Complex peptidyl nucleoside antibiotics: Efficient syntheses of the glycosyl nucleoside amino acid cores

Article abstract of DOI:10.1021/jo048586l

Employing an amino acid chiral template strategy, the present research describes a general and highly efficient protocol for the rapid construction of enantiopure furanosyl and pyranosyl nucleoside amino acid cores as present in various complex peptidyl n

Full text of DOI:10.1021/jo048586l

Complex Peptidyl Nucleoside Antibiotics: Efficient Syntheses of
the Glycosyl Nucleoside Amino Acid Cores
Pushpal Bhaket, Christina S. Stauffer, and Apurba Datta*
Department of Medicinal Chemistry, University of Kansas, 1251 Wescoe Hall Drive,
Lawrence, Kansas 66045
adutta@ku.edu
Received August 12, 2004
Employing an amino acid chiral template strategy, the present research describes a general and
highly efficient protocol for the rapid construction of enantiopure furanosyl and pyranosyl nucleoside
amino acid cores as present in various complex peptidyl nucleoside antibiotics. Starting from easily
available D-serine, the strategy and the approach involve rapid and efficient stereoselective synthe-
sis of five- or six-membered lactone amino alcohols, followed by incorporation of the required
functionalities of the target molecules on these strategically functionalized chiral templates.
The complex peptidyl nucleoside antibiotics are sec-
ondary microbial metabolites with impressive antifungal
activity against various human pathogenic fungi.1 In a
novel mode of action, many of these compounds act by
strong and selective inhibition of chitin synthase, the
enzyme responsible for the biosynthesis of chitin, an
essential component of the fungal cell wall.2 Because the
chitin biosynthetic pathway is absent in humans and
other vertebrates, inhibition of chitin biosynthesis is
considered to be of immense therapeutic potential for
combating various opportunistic fungal infections.3 By
virtue of their potent and selective chitin synthase
inhibitory action, the peptidyl nucleoside antibiotics
represent extremely promising leads for the development
of novel, nontoxic antifungal therapeutics.4 Representa-
tive structures of some complex peptidyl nucleoside
antibiotics are shown in Figure 1. Among these com-
pounds, the polyoxins and the nikkomycins are the best-
known and most effective inhibitors of chitin synthase.
The structurally more complex ezomycins, amipurimycin,
and miharamycins also exhibit a broad range of antifun-
gal activity, although the modes of action of these
compounds are yet to be determined.1
Typically, these unique natural products consist of
three distinct structural components: (i) nucleobase, (ii)
a central carbohydrate framework, and (iii) peptidyl
region. Interestingly, a recurring theme in these com-
pounds is the attachment of an R-amino acid (amino
alcohol in the ezomycins) functionality at the C4′ or C5′
position of the nucleoside component. A major structural
difference in these groups of compounds, however, is the
presence of a furanosyl nucleosidic core in the polyoxins,
nikkomycins, and ezomycins, while the amipurimycin
and miharamycin families of compounds consists of a
pyranosyl nucleoside core. Extensive efforts are being
directed toward synthesis and structure-activity rela-
tionship (SAR) studies of these peptidyl nucleosides
toward their pharmacophore elucidation, improvement
of inhibitory potencies, and enhancement of antifungal
properties.5
(1) (a) Isono, K. J. Antibiot. 1988, 41, 1711-1739. (b) Isono, K.
Pharmacol. Ther. 1991, 52, 269-286.
(2) Gooday, G. W. In Biochemistry of Cell Walls and Membranes in
Fungi; Kuhn, P. J., Trinci, A. P., Jung, M. J., Goosey, M. W., Copping,
L. G., Eds.; Springer: Berlin, 1990; p 61.
(3) (a) Behr, J. B. Curr. Med. Chem.-Anti-Infect. Agents 2003, 2,
173-189. (b) Ruiz-Herrera, J.; San-Blas, G. Curr. Drug Targets: Infect.
Disord. 2003, 3, 77-91. (c) Andriole, V. T. Int. J. Antimicrob. Agents
2000, 16, 317-321.
Among the various complex peptidyl nucleosides, total
syntheses of several polyoxins and nikkomycins have
been reported in the literature; however, the total
syntheses of the ezomycin, amipurimycin, and mihara-
mycin families of compounds have not yet been ac-
complished.5 Traditionally, a common strategy for the
synthesis of the central glycosyl amino acid core of the
peptidyl nucleosides has involved utilization of readily
available carbohydrate starting materials.6 However, a
(4) (a) Becker, J. M.; Covert, N. L.; Shenbagamurthi, P. S.; Steinfeld,
A.; Naider, F. Antimicrob. Agents Chemother. 1983, 23, 926-929. (b)
Krainer, E.; Becker, J. M.; Naider, F. J. Med. Chem. 1991, 34, 174-
180 and references therein. (c) Chapman, T.; Kinsman, O.; Houston,
J. Antimicrob. Agents Chemother. 1992, 36, 1909-1914. (d) Chander,
F. W. In Current Topics in Medical Mycology; Mcginnis, M., Ed.;
Springer-Verlag: New York, 1985; Vol. 1, pp 1-23. (e) Becker, J. M.;
Marcus, S.; Tullock, J.; Miller, D.; Krainer, E.; Khare, R. K.; Naider,
F. J. Infect. Dis. 1988, 157, 212-214. (f) Hector, R. F.; Zimmer, B. L.;
Pappagianis, D. Antimicrob. Agents Chemother. 1990, 34, 587-593.
(g) Hector, R. F.; Zimmer, B. L.; Pappagianis, D. In Recent Progress in
Antifungal Chemotherapy; Yamaguchi, H., Kobayashi, G. S., Taka-
hashi, H., Eds.; Dekker: New York, 1992; p 341. (h) Clemons, K. V.;
Stevens, D. A. Antimicrob. Agents Chemother. 1997, 41, 2026-2028.
(i) Graybill, J. R.; Najvar, L. K.; Bocanegra, R.; Hector, R. F.; Luther,
M. F. Antimicrob. Agents Chemother. 1998, 42, 2371-2374. (j) Sweezy,
R. R.; Hector, R. F.; Khandwala, A.; Sinha, S.; Carlson, T.; Charney,
M. R. 37th ICAAC, 1997, Abs. No. F87. (k) Hector, R. F.; Schaller, K.
Antimicrob. Agents Chemother. 1992, 36, 1284-1289.
(5) For reviews, see: (a) Zhang, D.; Miller, M. J. Curr. Pharm. Des.
1999, 5, 73-99. (b) Knapp, S. Chem. Rev. 1995, 95, 1859-1876. (c)
Garner, P. In Studies in Natural Products Chemistry; Atta-ur-Rahman,
Ed.; Elsevier: Amsterdam, 1988; Part A, Vol. 1, pp 397-435, and
references therein.
(6) For representative examples, see: (a) Kuzuhara, H.; Ohrui, H.;
Emoto, S. Tetrahedron Lett. 1973, 14, 5055-5058. (b) Dondoni, A.;
Franco, S.; Junquera, F.; Merchan, F. M.; Merino, P.; Tejero, T. J. Org.
Chem. 1997, 62, 2, 5497-5507. (c) Kato, K.; Chen, C. Y.; Akita, H.
10.1021/jo048586l CCC: $27.50 © 2004 American Chemical Society
Published on Web 11/16/2004
8594
J. Org. Chem. 2004, 69, 8594-8601

Complex Peptidyl Nucleoside Antibiotics
FIGURE 1. Representative examples of complex peptidyl nucleoside antibiotics.
disadvantage inherent in the carbohydrate approach has
been the often extensive protection-deprotection se-
quences necessitated by the presence of multiple hydroxy
groups, and the requirement of additional reaction steps
to incorporate the R-amino acid functionality as present
in the target products. Therefore, development of alter-
native strategies, involving asymmetric synthesis of the
above glycosyl amino acid core, starting from a more
simple non-carbohydrate synthon remains an attractive
proposition. In one such pioneering effort, Garner and
co-workers have utilized serine as a starting material to
develop a novel synthetic route to the polyoxins.7 Simi-
larly, employing a hetero Diels-Alder cycloaddition
involving a serine-derived homochiral oxazolidine alde-
hyde (Garner’s aldehyde8), the same research group has
also developed an efficient route to the branched carbo-
hydrate amino acid fragment of amipurimycin.9 Besides
circumventing the shortcomings of the carbohydrate
approach, the amino acid-based strategy affords greater
flexibility toward various structural modifications and
also allows more control over creation of new stereo-
centers, essential tools for pharmacophore modification
and further structure-activity relationship studies.
In view of the above observations, and in continuation
of our efforts toward amino acid chiral template-assisted
stereoselective synthesis of bioactive molecules,10 we have
initiated a research program exploring new and more
efficient methods for the synthesis and SAR studies of
various complex peptidyl nucleoside antibiotics. Details
of our preliminary studies, culminating in the develop-
ment of a versatile route to the glycosyl amino acid
nucleoside cores of the peptidyl nucleoside antibiotics, are
described herein.
Results and Discussion
A common structural feature of the peptidyl nucleo-
sides is the presence of a furanosyl or a pyranosyl
R-amino acid nucleoside subunit. Our retrosynthetic plan
therefore envisages a unified synthetic strategy based
upon initial stereocontrolled formation of a pivotal fura-
nosyl amino acid precursor 1 (for the polyoxin, nikkomy-
cin, and ezomycin series), or the corresponding pyranosyl
analogue 2 (for amipurimycin and miharamycins), fol-
lowed by construction of the remaining structural adorn-
ments on these strategically functionalized chiral tem-
plates (Figure 2). Further disconnection reveals the 1,2-
Synthesis 1998, 1527-1533. (d) Chen, A.; Thomas, E. J.; Wilson, P.
D. J. Chem. Soc., Perkin Trans. 1 1999, 3305-3310. (e) Kutterer, K.
M. K.; Just, G. Heterocycles 1999, 51, 1409-1420. (f) Ghosh, A. K.;
Wang, Y. J. Org. Chem. 1999, 64, 2789-2795. (g) Gonda, J.; Mar-
tinkova, M.; Walko, M.; Zavacka, E.; Budesinsky, M.; Cisarova, I.
Tetrahedron Lett. 2001, 42, 4401-4404.
FIGURE 2. Retrosynthetic analysis and strategy.
(10) For some recent studies, see: (a) Khalaf, J. K.; Datta, A. J.
Org. Chem. 2004, 69, 387-390. (b) Stauffer, C. S.; Datta, A. Tetrahe-
dron 2002, 58, 9765-9767. (c) Ravi Kumar, J. S.; Roy, S.; Datta, A.
Tetrahedron 2001, 57, 1169-1173. (d) Veeresa, G.; Datta, A. J. Org.
Chem. 2000, 65, 7609-7611 and references therein.
(7) Garner, P.; Park, J. M. J. Org. Chem. 1990, 55, 3772-3787.
(8) Garner, P. Tetrahedron Lett. 1984, 25, 5855-5858.
(9) Garner, P.; Yoo, J. K.; Sarabu, R.; Kennedy, V. O.; Youngs, W.
J. Tetrahedron 1998, 55, 9303-9316.
J. Org. Chem, Vol. 69, No. 25, 2004 8595

Bhaket et al.
anti-amino alcohol 3 as a convenient building block for
the pivotal lactones 1 or 2. Finally, easily available
enantiopure D-serine, containing an amine and two
potentially orthogonal (masked) carbonyl functionalities,
represents the ideal platform for launching our proposed
synthetic endeavor.
ketone derivative. Subsequently, instead of purification,
the crude ketone was directly subjected to the next
reaction. Accordingly, neighboring -NCbz group-assisted
chelation-controlled reduction of the ketone 5 with zinc-
borohydride in the presence of CeCl3‚7H2O14 provided the
required 1,2-anti-amino alcohol derivative 6 with excel-
lent stereocontrol (anti:syn > 95:5) and high overall
yield.10a
As per our retrosynthetic strategy (Figure 2), utiliza-
tion of 6 toward formation of the desired chiral amino
lactone derivative 8 constitutes the first step in our
present research goal. Thus, reaction of 6 with acryloyl
chloride under standard conditions resulted in the cor-
responding acrylate 7 in near quantitative yield. Subject-
ing 7 to ring closure under Grubbs’ olefin metathesis
protocol15 cleanly resulted in the lactone 8 (Scheme 1) in
high yield.
The next target in our synthetic scheme entailed
development of a similar route toward the five-membered
amino lactone 1. Unfortunately, unlike the formation of
the allylic ketone 5 (Scheme 1), direct conversion of the
Weinreb amide 4 to the corresponding vinyl ketone (via
addition of vinylmagnesium bromide) was found to be
problematic. Lability of the product vinylic ketone (a good
Michael acceptor) toward adventitious nucleophiles dur-
ing reaction workup, purification, and subsequent reac-
tions of this intermediate precluded its further use. In
an innovative solution to this problem, however, we found
an efficient protocol, whereupon the allylic ketone 5 itself
could be utilized for our intended synthesis. As mentioned
earlier (vide supra), the allylic ketone 5 was found to be
prone to double bond isomerization. Taking advantage
of this observation, treatment of 5 with neutral alumina
at rt resulted in its clean conversion to the corresponding
double bond isomerized R,â-unsaturated ketone 9 (E:Z
) 93:7) in high yield (Scheme 2). Gratifyingly, the
chelation-controlled reduction of the ketone 9 with zinc
As precedented in the literature, addition of vinyl- or
allyl-Grignard reagents to Garner’s aldehyde results in
the corresponding allylic- or homoallylic alcohol adducts
3a or 3b, respectively, with moderate anti-selectivity.11
Although methods have been developed, wherein use of
chiral reagents or chiral allyl substrates resulted in
improved selectivity in the formation of the homoallylic
alcohol 3b, these methods usually require the multistep
synthesis of the corresponding chiral catalysts/substrates
and their subsequent use in stoichiometric quantities.12
Moreover, these methods are not amenable toward the
synthesis of the allylic alcohol adduct 3a. We therefore
decided to investigate an alternative approach toward
more efficient formation of both the allylic and the
homoallylic anti-1,2-amino alcohol adducts required for
our proposed synthesis.
SCHEME 1
SCHEME 2
We have recently reported an efficient method for the
stereoselective synthesis of anti-1,2-amino alcohol 6
(Scheme 1).10a The method involves initial conversion of
D-serine to the corresponding N,O-acetonide protected
Weinreb amide 4 in good overall yield (Scheme 1).13
Reaction of the amide 4 with allylmagnesium bromide
cleanly results in the corresponding allyl ketone 5 in
quantitative yield. However, it was observed that pro-
longed storage or attempted column chromatographic
purification of 5 resulted in partial isomerization of the
terminal olefin to the corresponding R,â-unsaturated
(11) For addition of vinylmagnesium bromide, see: (a) Tamamura,
H.; Yamashita, M.; Nakajima, Y.; Sakano, K.; Otaka, A.; Ohno, H.;
Ibuka, T.; Fujii, N. J. Chem. Soc., Perkin Trans. I 1999, 2983-2996.
(b) Ojima, I.; Vidal, E. S. J. Org. Chem. 1998, 63, 7999-8003 and
references therein. For addition of allylmagnesium bromide, see: (c)
Jackson, M. D.; Gould, S. J.; Zabriskie, T. M. J. Org. Chem. 2002, 67,
2934-2941.
(12) (a) Pattenden, G.; Plowright, A. T. Tetrahedron Lett. 2000, 41,
983-986. (b) Roush, W. R.; Hunt, J. A. J. Org. Chem. 1995, 60, 798-
806. (c) Hafner, A.; Duthaler, R. O.; Marti, R.; Rihs, G.; Rothe-Streit,
P.; Schwarzenbach, F. J. Am. Chem. Soc. 1992, 114, 2321-2336.
(13) Collier, P. N.; Campbell, A. D.; Patel, I.; Raynham, T. M.; Taylor,
R. J. K. J. Org. Chem. 2002, 67, 1802.
(14) Campbell, J. E.; Englund, E. E.; Burke, S. D. Org. Lett. 2002,
4, 2273.
(15) For a similar lactonization approach, see: Ghosh, A. K.;
Cappielo, J.; Shin, D. Tetrahedron Lett. 1998, 39, 4651-4654.
8596 J. Org. Chem., Vol. 69, No. 25, 2004

Complex Peptidyl Nucleoside Antibiotics
borohydride proceeded smoothly to form the allylic
alcohol derivative 10 with high anti-selectivity (anti:syn
) 92:8). Thus, the above strategy resulted in an efficient
pathway in which the same ketone intermediate 5 could
be easily manipulated to afford either the homoallylic or
the allylic anti-1,2-amino alcohol adducts 6 and 10,
respectively. Following the same sequence of reactions
as in Scheme 1, the amino alcohol 10 was subsequently
converted to the desired amino butenolide 12 (Scheme
2) in good overall yield.
Following the concise and efficient pathways described
in the above schemes, we could readily synthesize gram
quantities of 8 and 12 in consistently good overall yields.
As is evident, these strategically functionalized interme-
diates already incorporate the desired amine functional-
ity as present in the various peptidyl nucleosides of our
interest. Moreover, the protected terminal primary hy-
droxy group in the above intermediates represents a
convenient precursor for carboxylic acid or aldehyde
functional groups. The ring olefinic bond allows for a one-
step introduction of the required diol functionality and
also provides an easy handle for carrying out future
structural modifications (epoxidation, nucleophilic/elec-
trophilic addition, deoxygenation, halogenation, hydro-
genation, etc.) at these sites. Similarly, the lactone
carbonyl can be utilized toward desired introduction of
nucleobases. Importantly, the chirality of the starting
amino acid can be easily utilized to control and “grow”
FIGURE 3. Ball-and-stick model of diol 13 (adapted from the
X-ray crystal structure).
SCHEME 4
16
asymmetry in the subsequent reactions, thereby pro-
viding access to various natural and nonnatural stereo-
isomeric products.
Successful attainment of our preliminary synthetic
goals (Figure 2) created the opportunity to further explore
the transformation of the pivotal lactones 8 and 12 to
more highly functionalized furanosyl and pyranosyl
nucleoside amino acid structural framework. Accordingly,
when the chiral aminopyrone 8 was subjected to osmium
tetroxide-assisted dihydroxylation, it underwent a highly
stereoselective oxidation (>95%) to form the correspond-
ing diol 13 (Scheme 3).
SCHEME 3
acid with diazomethane provided the N-Cbz-protected
amino acid ester 16 in good overall yield. Coupling of 16
with bis-silylated uracil in the presence of trimethyl-
silyltriflate (Vorbru¨ggen’s protocol)17 resulted in the
pyranosyl nucleoside 17a as the only product. Chemical
shift and coupling constant of H-1′ (J1′,2′ ) 9.7 Hz)
confirmed the product to be the â-anomer. Similarly,
reaction of 16 with bis-silylated thymine following the
same reaction conditions afforded the corresponding
pyranosyl thymine nucleoside 17b in 64% yield. The
stereoselectivity in the above nucleobase incorporation
reactions can be rationalized by invoking neighboring
C2′-acetoxy group-assisted stabilization of the oxonium
The structure and assigned stereochemistry of the diol
13 was confirmed by X-ray crystallographic studies
(Figure 3). The stereochemical outcome of the above
dihydroxylation can be attributed to the selective osmy-
lation of 8 from the less hindered R-face.
Reduction of the lactone to the corresponding lactol and
acetylation of the three hydroxy groups uneventfully
afforded the triacetate derivative 14 (Scheme 4). Toward
incorporation of the C-5 amino acid functionality, the
N,O-acetonide linkage was cleaved, unmasking the amino
alcohol 15. Subsequent oxidation of the primary hydroxy
group to carboxylic acid and esterification of the crude
(16) Hanessian, S. Total Synthesis of Natural Products: The “Chi-
ron” Approach; Pergamon Press: Oxford, 1983.
(17) For a review, see: Vorbru¨ggen, H.; Ruh-Polenz, C. Org. React.
2000, 55, 1-654.
J. Org. Chem, Vol. 69, No. 25, 2004 8597

Bhaket et al.
those reported in the literature,6c,d,7 thereby confirming
the assigned structures and stereochemical integrity.
As deprotection of 24 and 25 to form uracil polyoxin C
(26) and thymine polyoxin C (27) have already been
reported in the literature,6c,d,8 the reaction sequence
depicted in Scheme 5 represents formal total synthetic
routes to the above nucleosidic components as present
in various polyoxin and nikkomycin family of complex
peptidyl nucleoside antibiotics. In terms of brevity and
overall yield, the present method compares well with the
earlier reported syntheses of the above nucleoside frag-
ments.5,6 From an SAR investigation viewpoint too, the
versatility of the key lactone intermediate 12 toward easy
structural modifications and consequent possible access
to a variety of modified nucleoside analogues is expected
to be an added advantage of the present route.
SCHEME 5
In conclusion, utilizing a serine chiral template, the
strategy and the approach described herein demonstrates
a general protocol toward efficient construction of both
the five- and the six-membered glycosyl R-amino acid
components of the peptidyl nucleoside antibiotics. It is
expected that ongoing research involving logical exten-
sion of the present studies will provide access to some
as yet unattained targets in peptidyl nucleoside anti-
biotics research and have a positive contribution toward
realizing the high therapeutic potential of this unique
class of bioactive natural products.
Experimental Procedure
(4R)-4-[(1′S)-1-Acryloyloxy-but-3-enyl)-3-N-benzyloxy-
carbonyl-2,2-dimethyl-1,3-oxazolidine (7). To an ice-cooled
solution of the homoallylic alcohol 610a (7.98 g, 26.1 mmol) in
anhydrous CH2Cl2 (120 mL) was added N,N-diisopropylethy-
lamine (13.6 mL, 78.3 mmol), followed by dropwise addition
of acryloyl chloride (5.3 mL, 65.4 mmol) with stirring. The
reaction was allowed to come to rt and was stirred for 1 h.
After the reaction was quenched with ice-water, the organic
layer was separated, dried with Na2SO4, and concentrated
under vacuum. The residual oil was purified by flash chro-
matography (hexanes/EtOAc ) 7:3) to obtain the acrylate 7
ion intermediate (anchimeric assistance) and consequent
blocking of the R-face, followed by approach of the
nucleobase from the â-face, resulting in the observed
stereochemistry. Finally, in a two-step sequence, hydro-
lytic cleavage of the ester functionalities to form 18a and
18b, respectively, followed by hydrogenolytic removal of
the amine protecting group culminated in a concise route
to the desired pyranosyl nucleoside amino acid deriva-
tives 19a,b. The above reaction scheme clearly demon-
strates the potential utility of lactone 8 in the rapid
construction of the right-hand side nucleoside structural
framework of various pyranosyl peptidyl nucleoside
antibiotics (e.g., amipurimycin, miharamycins, etc.) and
modified analogues thereof.
In further studies, elaboration of the amino butenolide
12 to the furanosyl nucleoside amino acid was next
undertaken. It is worth mentioning that Garner and co-
workers have also utilized a similar amino lactone in
their synthetic studies on polyoxins.7 Following the same
sequence of reactions as described in Schemes 3 and 4
above, dihydroxylation of the lactone double bond af-
forded the corresponding diol 20 (Scheme 5) as the only
product.7 Partial reduction of the lactone to lactol and
subsequent peracetylation provided the triacetate 21 in
good overall yield. Hydrolysis of the acetonide to form
22, its oxidation to the corresponding carboxylic acid, and
subsequent esterification resulted in the amino acid ester
derivative 23. Coupling of this suitably protected glycosyl
donor with bis-silylated uracil and bis-silylated thymine,
respectively, afforded the corresponding nucleosides 24
and 25 in good yields. The spectral and analytical data
of both of these products were in good agreement with
as a thick yellow oil (8.9 g, 95%): [R]25 -29.2 (c 1, CH2Cl2);
D
IR (NaCl) 1726, 1700, 1634 cm-1; 1H NMR (400 MHz, CDCl3;
mixture of rotamers) δ 1.44-1.55, (4s, 6H), 2.21-2.37 (m, 2H),
3.96-4.14 (m, 3H), 4.97-5.19 (m, 4H), 5.45-5.86 (m, 3H), 6.13
(m, 1H), 6.44 (d, J ) 17.3 Hz, 1H), 7.38 (m, 5H); 13C NMR
(100.6 MHz, CDCl3; mixture of rotamers) 23.5, 24.9, 26.2, 27.2,
36.7, 58.9, 60.1, 63.6, 63.9, 67.5, 67.7, 72.0, 72.5, 94.6, 95.1,
118.5, 128.4, 128.5, 128.6, 128.7, 128.9, 131.8, 133.2, 133.5,
136.5, 152.7, 153.6, 165.9; HRMS calcd. for C20H26NO5 m/z
(M + H)+, 360.1811; found, 360.1812.
(6S)-6-[(4R)-3-N-Benzyloxycarbonyl-2,2-dimethyl-1,3-
oxazolidin-4-yl]-5,6-dihydro-pyran-2-one (8). To the acry-
late 7 (5.68 g, 15.8 mmol) dissolved in anhydrous CH2Cl2 (900
mL) was added a CH2Cl2 solution (10 mL) of bis(tricyclohex-
ylphosphine)benzylidene ruthenium(IV) dichloride [Grubbs’ 1st
generation catalyst] (0.65 g, 5 mol %), and the resulting
solution was refluxed for 12 h. A second portion of the catalyst
(0.65 g, 5 mol %) was then added to the reaction mixture, and
refluxing continued for another 12 h. After the solution was
cooled to rt, DMSO (0.1 mL), activated charcoal powder (10
g), and silica gel (25 g) were added to the reaction mixture
and stirred for 12 h. The solids were filtered off, the residue
was washed thoroughly with chloroform, and the combined
filtrate was concentrated under vacuum. The residual oily
liquid was purified by flash chromatography (EtOAc/hexanes
) 2:3) to afford the lactone 8 as a viscous yellow oil (4.29 g,
82%): [R]25D 29.1 (c 1.05, CH2Cl2); IR (NaCl) 1736, 1700 cm-1
1H NMR (400 MHz, CDCl3; mixture of rotamers) δ 1.50-1.61
;
8598 J. Org. Chem., Vol. 69, No. 25, 2004

Complex Peptidyl Nucleoside Antibiotics
(4s, 6H), 2.26-2.57 (m, 2H), 3.95 (m, 1H), 4.15-4.46 (4m, 3H),
5.08-5.21 (m, 2H), 5.95 and 6.03 (2d, J ) 9.4 Hz, 1H), 6.65
and 6.91 (2br s, 1H), 7.37 (s, 5H); 13C NMR (100.6 MHz, CDCl3;
mixture of rotamers) δ 23.2, 24.7, 26.9, 27.2, 27.5, 28.1, 59.1,
60.0, 64.8, 65.6, 67.6, 68.0, 94.9, 95.0, 121.9, 128.5, 128.7, 129.0,
136.1, 145.6, 145.9, 152.9, 154.3, 163.6, 163.8; HRMS calcd.
for C18H22NO5 m/z (M + H)+, 332.1498; found, 332.1506.
oxazolidin-4-yl]-2,5-dihydro-furan-2-one (12). Starting from
acrylate 11 (2.3 g, 6.4 mmol), the same experimental procedure
as described for preparation of 8 was followed. The crude
product was purified by flash chromatography (EtOAc/hexanes
) 3:7) to afford some unreacted starting material (0.48 g)
followed by the lactone 12 as a viscous yellow oil (1.37 g, 69%
[91% based on recovered starting material]): [R]25D -7.3 (c 1.0,
CHCl3); IR (NaCl) 1792, 1757, 1700 cm-1; 1H NMR (400 MHz,
CDCl3; mixture of rotamers) δ 1.45, 1.50, 1.58 and 1.62 (4s,
6H), 3.89-4.14 (m, 3H), 4.94-5.22 (m, 3H), 5.90 and 6.14 (2d,
J ) 4.5 Hz, 1H), 7.24 and 7.49 (2 brd, J ) 5.2 Hz,1H), 7.36 (s,
5H); 13C NMR (100.6 MHz, CDCl3; mixture of rotamers) δ 23.1,
24.7, 27.3, 28.0, 59.7, 60.2, 65.1, 66.0, 67.7, 68.2, 82.6, 95.1,
95.6, 121.6, 128.5, 128.8, 129.1, 135.9, 136.0, 152.4, 153.8,
155.5, 155.8, 172.6, 172.9; HRMS calcd. for C17H20NO5 m/z
(M + H)+, 318.1341; found, 318.1336.
1-[(4R)-3-N-Benzyloxycarbonyl-2,2-dimethyl-1,3-oxazo-
lidin-4-yl]-but-2-ene-1-one (9). To a solution of the ketone
5
10a (12 g, 39.6 mmol) in diethyl ether (250 mL) at rt was added
neutral alumina (25 g), and the mixture was stirred for 3 h.
The alumina was filtered off and washed thoroughly with
EtOAc (3 × 50 mL). The combined filtrate was concentrated,
and the residue was purified by flash chromatography (EtOAc/
hexanes ) 1:6 to 1:3) to afford the trans-R,â-unsaturated
ketone 9 as a colorless oil (10.92 g, 91%): [R]25 44.9 (c 1.02,
D
CHCl3); IR (NaCl) 1710, 1634 cm-1; 1H NMR (500 MHz, CDCl3;
mixture of rotamers) δ 1.53 and 1.59 (2s, 3H), 1.67 and 1.75
(2s, 3H), 1.88 and 1.93 (2d, J ) 6.6 Hz, 3H), 3.99 (m, 1H), 4.21
(m, 1H), 4.63 and 4.78 (2dd, J ) 3.1 & 7.5 Hz, 1H), 5.07 and
5.19 (2q, J ) 5.9 Hz, 2H), 6.23-6.31 (2d, J ) 15.6 Hz, 1H),
6.90-7.04 (m, 1H), 7.38 (m, 5H); 13C NMR (125 MHz, CDCl3;
mixture of rotamers) δ 18.4, 18.5, 23.9, 25.0, 25.1, 25.9, 63.5,
63.9, 65.5, 66.0, 66.7, 67.4, 94.7, 95.4, 126.8, 127.6, 127.7, 127.8,
127.9, 128.0, 128.3, 128.4, 136.0, 136.1, 145.0, 145.1, 151.9,
152.8, 194.9, 195.5; FABMS calcd. for C17H22NO4 m/z (M +
H)+, 304.16; found, 304.2.
Dihydroxylation of 8 to the Diol 13. Lactone 8 (4.47 g,
13.5 mmol) was dissolved in acetone/water (40 mL, 4:1), and
to this was added NMO (4.04 g, 33.7 mmol), followed by OsO4
(5% in toluene, 3.5 mL, 2 mol %). The resulting solution was
stirred at rt for 2 h. After completion of the reaction (TLC
monitoring), 10% aqueous NaHSO3 (10 mL) was added to the
reaction mixture and stirred for 30 min. The precipitate was
filtered off and washed with EtOAc (3 × 20 mL). The organic
layer was separated, and the aqueous layer was extracted with
EtOAc (3 × 20 mL). The combined organic extracts were dried
with Na2SO4 and concentrated under vacuum. Flash column
chromatography (EtOAc/hexanes ) 7:3 to 100% EtOAc) af-
forded the diol 13 as a white crystalline solid (3.46 g, 81%):
mp ) 172-173 °C; [R]25D 78.8 (c 1.02, MeOH); IR (NaCl) 3446,
(1S)-1-[(4R)-3-N-Benzyloxycarbonyl-2,2-dimethyl-1,3-
oxazolidin-4-yl]-but-2-en-1-ol (10). To a solution of the
ketone 9 (9.2 g, 30.3 mmol) in MeOH (150 mL) was added
CeCl3‚7H2O (3.72 g, 10 mmol) in one portion, and the resulting
solution was cooled to -10 °C (ice-salt bath) with continuous
stirring. A solution of Zn(BH4)2 (0.189 M in Et2O, 300 mL, 55
mmol) was then added dropwise to the reaction mixture (1.5
h), and stirring continued at the same temperature for another
1 h. The reaction was quenched by slow addition of saturated
aqueous NaHCO3 (60 mL), allowed to attain rt, and then
filtered through a sintered glass funnel. The residual solid was
washed thoroughly with EtOAc, the organic layer was sepa-
rated from the filtrate, and the aqueous layer was extracted
with EtOAc (3 × 100 mL). The combined organic extract was
washed with brine, dried (Na2SO4), and concentrated under
vacuum. The residue was purified by flash chromatography
(hexane/EtOAc ) 4:1 to 3:1) to afford the amino alcohol 10 as
1741, 1695 cm-1 1H NMR (400 MHz, DMSO-d6; mixture of
;
rotamers) δ 1.42 and 1.52 (2 br s, 6H), 1.81-1.85 (br s, 2H),
3.93-4.11 (m, 5H), 4.78 (br s, 1H), 5.12 (s, 2H), 5.43 (s, 1H),
5.61 (s, 1H), 7.38 (s, 5H); 13C NMR (100.6 MHz, DMSO-d6,
mixture of rotamers) δ 23.7, 25.3, 26.5, 27.4, 32.9, 59.9, 60.8,
63.7, 64.3, 66.8, 67.2, 67.4, 71.2, 75.5, 76.3, 94.4, 94.8, 128.5,
128.7, 129.3, 137.2, 137.3, 152.5, 153.3, 173.8; HRMS calcd.
for C18H24NO7 m/z (M + H)+, 366.1553; found, 366.1565.
Conversion of Diol 13 to the Triacetate 14. (Step 1):
The diol 13 (1.22 g, 3.34 mmol) was dissolved in anhydrous
CH2Cl2 (40 mL) and cooled to -78 °C. To this stirring solution
was added DIBAL-H (1 M in toluene, 11.0 mL, 11.0 mmol)
dropwise. The reaction was stirred at -78 °C for 1.5 h and
then quenched by careful addition of MeOH (1.0 mL). The
reaction mixture was brought to rt, diluted with EtOAc (50
mL), and saturated aqueous sodium potassium tartrate (50
mL) was added to it. The resulting mixture was stirred until
two clear layers were seen. The two layers were separated,
and the aqueous layer was extracted with EtOAc (3 × 20 mL).
The combined organic layers were dried (Na2SO4) and con-
centrated, and the crude lactol (1.06 g) was carried onto the
next step without further purification.
a colorless oil (8.15 g, 88%, anti/syn ) 92:8): [R]25 21.33 (c
D
1.05, CHCl3); IR (NaCl) 3458, 1701 cm-1; 1H NMR (400 MHz,
DMSO-d6, mixture of rotamers) δ 1.39-1.58 (m, 9H), 3.74-
4.10 (m, 4H), 4.98-5.10 (m, 3H), 5.30-5.59 (m, 2H), 7.39 (s,
5H); 13C NMR (125 MHz, CDCl3, mixture of rotamers) δ 18.1,
23.3, 25.1, 26.6, 61.4, 62.9, 64.8, 65.2, 67.2, 68.0, 73.4, 73.9,
95.1, 128.4, 128.6, 129.0, 129.9, 130.9, 136.3, 136.6, 152.9,
154.9; FABMS calcd. for C17H24NO4 m/z (M + H)+, 306.16;
found, 306.3. HPLC: CHIRALCEL OD-H, i-PrOH/hexanes )
5/95, 1.0 mL/min, 254 nm, tR major isomer (anti) ) 23.05 min
(92%), tR minor isomer (syn) ) 26.24 min (8%).
(Step 2): The lactol (1.06 g, 2.89 mmol) from the above
reaction was dissolved in anhydrous CH2Cl2 (20 mL) and
cooled to 0 °C (ice-bath), and to this solution was added
anhydrous pyridine (0.7 mL, 8.7 mmol), DMAP (25 mg,
catalytic), followed by Ac2O (2.75 mL, 28.9 mmol). The reaction
mixture was stirred at rt for 2 h and then quenched with the
addition of an ice-cooled water mixture (15 mL). The two layers
were separated, and the aqueous layer was extracted with CH2-
Cl2 (3 × 20 mL). The combined organic extracts were washed
with saturated aqueous NaHCO3 (1 × 20 mL) and brine (1 ×
20 mL), dried with Na2SO4, and concentrated under vacuum.
The residue was purified by flash chromatography (EtOAc/
hexanes ) 2:3) to obtain the triacetate 14 as a viscous
semisolid (1.27 g, 77% over two steps): IR (NaCl) 1746, 1700
(4R)-4-[(1′S)-1-Acryloyloxy-but-2-enyl)-3-N-benzyloxy-
carbonyl-2,2-dimethyl-1,3-oxazolidine (11). Starting from
allylic alcohol 10 (15.0 g, 49.2 mmol), the experimental
procedure as described for preparation of 7 was followed. The
product thus obtained was purified by flash chromatography
(hexanes/EtOAc ) 9:1) to obtain acrylate 11 as a thick yellow
oil (15.9 g, 90%): [R]25 7.2 (c 1.0, CHCl3); IR (NaCl) 1726,
D
1707 cm-1; 1H NMR (500 MHz, CDCl3; mixture of rotamers) δ
1.41-1.59 (4s, 6H), 1.67 (m, 3H), 3.97-4.19 (m, 3H), 5.10 and
5.19 (2d, J ) 12.2 Hz, 2H), 5.31-5.47 (m, 1H), 5.67-5.87 (m,
3H), 6.14 (m, 1H), 6.47 (d, J ) 17.3 Hz, 1H), 7.38 (m, 5H); 13
C
1
cm-1; H NMR (400 MHz, CDCl3, anomeric mixture) δ 1.26-
NMR (100 MHz, CDCl3; mixture of rotamers) δ 17.7, 23.1, 24.5,
25.9, 26.8, 59.3, 60.2, 63.6, 64.0, 66.9, 67.1, 73.5, 73.8, 94.2,
94.8, 126.0, 127.9, 128.0, 128.3, 128.4, 130.6, 130.7, 131.0,
131.2, 136.2, 152.3, 153.1, 165.0; FABMS calcd. for C20H26NO5
m/z (M + H)+, 360.17; found, 360.2.
1.66 (4s, 6H) 1.69-1.87 (m, 2H), 2.02-2.12 (4s, 9H), 3.86-
4.11 (m, 4H), 4.72-5.04 (m, 1H), 5.12 (br s, 2H), 5.43 and 5.55
(2s, 1H), 5.93-6.16 (m, 1H), 7.37 (s, 5H); 13C NMR (100.6 MHz,
CDCl3, anomeric mixture) δ 21.0, 21.1, 21.2, 21.3, 23.3, 24.8,
27.2, 27.6, 27.9, 32.1, 32.7, 32.8, 59.5, 60.4, 65.1, 65.7, 67.4,
(5S)-5-[(4R)-3-N-Benzyloxycarbonyl-2,2-dimethyl-1,3-
J. Org. Chem, Vol. 69, No. 25, 2004 8599

Bhaket et al.
67.6, 67.9, 69.8, 69.9, 72.1, 77.6, 89.6, 90.8, 94.5, 95.1, 128.5,
128.7, 128.8, 129.0, 136.2, 152.7, 154.0, 169.5, 169.7, 170.0,
170.1, 170.3; HRMS calcd. for C24H32NO10 m/z (M + H)+,
494.2026; found, 494.2007.
allowed to stir at rt for 5 h and then quenched by addition of
saturated aqueous NaHCO3 (10 mL). The precipitated solid
was removed by filtration and washed with CHCl3 (3 × 5 mL).
The organic layer was separated from the filtrate, and the
aqueous layer was extracted with CHCl3 (3 × 10 mL). The
combined organic extracts were washed once with brine, dried
(Na2SO4), concentrated under vacuum, and the residue was
purified by flash chromatography (EtOAc/hexanes ) 3:2 to
100%) to give the pyranosyl uracil nucleoside 17a as a white
Conversion of Triacetate 14 to the Amino Alcohol 15.
The triacetate 14 (1.4 g, 2.83 mmol) was dissolved in anhy-
drous CH2Cl2 (10 mL) and cooled to 0 °C, followed by addition
of 96% formic acid (7 mL). The reaction was stirred at 0 °C
for 2 h, after which the excess solvent was removed under high
vacuum. The residue was dissolved in CH2Cl2 (20 mL) and
washed with saturated aqueous NaHCO3 (1 × 10 mL). The
organic layer was dried (Na2SO4) and concentrated under
vacuum, and the residue was purified by flash chromatography
(EtOAc/hexanes ) 2:3 to 4:1) to afford the amino alcohol 15
as a low-melting semisolid (1.16 g, 91%): IR (NaCl) 3370, 1751,
solid (0.67 g, 67%): mp ) 103-105 °C; [R]25 18.1 (c 0.27,
D
CHCl3); IR (NaCl) 3262, 1741, 1701, 1695 cm-1; 1H NMR (400
MHz, CDCl3) δ 1.98 (s, 3H), 2.02-2.09 (m, 1H), 2.21 (s, 3H),
2.20-2.27 (m, 1H), 3.81 (s, 3H), 4.35 (br d, J ) 12.2 Hz, 1H),
4.51 (br d, J ) 8.9 Hz, 1H), 4.90 (br d, J ) 9.6 Hz, 1H), 5.14
(s, 2H), 5.58 (s, 1H), 5.74 (d, J ) 8.1 Hz, 1H), 5.95 (d, J ) 8.9
Hz, 1H), 6.10 (d, J ) 9.7 Hz, 1H), 7.14 (d, J ) 8.7 Hz, 1H),
7.38 (m, 5H), 8.93 (s, 1H); 13C NMR (100.6 MHz, CDCl3) δ 20.9,
21.4, 32.1, 53.2, 56.9, 67.3, 67.8, 68.7, 75.2, 78.7, 104.1, 128.5,
128.7, 128.9, 129.6, 136.2, 139.1, 150.6, 156.1, 162.7, 169.4,
170.1, 170.2; HRMS calcd. for C24H28N3O11 m/z (M + H)+,
534.1724; found, 534.1698.
1
1715 cm-1; H NMR (500 MHz, CDCl3, anomeric mixture) δ
1.96-2.12 (m, 11H), 2.61 (s, exchangeable with D2O, 1H),
3.58-3.82 (m, 2H), 3.87-4.35 (m, 2H), 4.84-5.10 (2m, 1H),
5.11 (br s, 2H), 5.44-5.56 (2m, 2H), 5.86 and 6.17 (2d, J ) 8.7
& 3.8 Hz, 1H), 7.38 (s, 5H); 13C NMR (125 MHz, CDCl3,
anomeric mixture) δ 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, 31.4, 32.2,
54.4, 54.5, 61.1, 61.3, 61.5, 65.3, 66.4, 66.9, 67.0, 67.2, 69.2,
71.8, 89.2, 90.8, 127.9, 128.0, 128.1, 128.2, 128.4, 128.5, 136.1,
156.1, 156.2, 169.4, 169.6, 169.7, 169.8, 170.0, 171.6; HRMS
calcd. for C21H28NO10 m/z (M + H)+, 454.1913; found, 454.2035.
Conversion of 16 to 17b. To a solution of triacetate 16
(0.096 g, 0.2 mmol) in anhydrous (CH2Cl)2 (2 mL) was added
bis(trimethylsilyl)thymine (0.13 g, 0.5 mmol), followed by
freshly distilled TMSOTf (0.22 mL, 1.0 mmol). The reaction
was stirred at rt for 5 h, and then saturated aqueous NaHCO3
(2 mL) was added. The two layers were separated, and the
aqueous layer was extracted with CHCl3 (3 × 5 mL). The
combined organic layers were washed with brine (1 × 10 mL),
dried (Na2SO4), concentrated under vacuum, and the residue
was purified by flash chromatography (EtOAc/hexanes ) 4:1)
to yield the pyranosyl thymine nucleoside 17b as a white solid
Conversion of Alcohol 15 to Methyl Ester 16. (Step 1):
To a mixture of CH3CN-CCl4-H2O (12 mL; 1:1:10) was added
NaIO4 (0.85 g, 3.9 mmol) and RuCl3‚3H2O (0.036 g, 0.14 mmol)
sequentially. The mixture was stirred at rt for 45 min and then
added into a solution of the alcohol 15 (0.96 g, 2.12 mmol) in
CH3CN (4 mL), followed by addition of a second portion of
NaIO4 (0.42 g, 1.9 mmol). The resulting mixture was stirred
at rt for 30 min, filtered through Celite, and the Celite layer
was washed with EtOAc (3 × 20 mL). The combined filtrate
was washed once with water, and the aqueous layer was re-
extracted with EtOAc (3 × 10 mL). The combined organic
extracts were dried (Na2SO4) and concentrated under vacuum.
The crude acid (∼1 g) thus obtained was carried to the next
step without further purification.
(0.070 g, 64%): mp ) 108-111 °C; [R]25 23.0 (c 0.2, CHCl3);
D
IR (NaCl) 3257, 1746, 1690 cm-1; 1H NMR (400 MHz, CDCl3)
δ 1.88 (s, 3H), 1.94 (s, 3H), 1.99-2.16 (m, 1H), 2.19 (s, 3H),
2.20-2.32 (m, 1H), 3.82 (s, 3H), 4.35 (d, J ) 11.7 Hz, 1H),
4.51 (d, J ) 7.4 Hz, 1H), 4.90 (br s, 1H), 5.13 (s, 2H), 5.58 (s,
1H), 6.10 (d, J ) 9.7 Hz, 1H), 6.16 (d, J ) 8.6 Hz, 1H), 6.99
(br s, 1H), 7.35 (s, 5H), 9.2 (s, 1H); 13C NMR (100.6 MHz,
CDCl3) δ 12.7, 12.9, 20.9, 21.4, 32.2, 51.3, 53.2, 57.0, 67.3, 67.7,
68.7, 75.0, 78.5, 112.5, 128.3, 128.4, 128.6, 128.8, 128.9, 129.5,
134.6, 135.8, 136.3, 140.1, 150.9, 156.2, 163.5, 169.6, 170.1,
170.2; HRMS calcd. for C25H30N3O11 m/z (M + H)+, 548.1880;
found, 548.1893.
(Step 2): [CAUTION: Diazomethane is an explosive and
a highly toxic gas. Explosions may occur if the substance is
dry and undiluted. All operations involving diazomethane
should be carried out in an efficient fumehood following
appropriate precaution.] To an ice-cooled biphasic solution of
KOH (8 g) in H2O (20 mL) and ether (30 mL) was added
N-methyl-N′-nitro-N-nitrosoguanindine (MNNG, 2 g) in one
lot. The organic layer turned bright yellow. The ethereal layer
was decanted into an ice-cooled Erlenmeyer flask containing
KOH pellets. The aqueous layer was washed with ether (3 ×
25 mL), and the ethereal layers were combined. The diaz-
omethane (CH2N2) thus prepared was added to a stirred
solution of the crude acid (1 g in 10 mL of ether) as obtained
from step 1 and was stirred for 30 min. Excess CH2N2 was
removed by bubbling nitrogen into the reaction mixture for
15 min, followed by removal of solvent under vacuum to yield
the crude product. Purification by flash chromatography
(EtOAc/hexanes ) 2:3) yielded the methyl ester 16 as a low-
melting solid (0.91 g, 89% over two steps): IR (NaCl) 1746
Conversion of 17a to 18a. To an ice-cooled solution of 17a
(0.096 g, 0.18 mmol) in THF/H2O (6 mL, 5:1) was added LiOH‚
H2O (0.026 g, 0.63 mmol), and the solution stirred at the same
temperature for 2 h. The reaction mixture was diluted with
H2O (5 mL) and then extracted with CH2Cl2 (1 × 10 mL). The
aqueous layer was cooled to 0 °C, and EtOAc (10 mL) was
added to it and acidified to pH ) 2-3 with 1 M HCl. The two
layers were separated, and the aqueous layer was extracted
thoroughly with EtOAc (5 ×10 mL). The combined organic
extracts were dried (Na2SO4), concentrated under vacuum, and
the residue was purified by flash chromatography (CHCl3/
MeOH ) 3:2 to 100% MeOH, with 0.01% AcOH) to yield 18a
as a white solid (0.046 g, 59%): mp ) decomposes >175 °C;
[R]25 16.4 (c 0.25, MeOH); IR (Teflon film) 3354, 1695 cm-1
;
D
1H NMR (400 MHz, CD3OD) δ 1.81-1.89 (m, 1H), 1.95-2.15
(m, 1H), 3.61 (d, J ) 7.7 Hz, 1H), 4.22 (s, 1H), 4.28 (s, 1H),
4.45 (d, J ) 11.8 Hz, 1H), 5.12 (m, 2H), 6.65 (d, J ) 8.0 Hz,
1H), 5.92 (d, J ) 9.3 Hz, 1H), 7.36 (m, 5H), 7.57 (d, J ) 7.8
Hz, 1H); 13C NMR (125 MHz, CD3OD) δ 32.7, 59.0, 66.0, 67.4,
69.3, 73.4, 80.4, 101.6, 127.3, 127.4, 127.9, 136.9, 141.3, 151.4,
156.7, 164.6, 174.7; FAB+ calcd. for C19H22N3O9 m/z (M + H)+,
436.13; found, 436.1.
1
cm-1; H NMR (500 MHz, CDCl3, anomeric mixture) δ 1.96-
2.17 (m, 11H), 3.79 (s, 3H), 4.24 (d, J ) 11.9 Hz, 1H), 4.44 (m,
1H), 4.80 (dd, J ) 3.0 & 8.5 Hz, 0.8H), 5.23 (t, J ) 3.7, 0.2H),
5.14 (s, 2H), 5.55-5.64 (m, 2H), 5.93 and 6.18 (2d, J ) 8.5 &
3.9 Hz, 1H), 7.38 (m, 5H); 13C NMR (125 MHz, CDCl3,
anomeric mixture) δ 20.4, 20.5, 20.8, 31.1, 31.5, 52.5, 52.6, 56.3,
65.3, 66.6, 67.1, 67.2, 69.1, 73.0, 89.0, 90.2, 128.1, 128.2, 128.4,
135.9, 155.6, 169.0, 169.1, 169.3, 169.5, 169.6, 169.7; FAB+
calcd. for C22H28NO11 m/z (M + H)+, 482.45; found, 482.3.
Conversion of 17b to 18b. Starting with 17b (0.059 g, 0.1
mmol), the experimental procedure for 18a was followed. The
crude product was purified by flash chromatography (CHCl3/
MeOH ) 7:3 to 100% MeOH) to afford 18b as a white solid
(0.035 g, 77%): mp ) decomposes >200 °C; [R]25D -3.08 (c 0.26,
MeOH); IR (Teflon film) 3380, 1695 cm-1; 1H NMR (400 MHz,
Conversion of 16 to 17a. To a solution of the triacetate
16 (0.96 g, 2.0 mmol) in anhydrous 1,2-dichloroethane (5 mL)
was added sequentially a solution of bis(trimethylsilyl)uracil
(2.56 g, 10 mmol) in 1,2-dichloroethane (5 mL) and freshly
distilled TMSOTf (2.17 mL, 12.0 mmol). The reaction was
8600 J. Org. Chem., Vol. 69, No. 25, 2004

Complex Peptidyl Nucleoside Antibiotics
CD3OD) δ 1.86 (s, 3H), 1.90-2.12 (m, 1H), 3.61-3.67 (m, 1H),
4.23 (br s, 2H), 4.42 (d, J ) 9.4 Hz, 1H), 5.08 (s, 2H), 5.91 (d,
J ) 9.1 Hz, 1H), 7.34 (s, 5H), 7.47 (s, 1H); 13C NMR (100.6
MHz, CD3OD) δ 11.4, 33.4, 59.5, 66.5, 67.9, 69.6, 75.1, 80.8,
110.7, 127.8, 127.9, 128.0, 128.4, 137.2, 137.5, 152.1, 157.2,
165.3, 175.4; FAB+ calcd. for C20H24N3O9 m/z (M + H)+,
450.14; found, 450.2.
followed. The crude product was purified by flash chromatog-
raphy (EtOAc/hexanes ) 3:7) to afford alcohol 22 as a thick
oil (0.167 g, 80%): 1H NMR (400 MHz, CDCl3, anomeric
mixture) δ 2.09, 2.12, 2.13 and 2.14 (4s, 9H), 2.23 (br s, 1H),
3.77 (br s, 1H), 3.88 (br s, 2H), 4.34 (m, 1 H), 5.13 (d, J ) 8.5
Hz, 2H), 5.21-5.53 (4m, 3H), 6.15 (s, 0.4H), 6.41 (d, J ) 4.3
Hz, 0.6H), 7.37 (br s, 5H); 13C NMR (125 MHz, CDCl3,
anomeric mixture) δ 20.2, 20.3, 20.4, 20.5, 20.9, 21.0, 53.4, 54.1,
61.2, 61.5, 67.0, 69.7, 70.2, 71.5, 74.1, 80.5, 83.3, 93.5, 98.0,
128.1, 128.2, 128.3, 128.4, 128.5, 136.0, 156.1, 168.0, 169.2,
169.3, 169.4, 169.5, 170.2; FAB+ calcd. for C20H26NO10 m/z
(M + H)+, 440.16; found, 440.1.
Conversion of 22 to 23. Starting with alcohol 22 (0.333 g,
0.76 mmol), the experimental procedure as in 16 was followed.
The crude product was purified by flash chromatography
(EtOAc/hexanes ) 3:7) to obtain methyl ester 23 as a semisolid
(0.291 g, 82% over two steps): IR (NaCl) 1745 cm-1; 1H NMR
(400 MHz, CDCl3, anomeric mixture) δ 1.99, 2.0 and 2.07 (3s,
9H), 3.71 (br s, 3H), 4.46-4.48 (m, 1H), 4.67-4.70 (m, 1H),
5.08 (s, 2H), 5.28 (d, J ) 4.6 Hz, 1H), 5.52-5.55 (m, 1H), 5.79
(d, J ) 8.6 Hz, 1H), 6.08 (s, 0.75H), 6.34 (d, J ) 4.4 Hz, 0.25H),
7.32 (s, 5H); 13C NMR (100.6 MHz, CDCl3, anomeric mixture)
δ 20.7, 20.8, 20.9, 21.0, 21.3, 21.4, 53.0, 53.4, 55.6, 55.8, 67.7,
69.9, 70.0, 70.6, 74.3, 77.6, 81.8, 85.3, 94.1, 98.2, 128.5, 128.7,
128.8, 128.9, 136.3, 156.1, 169.1, 169.3, 169.5, 169.7, 169.8,
169.9, 170.0, 170.5; HRMS calcd. for C21H26NO11 m/z (M + H)+,
468.1506; found, 468.1498.
Conversion of 18a to 19a. To a solution of 18a (0.028 g,
0.064 mmol) in anhydrous MeOH (3 mL) was added 10%
palladium on activated carbon (0.1 g), and the mixture was
stirred under an H2 atmosphere for 3 h. The reaction mixture
was filtered through Celite and charcoal, and the residue was
washed with MeOH. The combined filtrate was concentrated
to yield 19a as a white solid (0.015 g, 79%): mp ) decomposes
>190 °C; [R]25 -21.33 (c 0.3, MeOH); IR (Teflon film) 3380,
D
1685 cm-1; 1H NMR (400 MHz, CD3OD) δ 1.85-2.13 (m, 2H),
3.73-3.79 (m, 2H), 4.27 (br s, 1H), 4.59 (d, J ) 12.3 Hz, 1H),
5.75 (d, J ) 8.0 Hz, 1H), 5.95 (d, J ) 9.5 Hz, 1H), 7.77 (d, J )
8.1 Hz, 1H); 13C NMR (125 MHz, CD3OD) δ 32.4, 57.4, 67.6,
69.1, 71.6, 81.3, 102.1, 142.1, 151.9, 164.9, 179.2; HRMS calcd.
for C11H16N3O7 m/z (M + H)+, 302.0988; found, 302.0997.
Conversion of 18b to 19b. Starting from 18b (0.023 g, 0.05
mmol), the experimental procedure as in 19a was followed to
afford 19b as a white solid (0.011 g, 69%): mp ) decomposes
>175 °C; [R]25 -14.9 (c 0.55, MeOH); IR (Teflon film) 3365,
D
1695, 1664 cm-1; 1H NMR (500 MHz, CD3OD) δ 1.76-1.85 (m,
1H), 1.90 (s, 3H), 1.92-2.06 (m, 1H), 3.54 (dd, J ) 3.5, 10.8
Hz, 1H), 3.66-3.72 (m, 1H), 4.17-4.24 (m, 2H), 4.41 (br s, 1H),
5.95 (dd, J ) 9.4 & 15.8 Hz, 1H), 7.64 (d, J ) 15.2 Hz, 1H);
13C NMR (125 MHz, CD3OD) δ 10.8, 31.2, 32.2, 58.5, 62.3, 67.5,
67.6, 69.2, 69.4, 73.8, 74.4, 80.4, 82.2, 110.1, 137.3, 151.7, 165.0,
176.1, 176.8; ESI+ calcd. for C12H18N3O7 m/z (M + H)+, 316.11;
found, 316.1.
Conversion of 23 to 24. Starting with the triacetate 23
(0.894 g, 1.9 mmol) and bis(trimethylsilyl)uracil (2.56 g, 10
mmol), the same procedure as in 17a was followed. The
product was purified by flash chromatorgraphy (MeOH/CHCl3
) 1:49) to provide the uracil nucleoside 24 as a white solid
(0.749 g, 76%): mp ) 80-82 °C (lit.6c mp. 78-80 °C); [R]25
D
18.7 (c 1, CHCl3) [lit.6c [R]D +16 (c 1.043, CHCl3]; IR (NaCl)
Conversion of 12 to the Diol 20. Lactone 12 (1.35 g, 4.2
mmol) was dissolved in acetone/water (15 mL, 2:1), and to this
was added citric acid (0.61 g, 3.1 mmol), followed by K2OsO2-
(OH)4 (6.0 mg, 0.017 mmol). To this stirring mixture was added
NMO (0.54 g, 4.67 mmol), and stirring continued at rt for 16
h. Saturated aqueous Na2SO3 (1 mL) and EtOAc (15 mL) were
then added to the reaction mixture and stirred for 15 min. The
organic layer was separated, and the aqueous layer was
extracted with EtOAc (3 × 10 mL). The combined organic
extracts were dried (Na2SO4) and concentrated under vacuum,
and the residue was purified by flash chromatography (EtOAc/
hexanes ) 3:2) to obtain diol 20 as a white solid (1.14 g, 77%):
mp ) 147-149 °C; [R]25D 2.89 (c 0.65, CHCl3); IR (NaCl) 3420,
1
1745, 1709, 1687 cm-1; H NMR (400 MHz, CDCl3) δ 2.10 (s,
6H), 3.80 (s, 3H), 4.42 (br s, 1H), 4.85 (br s, 1H), 5.15 (ABq, J
) 7.8 & 16.2 Hz, 2H), 5.27 (t, J ) 5.9 Hz, 1H), 5.50 (t, J ) 5.7
Hz, 1H), 5.67 (d, J ) 6.4 Hz, 1H), 5.75 (br s, 1H), 5.92 (d, J )
5.5 Hz, 1H), 7.21 (d, J ) 8.2 Hz, 1H), 7.38 (s, 5H), 8.09 (br s,
1H); 13C NMR (100 MHz, CDCl3) δ 20.8, 53.4, 55.3, 67.8, 69.9,
72.7, 82.2, 88.3, 103.9, 128.5, 128.8, 129.0, 136.2, 140.2, 150.6,
163.0, 169.7, 170.0, 170.1; HRMS calcd. for C23H26N3O11 m/z
(M + H)+, 520.1567; found, 520.1571.
Conversion of 23 to 25. Starting with the triacetate 23
(0.317 g, 0.68 mmol) and bis(trimethylsilyl)thymine (0.65 g,
2.5 mmol), the same procedure as in 17b was followed. The
crude product was purified by flash chromatography (MeOH/
CHCl3 ) 1:49) to yield thymine nucleoside 25 as a white solid
3248, 1796, 1658 cm-1 1H (500 MHz, DMSO-d6, mixture of
;
rotamers) δ 1.45 and 1.52 (2s, 6H), 3.85 (d, J ) 9.4 Hz, 1H),
3.94 (dd, J ) 4.3 & 9.3 Hz, 1H), 4.04-4.20 (m, 3H), 4.32 and
4.49 (2 brs, 1H), 5.04-5.16 (m, 2H), 5.54 (s, 1H), 5.76-5.84
(m, 1H), 7.34-7.40 (m, 5H); 13C NMR (125 MHz, DMSO-d6,
mixture of rotamers) δ 22.9, 24.3, 27.0, 27.9, 55.2, 56.6, 57.2,
65.2, 65.4, 66.8, 67.2, 68.4, 68.5, 68.8, 84.2, 94.2, 94.4, 128.3,
128.4, 128.9, 136.5, 152.2, 153.6, 175.8, 175.4; HRMS calcd.
for C17H22NO7 m/z (M + H)+, 352.1396; found, 352.1384.
(0.297 g, 82%): mp ) 74-77 °C (lit. mp.7 80-82 °C); [R]25
D
21.0 (c 0.5, CHCl3) [lit.7 [R]D +19.8 (c 0.56, CHCl3]; IR (NaCl)
1
1753, 1718, 1702 cm-1; H NMR (500 MHz, CDCl3) δ 1.90 (s,
3H), 2.10 (s, 6H), 3.82 (s, 3H), 4.41 (br t, J ) 4.4 Hz, 1H), 4.85
(br s, 1H), 5.16 (dd, J ) 5.7 & 11.9 Hz, 2H), 5.31 (t, J ) 5.6
Hz, 1H), 5.54 (t, J ) 5.9 Hz, 1H), 5.95 (d, J ) 5.5 Hz, 2H),
7.07 (s, 1H), 7.33 (s, 5H), 9.18 (s, 1H); 13C NMR (100 MHz,
CDCl3) δ 12.9, 20.8, 53.4, 55.5, 67.8, 70.1, 72.7, 82.2, 88.0,
112.4, 128.5, 128.7, 128.8, 128.9, 136.0, 136.3, 151.0, 156.5,
164.1, 169.7, 170.0, 170.1; HRMS calcd. for C24H28N3O11 m/z
(M + H)+, 534.1724; found, 534.1714.
Conversion of 20 to the Triacetate 21. Starting with diol
20 (0.7 g, 2 mmol), the same experimental procedure as in 14
was followed. The crude product was purified by flash chro-
matography (EtOAc/hexanes ) 7:3) to obtain triacetate 21 as
a thick oil (0.681 g, 71% over two steps): IR (NaCl) 1752, 1709
Acknowledgment. We thank the Herman Frasch
Foundation (American Chemical Society) and The Uni-
versity of Kansas Medical Center-Center of Biomedical
Research Excellence (KUMC-COBRE) for supporting
this research. This paper is dedicated to Professor
Hiriyakkanavar Ila on the occasion of her 60th birthday.
1
cm-1; H NMR (400 MHz, CDCl3, anomeric mixture) δ 1.48,
1.56, 1.61 and 1.64 (4s, 6H), 1.87, 1.94, 2.03, 2.11, 2.12 and
2.14 (6s, 9H), 3.92-4.10 (m, 2H), 4.17-4.36 (m, 2H), 4.93-
5.42 (m, 3H), 5.63-5.45 (m, 1H), 6.09 and 6.14 (2s, 1H), 7.34-
7.47 (m, 5H); 13C NMR (100 MHz, CDCl3, anomeric mixture)
20.6, 20.9, 21.1, 21.5, 23.4, 24.9, 26.8, 27.5, 30.1, 59.3, 60.0,
65.3, 66.2, 67.7, 67.8, 71.8, 72.4, 74.7, 75.0, 80.4, 80.6, 94.6,
95.1, 98.1, 98.2, 128.5, 128.7, 128.9, 129.0, 129.1, 136.3, 136.4,
152.5, 154.0, 169.2, 169.5, 169.7, 169.8, 169.9, 170.0; HRMS
calcd. for C23H30NO10 m/z (M + H)+, 480.1870; found, 480.1879.
Supporting Information Available: General experimen-
tal methods and copies of 1H and 13C NMR spectra for all new
compounds. Crystallographic data in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
Conversion of 21 to 22. Starting with triacetate 21 (0.228
g, 0.48 mmol), the experimental procedure as in 15 was
JO048586L
J. Org. Chem, Vol. 69, No. 25, 2004 8601