Total synthesis of nucleoside antibiotic A201A

Article abstract of DOI:10.1021/ja501460j

A201A, a unique nucleoside antibiotic with potent antibacterial activities, has been synthesized for the first time in a total of 47 steps in a highly modular and linear manner, highlighting the elaboration/incorporation of an unprecedented hexofuranoside unit bearing an exocyclic enol ether moiety.

Full text of DOI:10.1021/ja501460j

Communication
pubs.acs.org/JACS
Total Synthesis of Nucleoside Antibiotic A201A
Shenyou Nie, Wei Li, and Biao Yu*
State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: A201A, a unique nucleoside antibiotic with
potent antibacterial activities, has been synthesized for the
first time in a total of 47 steps in a highly modular and
linear manner, highlighting the elaboration/incorporation
of an unprecedented hexofuranoside unit bearing an
exocyclic enol ether moiety.
201A (1) is a structurally unique nucleoside antibiotic,1
which consists of five units, i.e., 6-dimethylaminopurine
A
(A), 3-amino-3-deoxyribose (B), α-methyl-p-coumaric acid
(C), an unnamed hexofuranose (D), and 3,4-di-O-methyl-D-
rhamnose (E), connected linearly via one amide and three
glycosidic linkages. This compound was originally isolated from
a strain of Streptomyces capreolus in 1976 and was found to be
highly active against Gram-positive bacteria and most Gram-
negative anaerobic bacteria.2 Recently, it was rediscovered by Ju
et al. unexpectedly from the fermentation of a new strain of
Actinomycetes thermotolerans collected from a deep-sea sedi-
ment.3 To date, the only natural products known to be
structurally relevant to A201A are puromycin4 and hygromycin
A,5 which in fact bear only minor fragments of A201A (Figure
1). These two compounds also show potent antibacterial
activities. Puromycin, in particular, has been well-known as a
mimic of the 3′-end of aminoacyl-tRNA, which enters the A-
site of the ribosome and inhibits translation by attacking the
carbonyl group of the nascent peptidyl chain on the P-site.6
Hygromycin A and A201A are also believed to bind to the
ribosome so as to inhibit the protein synthesis.7
Figure 1.
designing the building blocks was on the unprecedented unit D,
which bears the acid-labile enol ether moiety and is embedded
via two glycosidic linkages between the units E and C. It is
known that a phenol 1,2-cis-furanosidic linkage (such as the D
→ C linkage) is extremely difficult to construct in a highly
stereoselective manner.13 In fact, both the Ogawa and Donohoe
synthesis of hygromycin A exploited the Mitsunobu glyco-
sylation to effect the relevant phenol 1,2-cis-furanosides.9,10
Especially, employing a furanose donor installed with a
triisopropylsilyl (TIPS) group at the 2-OH (thus, a 1,2-trans-
activation and subsequent SN2 substitution would be favored),
Donohoe et al. managed to obtain the desired 1,2-cis-anomer
predominantly under optimized conditions.10 The stage for
elaboration of the vulnerable enol methyl ether was scheduled
after the glycosidation, so as to avoid tedious screening of the
anomeric protecting group and its selective removal conditions.
Thus, furanose 5 was designed, in that the C-6 was masked as a
carboxylic ester to ensure the enolization of a later C-5 ketone
derivative to take place only at C-4. The terminal rhamnose E
To understand the structure−activity relationships (SAR)
and to develop drug candidates as well as probes for
investigating the translation process, many efforts have been
given to the chemical synthesis of puromycin and hygromycin
A derivatives.8−11 Especially, the total synthesis of hygromycin
A has been achieved by Ogawa et al. in 1989 and by Donohoe
et al. in 2009, respectively,9b,10 and a synthesis of the 1,2-trans-
furanoside analogue of hygromycin A was accomplished by
Trost et al.11 In contrast, study toward the synthesis of A201A,
which demands incorporation/elaboration of the unique
hexofuranose D unit with an exocyclic enol ether moiety, has
never been reported. Here, we communicate the first synthesis
of this complex nucleoside antibiotic (1).
A linear approach, with the shelf-stable compounds 2−6 as
building blocks, was planned for the total synthesis of A201A,
so that en route adjustment of the coupling sequence and
protecting groups would be flexible. In addition, the linear
approach would ensure divergent assembly of the congeners of
A201A to facilitate the SAR studies.12 A major concern in
Received: February 11, 2014
Published: March 10, 2014
© 2014 American Chemical Society
4157
dx.doi.org/10.1021/ja501460j | J. Am. Chem. Soc. 2014, 136, 4157−4160

Journal of the American Chemical Society
Communication
unit was designed as an ortho-alkynylbenzoate (i.e., 6), which is
capable of glycosylation under neutral conditions,14 so as to not
affect the enol ether. Since glycosylation of purine derivatives
with glycosyl ortho-alkynylbenzoates has already been proved to
be an efficient protocol,15 the coupling of ortho-alkynylbenzoate
3 and 6-chloro-purine (2) turned out to be a certain choice to
build the AB fragment.
Scheme 2
The synthesis commenced with the preparation of the
desired furanose building block 5 (Scheme 1). Thus, D-
Scheme 1
resulted from the Mitsunobu glycosylation step could be easily
separated. Subjection of ester 13(Z/E) to reduction with LiBH4
(THF, 0 °C to rt) led to the corresponding 1,6′-diols (S16(Z/
E)); NOE analysis of this pair of isomers confirmed
unambiguously the assigned Z/E configurations.16 Attempts
at selective cleavage of the trimethylsilylethyl (SE) ester in 13,
without affecting the enol ether and the TIPS ethers, were not
successful. Alternatively, the SE and TIPS groups in 13 were
cleaved with tris-(dimethylamino)sulfonium difluorotrimethyl-
silicate (TASF) in DMF at rt to afford 14 (85%),10,21 which
was a ready precursor for the subsequent amide bond formation
between the C and B units.
The required glycosyl ortho-alkynylbenzoates 3 and 6 were
prepared conveniently from D-xylose and D-mannose, respec-
tively.16 We then set on the final assembly of A201A (Scheme
3). Thus, glycosylation of 6-chloro-purine (2) with ribofur-
anosyl ortho-alkynylbenzoate 3 under the catalysis of
Ph3PAuNTf2 (0.1 equiv) in CH2Cl2 at rt provided the β-
glycoside 15 cleanly (86%).15 Treatment of 15 with aqueous
dimethylamine in refluxing ethanol led to replacement of the 6-
chloride together with cleavage of the 2′,5′-O-benzoyl groups;22
subsequent protection of the resulting diol with TES group
afforded 16 (76% for two steps). Azide 16 was then converted
into the 3′-amino-3′-deoxyadenosine 17 (Ph3P, THF, H2O, 50
°C, 92%), which has been the key precursor in the synthesis of
puromycin derivatives.8
arabinose, which possesses the required configurations at C-2
and C-3, was converted into 5-aldehyde-furanoside 7 in nine
transformations with a high 21% overall yield.16 Subjection of
aldehyde 7 to a THF solution of tris-(phenylthio)methyllithium
at −78 °C led to the phenylthioorthoester adduct,17 which was
found unstable. Immediate treatment of the crude product with
CuO/CuCl2 in a mixed solvent of MeOH/H2O/CH2Cl2 at
room temperature (rt) afforded methyl ester 8 as a single
isomer in 78% yield.18 The nascent 5-OH, which is assumed to
be at R configuration,17 was protected with an acetyl group.
Subsequent cleavage of the anomeric p-methoxyphenyl (MP)
group was achieved with ceric ammonium nitrate (CAN) as an
oxidant in aqueous MeCN, furnishing 5 in good yield (71−
85%). Interestingly, the quinone adduct 9 was isolated as a
byproduct (5%∼21%).
As expected, condensation of phenol 416 with furanose 5
under the optimized conditions (diisopropyl azodicarboxylate
(DIAD), Ph3P, toluene, 60 °C)10 afforded the desired glycoside
10 in a high yield (79%) and an excellent stereoselectivity (β/α
= 10:1; Scheme 2). Selective removal of the 5′-O-acetyl group
with K2CO3 in aqueous MeOH led to alcohol 11 (82%). The
resulting 5′-OH was then oxidized successfully with o-
iodoxybenzoic acid (IBX) in DMSO at 80 °C, leading to α-
keto-ester 12 (95%).19 Now the stage is set for elaboration of
the enol methyl ether. In fact, we first examined the relevant
transformations on simple substrates, including the methyl, p-
methoxyphenyl, and benzyl glycoside analogues of 12 (i.e., S10,
S12, and S14).16 The yields and Z/E ratios of the resulting enol
methyl ethers (S11, S13, and S15) were found to be highly
dependent on the base and the methylating agent, as well as the
reaction conditions.16,20 The optimal conditions were the
combination of Cs2CO3 and Me2SO4 in MeCN at rt, leading to
the corresponding enol methyl ethers in constantly >73% yield
and >3.5/1 Z/E ratio. Applying this set of conditions to the
transformation of 12 led to enol methyl ethers 13(Z/E) in an
acceptable 66% yield, albeit in a moderate Z/E ratio of 1.6:1.
Gratifyingly, we managed to convert 12 into 13(Z/E) in a
better yield of 69% (86% brsm) and Z/E ratio of 5.4:1 under
modified conditions (Me2SO4 was added 10 min after the
addition of Cs2CO3, so that the Z and E enols would reach at
an equilibrium). At this stage, the trace α-isomer that had
The condensation of amine 17 with acid 14, which contains
two hydroxyl groups, was effected in the presence of
benzotriazol-1-yloxytris(dimethylamino)phosphonium hexa-
10,23
i
fluorophosphate (BOP) and Pr2NEt in DMF at rt,
furnishing the desired amide in 78% yield. Subsequent
protection of the two hydroxyl groups with TES group gave
18. Reduction of the terminal ester in 18 succeeded with LiBH4
(THF, −40 °C to rt, 78%) to afford the desired alcohol 19.24
Reduction with DIBAl-H led to cleavage of the amide linkage.
The complex alcohol 19 was then subjected to the final
assembly. As planned, we performed the glycosylation of 19
with glycosyl o-alkynylbenzoate 6. However, under conven-
tional conditions (0.1 equiv Ph3PAuOTf or Ph3PAuNTf2,
CH2Cl2, 4 Å MS, rt), the reaction proceeded sluggishly. The
mechanistic studies have revealed that the gold(I)-catalyzed
glycosylation reaction requires a protodeauration step to
4158
dx.doi.org/10.1021/ja501460j | J. Am. Chem. Soc. 2014, 136, 4157−4160

Journal of the American Chemical Society
Communication
Scheme 3
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details, characterization data, and NMR spectra
for new compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
byu@mail.sioc.ac.cn
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the MOST
(2012CB822102) and NSFC (21302210 and 20921091). We
thank Prof. Jianhua Ju for providing the NMR spectra of the
natural product A201A and helpful discussion.
REFERENCES
■
(1) (a) Isono, K. Pharmacol. Ther. 1991, 52, 269−280. (b) Knapp, S.
Chem. Rev. 1995, 95, 1859−1876.
(2) (a) Kirst, H . A.; Dorman, D. E.; Occolowitz, J. L.; Szymanski, E.
F.; Paschal, J. W. Abstracts of Papers of 16th Interscience Conference on
Antimicrobial Agents and Chemotherapy No. 61, Chicago, IL, Oct 27−
29, 1976; ASM: Washington, DC, 1976. (b) Kirst, H. A.; Dorman, D.
E.; Occolowitz, J. L.; Jones, N. D.; Paschal, J. W.; Hamill, R. L.;
Szymanski, E. F. J. Antibiot. 1985, 38, 575−586. (c) Barrasa, M. I.;
Tercero, J. A.; Lacalle, R. A.; Jimenez, A. Eur. J. Biochem. 1995, 228,
562−569. (d) Barrasa, M. I.; Tercero, J. A.; Jimenez, A. Eur. J. Biochem.
1997, 245, 54−63.
regenerate the gold(I) catalyst; thus, the basic nitrogen atoms
in 19 could intercept the proton in situ and stop the catalytic
cycle.14c,d Therefore, the condensation of 19 and 6 was
promoted with stoichiometric amount of Ph3PAuOTf; the
reaction proceeded smoothly (CH2Cl2, 5 Å MS, 0 °C) to lead
to the desired α-rhamnoside 20 in 55% isolated yield. We have
also tried the glycosylation of 19 with the relevant imidate
donors (i.e., 2-O-benzoyl-3,4-di-O-methyl-D-rhamnopyranosyl
trichloroacetimidate and N-phenyl trifluoroacetimidate).25 Not
surprisingly, under the action of TMSOTf, enol ether 19
underwent decomposition easily, while with BF3·OEt2 as the
promoter, the reaction hardly took place before decomposition.
Finally, the benzoyl group and the four TES groups on 20 were
removed with NaOMe in HOMe/CH2Cl2, furnishing A201A
(1) in 76% yield. By the same token, we also synthesized the E-
isomer of A201A (S28) starting from 13(E).16 The analytical
data of 1 were in full agreement with those obtained for the
natural product.16
Summarizing, the total synthesis of A201A, a unique
nucleoside antibiotic, has been achieved for the fist time in a
total of 47 steps starting from cheap materials, i.e., D-xylose, D-
mannose, D-arabinose, 6-chloro-purine, and α-methyl-p-couma-
ric acid. The synthetic challenge of incorporation/elaboration
of the unique furanoside unit bearing an exocyclic enol ether
moiety has been addressed. The glycosylation of the complex
alcohol (i.e., 19) containing the acid-labile enol ether and basic
nitrogen atoms was realized with the glycosyl ortho-
alkynylbenzoate as donor under the promotion of stoichio-
metric Ph3PAuOTf. Given its highly modular and linear nature,
the present synthesis offers the prospect of being able to access
numerous congeners of A201A and, thus, facilitates in-depth
studies on the biological activities of this unique type of natural
products.
(3) Zhu, Q.; Li, J.; Ma, J.; Luo, M.; Wang, B.; Huang, H.; Tian, X.; Li,
W.; Zhang, S.; Zhang, C.; Ju, J. Antimicrob. Agents Chemother. 2012, 56,
110−114.
(4) (a) 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, 409−410. (b) Waller, C. W.; Fryth, P. W.;
Hutchings, B. L.; Williams, J. H. J. Am. Chem. Soc. 1953, 75, 2025−
2025.
(5) (a) Pittenger, R. C.; Wolfe, R. N.; Hoehn, M. M.; Marks, P. N.;
Daily, W. A.; McGuire, J. M. Antibiot. Chemother. 1953, 3, 1268−1278.
(b) Mann, R. L.; Gale, R. M.; van Abeele, F. R. Antibiot. Chemother.
1953, 3, 1279−1282. (c) Isono, K.; Yamashita, S.; Tomiyama, Y.;
Suzuki, S. J. Antibiot. 1957, 10, 21−30. (d) Mann, R. L.; Woolf, D. O. J.
Am. Chem. Soc. 1957, 79, 120−126. (e) Wakisaka, Y.; Koizumi, K.;
Nishimoto, Y.; Kobayashi, M.; Tsuji, N. J. Antibiot. 1980, 33, 695−704.
(f) Uyeda, M.; Mizukami, M.; Yokomizo, K.; Suzuki, K. Biosci.
Biotechnol. Biochem. 2001, 65, 1252−1254.
(6) For selected reports, see: (a) Yarmolinsky, M. B.; de la Haba, G.
L. Proc. Natl. Acad. Sci. U.S.A. 1959, 45, 1721−1729. (b) Allen, D. W.;
Zamecnik, P. C. Biochim. Biophys. Acta 1962, 55, 865−874.
(c) Hohsaka, T.; Sato, K.; Sisido, M.; Takai, K.; Yokoyama, S. FEBS
Lett. 1993, 335, 47−50. (d) Starck, S. R.; Qi, X.; Olsen, B. N.; Roberts,
R. W. J. Am. Chem. Soc. 2003, 125, 8090−8091. (e) Okuda, K.; Seila,
A. C.; Strobel, S. A. Tetrahedron 2004, 60, 12101−12112. (f) Kingery,
D. A.; Pfund, E.; Voorhees, R. M.; Okuda, K.; Wohlgemuth, I.;
Kitchen, D. E.; Rodnina, M. V.; Strobel, S. A. Chem. Biol. 2008, 15,
493−500. (g) Mizusawa, K.; Abe, K.; Sando, S.; Aoyama, Y. Bioorg.
Med. Chem. 2009, 17, 2381−2387.
(7) (a) Guerrero, M. C.; Modolell, J. Eur. J. Biochem. 1980, 107,
409−414. (b) Hecker, S. J.; Lilley, S. C.; Minich, M. L.; Werner, K. M.
Bioorg. Med. Chem. Lett. 1993, 3, 295−298.
(8) For selected reports on the synthesis of puromycin derivatives,
see: (a) Baker, B. R.; Schaub, R. E.; Joseph, J. P.; Williams, J. H. J. Am.
Chem. Soc. 1954, 76, 4044−4045. (b) Baker, B. R.; Schaub, R. E.;
Joseph, J. P.; Williams, J. H. J. Am. Chem. Soc. 1955, 77, 12−15.
(c) Robins, M. J.; Miles, R. W.; Samano, M. C.; Kaspar, R. L. J. Org.
4159
dx.doi.org/10.1021/ja501460j | J. Am. Chem. Soc. 2014, 136, 4157−4160

Journal of the American Chemical Society
Communication
Chem. 2001, 66, 8204−8210. (d) Nguyen-Trung, N. Q.; Botta, O.;
Terenzi, S.; Strazewski, P. J. Org. Chem. 2003, 68, 2038−2041.
(e) Krishnakumar, K. S.; Goudedranche, S.; Bouchu, D.; Strazewski, P.
J. Org. Chem. 2011, 76, 2253−2256.
(9) (a) Chida, N.; Ohtsuka, M.; Ogawa, S. Chem. Lett. 1988, 969−
972. (b) Chida, N.; Ohtsuka, M.; Nakazawa, K.; Ogawa, S. J. Chem.
Soc., Chem. Commun. 1989, 436−438. (c) Chida, N.; Ohtsuka, M.;
Nakazawa, K.; Ogawa, S. J. Org. Chem. 1991, 56, 2976−2983.
(10) Donohoe, T. J.; Flores, A.; Bataille, C. J. R.; Churruca, F. Angew.
Chem., Int. Ed. 2009, 48, 6507−6510.
(11) (a) Trost, B. M.; Dirat, O.; Dudash, J.; Hembre, E. J. Angew.
Chem., Int. Ed. 2001, 40, 3658−3660. (b) Trost, B. M.; Dudash, J., Jr.;
Dirat, O. Chem.Eur. J. 2002, 8, 259−268.
(12) Yu, B.; Sun, J.; Yang, X. Acc. Chem. Res. 2012, 45, 1227−1236.
(13) (a) Jacobsson, M.; Malmberg, J.; Ellervik, U. Carbohydr. Res.
2006, 341, 1266−1281. (b) Demchenko, A. V. Synlett 2003, 1225−
1240. (c) Buchanan, J. G.; Hill, D. G.; Wrightman, R. H.; Boddy, I. K.;
Hewitt, B. D. Tetrahedron 1995, 51, 6033−6050.
(14) (a) Li, Y.; Yang, Y.; Yu, B. Tetrahedron Lett. 2008, 49, 3604−
3608. (b) Li, Y.; Yang, X.; Liu, Y.; Zhu, C.; Yang, Y.; Yu, B. Chem.
Eur. J. 2010, 16, 1871−1882. (c) Zhu, Y.; Yu, B. Angew. Chem., Int. Ed.
2011, 50, 8329−8332. (d) Tang, Y.; Li, J.; Zhu, Y.; Li, Y.; Yu, B. J. Am.
Chem. Soc. 2013, 135, 18396−18405.
(15) (a) Zhang, Q.; Sun, J.; Zhu, Y.; Zhang, F.; Yu, B. Angew. Chem.,
Int. Ed. 2011, 50, 4933−4936. (b) Yang, F.; Zhu, Y.; Yu, B. Chem.
Commun. 2012, 48, 7097−7099.
(16) See Supporting Information for details.
(17) (a) Seebach, D. Angew. Chem., Int. Ed. Engl. 1967, 6, 442−443.
́
(b) Lubineau, A.; Gavard, O.; Alais, J.; Bonnaffe, D. Tetrahedron Lett.
2000, 41, 307−311. (c) Gavard, O.; Hersant, Y.; Alais, J.; Duverger, V.;
Dilhas, A.; Bascou, A.; Bonnaffe,
́
D. Eur. J. Org. Chem. 2003, 3603−
3620. (d) Lohman, G. J. S.; Hunt, D. K.; Hogermeier, J. A.; Seeberger,
̈
P. H. J. Org. Chem. 2003, 68, 7559−7561.
(18) Mukaiyama, T.; Narasaka, K.; Hokonok, H. J. Am. Chem. Soc.
1969, 91, 4315−4317.
(19) Frigerio, M.; Santagostino, M. Tetrahedron Lett. 1994, 35,
8019−8022.
(20) For selected examples on enol ether formation, see:
(a) Oplinger, J. A.; Paquette, L. A. Tetrahedron Lett. 1987, 28,
5441−5444. (b) Bates, R. B.; Caldera, S. J. Org. Chem. 1993, 58,
6920−6921. (c) Corelli, F.; Dei, D.; Menichincheri, M.; Snyder, J. P.;
Botta, M. Tetrahedron Lett. 1997, 38, 2759−2762. (d) Werschkun, B.;
Thiem, J. Synthesis 1999, 121−137. (e) Damoun, S.; Van de Woude,
G.; Choho, K.; Geerlings, P. J. Phys. Chem. A 1999, 103, 7861−7866.
(f) Li, F.; Tartakoff, S. S.; Castle, S. L. J. Am. Chem. Soc. 2009, 131,
6674−6675. (g) Faber, J. M.; Williams, C. M. Chem. Commun. 2011,
47, 2258−2260.
(21) Scheidt, K. A.; Chen, H.; Follows, B. C.; Chemler, S. R.; Coffey,
D. S.; Roush, W. R. J. Org. Chem. 1998, 63, 6436−6437.
(22) Choi, Y.; George, C.; Strazewski, P.; Marquez, V. E. Org. Lett.
2002, 4, 589−592.
(23) Castro, B.; Dormoy, J. R.; Evin, G.; Selve, C. Tetrahedron Lett.
1975, 1219−1222.
(24) (a) Laïb, T.; Zhu, J. Synlett 2000, 1363−1365. (b) Barrett, A. G.
́
M.; Hennessy, A. J.; Le Vezouet, R.; Procopiou, P. A.; Seale, P. W.;
̈
Stefaniak, S.; Upton, R. J.; White, A. J. P.; Williams, D. J. J. Org. Chem.
2004, 69, 1028−1037.
(25) Yu, B.; Sun, J. Chem. Commun. 2010, 46, 4668−4679.
4160
dx.doi.org/10.1021/ja501460j | J. Am. Chem. Soc. 2014, 136, 4157−4160