hz, 3J = 3.3 Hz, HB5¢), 4.34 (‘ddd’,
1 H, 3J = 3.3, 3.6, 6.9 Hz, H4¢), 4.43 (t, 1 H, 3J = 5.1 Hz, H2¢),
4.60 (dd, 1 H, 3J = 5.4, 5.7 Hz, H3¢), 5.79 (d, 1 H, 3J = 4.8
Hz, H1¢), 6.73 [d, 2 H, 3J = 8.7 Hz, H-o-Ph(OMe)], 7.11 [d,
2 H, 3J = 8.7 Hz, H-m-Ph(OMe)], 8.18 (s, 1 H, H8), 8.22 (s,
1 H, H2). 13C NMR (125 MHz, CD3OD): d = 40.9 (Cb), 55.6
(OMe), 57.6 (C3¢), 58.6 (Ca), 62.1 (C5¢), 79.4 (C2¢), 81.4
(C4¢), 92.5 (C1¢), 115.0 [2 × C, C-o-Ph(OMe)], 121.3 (C5),
129.8 [C-p-Ph(OMe)], 131.6 [2 × C, C-m-Ph(OMe)], 142.5
(C8), 149.4 (C4), 153.6 (C2), 157.7 (C6), 160.2 [C-i-
Ph(OMe)], 175.2 [3¢-NHC(O)R¢]. HRMS (ESI+): m/z [M +
Na]+ calcd for C20H25N7O5: 466.1815; found: 466.1817.
The supporting information for this article contains
protocols and experimental details for the syntheses of 4, 5,
9, and 10, as well as the 1H NMR, DEPT, 13C NMR, 1H–1H
COSY, 1H–13C HSQC, and (in part) 1H–13C HMBC spectra
of all compounds.
Synlett 2008, No. 16, 2461–2464 © Thieme Stuttgart · New York