A versatile strategy for the synthesis of N-acetyl-bacillosamine-containing disaccharide building blocks related to bacterial O-antigens

Article abstract of DOI:10.1055/s-2006-939057

A N-phenyltrifluoroacetimidate glycosyl donor of bacillosamine, a 2,4-diaminosugar contained in several O-antigens from pathogenic bacteria, was synthesized starting from the known peracetylated D-fucal and was demonstrated to be effective for the high-yi

Full text of DOI:10.1055/s-2006-939057

LETTER
825
A Versatile Strategy for the Synthesis of N-Acetyl-bacillosamine-Containing
Disaccharide Building Blocks Related to Bacterial O-Antigens
N
-Acetyl-bacill
m
osamine-Containing
i
D
isac
l
i
B
uildi
a
Dipartimento di Chimica Organica e Biochimica, Università di Napoli ‘Federico II’, Complesso Universitario Monte Santangelo,
Via Cintia 4, 80126 Napoli, Italy
Fax +39(81)674393; E-mail: ebedini@unina.it
Received 27 January 2006
O
Abstract: A N-phenyltrifluoroacetimidate glycosyl donor of bacil-
RHN
losamine, a 2,4-diaminosugar contained in several O-antigens from
pathogenic bacteria, was synthesized starting from the known per-
acetylated D-fucal and was demonstrated to be effective for the
high-yield coupling to bacillosamine-containing disaccharides. The
stereoselectivity of the glycosylations was from moderate to very
good depending on the solvent and glycosyl acceptor. The synthetic
path was then slightly modified to obtain a similar glycosyl donor
with an axial acetyl group on position 4. This building block could
be coupled to give a disaccharide, that after five steps (azido reduc-
tion, acetylation, O-deacetylation, mesylation, and azide substitu-
O
AcNH
O
R = Ac,
(3S)-CH3CH(OH)CH2CO-
(3S,5S)-CH3CH(OH)CH2CH(OH)CH2CO-
Figure 1 Structural features of bacillosamine in natural polysaccha-
rides.
polysaccharides N-acetyl-bacillosamine can occur in dif-
ferent structural features: the amino group at position 2 is
almost always masked as an acetamido, whereas three dif-
ferent groups were found to acylate the amino group at po-
sition 4. In addition, it can occur as both an a- and b-
glycoside (Figure 1).
tion) afforded
a bacillosamine-containing disaccharide with
differently protected amino functions, in order to provide access to
all the currently known structural features of bacillosamine-contain-
ing disaccharides known to date contained in natural polysaccha-
rides.
Key words: carbohydrates, O-antigens, aminosugar, bacillos-
In spite of the wide occurrence of bacillosamine species in
O-antigenic polysaccharides isolated from microorgan-
isms, they are pathogenic for humans and mam-
mals.3b,e,f,i,k,l,m,p It can be isolated from phytopathogenic
amine, glycosylation
Bacillosamine is a diaminosugar (2,4-diacetamido-2,4,6-
trideoxy-D-glucose) exclusively found in the prokaryotic
kingdom. Its name derives from Bacillus licheniformis
ATCC 9945, since it was isolated for the first time from
this microorganism as a component of a cell-wall associ-
ated polysaccharide.1,2 N-Acetyl-bacillosamine and its
differently N-acylated derivatives were subsequently
demonstrated to be distributed widely in the prokaryotic
kingdom. They were recognized to be components of the
repeating unit of O-antigens from several Gram-negative
bacterial genera (Vibrio, Flavobacterium, Pseudomonas,
Pseudoalteromonas, Shewanella, Acinetobacter, Thioba-
cillus, Ralstonia, Fusobacterium)3 and of the core region
of LPS from Francisella novicida U112.4 N-Acetyl-bacil-
losamine was also found in exopolysaccharides from both
bacilli5 and an alkaliphilic bacterium,6 in a capsular
polysaccharide from Alteromonas sp. CMM 155,7 in a
teichoic acid from Streptococcus pneumoniae,8 and in the
S-layer glycoprotein from Clostridium symbiosum
HB25.9 Recently, it was also demonstrated that N-acetyl-
bacillosamine anchors N-glycan to asparagine in the first
glycoprotein extracted from a Gram-negative bacterium,
OAc
OAc
O
O
a
AcO
AcO
N3
SePh
1
2
b
OMs
OH
O
O
d
BnO
BnO
c
N3
N3
SePh
SePh
4
3
e
O
O
f
N3
BnO
N3
BnO
N3
N3
O
CF3
SePh
PhN
7
5
Scheme 1 Reagents and conditions: a) TMSN3, Ph2Se2, PhI(OAc)2,
CH2Cl2, –30 °C to –10 °C, 150 min, 74%; b) i. NaOMe, MeOH, r.t.,
4 h; ii. Bu2SnO, 10:1 benzene–MeOH, reflux, 90 min; iii. BnBr,
TBAB, toluene, 65 °C, 3 h, 75% over three steps; c) i. Tf2O, 1:1 py–
CH2Cl2, 0 °C to r.t., 3 h; ii. NaN3, TBAB, DMF, 80 °C, 2 h; d) MsCl,
DMAP, CH2Cl2, r.t., 3 h, 68%; e) NaN3, TBAB, DMF, 80 °C, 48 h,
72% (20% recovered 3); f) i. NIS, 1:1 THF–H2O, r.t., 1 h; ii.
CF3C(NPh)Cl, NaH, 4 Å MS, CH2Cl2, 0 °C to r.t., 4 h, 75% (b/a 2:1)
over 2 steps.
namely the PEB3 protein from Campylobacter jejuni,10
bacterium involved in human gastroenteritis.11 In natural
a
SYNLETT 2006, No. 6, pp 0825–0830
Advanced online publication: 14.03.2006
DOI: 10.1055/s-2006-939057; Art ID: G02806ST
© Georg Thieme Verlag Stuttgart · New York
0
4.
0
4.
2
0
0
6

826
E. Bedini et al.
LETTER
15
bacteria,3d but there has been little attention given to the and PhI(OAc)2 in CH2Cl2 afforded stereoselectively 2-
synthesis of oligosaccharides related to these sugars. azido-a-selenoglycoside 2 in 74% yield (Scheme 1). After
Three decades ago two syntheses of N-acetyl-bacil- de-O-acetylation with sodium methoxide, a stannylidene-
losamine were performed to confirm the structure mediated benzylation gave alcohol 3 (75% after two
assigned to the new monose found in Bacillus lichenifor- steps), which was derivatized as a triflate and subsequent-
mis.12 Recently, a new synthesis has been reported; it ly treated with NaN3 to install a masked amino function at
starts from benzyl 2-acetamido-2-deoxy-b-D-galacto- position 4. In spite of a very recent report regarding the
pyranoside and affords an undecaprenyl-diphosphate- successful azide displacement of the axial triflate at posi-
linked N-acetyl-bacillosamine, suitable for biochemical tion 4 of a 3-benzylated-fucose derivative very closely re-
studies towards the understanding of C. jejuni protein lated to 3,16 the reaction proceeded with low yields,
glycosylation pathway.13 No disaccharide-containing resulting predominantly in b-elimination. As already re-
bacillosamine has been synthesized to date.
ported on galacto-configured derivatives, nucleophilic
displacement at the axial position 4 could be performed in
high yield by installing a mesyl leaving group rather than
a triflate.17 The mesylation of 3 gave compound 4 in sim-
ilar yield when conducted with DMAP (68%) or with a
weaker base such as pyridine (67%).18
In this work, the synthesis of a bacillosamine glycosyl do-
nor and its coupling with several glycosyl acceptors are
reported in order to obtain disaccharide building blocks
closely related to the repeating unit of natural N-acetyl-ba-
cillosamine-containing polysaccharides. The synthesis
started from the known peracetylated D-fucal 1;14 homo- Compound 4 was then treated with NaN3 and TBAB in
geneous azidophenylselenylation with TMSN3, Ph2Se2, DMF at 80 °C to afford the diazido-selenoglycoside 5
Table 1 Glycosylation Reactions of Bacillosamine Donors 5 or 7a
Entry
Acceptor
Donor
Yield (%)a
Reaction
Product
(a/b ratio)b
conditionsc
BnO
OMe
OMe
O
N3
BnO
B
O
A
O
O
N3
1
5
35% (2:1)
A
BnO
AllO
HO
8
OAll
6
6
2
3
4
5
5
traces
B
C
C
D
8
8a
8a
8
6
6
6
7a
7b
7
75% (only a)
86% (only a)
84% (23:77)d
OAll
OBz
O
BzO
O
O
N3
BnO
6
7
77% (55:45)
C
BzO
B
O
A
BzO
N3
OH
OAll
9
10
O
O
O
O
O
O
HO
N3
BnO
A
B
O
O
7
8
7
7
76% (36:64)
D
D
N3
OMe
OMe
11
12
BnO
O
BnO
BnO
HO
BnO
BnO
BnO
O
O
O
N3
BnO
B
A
N3
57% (only b)
OAll
OAll
13
14b
a Isolated yield.
b Measured after separation of the two anomers unless otherwise stated.
c Reaction conditions: A: AgOTf, K2CO3, CH2Cl2, 4 Å MS, r.t., 210 min. B: NIS, TfOH, AW-300 4 Å MS, CH2Cl2–Et2O, 1:1, 0 °C to r.t., 1 h.
C: TMSOTf, AW-300 4 Å MS,CH2Cl2, 0 °C, 1–2 h. D: TMSOTf, AW-300 4 Å MS, CH3CN, 0 °C to r.t., 1–4 h.
d Measured by 1H NMR spectroscopy.
Synlett 2006, No. 6, 825–830 © Thieme Stuttgart · New York

LETTER
N-Acetyl-bacillosamine-Containing Disaccharide Building Blocks
827
(72%) together with a smaller amount of alcohol 3 (20%). resents a protected fragment of the O-antigen from
Since selenoglycosides were shown to be activated as gly- Pseudomonas aeruginosa NCTC 85053p and Shewanella
cosyl donors by AgOTf in the presence of K2CO3,19 the algae BrY.3c The similar behavior of 7a and 7b towards
coupling of 5 with the rhamnosyl acceptor 620 was at- glycosylation with acceptor 6 suggested that a mixture of
tempted, but both yield and stereoselectivity were not sat- the two anomers could be used for glycosylations.
isfactory (Table 1, entry 1). By activating selenoglycoside
As already observed in natural polysaccharides, bacil-
5 with NIS and TfOH21 only traces of the desired disac-
losamine species are present both as a- and b-glycosides
charide were recovered because degradation of the allyl
group on acceptor 6 by iodonium ions generated from
NIS/TfOH evidently proceeded faster than glycosylation.
Attempts to enhance the yield of glycosylation by de-
creasing the reaction temperature did not activate 5. A dif-
ferent leaving group had to be installed at the anomeric
(Figure 1). Thus, glycosylation reactions of 7 were per-
formed in some cases in CH3CN rather than CH2Cl2, since
nitriles are known to be b-directing solvents for
glycosylations26 and in particular perform well in the b-
coupling of 2-azido-glycosyl trihaloacetimidates.27 In ev-
ery case disaccharides were obtained in good to excellent
yield, whereas the stereoselectivity was from moderate to
very good depending on the solvent and glycosyl acceptor
center to circumvent this problem. Recently, N-phenyltri-
fluoroacetimidate glycosyl donors22 have been shown to
be effective in glycosylation reactions involving even
(Table 1).28 It is noteworthy that many of the synthesized
very reactive deoxy- and amino-deoxy-sugars such as fu-
disaccharides29 represent protected fragments of repeating
cosyl-23 and 3-acetamido-fucosyl donors;24 for this reason
units from O-antigens (10a is related to Flavobacterium
selenoglycoside 5 was hydrolyzed with NIS in THF and
psycrophilum O-antigen,3e 10b to Pseudomonas aerugi-
water and the resulting hemi-acetal was treated with
nosa IID 1001,3n 12 to Ralstonia picketti,3b and 14 to
CF3C(NPh)CCl and NaH25 to give a mixture of a- and b-
N-phenyltrifluoroacetimidates 7, that, after chromatogra-
phy on neutral alumina, could be separated to give pure 7a
(26% from 5) and 7b (49% from 5). Both anomers were
able to glycosylate rhamnosyl acceptor 6 in high yield
with complete a-stereoselectivity (Table 1, entries 3 and
4) to give the disaccharide building block 8a, which rep-
Francisella novicida U 112 core).4
So far, as already indicated (Figure 1), in natural polysac-
charides, three different groups were found to acylate the
amino group at position 4 of bacillosamine, whereas the
amino moiety at position 2 was always acetylated except
for a single case.3n It would be interesting to try to differ-
entiate the two amino functions of a disaccharide, for ex-
O
O
N3
BnO
AcHN
BnO
a
OBn
B
OBn
AcNH
N3
8α
+
O
O
O
A
O
15
16
AllO
AllO
OMe
OMe
OAc
OAc
O
O
OBn
c
b
BnO
3
BnO
N3
N3
O
O
O
PhN
17
18
CF3
AllO
OMe
d
OH
OMs
O
O
OBn
OBn
BnO
BnO
AcNH
AcNH
e
f
O
16
O
O
O
19
20
AllO
AllO
OMe
OMe
Scheme 2 Reagents and conditions: a) i. PMe3, 15:1 toluene–H2O, –78 °C to r.t., 2 h; ii. AcCl, –78 °C to r.t., 2 h, 47% (15/16 7:4) over two
steps; b) i. Ac2O, py, r.t., overnight; ii. NIS, 1:1 THF–H2O, r.t., 1 h; iii. CF3C(NPh)Cl, NaH, 4 Å MS, CH2Cl2, 0 °C, 2 h, 65% (a/b 1:1) over 3
steps; c) 6, TMSOTf, AW-300 4 Å MS, CH2Cl2, 0 °C, 3 h, 89%; d) i. PPh3, 9:1 THF–H2O, r.t., overnight; ii. Ac2O, py, r.t., overnight; iii. NaO-
Me, 2:1 MeOH–CH2Cl2, r.t., 4 h, 94% over three steps; e) MsCl, Et3N, CH2Cl2, r.t., 4 h, 71%; f) NaN3, TBAB, DMF, 80 °C, 4 d, 82%.
Synlett 2006, No. 6, 825–830 © Thieme Stuttgart · New York

828
E. Bedini et al.
LETTER
ample, by performing a regioselective azide reduction.30
We chose disaccharide 8a as our test substrate because
this fragment was found in bacterial O-antigens both with
a 2,4-diacetamido-3p and a 4-N-acyl-2-acetamido-bacil-
losamine moiety.3c
Mancino, A.; Parrilli, M. Carbohydr. Res. 2002, 337, 467.
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Shashkov, A. S.; Knirel, Y. A.; Jansson, P.-E.; Weintraub,
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B. Carbohydr. Res. 1993, 248, 199. (m) Chowdury, T. A.;
Jansson, P.-E.; Lindberg, P.; Lindberg, J.; Gustafsson, B.;
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Unfortunately, the reaction of 8a with PMe3 at low tem-
peratures, followed by acetylation in situ31 proceeded in
an unsatisfactory 47% yield, moreover, the regioselectiv-
ity of the reduction of 2- vs. 4-azido was poor (15/16, 7:4)
(Scheme 2). To circumvent this problem and to open a
general route to disaccharides containing 4-N-acyl-2-acet-
amido-bacillosamine residues, we decided to install the
4-azido function on the disaccharide only after reduction
of the azido group at position 2. Thus, compound 3 was
acetylated and then the selenoglycoside was hydrolyzed
with NIS in THF and water to give a hemi-acetal, that was
treated with CF3C(NPh)CCl and NaH to give a 1:1 mix-
ture of a- and b-N-phenyltrifluoroacetimidates 17 (65%,
over three steps). Coupling of 17 with the glycosyl accep-
tor 6 in CH2Cl2 afforded a-disaccharide 18 in excellent
yield (89%). Staudinger reduction of the azido group of 18
with PPh3 in THF and water, followed by treatment with
Ac2O and pyridine, afforded a 2¢-acetamido-disaccharide,
that was in turn de-O-acetylated by treatment with
NaOMe to give alcohol 19 in nearly quantitative yield
(94% over three steps). Finally, 19 was mesylated to give
20 (71%) and then treated with NaN3 and TBAB in DMF
at 80 °C to afford compound 16 (82%), a disaccharide that
contains a bacillosamine unit with diversely protected
amino moieties.32
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In conclusion, we have reported the first synthesis of ba-
cillosamine-containing disaccharides through a versatile
strategy that uses N-phenyltrifluoroacetimidate glycosyl
donors for the glycosylation step. This strategy allows ac-
cess to all the known structural features of bacillosamine,
opening a versatile route towards oligosaccharide frag-
ments of O-antigenic polysaccharides, which could help
the development of sugar-based vaccines, a topic of in-
creasing interest in the field of carbohydrate chemistry.33
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Acknowledgment
We thank MIUR, Rome (Progetti di Ricerca di Interesse Nazionale
2004, M.P.) for financial support. The NMR spectra were perfor-
med at CIMCF (Centro di Metodologie Chimico-Fisiche) of the
University ‘Federico II’ of Naples.
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Synlett 2006, No. 6, 825–830 © Thieme Stuttgart · New York

LETTER
N-Acetyl-bacillosamine-Containing Disaccharide Building Blocks
829
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60, 10711.
CHHCH=CH2), 4.12 (m, 2 H, H-5A, CHHCH=CH2), 3.96 (t,
1 H, J3,4 = J3,2 = 9.6 Hz, H-3B), 3.73 (dq, 1 H, J5,4 = 9.6 Hz,
J
5,6 = 6.4 Hz, H-5B), 3.20 (dd, 1 H, J2,3 = 9.6 Hz, J2,1 = 3.6
Hz, H-2B), 3.02 (t, 1 H, J4,3 = J4,5 = 9.6 Hz, H-4B), 1.34 (d, 3
H, J6,5 = 6.3 Hz, H-6A), 1.34 (d, 3 H, J6,5 = 6.4 Hz, H-6B). 13
C
NMR (CDCl3, 75 MHz): d = 165.6, 165.5 (2 × COPh), 137.3,
135.0, 133.4, 133.3 (3 × Cipso, CH2CH=CH2), 129.6–126.3
(ArC), 117.8 (OCH2CH=CH2), 97.1, 96.0 (C-1A, C-1B),
78.7, 76.2, 75.3, 74.3, 71.3, 71.1, 68.5, 68.4, 67.1, 63.1
(C-2A, C-2B, C-3A, C-3B, C-4A, C-4B, C-5A, C-5B, CH2Ph,
CH2CH=CH2), 17.5, 17.4 (C-6A, C-6B). ESI-MS: m/z calcd
for C36H38N6NaO9: 721.26 [M + Na]+; found: 720.89.
Compound 10b: [a]D +40 (c 0.5, CH2Cl2). 1H NMR (CDCl3,
400 MHz): d = 8.06–7.34 (m, 15 H, ArH), 5.95 (m, 1 H,
CH2CH=CH2), 5.65 (m, 2 H, H-3A, H-4A), 5.37 (dd, 1 H,
Jvic = 17.2 Hz, Jgem = 1.6 Hz, OCH2CH=CHtransH), 5.30 (dd,
1 H, Jvic = 10.4 Hz, Jgem = 1.6 Hz, CH2CH=CHcisH), 5.05 (d,
1 H, J1,2 = 1.6 Hz, H-1A), 4.85 (d, 1 H, Jgem = 10.8 Hz,
CHHPh), 4.73 (d, 1 H, Jgem = 10.8 Hz, CHHPh), 4.69 (br s,
1 H, H-2A), 4.33–4.22 (3 H, H-1B, CH2CH=CH2), 4.08 (dq,
1 H, J5,4 = 9.6 Hz, J5,6 = 6.0 Hz, H-5A), 3.51 (t, 1 H,
(28) Glycosylation Procedure C: A mixture of acceptor (0.044
mmol) and donor (0.057 mmol) was co-evaporated three
times with toluene, the residue was then mixed with freshly
powdered AW-300 4 Å molecular sieves and suspended
under argon in CH2Cl2 (1.0 mL). The mixture was cooled
and stirred at 0 °C and a 28 mM solution of TMSOTf in
CH2Cl2 (50 mL) was added. After completion of the reaction
(TLC analysis), the mixture was neutralized by adding a few
drops of Et3N. The mixture was then filtered through a pad
of Celite and concentrated to give a residue that was purified
by column chromatography.
J3,4 = J3,2 = 9.6 Hz, H-3B), 3.08 (m, 3 H, H-2B, H-4B, H-5B),
1.32 (d, 3 H, J6,5 = 6.0 Hz, H-6A), 1.27 (d, 3 H, J6,5 = 6.0 Hz,
H-6B). 13C NMR (CDCl3, 75 MHz): d = 165.6, 165.4 (2 ×
COPh), 137.2, 133.5, 133.2, 133.0 (3 × Cipso, CH2CH=CH2),
129.7–128.4 (ArC), 117.7 (OCH2CH=CH2), 103.1, 98.3 (C-
1A, C-1B), 80.9, 76.5, 75.9, 75.3, 71.7, 70.8, 68.2, 67.3, 66.7,
66.5 (C-2A, C-2B, C-3A, C-3B, C-4A, C-4B, C-5A, C-5B,
CH2Ph, CH2CH=CH2), 18.4, 17.7 (C-6A, C-6B). ESI-MS:
m/z calcd for C36H38N6NaO9 [M + Na]+: 721.26; found:
720.93.
Glycosylation Procedure D: A mixture of acceptor (0.044
mmol) and donor (0.077 mmol) was co-evaporated three
times with toluene, the residue was then mixed with freshly
powdered AW-300 4 Å molecular sieves and suspended
under argon in CH3CN (1.0 mL). The mixture was cooled
and stirred at 0 °C and TMSOTf (1.3 mL, 7.7 mmol) was
added and the temperature was allowed to rise gradually to
r.t. After completion of the reaction (TLC analysis), the
mixture was worked up as for Procedure C.
Compound 12a: [a]D +127 (c 0.5, CH2Cl2). 1H NMR
(CDCl3, 300 MHz): d = 7.47–7.30 (m, 5 H, ArH), 5.55 (d, 1
H, J1,2 = 3.3 Hz, H-1B), 4.86 (app d, 3 H, H-1A, CH2Ph), 4.28
(dd, 1 H, J3,4 = 7.2 Hz, J3,2 = 5.7 Hz, H-3A), 4.11 (d, 1 H,
J2,3 = 5.7 Hz, H-2A), 3.76–3.61 (m, 3 H, H-3B, H-5A, H-5B),
(29) Compound 8a: [a]D +109.3 (c 1.2, CH2Cl2). 1H NMR
(CDCl3, 300 MHz): d = 7.43–7.33 (m, 10 H, ArH), 6.01 (m,
1 H, CH2CH=CH2), 5.33 (dd, 1 H, Jvic = 17.7 Hz, Jgem = 1.8
Hz, OCH2CH=CHtransH), 5.25 (dd, 1 H, Jvic = 10.2 Hz,
3.49 (dd, 1 H, J4,5 = 9.9 Hz, J4,3 = 7.2 Hz, H-4A), 3.37 (m, 4
H, H-2B, OMe), 3.12 (t, 1 H, J4,3 = J4,5 = 9.9 Hz, H-4B), 1.53
(s, 3 H, CH3), 1.35 (s, 3 H, CH3), 1.31 (d, 3 H, J6,5 = 6.0 Hz,
H-6B), 1.28 (d, 3 H, J6,5 = 6.3 Hz, H-6A). 13C NMR (CDCl3,
75 MHz): d = 137.1 (Cipso), 128.5–128.1 (ArC), 109.5
[C(CH3)2], 98.0, 95.6 (C-1A, C-1B), 78.3, 78.1, 77.1, 76.1,
75.4, 68.4, 66.9, 63.5, 54.8 (C-2A, C-2B, C-3A, C-3B, C-4A,
C-4B, C-5A, C-5B, CH2Ph), 27.9, 26.3 (2 × CH3), 18.3, 18.1
(C-6A, C-6B). ESI-MS: m/z calcd for C23H32N6NaO7
[M + Na]+: 527.22; found: 526.99.
Jgem = 1.8 Hz, CH2CH=CHcisH), 5.02 (d, 1 H, J1,2 = 3.6 Hz,
H-1B), 4.87 (d, AB, 1 H, Jgem = 10.8 Hz, CHHPh), 4.83 (d,
AB, 1 H, Jgem = 10.8 Hz, CHHPh), 4.79 (d, 1 H, Jgem = 11.1
Hz, CHHPh), 4.71 (d, 1 H, Jgem = 1.5 Hz, H-1A), 4.61 (d, 1
H, Jgem = 11.1 Hz, CHHPh), 4.19 (m, 2 H, CH2CH=CH2),
4.00 (dd, 1 H, J3,4 = 9.3 Hz, J3,2 = 3.0 Hz, H-3A), 3.86 (m, 2
H, H-3B, H-5B), 3.76 (dd, 1 H, J2,3 = 3.0 Hz, J2,1 = 1.5 Hz, H-
2A), 3.65 (dq, 1 H, J5,4 = 9.3 Hz, J5,6 = 6.0 Hz, H-5A), 3.57 (t,
1 H, J4,5 = J4,3 = 9.3 Hz, H-4A), 3.36 (dd, 1 H, J2,3 = 10.5 Hz,
Compound 12b: [a]D +20 (c 0.7, CH2Cl2). 1H NMR (CDCl3,
300 MHz): d = 7.59–7.22 (m, 5 H, ArH), 4.90–4.79 (m, 3 H,
H-1A, CH2Ph), 4.37 (d, 1 H, J1,2 = 8.1 Hz, H-1B), 4.22 (dd, 1
H, J3,4 = 7.2 Hz, J3,2 = 5.7 Hz, H-3A), 4.12 (d, 1 H, J2,3 = 5.7
Hz, H-2A), 3.72 (dq, 1 H, J5,4 = 9.9 Hz, J5,6 = 6.0 Hz, H-5A),
3.45 (m, 2 H, H-2B, H-4A), 3.37 (s, 3 H, OMe), 3.26 (t, 1 H,
J3,4 = J3,2 = 9.6 Hz, H-3B), 3.20 (m, 2 H, H-4B, H-5B), 1.52 (s,
3 H, CH3), 1.36 (m, 9 H, H-6A, H-6B, CH3). 13C NMR
(CDCl3, 75 MHz): d = 137.2 (Cipso), 129.3–128.1 (ArC),
109.4 [C(CH3)2], 101.6, 98.0 (C-1A, C-1B), 82.2, 81.2, 76.0,
75.5, 71.0, 67.5, 66.8, 64.4, 54.9 (C-2A, C-2B, C-3A, C-3B, C-
4A, C-4B, C-5A, C-5B, CH2Ph), 28.1, 26.2 (2 CH3), 18.3, 17.7
(C-6A, C-6B). ESI-MS: m/z calcd for C23H32N6NaO7
[M + Na]+: 504.23; found: 527.18.
J2,1 = 3.6 Hz, H-2B), 3.33 (s, 3 H, OMe), 3.14 (t, 1 H,
J4,5 = J4,3 = 9.3 Hz, H-4B), 1.31 (d, 3 H, J6,5 = 6.0 Hz, H-6A),
1.18 (d, 3 H, J6,5 = 6.0 Hz, H-6B). 13C NMR (CDCl3, 100
MHz): d = 138.5, 138.0 (2 Cipso), 134.7 (CH2CH=CH2),
128.5–127.9 (ArC), 118.1 (OCH2CH=CH2), 98.4, 93.5 (C-
1A, C-1B), 79.6, 78.4, 75.7, 75.3, 74.6, 73.2, 72.1, 68.9, 67.8,
66.6, 63.4 (C-2A, C-2B, C-3A, C-3B, C-4A, C-4B, C-5A, C-5B,
CH2Ph, CH2CH=CH2), 54.8 (OMe), 18.3, 18.0 (C-6A, C-6B).
ESI-MS: m/z calcd for C30H38N6NaO7 [M + Na]+: 617.27;
found: 617.10.
Synlett 2006, No. 6, 825–830 © Thieme Stuttgart · New York

830
E. Bedini et al.
LETTER
Compound 14b: [a]D +19 (c 0.7, CH2Cl2). 1H NMR (CDCl3,
300 MHz): d = 7.41–7.25 (m, 20 H, ArH), 5.86 (m, 1 H,
CH2CH=CH2), 5.23 (dd, 1 H, Jvic = 17.7 Hz, Jgem = 1.8 Hz,
OCH2CH=CHtransH), 5.17 (dd, 1 H, Jvic = 10.2 Hz, Jgem = 1.8
Hz, CH2CH=CHcisH), 4.91 (d, 1 H, J1,2 = 1.8 Hz, H-1A),
4.82–4.65 (m, 6 H, CHHPh), 4.58 (d, 1 H, Jgem = 11.4 Hz,
CHHPh), 4.51 (d, 1 H, Jgem = 11.7 Hz, CHHPh), 4.31–4.15
(m, 3 H, H-1B, H-4A, CHHCH=CH2), 3.99–3.77 (m, 6 H, H-
2A, H-3A, H-5A, H-6A, CHHCH=CH2), 3.23 (t, 1 H,
(31) Friedrich-Bochnitschek, S.; Waldmann, H.; Kunz, H. J. Org.
Chem. 1989, 54, 751.
(32) Compound 16: [a]D +48 (c 0.4, CH2Cl2). 1H NMR (CDCl3,
400 MHz): d = 7.36–7.26 (m, 10 H, ArH), 6.01 (m, 1 H,
CH2CH=CH2), 5.33 (dd, 1 H, Jvic = 17.2 Hz, Jgem = 1.5 Hz,
OCH2CH=CHtransH), 5.25 (dd, 1 H, Jvic = 10.3 Hz, Jgem = 1.5
Hz, CH2CH=CHcisH), 5.00 (d, 1 H, J1,2 = 3.3 Hz, H-1B), 4.81
(d, 1 H, Jgem = 12.6 Hz, CHHPh), 4.77 (d, 1 H, Jgem = 12.6
Hz, CHHPh), 4.75 (d, 1 H, Jgem = 11.3 Hz, CHHPh), 4.70
(m, 2 H, H-1A, NH), 4.47 (d, 1 H, Jgem = 11.3 Hz, CHHPh),
4.21 (app d, 2 H, CH2CH=CH2), 4.04 (dd, 1 H, J3,4 = 9.8 Hz,
J
2,1 = J2,3 = 9.3 Hz, H-2B), 3.06 (t, 1 H, J3,2 = J3,4 = 9.3 Hz,
H-3B), 3.02 (t, 1 H, J4,3 = J4,5 = 9.3 Hz, H-4B), 2.89 (dq, 1 H,
5,4 = 9.3 Hz, J5,6 = 5.7 Hz, H-5B), 1.16 (d, 3 H, J6,5 = 5.7 Hz,
J
J3,2 = 3.2 Hz, H-3A), 3.86–3.71 (m, 3 H, H-2A, H-4A, H-5A),
H-6B). 13C NMR (CDCl3, 100 MHz): d = 139.1, 138.5,
138.4, 137.6 (4 × Cipso), 133.8 (CH2CH=CH2), 129.7–127.0
(ArC), 117.3 (OCH2CH=CH2), 100.9, 97.4 (C-1A, C-1B),
81.6, 78.2, 75.5, 75.4, 75.3, 73.4, 72.8, 72.4, 71.5, 70.5, 68.9,
68.0, 67.8, 67.2 (C-2A, C-2B, C-3A, C-3B, C-4A, C-4B, C-5A,
C-5B, C-6A, 4 CH2Ph, CH2CH=CH2), 18.3 (C-6B). ESI-MS:
m/z calcd for C43H48N6NaO8 [M + Na]+: 799.34; found:
799.01.
3.66–3.56 (m, 2 H, H-4B, H-5B), 3.44 (t, 1 H, J3,4 = J3,2 = 9.8
Hz, H-3B), 3.37 (m, 4 H, H-2B, OMe), 1.61 (s, 3 H, NAc),
1.37 (d, 3 H, J6,5 = 6.2 Hz, H-6A), 0.97 (d, 3 H, J6,5 = 6.2 Hz,
H-6B). 13C NMR (CDCl3, 75 MHz): d = 169.6, 139.5, 137.8,
134.7, 129.7, 125.9 118.2, 98.8, 92.7, 79.3, 76.9, 74.0, 73.3,
73.1, 72.4, 72.2, 67.8, 66.6, 63.1, 54.9, 54.7, 23.3, 17.9, 17.2.
ESI-MS: m/z calcd for C32H42N4NaO8 [M + Na]+: 610.30;
found: 633.19.
(30) (a) Li, J.; Chen, H.-N.; Chang, H.; Wang, J.; Chang, C.-W.
Org. Lett. 2005, 7, 3061. (b) Nyffeler, P. T.; Liang, C.-H.;
Koeller, K. M.; Wong, C.-H. J. Am. Chem. Soc. 2002, 124,
10773. (c) Rai, R.; Chen, H.-N.; Czyryca, P. G.; Li, J.;
Chang, C.-W. T. Org. Lett. 2006, 8, 887.
(33) Werz, D. B.; Seeberger, P. H. Chem. Eur. J. 2005, 11, 3194.
Synlett 2006, No. 6, 825–830 © Thieme Stuttgart · New York