Total synthesis of (-)-muraymycin D2 and its epimer

Article abstract of DOI:10.1021/jo9027193

Chemical Equetion Presentation Full details of the first total synthesis of (-)-muraymycin (MRY) D2 and its epimer, the antibacterial nucleoside natural product, are described. Key strategic elements of the approach include the preparation of the urea dipeptide moiety found in the muraymycins containing an L-epi-capreomycidine via a nitrene C-H insertion of the sulfamate 10 and the fully protected muraymycin skeleton at a late stage by an Ugi four-component reaction. Thus, the nitrene C-H insertion of the sulfamate 10 with 10 mol % of Rh2(esp)2 catalyst gave the cyclic sulfamates 11a and 11b in 47% yield (11a:11b = 1:2.0). Construction of the cyclic guanidine skeleton was effected through the HgBr₂-promoted cyclization of 42 followed by desulfonylation upon acetolysis of the oxathiazinane ring to give 43 in good yield. The amine obtained by selective removal of the Cbz group of the alcohol 44 was reacted with MeSC(=O)-L-Val-O-t-Bu (38) to provide 45, which was oxidized to the carboxylic acid 46. Reaction of 46, isonitrile 51, isovaleraldehyde, and 2,4-dimethoxybenzylamine furnished the desired Ugi products, the final deprotection of which successfully afforded (-)-MRY D2 and epi-MRY D2 (53) after HPLC separation of the diastereomers. This approach would afford ready access to a range of analogues simply by altering each component.

Full text of DOI:10.1021/jo9027193

pubs.acs.org/joc
Total Synthesis of (-)-Muraymycin D2 and Its Epimer
Tetsuya Tanino, Satoshi Ichikawa,* Motoo Shiro, and
Akira Matsuda*
Faculty of Pharmaceutical Sciences, Hokkaido University Kita-12, Nishi-6, Kita-ku,
Sapporo 060-0812, Japan, Rigaku Corporation, 3-9-12 Matsubara, Akishima,
Tokyo 196-0003, Japan
matuda@pharm.hokudai.ac.jp; ichikawa@pharm.hokudai.ac.jp
Received January 4, 2010
Full details of the first total synthesis of (-)-muraymycin (MRY) D2 and its epimer, the antibacterial
nucleoside natural product, are described. Key strategic elements of the approach include the
preparation of the urea dipeptide moiety found in the muraymycins containing an L-epi-capreomy-
cidine via a nitrene C-H insertion of the sulfamate 10 and the fully protected muraymycin skeleton at
a late stage by an Ugi four-component reaction. Thus, the nitrene C-H insertion of the sulfamate 10
with 10 mol % of Rh2(esp)2 catalyst gave the cyclic sulfamates 11a and 11b in 47% yield (11a:11b =
1:2.0). Construction of the cyclic guanidine skeleton was effected through the HgBr2-promoted
cyclization of 42 followed by desulfonylation upon acetolysis of the oxathiazinane ring to give 43 in
good yield. The amine obtained by selective removal of the Cbz group of the alcohol 44 was reacted
with MeSC(dO)-L-Val-O-t-Bu (38) to provide 45, which was oxidized to the carboxylic acid 46.
Reaction of 46, isonitrile 51, isovaleraldehyde, and 2,4-dimethoxybenzylamine furnished the desired
Ugi products, the final deprotection of which successfully afforded (-)-MRY D2 and epi-MRY D2
(53) after HPLC separation of the diastereomers. This approach would afford ready access to a range
of analogues simply by altering each component.
Introduction
for growth, the agent different from existing drugs, and
the initial “hit” scaffold amenable to structural changes
that allow for potency optimization and efficacy to generate
“lead” compounds.2-4 Antibacterial drugs tend to have
higher molecular weight and increased polarity, and they
are known to occupy a unique physicochemical property
Multidrug resistant pathogens, such as methicillin-resistant
Staphylococcus aureus (MRSA) and vancomycin-resistant
Staphylococcus aureus (VRSA), pose an ongoing public health
concern. Keeping pace with their mutations continues to be a
priority and challenge for the medical community.1 In choosing
novel antibacterial agents to address this problem, several
factors come into consideration: the target must be essential
(2) Payne, D. J.; Gwynn, M. N.; Holms, D. J.; Pompliano, D. L. Nature
Rev. Drug Discov. 2007, 6, 29–40.
(3) (a) Talbot, G. H.; Bradley, J.; Edwards, J. E., Jr.; Gilbert, D.; Scheld,
M.; Bartlett, J. G. Clin. Infect. Dis. 2006, 42, 657–668. (b) Overbye, K. M.;
Barrett, J. F. Drug Discov. Today 2005, 10, 45–52. (c) Monagham, R. L;
Barrett, J. F. Biochem. Pharmacol. 2006, 71, 901–909.
*To whom correspondence should be addressed. Phone: (þ81) 11-706-
3228. Fax: (þ81) 11-706-4980.
(1) Rice, L. B. Biochem. Pharmacol. 2006, 71, 991–995.
(4) Walsh, C. Nature Rev. Microbiol. 2003, 1, 65–70.
1366 J. Org. Chem. 2010, 75, 1366–1377
Published on Web 02/09/2010
DOI: 10.1021/jo9027193
r
2010 American Chemical Society

Tanino et al.
JOCFeatured Article
FIGURE 1. Structures of muraymycins.
space and are remarkably different from drugs of other
therapeutic areas.5-9 The antibacterial drugs currently
in use originated largely from natural products, in part
because they are likely to cover the physicochemical pro-
perty space required for antibacterial compounds better
than synthetic compounds. Therefore, natural products are
still a rich source for the discovery of novel antibacterial
agents.10
chemical structure render the MRYs intriguing and challen-
ging synthetic targets.14 However, their total synthesis has
not yet been accomplished. Since chemical modifications of
the natural product are limited, a synthetic supply would be
necessary for pursuing a structure-activity relationship in
order to develop novel antibacterial agents, and the synthetic
route is preferred because of its accessibility to a range of
analogues. Herein, we provide full details of the total syn-
thesis of MRY D2 and its epimer,15 thereby establishing a
general synthetic route toward a range of MRY analogues.
Muraymycins (MRYs) (Figure 1, 1), isolated from a
culture broth of Streptomyces sp.,11 are members of a class
of naturally occurring 60-N-alkyl-50-β-O-aminoribosyl-C-
glycyluridine antibiotics.12 The MRYs possessing a lipophi-
lic side chain have been shown to exhibit excellent antimi-
crobial activity against Gram-positive bacteria. In
particular, the efficacy of the MRYs in S. aureus infected
mice represents a promising lead for the development of new
antibacterial agents. The MRYs are strong inhibitors of the
phospho-MurNAc-pentapeptide translocase (MraY), which
is responsible for the formation of the lipid I in the pepti-
doglycan biosynthesis. Since MraY is an essential enzyme
among bacteria, it is potentially a novel target for the
development of general antibacterial agents.13 Common
features of the molecules include a 50-O-aminoribosyl-50-
C-glycyluridine moiety and an amino acid-urea-amino
acid motif involving an L-epi-capreomycidine (L-epi-Cpm),
which is a cyclic guanidine amino acid. MRYs possess a
relatively higher molecular weight and polarity, and these
structural features are in good agreement with the property
space characteristic of antibacterial agents. The promising
biological properties in conjunction with their interesting
Results and Discussion
The Ugi four-component reaction (U4CR) has long been
considered a useful method for the preparation of N-acyl-R-
aminocarboxyamides from an aldehyde, amine, isonitrile, and
carboxylic acid.16 Because of the inherent high convergent
potential of the multicomponent assembly, the U4CR has
been applied not only to medicinal chemistry for the prepara-
tion of libraries but also to the total synthesis of complex
molecules.17 The MRYs consist of three fragments, namely,
the aminoribosyluridine, lipophilic side chain, and urea dipep-
tide. Mindful of the contribution of these fragments to anti-
bacterial activity and of their efficacy in obtaining a set of
analogues, we retrosynthetically divided the target MRY
D2 into the urea dipeptide 3, ammonia, isovaleraldehyde,
and the isonitrile derivative of the aminoribosyluridine 2
for U4CR (Scheme 1). The final goal of our study is to reveal
the structure-activity relationship of MRYs. Basically, the
U4CR is nonstereoselective at the newly formed stereogenic
center to give a mixture of products, and the number of steps is
almost the same as a conventional peptide coupling strategy.
In terms of the total synthesis of MRYs itself, it is true that it is
less advantageous to use the U4CR in the final assemblage
of the nucleoside and urea dipeptide moieties. From the
medicinal chemical point of view, however, this strategy is
appropriate to examine the structure-activity relationship.
Thus, the U4CR gives us a diastereomer, which is a useful
(5) Garcia-Domenech, R.; de Julian-Ortiz, J. V. J. Chem. Inf. Comput.
Sci. 1998, 38, 445–449.
(6) Mishra, R. K.; Garcia-Domenech, R.; Galvez, J. J. Chem. Inf.
Comput. Sci. 2001, 41, 387–393.
(7) Cronin, M. T.; Aptula, A. O; Dearden, J. C.; Duffy, J. C.; Netzeva, T.
I.; Patel, H.; Rowe, P. H.; Schultz, T. W.; Worth, A. P.; Voutzoulidis, K.;
Schuurman, G. J. Chem. Inf. Comput. Sci. 2002, 42, 869–878.
(8) Murcia-Soler, M.; Perez-Gimenez, F.; Garcia-March, F. J.; Salabert-
Salvador, M T.; az-Villanueva, W.; Castro-Blea, M. J.; Villanueva-Pareja, A.
J. Chem. Inf. Comput. Sci. 2004, 44, 1031–1041.
(9) O’Shea, R.; Moser, H. E. J. Med. Chem. 2008, 51, 2871–2878.
(10) (a) Newman, D. J. J. Med. Chem. 2008, 51, 2589–2599. (b) Newman,
D. J.; Cragg, G. M. J. Nat. Prod. 2007, 70, 461–477.
(11) (a) McDonald, L. A.; Barbieri, L. R.; Carter, G. T.; Lenoy, E.;
Lotvin, J.; Petersen, P. J.; Siegel, M. M.; Singh, G.; Williamson, R. T. J. Am.
Chem. Soc. 2002, 124, 10260–10261. (b) Carter, G. T.; Lotvin, J. A.; McDonald,
L. A. WO 2002085310 A2.
(12) For FR-900493: (a) Ochi, K.; Ezaki, M.; Iwani, M.; Komori, T.;
Kohsaka, M. EP-333177, 1989. (b) Yoshida, Y.; Yamanaka, H.; Sakane, K. JP
H05-78385, 1993.
(13) (a) Bugg, T. D. H.; Lloyd, A. J.; Roper, D. I. J. Infect. Dis. Drug
Targets 2006, 6, 85–106. (b) Kimura, K.; Bugg, T. D. H. Nat. Prod. Rep.
2003, 20, 252–273.
(14) (a) Yamashita, A.; Norton, E.; Petersen, P. J.; Rasmussen, B. A.;
Singh, G.; Yang, Y.; Mansour, T. S.; Ho, D. M. Bioorg. Med. Chem. Lett.
2003, 13, 3345–3350. (b) Lin, Y. -I.; Li, Z.; Francisco, G. D; McDonald, L.
A.; Davis, R. A.; Singh, G.; Yang, Y.; Mansour, T. S. Bioorg. Med. Chem.
Lett. 2002, 12, 2341–2344.
(15) Abstract was published in:
557-558.
Nucleic Acid Symp. Ser. 2008, 52,
€
(16) For a review, see: Domling, A.; Ugi, I. Angew. Chem., Int. Ed. 2000,
39, 3168–3210.
(17) For examples, see: (a) Bauer, S. M.; Armstrong, R. W. J. Am. Chem.
Soc. 1999, 121, 6355–6366. (b) Endo, A.; Yanagisawa, A.; Abe, M.; Tohma,
S.; Kan, T.; Fukuyama, T. J. Am. Chem. Soc. 2002, 124, 6552–6554. (c)
Isaacson, J.; Loo, M.; Kobayashi, Y. Org. Lett. 2008, 10, 1461–1463.
J. Org. Chem. Vol. 75, No. 5, 2010 1367

Tanino et al.
JOCFeatured Article
SCHEME 1
TABLE 1. Nitrene C-H Insertion of 10
entry
catalyst
solvent
yield of 11 (%)
ratio (11a/11b)
1
2
3
4
5
6
Rh2(OAc)4
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
CH2Cl2
CH2Cl2
(CH2Cl)2
benzene
CF3Ph
21
47
27
35
45
45
1:1.6
1:2.0
1:2.0
1:1.9
1:1.5
1:2.0
MeCN
FIGURE 2. Selected NMR data for 11a and 11b.
SCHEME 2
compound in order to examine the structure-activity rela-
tionship. In conjunction with the nature of the multicompo-
nent assemblage, this strategy allows us to diversify accessible
analogues. For these reasons, the U4CR was chosen for the
total synthesis of MRYs in this study. Among the four
components, the urea dipeptide moiety contains a rare L-epi-
Cpm (4). Most of the previous syntheses of the Cpm class of
amino acids were racemic.18 Although an elegant asymmetric
synthesis of L-Cpm has been reported by the Williams
group,19 only a few asymmetric and stereoselective syntheses
of its epimer, L-epi-Cpm, have been reported.20 Thus, an
efficient asymmetric preparation of L-epi-Cpm was required
for the total synthesis. The structure of the L-epi-Cpm can be
regarded as an arginine analogue, where the terminal nitrogen
atom of the guanidine is inserted into the C-H bond at the
β-position constructing a cyclic guanidine moiety. Therefore,
the C-H insertion of a nitrogen atom is a straightforward
strategy to functionalize the β-position. Nitrene C-H inser-
tion has recently attracted much attention in organic syn-
thesis.21 Consequently, we embarked on the synthesis of an
L-epi-Cpm unit by using the C-H insertion of the sulfamate
10 as summarized in Scheme 2. This strategy can be quite
challenging since the C-H bond at the 3-position is less
activated toward nitrene insertion. Methylation of the com-
mercially available δ-N-Boc-R-N-Cbz-L-ornithine (7) followed
by reduction of the resulting ester 8 gave the alcohol 9, which
was subsequently converted to the corresponding sulfamate 10
without chromatography in 66% yield over three steps. With
the sulfamate 10 in hand, we then examined the C-H inser-
tion, the first key reaction of the synthesis of the MRYs; the
results are summarized in Table 1. The precursor 10 was
treated with 10 mol % of Rh2(OAc)4 in the presence of
PhI(OAc)2 and MgO in refluxing CH2Cl2 for 1.5 h, and the
desired oxathiazinane derivatives 11a and 11b were obtained in
21% yield, respectively (entry 1, 11a/11b = 1:1.6). Structures
11a and 11b were confirmed by several NMR measurements,
including HMBC and HMQC. For instance, the preferred
conformation of the oxathiazinane ring moiety of 11a was
initially postulated from the fact that relatively large coupling
constants were observed for H-4 and H-5 (J4,5 = 9.8 Hz) and
H-5 and H-6a (J5,6a = 11.0 Hz) in acetone-d6 (Figure 2),
indicating that both the N-Boc-aminoethyl group at the
4-position and the benzyloxycarbonylamino group at the
5-position are in the equatorial orientation. This was confir-
med by NOE experiments, where correlations were observed
between H-4 and H-6a (4.2%), and H-5 and H-6b (3.4%). As
for 11b, H-5 was observed as a singlet which implies that the
coupling constants for H-4 and H-5, H-5 and H-6a, and H-5
and H-6b were 0 Hz in CD3OD. NOEs were also observed for
(18) (a) Bycroft, B. W.; Cameron, D.; Johson, A. W. J. Chem. Soc. 1971,
3041–3049. (b) Bycroft, B. W.; Cameron, D.; Croft, L. R.; Johson, A. W.
Chem. Commun. 1968, 1301–1302. (c) Yamashita, A.; Norton, E. B.;
Mansour, T. S. Synth. Commun. 2004, 34, 795–803.
(19) (a) DeMong, D. E.; Williams, R. M. Tetrahedron Lett. 2001, 42,
3529–3532. (b) DeMong, D. E.; Williams, R. M. J. Am. Chem. Soc. 2003, 125,
8561–8565.
(20) Teshima, T.; Konishi, K.; Shiba, T. Bull. Chem. Soc. Jpn. 1980, 53,
508–511.
(21) For recent reviews, see: (a) Du Bois, J. Chemtracts 2005, 18, 1–13. (b)
Davies, H. M. L.; Long, M. S. Angew. Chem., Int. Ed. 2005, 44, 3518–3520.
€
(c) Muller, P.; Fruit, C. Chem. Rev. 2003, 103, 2905–2919.
1368 J. Org. Chem. Vol. 75, No. 5, 2010

Tanino et al.
JOCFeatured Article
FIGURE 3. X-ray crystal structures of 11b and 12.
removal of the sulfamate group of 10 occurred to give 9 (4%
yield) and 15 (9% yield). In order to circumvent the observed
regio- and diastereochemical outcome, the following experi-
ments were conducted. Generally, carbenes react with an
electron-rich C-H bond and the reaction rate is governed by
the electron density of the inserted C-H bond,24 and nitrenes
behave in a similar manner. It was expected that reducing
the electron density at the carbon atom at the 5-position of the
sulfamate might prevent the undesired 1,8-insertion. In order to
improve the regioselectivity of the nitrene C-H insertion, the
protecting group of the amine at the 5-position was changed to
a more electron-withdrawing phthaloyl (Phth) group and the
C-H insertion was examined (Scheme 3). Treatment of 16 with
10 mol % of Rh2(esp)2, PhI(OAc)2, and MgO in refluxing
CH2Cl2 gave the 1,6-insertion products 17a (17% yield)
and 17b (30% yield), the 1,5-insertion product 18 (17% yield),
and other decomposition products such as 19 (5% yield) and 20
(7% yield). As expected, formation of the 1,8-insertion product
was not observed at all. Because of the electron-withdrawing
nature of the Phth group, the reaction rate became slower,
and the reaction took 7 h to complete. The diastereoselectivity
(17a/17b = 1:1.8) was similar to that in the C-H insertion of 10.
Du Bois et al. reported the stereoselective nitrene insertion of
3-(2-N-phthalimido-3-sulfamoyloxypropyl)indole derivative in
which the amino group was protected with a Phth group.25 Two
possible transition states were proposed in the reaction, and the
reaction predominantly proceeded via the transition state 1
(TS1) with less steric repulsion than TS2 (Figure 5).25 Contrary
to this study, the undesired diastereomers 11b and 17b were
obtained as the major products in our case. We hypothesized
that the reversed stereoselectivity observed in the nitrene C-H
insertion of 10 or 16 could be attributed to the existence of a free
hydrogen atom attached to the nitrogen atom at the
2-position, presumably affording an intramolecular hydrogen
bond to the oxygen atom of the sulfamate group. This being the
case, TS4 would be expected to be more stable than TS3 due to
the formation of the intramolecular hydrogen bond with the
substituent at the 2-position in a pseudoaxial orientation as
shown in Figure 5. As a result, the reaction via TS4 would be
favored to give the undesired oxathiazinane derivatives such
as 11b and 17b with the 4R-configuration. Therefore, we
decided to study the effect of the protecting group at the
FIGURE 4. Structure of byproduct in the reaction of 10.
H-4 (6.5%) “and H-5 (6.0%)” upon irradiation of H-6b and
for H-5 (3.0%) upon irradiation of H-4. These results would
indicate that the N-Boc-aminoethyl group at the 4-position
and the benzyloxycarbonylamino group at the 5-position are
in the equatorial and axial orientation, respectively. In addi-
tion to the structural analysis by NMR experiments, the newly
introduced stereogenic center at the 4-position of 11a was
unambiguously determined to be the S-configuration by
X-ray crystal structure analysis of 12, which was obtained
from 11a by deprotection of the Boc group followed by
protection of the liberated amine with a Cbz group (Figure 3).
The X-ray crystal structural analysis of 12 further revealed that
the oxathiazinane ring of 12 adopted a chairlike conformation
in the solid state. The structure of 11b was also determined by its
X-ray crystal structure analysis, revealing that the oxathia-
zinane ring of 11b had a similar conformation to that of 11a.
Structural determination of 11a and 11b indicated that
the major diastereomer was the undesired 11b in entry 1.
With 10 mol % of bis[rhodium(R,R,R0,R0-tetramethyl-1,3-ben-
zenedipropionic acid)] (Rh2(esp)2) catalyst,22 the yields of the
oxathiazinanes 11a and 11b were improved to 47% yield with
10 being recovered in 11% yield (entry 2). However the catalyst
had little influence on the diastereoselectivity (11a/11b =
1:2.0). We also examined the effect of solvents in the reaction
of 10; however, no appreciable improvement in diastereoselec-
tivity was observed (entries 3-6). It should be noted that the
chemical yields of 11a and 11b were moderate and some
byproduct were isolated during the course of the reaction in
entry 2, the structures of which are described in Figure 4.
Presumably, 13 (17% yield) and 14 (5% yield) were produced
via 1,5- or 1,8-insertion of the nitrene, respectively.23 Partial
(22) Espino, C. G.; Fiori, K. W.; Kim, M.; Du Bois, J. J. Am. Chem. Soc.
2004, 126, 15378–15379.
(23) It was reported that these type of compounds were obtained in the
nitrene C-H insertion. See: Toumieux, S.; Compain, P.; Martin, O. R.;
Selkti, M. Org. Lett. 2006, 8, 4493–4496.
(24) For recent reviews, see: (a) Davies, H. M. L.; Beckwith, R. E. J.
Chem. Rev. 2003, 103, 2861–2903. (b) Davies, H. M. L.; Antoulinakis., E. G.
J. Organomet. Chem. 2001, 617-618, 47–55.
(25) When, P. M.; Lee, J.; Du Bois, J. D. Org. Lett. 2003, 5, 4823–4826.
J. Org. Chem. Vol. 75, No. 5, 2010 1369

Tanino et al.
JOCFeatured Article
SCHEME 3
activities is of interest. Muraymycin analogues containing an
L-Cpm residue, a diastereomer of the L-epi-Cpm, are key in
determining the structure-activity relationship (SAR). For a
future SAR study of the MRYs that would be analogous to
our previous studies of the caprazamycins,26 we decided to
establish a synthetic route to the urea dipeptide containing
either L-epi-Cpm or L-Cpm. The major isomer 11b was first
used to test the synthetic route to the urea dipeptide 41. Initially,
we planned to construct the bicyclic S-methylisothiourea deri-
vative 28 as the key intermediate, which could be transformed
to the bicyclic guanidine derivative 29 upon substitution of the
methylthio group with nitrogen nucleophiles as shown in
Scheme 4. Therefore, the amine 26, obtained by removal of
the Boc protecting group of 11b, would be converted to the
S-methylisothiourea 28 (SO2(OMe)2, K2CO3) via the cyclic
thiourea 27 (N,N0-thiocarbonyldiimidazole) (Scheme 4).
Substitution of the methylthio group of 28 under a variety
of conditions with nitrogen nucleophiles (e.g., ammonia,
O-benzylhydroxylamine) in the presence of AgNO3 was then
examined. However none of these efforts was successful to give
29, partly because of a competitive ring-opening of the oxa-
thiazinane moiety by attack of the nitrogen nucleophiles on the
carbon atom attached to the sulfamate group. Next, direct
formation of the cyclic guanidine was attempted by cyclization
of the methylisothiourea 30 protected with 2,2,2-trichloro-
ethoxysulfonyl (Tces) group as shown in Scheme 5. Thus, the
amine 26 was treated with MeSC(dNTces)Cl27 to afford 30 in
84% yield over two steps. Construction of the cyclic guanidine
skeleton was realized through HgBr2-promoted cyclization in
the presence of Et3N in MeCN, and the desired 31 was obtained
in 74% yield. Desulfonylation of 31 upon solvolysis of the
oxathiazinane ring was first conducted in refluxing aq MeCN
to give the desired alcohol 33 in 58% yield. No improvement of
the chemical yield of 33 was achieved under basic conditions,
the aim of which was to neutralize the sulfonic acid generated
during the reaction. The corresponding acetate 32 was obtained
in 81% yield when 31 was treated with Bu4NOAc in AcOH and
MeCN. Removal of the acetyl group of 32 (K2CO3, MeOH)
followed by protection of the resulting primary hydroxyl group
with a TBDPS group gave 34 quantitatively. The next task
involved the removal of the Cbz group selectively in the
presence of the Tces group by catalytic hydrogenolysis. In fact,
a conventional procedure for the catalytic hydrogenation of 34
(H2, Pd/C, MeOH) resulted in removal of both the Cbz and
Tces groups to give the undesired amine 36 instead of the
desired amine 35, which was obtained only in a trace amount.
The selective reduction was accomplished by the procedure
previously reported using trichloroacetic acid (TCA) as an
additive.28 Therefore, hydrogenolysis of 34 in the presence of
10 equiv of TCA in MeOH selectively afforded the amine 35 in
76% yield. With the key amine 35 in hand, we then pursued
the synthesis of the urea dipeptide 41 as shown in Scheme 6.
L-Val-O-tBu 37 was treated with N,N0-carbonyldiimidazole to
give a carbonylimidazolate intermediate, which was reacted
2-amino group. The 2-Phth derivative 21 was prepared to
examine the impact of the hydrogen atom on the diastereos-
electivity (Scheme 3). The nitrene C-H insertion of 21 pro-
ceeded under the same conditions as those for the reactions of
10 and 16, and the desired oxathiazinane derivative 22a with the
S-configuration at the 4-position was obtained selectively in
26% yield (35% based on 26% recovered starting material) in
addition to some byproducts including 13 (5% yield), 23 (4%
yield), and 24 (13% yield). The corresponding diastereomer 22b
was not obtained at all, and good diastereoselectivity was
achieved. These results suggest that the free hydrogen atom at
the 2-amino group influences the diastereoselectivity, although it
should be further elucidated in detail. The electron-withdrawing
nature of the Phth group also reduced the reactivity of the C-H
insertion, and the reaction rate was much slower than that of 10
which was protected with the Cbz group (24 h vs 1.5 h). We
further conducted the C-H insertion of a substrate 25, where
both the amino groups were protected with Phth groups in order
to control both the regio- and diastereoselectivity. However, the
electron density of the substrate in the nitrene C-H insertion was
so sensitive that no reaction occurred to provide the oxathiazi-
nane derivative even over 48 h. Further efforts will be made to
improve the yield and stereochemical outcome of the nitrene
C-H insertion reaction and verify that TS4 is indeed favored
over TS3 in Figure 5 because it is not ideal.
(26) (a) Hirano, S.; Ichikawa, S.; Matsuda, A. J. Org. Chem. 2008, 73,
569–577. (b) Hirano, S.; Ichikawa, S.; Matsuda, A. Bioorg. Med. Chem. 2008,
16, 5123–5133. (c) Hirano, S.; Ichikawa, S.; Matsuda, A. Bioorg. Med. Chem.
2008, 16, 428–436.
(27) Kim, M.; Mulcahy, J. V.; Espino, C. G.; Du Bois, J. Org. Lett. 2006,
8, 1073–1076.
(28) (a) Boger, D. L.; Kim, S. H.; Mori, Y.; Weng, J.; Rogel, O.; Castle, S.
L.; McAtee, J. J. J. Am. Chem. Soc. 2001, 123, 1862–1871. (b) Hirano, S.;
Ichikawa, S.; Matsuda, A. Tetrahedron 2007, 63, 2798–2804.
In terms of medicinal chemistry, the impact of the L-epi-Cpm
residue of MRYs on the MraY inhibitory and antibacterial
1370 J. Org. Chem. Vol. 75, No. 5, 2010

Tanino et al.
JOCFeatured Article
FIGURE 5. Proposed transition states.
SCHEME 4
SCHEME 6
TABLE 2. Optimization of Urea Formation
yield of
39 (%)
entry
R
reagents and conditions
N,N0-carbonyldiimidazole, CH2Cl2
N,N0-carbonyldiimidazole, DMAP,
CH2Cl2
trace
30a
SCHEME 5
1
2
H, 37
H
3
4
H
COSMe, 38
triphosgene, Et3N, CH2Cl2
HgBr2, N-methylmorpholine
62
82
aEpimerization at the R-position to the ester group of L-Val moiety
was observed.
carbonyl group, resulting in a failure to obtain pure 39 (entry2).
On the other hand, once we had obtained the isocyanate as a
more reactive intermediate derived from the reaction of 37
with triphosgene, the desired 39 was produced in 62% yield
(entry 3). Ultimately the urea 39 was prepared in 82% yield
without any epimerization by the reaction with MeSC(dO)-L-
Val-O-t-Bu (38) in the presence of HgBr2 and N-methylmor-
pholine in AcOEt (entry 4). After the TBDPS group deprotec-
tion, the resulting primary alcohol in 40 was oxidized in a
one-pot procedure29 to provide the carboxylic acid 41. Since we
had established the synthetic route to the urea carboxylic acid 41,
we next applied the route to synthesize the urea dipeptide
containing L-epi-Cpm as shown in Scheme 7; namely the S-
methylisothiourea derivative 42 was first prepared from 11a.
Construction of the cyclic guanidine skeleton was effected
through cyclization of 42 promoted by HgBr2, and the follow-
ing desulfonylation upon acetolysis of the oxathiazinane ring
gave 43 in 82% yield over two steps. After removal of the acetyl
group of 43, the amine obtained by selective removal of the Cbz
group of 44 was reacted with 38 to provide 45 in 64% yield over
with the amine 35. However, only a trace amount of the urea
derivative 39 was isolated from the reaction mixture (Table 2,
entry 1). Presumably, the primary amine 35 was sterically
encumbered by the presence of the cyclic guanidine moiety.
In order to increase the reactivity, DMAP was used as an
additive. Although the yield of 39 was increased to 30%,
significant epimerization occurred at the R-position to the Val
(29) Zhao, M.; Li, J.; Mano, E.; Song, Z.; Tschaen, D. M.; Grabowski,
E. J. J.; Reider, P. J. J. Org. Chem. 1999, 64, 2564–2566.
J. Org. Chem. Vol. 75, No. 5, 2010 1371

Tanino et al.
JOCFeatured Article
SCHEME 7
SCHEME 8
two steps. Finally, the alcohol 45 was oxidized to the carboxylic
acid 46. In this reaction scheme, it turned out that the primary
alcohol in 44 did not have to be protected with a TBDPS group;
consequently, the number of steps could be reduced to prepare 46.
The isonitrile component 51 linked to the 60-N-alkyl-50-
β-O-aminoribosyl-C-glycyluridine, a key structural feature
of this class of natural products, was prepared from 47,
which was previously synthesized by our group.30 In order to
employ a final global deprotection at the last stage under
acidic conditions to obtain the highly polar and base-sensitive
target molecule, the carboxylic acid 47 was protected as a t-Bu
ester by a conventional esterification (t-BuO(CdNH)CCl3,
dehyde, and 2,4-dimethoxybenzylamine were mixed in EtOH
at room temperature; however, progress of the reaction was
very slow, and only a trace amount of the Ugi products 52
was obtained after 72 h. Reaction without any solvent33 at
room temperature for 72 h provided the desired Ugi products
in 54% yield as a mixture of diastereomers (1:1) at the
R-position of the Leu residue after purification by silica gel
column chromatography. The 1H NMR analysis of the
mixture 52 gave a rather complex spectrum because each
diastereomer was observed as a mixture of rotamers. There-
fore, the final deprotection of 52 was carried out with no
further purification, and global deprotection (Zn, THF-aq
NaH2PO4, then aq 80% TFA, quant over two steps) success-
fully afforded (-)-MRY D2 and epi-MRY D2 (53) after
HPLC separation of the diastereomers. The 1H NMR spec-
trum of the synthetic (-)-MRY D2 was in good agreement
with that reported for the natural material.11b The newly
formed stereogenic center at the Leu residue of each diaster-
eomer was determined by conventional amino acid analysis34
as shown in Scheme 10. Thus, (-)-MRY D2 or 53 was heated
under reflux in 6 M aq HCl for 24 h, and the resulting mixture
was treated with Marfey’s reagent.34 The reaction mixture
was analyzed by reversed-phase HPLC (ODS, 10-60%
MeCN-H2O linear gradient containing 0.1% TFA) with
an authentic material derived from L- or D-Leu. HPLC
analysis of the reaction mixture obtained from the synthetic
MRY D2 revealed the existence of a peak with the reten-
tion time of 36.5 min, which was completely matched to that
of the authentic material derived from L-Leu (Suppor-
ting Information). These results revealed that the isomer
matching with the natural product by the 1H NMR spectrum
BF3 OEt2) to give 48 in 66% yield (Scheme 8). Hydrogeno-
3
lysis of the Cbz protecting group cleanly afforded the amine,
which was then alkylated with N-2,2,2-trichloroethoxycar-
bonyl (Troc)-3-aminopropanal by reductive alkylation to give
the secondary amine 49 in 94% yield over two steps. Upon
removal of the Troc group of 49 with Zn, the corresponding
amine derivative was treated with formic acid and 1-(3-di-
methylaminopropyl)-3-ethylcarbodiimide hydrochloride
(EDCI) in CH2Cl2 to selectively afford the terminal form-
amide 50. After extensive efforts to dehydrate 50, it was
found that treating it with triphosgene and Et3N in
CH2Cl2 at -78 °C gave the isonitrile 51 in a clean and
quantitative conversion.
With the carboxylic acid 46 and the isonitrile 51 in hand,
we undertook the final assemblage by U4CR (Scheme 9).
The U4CR in our synthetic strategy to the MRYs required
the use of ammonia as an amine. Usually ammonium acetate
or ammonium chloride is used; however, because of reac-
tivity or side reactions, the yield was low.31 In this study, 2,4-
dimethoxybenzylamine was chosen as a “masked” ammonia,
and the resulting 2,4-dimethoxybenzyl (DMB) group at
the tertiary amide site after the U4CR can be removed by
acid-catalyzed hydrolysis.32 Compounds 46, 51, isovaleral-
(30) (a) Hirano, S.; Ichikawa, S.; Matsuda, A. Angew. Chem., Int. Ed.
2005, 44, 1854–1856. (b) Hirano, S.; Ichikawa, S.; Matsuda, A. J. Org. Chem.
2007, 72, 9936–9946.
(31) (a) Rigobert, R.; Michael, B.; Uli, K.; Christin, H. Synlett 2005, 5,
757–760. (b) Uli, K.; Christina, H. Synlett 2003, 11, 1591–1594.
(32) (a) Abbas, M.; Bethke, J.; Wessjohhann, L. A. Chem. Commun. 2006,
541–543. (b) Scheffelaar, R.; Nijenhuis, R. A. K.; Paravidino, M.; Lutz, M.;
Spek, A. L.; Ehlers, A. W.; de Kanter, F. J. J.; Groen, M. B.; Orru, R. V. A.;
Ruijter, E. J. Org. Chem. 2009, 74, 660–668. (c) Plant, A.; Thompson, P.;
Williams, D. M. J. Org. Chem. 2009, 74, 4870–4873.
(33) Liu, N.; Cao, S.; Wu, J.; Yu, J.; Shen, Li.; Feng, X.; Qian, X.
Tetrahedron 2008, 64, 3966–3974.
€
(34) For a review, see: Bhushan, R.; Bruckner, H. Amino Acids 2004, 27,
231–247.
1372 J. Org. Chem. Vol. 75, No. 5, 2010

Tanino et al.
JOCFeatured Article
SCHEME 9
SCHEME 10
q, quartet; m, multiplet; br, broad. Data are presented as
follows: chemical shift (multiplicity, integration, coupling
constant). Assignments are based on 1H-1H COSY, HMBC,
and HMQC NMR spectra.
(2S)-2-Benzyloxycarbonylamino-5-tert-butoxycarbonylamino-
pentane-1-sulfamate (10). A suspension of Z-Orn(Boc)-OH (7,
50.0 g, 136 mmol) and KHCO3 (27.3 g, 272 mmol) in DMF
(1.4 L) were treated with MeI (17.0 mL, 272 mmol) at room
temperature for 10 h. The resulting mixture was concentrated in
vacuo. The residue was diluted with AcOEt (800 mL), which was
washed with H2O and saturated aq NaCl. The organic phase was
dried (Na2SO4) and concentrated in vacuo. The resulting crude
methyl ester 8 in EtOH (1.5 L) was treated with LiBH4 (3.6 g,
164 mmol) at 0 °C for 24 h. The mixture was concentrated in
vacuo, and the residue was diluted with AcOEt (800 mL), which
was washed with 1 M aq HCl, saturated aq NaHCO3, and
saturated aq NaCl. The organic phase was dried (Na2SO4) and
concentrated in vacuo to give alcohol 9. A solution of sulfamoyl
chloride in MeCN was prepared as follows. Formic acid
(26.2 mL, 683 mmol) was added dropwise over 10 min to
chlorosulfonyl isocyanate (59.5 mL, 683 mmol) at 0 °C, and
the mixture was stirred for 10 min at the same temperature.
Acetonitrile (1.5 L) was then added to the mixture, which was
stirred at room temperature for an additional 8 h. A solution
of 9 and Et3N (96 mL, 690 mmol) in N,N0-dimethylacetamide
(DMA) (100 mL) was added dropwise to the solution of
sulfamoyl chloride in MeCN at 0 °C. The mixture was
warmed to room temperature and stirred for 10 h. Saturated
aq NaHCO3 (30 mL) was added to the mixture, which was
stirred for additional 1 h. The resulting mixture was concen-
trated in vacuo, and the residue was diluted with AcOEt
(800 mL), which was washed with H2O and saturated aq
NaCl. The organic phase was dried (Na2SO4), filtered, and
concentrated in vacuo. The residue was crystallized from
hexane-AcOEt to give 10 as a white solid (38.9 g, 66%
contained the L-Leu residue as reported.11 By similar experi-
ments with the epimer 53, the Leu residue was unambi-
guously determined to be D-Leu.
Conclusions
The first total synthesis of MRY D2 and its epimer at the
Leu residue has been accomplished and the details are
described. By virtue of the multicomponent assemblage at
a late stage of the synthesis and despite the challenges this
poses because of the inherent labile nature of the MRYs due
to potential epimerization, our approach provided ready
access to a range of analogues simply by altering each
component. This initial study has set the stage for the
generation of novel antibacterial “lead” compounds based
on MRYs.
over three steps): [R]22 -17.3 (c 1.08, MeOH); mp 100 °C
D
(hexane-AcOEt); 1H NMR (DMSO-d6, 400 MHz) δ 7.48 (br
s, 2H, SO2NH2), 7.34 (m, 6H, phenyl and NH-Cbz), 6.79 (br d,
1H, NH-Boc, JNH,1 = 5.5 Hz), 5.01 (d, 2H, CH2Ph, J = 12.0
Hz), 3.90 (d, 2H, H-1, J1,2 = 5.5 Hz), 3.67 (m, 1H, H-2), 2.87
(d, 2H, H-5, J5,4 = 6.0 Hz), 1.44 (m, 2H, H-3), 1.35 (m, 11H,
Experimental Section
General Experimental Methods. NMR spectra are reported
in parts per million (δ) relative to tetramethylsilane (0.00
ppm) as internal standard unless otherwise noted. Coupling
constants (J) are reported in hertz (Hz). Abbreviations
of multiplicity are as follows: s, singlet; d, doublet; t, triplet;
t
H-4, Bu); 13C NMR (DMSO-d6, 100 MHz) δ 154.3, 154.0,
135.5, 126.8, 126.2, 126.1, 75.8, 68.5, 63.7, 48.0, 37.3, 26.7,
26.3, 24.3; FABMS-LR m/z 432 [(M þ H)þ]; FABMS-HR
calcd for C18H30N3O7S 432.1805, found 432.1799.
J. Org. Chem. Vol. 75, No. 5, 2010 1373

Tanino et al.
JOCFeatured Article
(4S,5S)-5-Benzyloxycarbonylamino-4-(2-tert-butoxycarbonyl-
amino)ethyl-2,2-dioxo-1,2,3-oxathiazinane (11a), (4R,5S)-5-Ben-
zyloxycarbonylamino-4-(2-tert-butoxycarbonylamino)ethyl-2,2-
dioxo-1,2,3-oxathiazinane (11b), 4-(3-tert-Butoxycarbonyl-
amino)propyl-2,2-dioxo-1,2,3-oxathiazole (13), (5S,8R)-9-
Benzyloxycarbonyl-8-tert-butoxycarbonylamino-2,2-dioxo-9-imino-
bicyclo[3,3,1]-1,2,3-oxathiazecane (14), and (4S)-4-(3-tert-Butoxy-
carbonylamino)propyl-2-oxazolidinone (15) (Entry 2, Table 1). A
suspension of 10 (10.0 g, 23.3 mmol), MgO (2.8 g, 70 mmol),
diacetoxyiodobenzene (12.0 g, 37.3 mmol) in CH2Cl2 were
treated with bis[rhodium (R,R,R0,R0-tetramethyl-1,3-benzene-
dipropionic acid)] (1.11 g, 2.3 mmol) at 40 °C for 1.5 h. The
insoluble portion was filtered off through a Celite pad, and the
filtrate was concentrated in vacuo. The catalyst was removed
by an amino silica gel column (6 ꢀ 20 cm, 25% AcOEt/hexane)
and concentrated in vacuo. The residue was purified by silica
gel column chromatography (6 ꢀ 20 cm, 0.3% MeOH/CHCl3)
to afford 11a (1.57 g, 16%) as a white solid, 11b (3.15 g, 32%) as
white crystals, 13 (11 mg, 17%) as a white foam, 14 (4.3 mg,
4.5%) as a yellow foam, 9 (3 mg, 3.7%) as a white solid, and 15
Hz), 4.01 (dd, 1H, H-5b, J5b,4 = 6.3, J5b,5a = 8.0 Hz), 3.90
(m, 1H, H-4), 3.14 (m, 2H, H-30), 1.52 (m, 4H, H-10and 20),
1.43 (s, 9H, tBu); 13C NMR (CDCl3, 100 MHz) δ 159.7, 156.2,
79.7, 70.3, 52.2, 39.9, 32.4, 28.5, 26.0; ESIMS-LR m/z 267
[(M þ Na)þ]; ESIMS-HR calcd for C11H20N2NaO4 267.1315,
found 267.1316.
(4S,5S)-5-Benzyloxycarbonylamino-4-(2-benzyloxycarbonyl-
amino)ethyl-2,2-dioxo-1,2,3-oxathiazinane (12). Compound 11a
(50 mg, 0.12 mmol) was treated with 4 M HCl in AcOEt for 1 h.
The resulting solution was concentrated in vacuo. A suspension
of the residue in AcOEt (3 mL) was treated with saturated
aq NaHCO3 (3 mL) and benzyl chloroformate (18.3 μL,
0.13 mmol), and the resulting biphasic layers were vigorously
stirred at room temperature for 1 h. The organic phase was
washed with H2O and saturated aq NaCl, dried (Na2SO4),
filtered, and concentrated in vacuo. The residue was crystallized
from CHCl3 to afford 12 (41 mg, 76% over two steps) as
colorless prisms. A part of the material was recrystallized from
hexane-AcOEt for an analytical sample: [R]22D -27.8 (c 0.46,
1
MeOH); mp 144 °C (hexane-AcOEt); H NMR (DMSO-d6,
(5.3 mg, 9.3%) as a white foam. Data for 11a: [R]22 -28.8
500 MHz) δ 7.59 (br d, 1H, NH-3, JNH,4 = 10.0 Hz), 7.43 (d,
1H, NH-5, JNH,5 = 8.2 Hz), 7.30 (m, 11H, phenyl and NH-20),
5.07 (s, 2H, CH2Ph), 5.00 (s, 2H, CH2Ph), 4.37 (dd, 1H, H-6a,
D
1
(c 1.17, MeOH); mp 155-157 °C; H NMR (acetone-d6, 500
MHz) δ 7.40 (m, 5H, phenyl), 6.73 (d, 1H, NH-3, J = 8.6 Hz),
6.55 (br d, 1H, NH-Cbz, J = 10.3 Hz), 6.11 (br s, 1H, NH-Boc),
5.13 (s, 2H, CH2Ph), 4.51 (dd, 1H, H-6a, J6a,5 = 5.5, J6a,6b =
J
11.0 Hz), 3.60 (dd, 1H, H-5, J5,6a = 4.5, J5,6b = 11.0 Hz), 3.43
6a,5 = 4.5, J6a,6b = 11.0 Hz), 4.18 (t, 1H, H-6b, J6b,5 = J6b,6a
=
(m, 1H, H-4), 3.10 (ddd, 1H, H-20a, J2 a,1 a = 4.6, J2 a,1 b = 8.6,
J
0
0
0
0
11.0 Hz), 4.43 (t, 1H, H-6b, J6b,5 = J6b,6a = 11.0 Hz), 3.91
(ddd, 1H, H-4, J5,6a = 5.5, J5,4 = 9.8, J5,6b = 11.0 Hz), 3.76 (dt,
1 a,1 b = 17.0 Hz), 2.96 (dt, 1H, H-20b, J2 b,1 a = J2 b,1 b = 7.6,
0
0
0
0
0
0
J2 b,2 a = 17.0 Hz), 1.84 (m, 1H, H-10a), 1.50 (m, 1H, H-10b); 13C
NMR (DMSO-d6, 100 MHz) δ 156.2, 156.0, 137.4, 136.8, 128.6,
128.6, 128.1, 128.0, 71.4, 66.1, 65.4, 56.2, 47.6, 36.9, 30.6;
FABMS-LR m/z 464 [(M þ H)þ]; FABMS-HR calcd for
C21H26N3O7S 464.1492, found 464.1484. Anal. Calcd for
0
0
0
0
1H, H-4, J4,1 a = 4.0, J4,1 b = J4,5 = 9.8 Hz), 3.32 (m, 1H,
H-20a), 3.18 (m, 1H, H-20b), 2.12 (m, 1H, 10a), 1.75 (m, 1H,
H-10b), 1.43 (s, 9H, Bu); 13C NMR (DMSO-d6, 100 MHz) δ
t
156.2, 156.0, 137.1, 128.9, 128.4, 128.3, 78.1, 71.7, 66.4, 56.5,
47.8, 36.8, 28.8; FABMS-LR m/z 452 [(M þ Na)þ]; FABMS-
HR calcd for C18H28N3NaO7S 452.1467, found 452.1448.
Anal. Calcd for C18H27N3O7S: C, 50.34; H, 6.34; N, 9.78; S,
7.47. Found: C, 50.35; H, 6.28; N, 9.70; S, 7.56. Data for 11b:
C21H25N3O7S 1/2H2O: C, 53.89; H, 5.49; N, 8.98; S, 6.85.
Found: C, 53.74; H, 5.28; N, 8.86; S 6.98.
3
(4S,5S)-5-Benzyloxycarbonylamino-4-[2-[S-methyl-N-(2,2,2-tri-
chloroethoxysulfonyl)isothioureido]]ethyl-2,2-dioxo-1,2,3-oxathia-
zinane (42). Compound 11a (100 mg, 0.23 mmol) was treated with
4 M HCl in AcOEt (10 mL) at room temperature for 3 h. The
mixture was concentrated in vacuo. A suspension of the residue in
AcOEt (10 mL) was treated with saturated aq NaHCO3 (10 mL)
and S-methyl-N-(2,2,2-trichloroethoxysulfonyl)carbonchloro-
imidothioate (97.3 mg, 0.30 mmol) at room temperature for 1 h.
The organic phase was washed with H2O, saturated aq NaCl,
dried (Na2SO4), filtered, and concentrated in vacuo. The residue
waspurifiedby silica gelcolumnchromatography(2ꢀ 2cm, 2.4%
acetone/CHCl3) to afford 42 (163 mg, 99% over two steps) as a
white foam: [R]22D -19.9 (c 1.02, CHCl3); 1H NMR (DMSO-d6,
[R]22 -30.4 (c 0.32, MeOH); mp 134-135 °C; 1H NMR
D
(CD3OD, 500 MHz) δ 7.33 (m, 5H, phenyl), 5.11 (d, 1H,
CH2Ph, J = 12.6 Hz), 5.10 (d, 1H, CH2Ph, J = 12.6 Hz),
4.84 (d, 1H, H-6a, J6a,6b = 10.3), 4.43 (d, 1H, H-6b, J6b,6a =
0
0
10.3 Hz), 3.88 (t, 1H, H-4, J4,1 a = J4,1 b = 5.2 Hz), 3.79 (s, 1H,
H-5), 3.17 (m, 1H, H-20a), 3.05 (m, 1H, H-20b), 1.68 (m, 1H,
H-10a), 1.54 (m, 1H, H-10b), 1.41 (s, 9H, Bu); 13C NMR
t
(DMSO-d6, 100 MHz) δ 156.8, 156.7, 137.3, 129.4, 129.0,
128.6, 79.0, 77.0, 56.3, 45.4, 36.6, 31.5, 29.0; FABMS-LR m/z
452 [(M þ Na)þ]; FABMS-HR calcd for C18H27N3NaO7S
452.1467, found 452.1448. Data for 13: 1H NMR (CDCl3,
500 MHz) δ 5.09 (s, 2H, H-5), 4.66 (br s, 1H, NH-Boc), 3.24
(dd, 2H, H-30, J3 ,2 = 6.9, J3 a,3 b = 12.6 Hz), 2.66 (t, 2H, H-10,
0
0
0
0
0
400 MHz) δ8.33 (br t, 1H, NH-isothiourea, JNH,2 =5.6Hz), 7.64
J1 ,2 = J1 a,1 b = 6.9 Hz), 1.99 (dt, 2H, H-20, J2 ,3 = J2 ,1 = 6.9,
0
0
0
0
0
0
0
0
(br d, 1H, NH-3, JNH,3 = 10.0 Hz), 7.47 (d, 1H, NH-5, JNH,5
8.8 Hz), 7.34 (m, 5H, phenyl), 5.03 (d, 2H, CH2Ph, J = 12.8 Hz),
4.67 (s, 2H, CH2CCl3), 4.38 (dd, 1H, H-6a, J6a,5 = 5.2, J6a,6b
11.8 Hz), 4.20 (t, 1H, H-6b, J6b,5 = J6b,6a = 11.8 Hz), 3.60 (dd,
1H, H-5, J5,6a = 5.2, J5,6b = 11.8 Hz), 3.45 (m, 2H, H-4 and H-
10a), 3.33 (m, 1H, H-10b), 1.98(m,1H, H-20a), 1.62 (m, 1H, H-20b);
13C NMR (DMSO-d6, 100 MHz) δ 168.0, 156.3, 137.1, 129.0,
128.5, 128.4, 128.1, 94.8, 78.0, 71.7, 66.3, 56.8, 47.7, 40.0, 29.5,
14.8; FABMS-LR m/z 613 [(M þ H)þ]; FABMS-HR calcd for
C17H24Cl3N4O8S3 612.9823, found 612.9828.
=
J2 a,2 b = 13.2 Hz); 13C NMR (CDCl3, 100 MHz) δ 184.8,
156.7, 80.1, 39.6, 30.1, 29.3, 28.7, 26.3; ESIMS-LR m/z 301 [(M
þ Na)þ]; ESIMS-HR calcd for C10H18N5NaO5S 301.0829,
0
0
=
found 301.0827. Data for 14: [R]22 þ57.4 (c 0.90, DMSO);
D
1H NMR (CD3CN, 400 MHz) δ 7.38 (m, 5H, phenyl), 6.46
(br d, 1H, NH-8, JNH,8 = 9.2 Hz), 5.25 (d, 1H, CH2Ph, J =
13.0 Hz), 5.13 (d, 1H, CH2Ph, J = 13.0 Hz), 4.98 (dt, 1H, H-4a,
J4a,5 = J4a,6b = 2.5, J4a,4b = 12.0 Hz), 4.66 (d, 1H, H-4b,
J
4b,4a = 12.0 Hz), 4.22 (t, 1H, H-5, J5,4b = J5,6 = 2.5 Hz), 2.63
(ddd, 1H, H-7b, J7b,6b = 5.8, J7b,6a = 8.6, J7b,6a = 14.3 Hz),
2.29 (ddd, 1H, H-6a, J6a,7a = 5.5, J6a,7b = 8.6, J6a,6b = 13.6
Hz), 1.89 (dd, 1H, H-6b, J6b,7b = 5.5, J6b,6a = 13.6 Hz), 1.64
(dd, 1H, H-7a, J7a,6a = 5.2, J7a,6b = 14.3 Hz), 1.37 (s, 9H, tBu);
13C NMR (CD3CN, 125 MHz) δ 155.3, 136.8, 129.1, 129.0,
127.7, 80.2, 79.6, 68.4, 64.9, 43.1, 28.0, 22.8, 22.1; ESIMS-LR
m/z 450 [(M þ Na)þ]; ESIMS-HR calcd for C18H25N3NaO7S1
(4S)-4-(2-Acetoxy-1S-benzyloxycarbonylaminoethyl)-2-(2,2,2-
trichloroethoxysulfonyl)iminotetrahydropyrimidine (43). Compound
42 (1.03 g, 1.68 mmol) in AcOEt (15 mL) was treated with saturated
aq NaHCO3 (15 mL) and HgBr2 (725 mg, 2.0 mmol) at room
temperature for 2 h. The insoluble portion was filtered off through a
Celite pad, and the filtrate was partitioned between AcOEt and 1 M
aq HCl. The organic phase was washed with saturated aq NaHCO3,
H2O, and saturated aq NaCl, dried (Na2SO4), and concentrated
in vacuo. The residue in MeCN (20 mL) was treated with
AcOH (106 μL, 1.84 mmol) and tetrabutylammonium acetate
450.1311, found 450.1305. Data for 15: [R]22 -6.72 (c 0.24,
D
CHCl3); 1H NMR (CDCl3, 400 MHz) δ 5.71 (br s, 1H, NH-3),
4.61 (br s, 1H, NH-Boc), 4.49 (t, 1H, H-5a, J5a,5b = J5a,4 = 13.0
1374 J. Org. Chem. Vol. 75, No. 5, 2010

Tanino et al.
JOCFeatured Article
(1.01 g, 3.36 mmol) at room temperature for 4 h. The resulting
mixture was concentrated in vacuo. The residue was suspended in
AcOEt (15 mL) and 0.4 M aq HCl (15 mL), and the resulting
biphasic layers were vigorously stirred for 1 h. The organic phase
was washed with saturated aq NaHCO3 and saturated aq NaCl,
dried (Na2SO4), filtered, and concentrated in vacuo. The residue was
purified by silica gel column chromatography (3 ꢀ 12 cm, 40%
FABMS-LR m/z 591 [(M þ Na)þ]; FABMS-HR calcd for
C18H32Cl3N5NaO7S 590.0986, found 590.0981.
Ureido Carboxylic Acid (46). A mixture of 45 (83.1 mg, 0.146
mmol) and 2,2,6,6-tetramethyl-1-piperidinyloxy radical
(2.28 mg, 0.015 mmol) in MeCN (2 mL) and phosphate buffer
(pH 6.7, 0.67 M, 1.2 mL) was treated with NaClO2 (39.6 mg,
0.53 mmol) and 5% aq NaClO (592 μL, 0.53 mmol) at room
temperature for 15 min and at 40 °C for 10 min. The resulting
mixture was partitioned between AcOEt and saturated aq
Na2S2O3, and the organic phase was washed with 1 M aq HCl
and saturated aq NaCl, dried (Na2SO4), filtered, and concen-
trated in vacuo. The residue was purified by silica gel column
chromatography (1 ꢀ 3 cm, 4% MeOH/CHCl3 containing 0.1%
AcOEt/hexane) to afford 43 (750 mg, 82% over two steps) as a white
foam: [R]22 -0.62 (c 1.03, CHCl3); H NMR (DMSO-d6, 400
1
D
MHz) δ 7.81 (br d, 2H, NH-1 and 3, JNH-1,6 = JNH-3,4 = 12.0 Hz),
7.50(brd, 1H, NH-Cbz, J= 12.0 Hz), 7.34 (m, 5H, phenyl), 5.02 (d,
2H, CH2Ph, J = 13.0 Hz), 4.56 (s, 2H, CH2CCl3), 4.17 (dd, 1H, H-
20a, J2 a,1 = 3.0, J2 a,2 b = 11.0 Hz), 3.99 (dd, 1H, H-20b, J2 b,1
=
0
0
0
0
0
0
AcOH) to afford 46 (94.0 mg, quant) as a white foam: [R]22
3.0, J2 b,2 a = 11.0 Hz), 3.76 (m, 1H, H-10), 3.47 (m, 1H, H-4), 3.23
(m, 2H, H-6), 1.96 (s, 3H, OAc), 1.74 (m, 2H, H-5); 13C NMR
(DMSO-d6, 100 MHz) δ 170.6, 156.6, 153.8, 137.2, 128.6, 128.1,
127.9, 95.0, 77.3, 65.8, 63.7, 52.0, 49.4, 36.4, 20.8, 20.5; FABMS-LR
m/z 545 [(M þ H)þ]; FABMS-HR calcd for C18H24Cl3N4O7S
545.0431, found 545.0424.
0
0
D
-1.16 (c 0.83, CHCl3); 1H NMR (DMSO-d6, 500 MHz) δ 7.83
(br s, 1H, NH-3), 7.69 (br s, 1H, NH-5), 6.58 (br d, 1H, NH-2-
epi-Cpm, JNH,2 = 9.0 Hz), 6.40 (br d, 1H, NH-2-Val, JNH-2
8.7 Hz), 4.55 (s, 1H, CH2CCl3), 4.25 (t, 1H, H-2-Val, J2,NH
J2,3 = 8.7 Hz), 3.94 (dd, 1H, H-2-epi-Cpm, J2,3 = 5.0, J2,NH
=
=
=
(4S)-4-(1S-Benzyloxycarbonylamino-2-hydroxyethyl)-2-(2,2,2-
trichloroethoxysulfonyl)iminotetrahydropyrimidine (44). A solu-
tion of 43 (53.2 mg, 0.098 mmol) in MeOH (20 mL) was treated
with K2CO3 (138 mg, 1.00 mmol) at 0 °C for 45 min. The
resulting mixture was neutralized by AcOH (114 μL, 2.0 mmol)
and concentrated in vacuo. The residue was partitioned bet-
ween AcOEt and saturated aq NaCl, and the organic layer was
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was purified by silica gel column chromatography
(1 ꢀ 6 cm, 1% MeOH/CHCl3) to afford 44 (49.0 mg, quant)
9.0 Hz), 3.70 (m, 1H, H-3-epi-Cpm, J3,2 = 5.0 Hz), 3.30 (m, 1H,
H-5a-epi-Cpm), 3.19 (m, 1H, H-5b-epi-Cpm), 1.95 (dt, 1H, H-3-
Val, J3,4a = J3,4b = 6.8, J3,2 = 13.8 Hz), 1.68 (m, 2H, H-4-epi-
Cpm), 1.39 (s, 9H, tBu), 0.83 (t, 6H, H-4a and 4b-Val, J4a,3
=
J4b,3 = 6.8 Hz); 13C NMR (DMSO-d6, 125 MHz) δ 172.4, 171.9,
158.7, 153.6, 95.1, 80.3, 77.3, 58.8, 56.3, 53.5, 38.23, 30.6, 27.9, 22.8,
19.3, 18.1; FABMS-LR (negative mode) m/z 580 [(M - H)-];
FABMS-HR calcd for C18H29Cl3N5O8S 580.0802, found 580.0790.
tert-Butyl 6-Benzyloxycarbonylamino-5-O-[5-tert-butoxycar-
bonylamino-5-deoxy-2,3-O-(3-pentylidene)-β-D-ribo-pentofura-
nosyl]-6-deoxy-2,3-O-isopropylidene-1-(uracil-1-yl)-β-D-glycelo-
L-talo-heptofuranuronate (48). Compound 4726a (1.65 g, 2.09
mmol) in CH2Cl2 (23 mL) was treated with t-BuOC(NH)CCl3
as a white foam: [R]22 -4.43 (c 1.15, MeOH); 1H NMR
D
(DMSO-d6, 500 MHz) δ 7.81 (br s, 1H, NH-6), 7.65 (br s,
1H, NH-4), 7.31 (m, 5H, phenyl), 7.26 (br d, 1H, NH-Cbz,
0
JNH,1 = 9.0 Hz), 5.01 (s, 2H, CH2Ph), 4.93 (br s, 1H, OH), 4.56
(1.17 mL, 6.6 mmol) and BF3 OEt2 (66.0 μL, 0.52 mmol) at 0 °C
3
(s, 2H, CH2CCl3), 3.53 (m, 1H, H-10), 3.49 (m, 2H, H-4 and H-
20), 3.24 (m, 1H, H-6a), 3.19 (m, 1H, H-6b), 1.72 (m, 1H, H-5a),
1.67 (m, 1H, H-5b); 13C NMR (DMSO-d6, 125 MHz) δ 156.6,
153.9, 137.2, 128.7, 128.1, 128.0, 95.1, 77.4, 65.8, 61.3, 54.8,
50.4, 37.0, 21.1; FABMS-LR m/z 503 [(M þ H)þ]; FABMS-HR
calcd for C16H22Cl3N4O6S 503.0326, found 503.0324.
for 8 h. BF3 OEt2 (66.0 μL, 0.52 mmol) was further added to the
3
mixture, which was stirred for an additional 10 h. The reaction
mixture was quenched by saturated aqueous NaHCO3 (10 mL),
and the whole mixture was extracted by AcOEt. The organic
phase was washed with saturated aq NaCl, dried (Na2SO4),
filtered, and concentrated in vacuo. The residue was purified by
neutral silica gel column chromatography (3 ꢀ 15 cm, 33%
AcOEt/hexane) to afford 48 (1.38 g, 66%) as a white foam:
Ureido Alcohol (45). A mixture of 44 (252 mg, 0.50 mmol),
Pd(OH)2 (250 mg), and trichloroacetic acid (1.63 g, 10.0 mmol)
in MeOH (10 mL) was vigorously stirred under H2 atmosphere
at room temperature for 35 min. The mixture was neutralized
with NaHCO3 (1.26 g), the insoluble was filtered off through
Celite pad, and the filtrate was concentrated in vacuo. The
residue was semipurified by silica gel column chromatography
(2 ꢀ 2 cm, 10% MeOH/CHCl3) to afford the amine, which was
immediately used to the next step. A mixture of the amine, N-
methylmorpholine (340 μL, 3.1 mmol) and (S)-tert-butyl N-(S-
methylthiocarbonyl)valinate (38, 370 mg, 1.50 mmol) in AcOEt
(10 mL) was treated with HgBr2 (540 mg, 1.50 mmol) at room
temperature for 3 h. The insoluble was filtered off through Celite
pad, and the filtrate was concentrated in vacuo. The residue was
purified by silica gel column chromatography (0.5 ꢀ 5 cm, 2%
MeOH/CHCl3) to afford 45 (181 mg, 64% over two steps) as a
white foam: [R]22D -3.19 (c 3.30, CHCl3); 1H NMR (DMSO-d6,
400 MHz) δ 7.83 (br s, 1H, NH-6), 7.61 (br s, 1H, NH-4), 6.27 (br
d, 1H, NH-2-Val, J = 5.2 Hz), 6.26 (br d, 1H, NH-10, J = 3.6
Hz), 4.96 (br t, 1H, OH, J = 6.9 Hz), 4.56 (s, 2H, CH2CCl3), 3.86
(dd, 1H, H-2-Val, J2,NH = 6.8, J2,3 = 11.4 Hz), 3.65 (m, 1H,
[R]22 þ18.5 (c 3.22, CHCl3); 1H NMR (CDCl3, 500 MHz)
D
δ 9.44 (br s, 1H, NH-3), 7.31 (m, 6H, phenyl and H-6), 5.68 (d,
1H, H-5, J5,6 = 8.0 Hz), 5.57 (s, 1H, H-10), 5.54 (br d, 1H, NH-
0
00
=
Cbz, JNH,6 = 6.3 Hz), 5.43 (br d, 1H, NH-Boc, JNH,5
9.2 Hz), 5.18 (d, 1H, CH2Ph, J = 12.0 Hz), 5.07 (s, 1H, H-100),
5.00 (d, 1H, CH2Ph, J = 12.0 Hz), 4.93 (m, 1H, H-20), 4.80 (m,
1H, H-30), 4.53 (br s, 2H, H-60, H-300), 4.48 (d, 1H, H-200, J2 ,3
=
00 00
9.7 Hz), 4.32 (d, 1H, H-50, J5 ,4 = 8.0 Hz), 4.21 (m, 1H, H-400),
4.16 (m, 1H, H-40), 3.23 (m, 1H, H-500a), 3.06 (m, 1H, 500b), 1.47
(m, 25H, tBu, acetonide, and CH2CH3), 1.30 (s, 3H, acetonide),
0.77 (t, 6H, CH2CH3, J = 7.2 Hz); 13C NMR (CDCl3, 125 MHz)
δ 169.8, 163.5, 156.3, 156.2, 150.1, 143.1, 136.3, 128.6, 128.4,
116.5, 115.0, 112.3, 102.6, 94.9, 87.1, 86.8, 86.5, 84.1, 83.4, 82.2,
81.1, 79.4, 67.3, 55.0, 43.4, 29.4, 28.9, 28.5, 28.1, 27.1, 25.5, 8.5,
7.4; FABMS-LR m/z 847 [(M þ H)þ]; FABMS-HR calcd for
C41H59N4O15 847.3977, found 847.3978.
0
0
tert-Butyl 5-O-[5-tert-Butoxycarbonylamino-5-deoxy-2,3-O-(3-
pentylidene)-β-D-ribo-pentofuranosyl]-6-N-[3-(2,2,2-trichloroethoxy-
carbonylamino)propyl]amino-6-deoxy-2,3-O-isopropylidene-
1-(uracil-1-yl)-β-D-glycelo-L-talo-heptofuranuronate (49). A
mixture of 48 (115 mg, 0.13 mmol) and 10% Pd/C (40 mg) in
MeOH (2 mL) was vigorously stirred under H2 atmosphere
at room temperature for 30 min. The catalyst was filtered off
through a Celite pad, and the filtrate was concentrated in
vacuo to give a crude amine. A solution of the amine and
3-(2,2,2-trichloroethoxycarbonyl)aminopropanal (33 mg,
0.13 mmol) and AcOH (80 μL, 1.3 mmol) in CH2Cl2 (2 mL)
H-20a), 3.55 (ddd, 1H, H-10, J1 ,4 = 4.6, J1 ,2 a = 11.4, J1 ,2 b
16.5 Hz), 3.42 (m, 1H, H-20b), 3.39 (m, 1H, H-4-epi-Cpm, J4,1
=
=
0
0
0
0
0
0
4.6 Hz), 3.29 (m, 1H, H-6a), 3.19 (dd, 1H, H-6b, J6b,5 = 4.5,
J6b,6a = 11.2 Hz), 1.95 (dd, 1H, H-3-Val, J3,4 = 8.6, J3,2 = 11.4
Hz), 1.72 (m, 2H, H-5), 1.32 (s, 9H, tBu), 0.85 (d, 3H, H-4a-Val,
J4a,3 = 8.6 Hz), 0.82 (d, 3H, H-4b-Val, J4b,3 = 8.6 Hz); 13C
NMR (DMSO-d6, 100 MHz) δ 172.0, 158.1, 153.7, 95.1, 80.4,
77.3, 60.9, 58.7, 52.3, 49.8, 36.6, 30.5, 27.9, 20.5, 19.3, 17.9;
J. Org. Chem. Vol. 75, No. 5, 2010 1375

Tanino et al.
JOCFeatured Article
was treated with NaBH(OAc)3 (85 mg, 0.39 mmol) at room
temperature for 30 min. The reaction was quenched by saturated
aqueous NaHCO3 (500 μL), and the whole mixture was parti-
tioned between AcOEt and saturated aq NaHCO3. The organic
phase was washed with saturated aq NaCl, dried (Na2SO4),
filtered, and concentrated in vacuo. The residue was purified by
neutral silica gel column chromatography (2 ꢀ 2 cm, 60% AcOEt/
hexane) to afford 49 (119 mg, 94% over two steps) as a white foam:
[R]22D þ38.6 (c 1.03, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 8.67
(br s, 1H, NH-3), 7.21 (d, 1H, H-6, J6,5 = 8.0 Hz), 5.98 (br s, 1H,
NH-Troc), 5.75 (br s, 1H, NH-Boc), 5.68 (d, 1H, H-5, J5,6 = 8.0
treated with triphosgene (22.0 mg, 0.075 mmol) at -78 °C for
20 min. The mixture was partitioned between AcOEt and
saturated aq NaHCO3, and the organic phase was washed
with saturated aq NaCl, dried (Na2SO4), filtered, and concen-
trated in vacuo to give 51 (19.5 mg, quant) as a white foam:
[R]22 þ26.2 (c 1.04, CHCl3); H NMR (CDCl3, 400 MHz) δ
1
D
8.68 (br s, 1H, NH-3), 7.22 (d, 1H, H-6, J6,5 = 8.2 Hz), 5.81 (br
s, 1H, NH-Boc), 5.67 (d, 1H, H-5, J5,6 = 8.2 Hz), 5.470(0s, 1H,
H-10), 5.14 (d, 1H, H-20, J2 ,3 = 6.4 Hz), 4.97 (s, 1H, H-1 ), 4.77
0
0
0
00
(dd, 1H, H-30, J3 ,2 = 6.4, J3 ,4 = 5.6 Hz), 4.51 (m, 3H, H-4 , 2
0
0
0
0
and 300), 4.22 (m, 1H, H-400), 4.07 (m, 1H, H-50), 3.50 (m, 2H, H-
Hz), 5.46 (s, 1H, H-10), 5.17 (d, 1H, H-20, J2 ,3 = 5.7 Hz), 4.95 (s,
100), 3.20 (m, 2H, H-60, 500a), 3.09 (ddd, 1H, H-500b, J5 b,NH
=
0
0
00
1H, H-100), 4.84 (t, 1H, H-30, J3 ,2 = J3 ,4 = 5.7 Hz), 4.75 (d, 1H,
CH2CCl3, J = 13.0 Hz), 4.69 (d, 1H, CH2CCl3, J = 13.0 Hz), 4.55
4.0, J5 b,4 = 7.2, J5 b,5 a = 15.1 Hz), 2.91 (dt, 1H, H-80a,
0
0
0
0
00
00
00
00
J8 a,9 a = 5.7, J8 a,9 b = J8 a,8 b = 12.0 Hz), 2.44 (dt, 1H, H-80b,
0 0 0 0 0 0
(m, 2H, H-40 and 300, J4 ,3 = 5.7 Hz), 4.49 (m, 1H, H-2 ), 4.22 (m,
8 b,9 a = 6.0, J8 b,9 b = J8 b,8 a = 12.0 Hz), 1.77 (m, 2H, H-90),
0 0 0 0 0 0
J
00
0
0
1H, H-400), 4.08 (m, 1H, H-50), 3.33 (d, 2H, H-80, J8 a,8 b = 5.2 Hz),
1.56 (s, 4H, CH2CH3), 1.51 (s, 9H, tBu), 1.44 (s, 9H, tBu), 1.35
(s, 3H, acetonide), 1.24 (s, 3H, acetonide), 0.75 (m, 6H,
CH2CH3); 13C NMR (CDCl3, 100 MHz) δ 172.1, 162.9,
156.1, 155.4, 149.8, 143.7, 115.9, 114.7, 112.8, 102.3, 96.5,
88.5, 86.8, 86.6, 84.9, 82.7, 82.0, 81.9, 79.0, 61.5, 45.7, 44.0,
43.1, 39.2, 29.7, 29.3, 28.7, 28.4, 28.2, 27.0, 25.2, 8.4, 7.2;
0
0
3.26 (m, 1H, 500a), 3.23 (s, 1H, H-60), 3.05 (d, 1H, 500b, J5 b,5 a
00
00
=
6.9 Hz), 2.90 (m, 1H, H-100a), 2.33 (m, 1H, H-100b), 1.70 (m, 1H,
H-90a), 1.56 (m, 1H, H-90b), 1.55 (s, 4H, CH2CH3), 1.51 (s, 9H,
tBu), 1.44 (s, 12H, tBu and acetonide), 1.37 (s, 3H, acetonide), 0.76
(m, 6H, CH2CH3); 13C NMR (CDCl3, 125 MHz) δ 172.0, 162.9,
156.1, 154.5, 149.9, 143.8, 115.9, 114.8, 112.8, 102.3, 96.7, 95.8,
89.0, 86.7, 84.8, 82.6, 82.0, 81.8, 81.5, 79.0, 74.4, 62.5, 45.2, 43.3,
38.7, 29.3, 28.8, 28.4, 28.2, 26.8, 25.1, 8.4, 7.3; ESIMS-LR m/z 946
[(M þ H)þ]; ESIMS-HR calcd for C39H61Cl3N5O15 944.3222,
found 944.3230.
tert-Butyl 5-O-[5-tert-Butoxycarbonylamino-5-deoxy-2,3-
O-(3-pentylidene)-β-D-ribo-pentofuranosyl]-6-deoxy-6-N-(3-formyl-
aminopropyl)amino-2,3-O-isopropylidene-1-(uracil-1-yl)- β-D-
glycelo-L-talo-heptofuranuronate (50). A mixture of 49 (28.9
mg, 0.031 mmol) and NH4Cl (50.0 mg, 0.93 mmol) in MeOH
(1 mL) was treated with activated Zn powder (85% purity,
33.3 mg, 0.51 mmol) at room temperature for 2 h. The
insoluble portion was filtered off through a Celite pad, and
the filtrate was concentrated in vacuo. A mixture of the
residue and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide
hydrochloride (EDCI, 35 mg, 0.18 mmol) in CH2Cl2 (1 mL) at
0 °C was treated with formic acid (10.0 μL, 0.25 mmol) for
15 h. The mixture was partitioned between AcOEt and H2O,
and the organic phase was washed with saturated aq NaCl,
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was purified by neutral silica gel column chromatog-
raphy (2 ꢀ 4 cm, 66% AcOEt/hexane containing 3% MeOH)
to afford 50 (30.4 mg, 99% over two steps) as a white foam:
[R]22D þ30.7 (c 1.09, CHCl3); 1H NMR (CDCl3, 500 MHz) δ
8.67 (br s, 1H, NH-3), 7.21 (d, 1H, H-6, J6,5 = 8.0 Hz), 5.98 (br
s, 1H, NH-Troc), 5.75 (br s, 1H, NH-Boc), 5.68 (d, 1H, H-5,
ESIMS-LR m/z 802 [(M þ Na)þ]; ESIMS-HR calcd for C37
-
H57N5NaO13 802.3851, found 802.3824.
(-)-Muraymycin D2 and epi-Muraymycin D2 (53). Carbo-
xylic acid 46 (33.0 mg, 0.052 mmol), isovaleraldehyde (19.5 μL,
0.13 mmol), and 2,4-dimethoxybenzylamine (19.2 μL, 0.13
mmol) in EtOH (1 mL) were concentrated in vacuo. The residue
was coevaporated with EtOH (1 mL), and this was repeated
3 times. The residue and the isonitrile 51 (20.9 mg, 0.026 mmol)
in EtOH (1 mL) were concentrated in vacuo, and the resulting
syrup was kept at room temperature for 72 h. The mixture was
diluted with AcOEt, and the solution was washed with H2O and
saturated aq NaCl, dried (Na2SO4), filtered, and concentrated in
vacuo. The residue was purified by neutral silica gel column
chromatography (0.5 ꢀ 2 cm, 66% AcOEt/hexane) to afford 52
(22.0 mg, 54%, ESIMS-LR m/z 1621 [(M þ Na)þ]) as a white
foam. Compound 52 (8.7 mg, 5.6 mmol) in THF (1 mL) and 1 M
aq NaH2PO4 (500 μL) was treated with Zn (5.7 mg, 0.088 mmol)
at room temperature for a week. After the mixture was con-
centrated in vacuo, the residue was suspended in AcOEt. The
resulting insoluble was filtered off through a short silica gel pad,
and the filtrate was concentrated in vacuo. The residue was
treated with 80% aq TFA at room temperature for 8 h. After the
mixture was concentrated in vacuo, the residue was purified by
HPLC (YMC J0sphere ODS M80, 4.6 ꢀ 150 mm, 0.1% TFA,
23% MeOH-H2O, 7.2 min for 53, 20.0 min for muraymycin
D2) to afford (-)-muraymycin D2 (2.6 mg, 52%) and 53
(2.4 mg, 48%) as a white foam. Data for muraymycin D2:
[R]22D -3.33 (c 0.32, H2O); 1H NMR (D2O, 500 MHz) δ 7.72 (d,
1H, H-6, J6-5 = 8.0 Hz), 5.89 (d, 1H, H-5, J5,6 = 8.0 Hz), 5.82
J
5,6 = 8.0 Hz), 5.46 (s, 1H, H-10), 5.17 (d, 1H, H-20, J2 ,3 = 5.7
0 0
Hz), 4.95 (s, 1H, H-100), 4.84 (t, 1H, H-30, J3 ,2 = J3 ,4 = 5.7
Hz), 4.75 (d, 1H, CH2CCl3, J = 13.0 Hz), 4.69 (d, 1H,
0
0
0
0
CH2CCl3, J = 13.0 Hz), 4.55 (m, 2H, H-40 and 300, J4 ,3
=
(s, 1H, H-10), 5.23 (s, 1H, H-100), 4.61 (d, 1H, H-50, J5 ,6
=
0
0
0
0
5.7 Hz), 4.49 (m, 1H, H-200), 4.22 (m, 1H, H-400), 4.08 (m, 1H,
3.5 Hz), 4.45 (t, 1H, H-20, J2 ,3 = J2 ,1 = 3.7 Hz), 4.41 (d, 1H,
H-2-epi-Cpm, J2,3 = 7.5 Hz), 4.33 (m, 1H, H-30), 4.30 (m, 1H, H-
30), 4.27 (m, 1H, H-2-Leu), 4.16-4.17 (m, 3H, H-200, 300 and 400),
3.99 (s, 1H, H-60), 3.92 (d, 1H, H-2-Val, J2,3 = 5.2 Hz), 3.95 (dd,
1H, H-3-epi-Cpm, J3,4a = 6.6, J3,4b = 12.3 Hz), 3.35 (m, 2H, H-
0
0
0
0
H-50), 3.33 (d, 2H, H-80, J8 a,8 b = 5.2 Hz), 3.26 (m, 1H, 500a),
0
0
3.23 (s, 1H, H-60), 3.05 (d, 1H, H-500b, J5 b,5 a = 6.9 Hz), 2.90
(m, 1H, H-100a), 2.33 (m, 1H, H-100b), 1.70 (m, 1H, H-90a),
1.56 (m, 1H, H-90b), 1.55 (s, 4H, CH2CH3), 1.51 (s, 9H, tBu),
1.44 (s, 12H, tBu and acetonide), 1.37 (s, 3H, acetonide), 0.76
(m, 6H, CH2CH3); 13C NMR (CDCl3, 125 MHz) δ 172.1,
162.9, 156.1, 154.5, 149.9, 143.8, 116.0, 114.8, 112.8, 102.3,
96.7, 95.8, 89.0, 86.7, 84.8, 82.6, 82.0, 81.8, 81.5, 79.0, 74.4,
62.5, 45.2, 43.3, 38.7, 29.3, 28.8, 28.4, 28.2, 26.8, 25.1, 8.4, 7.3;
00
00
5-epi-Cpm), 3.31 (m, 1H, H-500a), 3.27 (t, 2H, H-100, J10 ,9 a
0
0
=
J10 ,9 b = 6.0 Hz), 3.18 (m, 1H, H-80), 3.14 (dd, 1H, H-500b,
0
0
00
00
00
J5 b,4 = 8.0, J5 b,5 a = 13.8 Hz), 2.11 (ddd, 1H, H-3-Val,
00
J
3,4a = 3.4, J3,4b = 6.3, J3,2 = 12.6 Hz), 1.91 (m, 2H, H-4-epi-
Cpm), 1.91 (m, 2H, H-90), 1.67 (m, 1H, H-3a-Leu), 1.61 (m, 1H,
H-4-Leu), 1.55 (m, 1H, H-3b-Leu), 0.94 (d, 6H, H-4-Val and H-
5-Leu, J = 6.3 Hz), 0.87 (m, 3H, H-4-Val), 0.86 (d, 3H, H-4-Leu,
ESIMS-LR m/z 798 [(M þ H)þ]; ESIMS-HR calcd for C37
-
H
60N5O14 798.4137, found 798.4142.
tert-Butyl 5-O-[5-tert-Butoxycarbonylamino-5-deoxy-2,3-
J
5,4 = 5.3 Hz); 13C NMR (D2O, 125 MHz) δ 177.5, 174.9, 171.9,
O-(3-pentylidene)-β-D-ribo-pentofuranosyl]-6-deoxy-6-(3-isocyano-
propyl)amino-2,3-O-isopropylidene-1-(uracil-1-yl)-β-D-glycelo-
L-talo-heptofuranuronate (51). A mixture of 50 (20 mg, 0.025
mmol) and Et3N (62.0 μL, 0.45 mmol) in CH2Cl2 (2 mL) was
170.9, 166.1, 159.1, 153.9, 151.4, 142.6, 109.0, 102.3, 91.9, 84.4,
79.0, 75.8, 74.8, 72.5, 71.9, 69.2, 63.6, 59.5, 55.7, 52.7, 49.5, 45.8,
42.5, 39.7, 36.0, 35.9, 30.2, 25.2, 24.4, 22.2, 20.6, 20.5, 18.7, 16.9;
ESIMS-LR m/z 458 [(M þ 2H)2þ]; ESIMS-HR calcd for
1376 J. Org. Chem. Vol. 75, No. 5, 2010

Tanino et al.
JOCFeatured Article
C37H61N11O16 915.4298, found 915.4337. Data for 32: [R]22
ESIMS-LR m/z 458 [(M þ 2H)2þ]; ESIMS-HR calcd for
D
þ3.25 (c 0.37, H2O); 1H NMR (D2O, 500 MHz) δ 7.73 (d, 1H,
H-6, J6,5 = 8.0 Hz), 5.90 (d, 1H, H-5, J5,6 = 8.0 Hz), 5.84 (s, 1H,
H-10), 5.21 (s, 1H, H-100), 4.62 (s, 1H, H-50), 4.43 (s, 1H, H-20),
4.35 (m, 3H, H-30,40 and H-2-epi-Cpm), 4.19 (m, 4H, H-200,300,400
and H-2-Leu), 4.00 (m, 1H, H-2-Val), 3.98 (s, 1H, H-60), 3.89 (m,
1H, H-3-epi-Cpm), 3.36 (m, 4H, H-500 and H-5-epi-Cpm), 3.20
(m, 3H, H-100 and H-80a), 3.17 (m, 1H, H-80b), 2.15 (m, 1H,
H-3-Val), 1.92 (m, 3H, H-90a and H-4-epi-Cpm), 1.84 (m, 1H,
H-90b), 1.61 (m, 4H, H-3 and H-4-Leu), 0.95 (d, 6H, H-4-Val
and H-5-Leu, J = 8.0 Hz), 0.93 (m, 6H, H-4-Val and H-4-Leu);
13C NMR (D2O, 125 MHz) δ 177.5, 175.0, 172.3, 170.8, 166.1,
159.2, 153.7, 151.3, 142.6, 108.9, 102.2, 91.8, 84.4, 79.1, 75.7,
74.9, 72.6, 71.9, 69.0, 63.5, 59.6, 55.8, 52.9, 49.5, 45.2, 42.4,
39.5, 35.7, 35.5, 29.9, 25.0, 24.5, 22.3, 20.6, 20.3, 18.7, 17.0;
C37H61N11O16 915.4298, found 915.4343.
Acknowledgment. This work was supported by grants-
in-aid for scientific research from the Ministry of Education,
Science, Sports, and Culture. We thank Dr. L. A. McDonald
for kindly providing the characterization data of MRY D2.
We also thank Dr. S. Hirano for initial contribution to this
work and Ms. S. Oka (Center for Instrumental Analysis,
Hokkaido University) for measurement of the mass spectra.
Supporting Information Available: NMR data for 1H NMR
and 13C NMR spectra for all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 5, 2010 1377