A chiron approach to aminocytitols by petasis-borono-mannich reaction: Formal synthesis of (+)-conduramine e and (-)-conduramine e

Article abstract of DOI:10.1021/jo300804d

A chiron approach to a stereoselective route for the synthesis of aminocytitols from carbohydrates is described. The formal synthesis of (+)-conduramine E and (-)-conduramine E was achieved by utilizing this strategy. The key features of the synthetic strategy include one-pot three-component Petasis-Borono-Mannich reaction to introduce the syn-β-amino alcohol functionality of conduramine E and ring-closing metathesis to construct its carbocyclic core. The present synthetic approach paves the way for stereoselective synthesis of several conduramines starting from carbohydrates.

Full text of DOI:10.1021/jo300804d

Note
pubs.acs.org/joc
A Chiron Approach to Aminocytitols by Petasis-Borono-Mannich
Reaction: Formal Synthesis of (+)-Conduramine E and
(−)-Conduramine E
Partha Ghosal and Arun K. Shaw*
Division of Medicinal and Process Chemistry, CSIR-Central Drug Research Institute (CDRI), Lucknow 226 001, India
S
* Supporting Information
ABSTRACT: A chiron approach to a stereoselective route for
the synthesis of aminocytitols from carbohydrates is described.
The formal synthesis of (+)-conduramine E and (−)-condur-
amine E was achieved by utilizing this strategy. The key
features of the synthetic strategy include one-pot three-
component Petasis-Borono-Mannich reaction to introduce
the syn-β-amino alcohol functionality of conduramine E and
ring-closing metathesis to construct its carbocyclic core. The
present synthetic approach paves the way for stereoselective
synthesis of several conduramines starting from carbohydrates.
minocyclohexenetriols formally called conduramines are
the amino derivatives of conduritols, in which an amino
functionality is present in place of one of the hydroxyl groups
(Figure 1). These densely functionalized aminocyclitols and
(CBBs)29 and their exploitation in syntheses of natural
products or natural-product-like molecules of significant
biological importance30−36 prompted us to develop an efficient
methodology for synthesis of enantiomerically pure amino-
cyclohexenetriols by a chiron approach. Herein, we wish to
disclose a short and efficient formal synthesis of both
enantiomers of conduramine E (Figure 2) from carbohydrates
involving Petasis-Borono-Mannich (PBM) chemistry37−41 and
ring-closing metathesis.
A
Figure 1. Structure of some important aminocytitols.
structurally related compounds form the basic skeleton of
pseudo oligosaccharides and several complex aminoglycoside
antibiotics.1−3 Such units are also the synthetic precursors of
pharmacologically important molecules such as Pancratistatin,4
(+)-lycoricidine,5 (+)-narciclasine,6 and (−)-lycorine,7 with
important bioactivities such as antibacterial, antihypertensive,
platelet-inhibiting, and cytotoxic (Figure 1). In addition,
utilization of aminocyclitols for the syntheses of azasugars,8
aminosugars,9 sphingosines,10 and narcissus alkaloids11 ampli-
fied their importance as synthetic building blocks. Therefore,
several elegant approaches to the synthesis of racemic as well as
optically pure aminocyclitols and their structural variants have
been disclosed to date.12−27 Very recently Norsikian et al.
disclosed a novel approach to conduramines starting from
carbohydrate via an unprecedented intramolecular Petasis-
Borono-Mannich reaction with an exclusive anti stereo-
selectivity for the newly created β-amino alcohol motif.28
The interesting structural features associated with biological
activities and also as a result of our involvement toward the
synthesis of carbohydrate-based chiral building blocks
Figure 2. Structures of conduritol E, (+)-conduramine E, and
(−)-conduramine E.
The synthesis of (+)-conduramine E was commenced with
the selective acetonide protection of hydroxyls at C3 and C4 in
methyl-α-D-galactopyranoside 1 to give 3,4-O-isopropylidine-
methyl-α-D-galactopyranoside 2 (Scheme 1). Iodination of the
primary alcohol was carried out by treating the diol 2 under
Garegg and Samuelsson conditions to obtain the iodide 3,
which on treatment with Zn dust in the presence of a catalytic
amount cyanocobalamine42 (vitamin B12) gave the required
hydroxy aldehyde 4, but unfortunately the α-hydroxy aldehyde
4 was unstable (Scheme 1).
At this stage, we modified our synthetic strategy by
protecting the remaining hydroxyl group at C2 in 3 as its
Received: April 27, 2012
Published: August 17, 2012
© 2012 American Chemical Society
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Note
a
synthetic strategy from D-galactose 9. Thus, the 1,2;3,4-di-O-
isopropylidine-α-D-galactopyranoside43 10 prepared from 9 on
iodination furnished iodide 11 in 86% yield. Its reaction with
Zn dust in the presence of a catalytic amount of cyanocobal-
amine smoothly afforded the hemiacetal 12, which was then
subjected to PBM reaction with trans-2-phenylvinyl boronic
acid and tert-butylamine to afford exclusively the erythro-1,2
amino alcohol 7. Its treatment with (Boc)2O in THF in the
presence of Et3N/DMAP furnished the oxazolidinone 8 in 40%
yield over two steps (Scheme 2). The cyclization of 8 was
achieved by using ring-closing metathesis reaction in the
presence of Grubbs second generation catalyst to afford
conduramine core 13. Cleavage of the acetonide protection
in 13 was done by treating it with TFA to obtain diol 14, a
known intermediate reported by Russell et al. during
( )-conduramine E synthesis.26 Its spectral data was in close
agreement with the data reported by Russell et al. Now, the
synthesis of (+)-conduramine E 16 could be completed by
Scheme 1. Synthesis of Oxazolidinone 8
a
Reagent and conditions: (a) I2, acetone, 4 h, 70%; (b) I2, PPh3,
imidazole, toluene, 80 °C, 3 h, 82%; (c) Zn, NH4Cl, vit. B12, MeOH, 5
min; (d) TBDPSCl, imidazole, DCM, 6 h, 85%; (e) TBAF, EtOH, 30
min; (f) trans-2-phenylvinyl boronic acid, BuNH2, 80 °C, 24 h; (g)
(Boc)2O, Et3N, DMAP, THF, rt, 12 h, 15% over three steps.
26
t
t
TFA-mediated Bu deprotection of 14 followed by basic
hydrolysis of the oxazolidinone ring18 in 15 by adopting the
procedure reported by Prinzbach et al. (Scheme 2).
We were also interested in synthesis of (−)-conduramine E
(29), the enantiomer of (+)-conduramine E, involving the
PBM reaction on masked α-hydroxy aldehyde of the type 22.
We achieved our goal by adopting the synthetic strategy shown
in Scheme 3. Thus, the 2,3;5,6-di-O-isopropylidine-α-D-
mannofuranose hemiacetal 18 prepared from D-mannose 17
by the standard literature procedure (I2/acetone)44 was
subjected to undergo Wittig methylenation on anomeric
carbon to furnish the alkene 19. The free hydroxyl group in
19 was protected with TBDPSCl to afford silyl ether 20. The
selective deprotection of terminal acetonide in 20 was done by
treating it with 80% aqueous AcOH to obtain the diol 21
(Scheme 3). Its oxidative cleavage with NaIO4 afforded an
aldehyde 22, which was desilylated with TBAF followed by
PBM reaction of the resulting α-hydroxy aldehyde 23 with
trans-2-phenylvinyl boronic acid and tert-butylamine under
refluxing condition to afford the desired amine 24 in a one-pot
fashion. Its protection with (Boc)2O in THF in the presence of
Et3N/DMAP furnished the oxazolidinone 25 (Scheme 3).
The diene 25 was the enantiomer of diene 8. The NMR
spectra of these two enantiomers (8 and 25) were identical, and
their optical rotation values were close in magnitude but
silyl ether. Thus, the iodide 3 was protected as its silyl ether 5,
which on Zn-dust-mediated ring opening in the presence of
catalytic amount cyanocobalamine afforded the stereochemi-
cally pure silyl protected hydroxy aldehyde 6. It was then
subjected to one-pot desilylation by TBAF followed by PBM
reaction of the resulting aldehyde 4 with trans-2-phenylvinyl
boronic acid and tert-butylamine under refluxing condition to
obtain the unsaturated amino alcohol 7 (Scheme 1). Since it is
well documented in the literature that the chiral α-hydroxy
aldehyde furnishes the corresponding erythro-1,2 amino alcohol
as a single diastereomer,41 herein the erythro-1,2 amino alcohol
7 was also obtained exclusively as a single diastereoismer from
the aldehyde 6. Unfortunately, we could not isolate 7 in its pure
form by column chromatographic purification of the crude
reaction product (TLC). At this stage, the amino group in 7
was protected by treating it with (Boc)2O in THF in the
presence of Et3N and DMAP. Here, the Boc protection of the
amine 7 with simultaneous oxazolidinone ring formation
furnished the oxazolidinone 8 with low yield (15%) in three
steps (Scheme 1).
The low yield of 8 was presumably attributed to the
instability of the α-hydroxy aldehyde intermediate 4, and
therefore to evade this problem we decided to start our
opposite in sign {[α]28D = −55.3 (c 0.77, CHCl3) for 8; [α]26
D
a
Scheme 2. Formal Synthesis of (+)-Conduramine E 16
a
Reagent and conditions: (a) I2, acetone, 24 h, 80%; (b) I2, PPh3, imidazole, toluene, 80 °C, 3 h, 86%; (c) Zn, NH4Cl, Vit. B12, MeOH, 15 min, 90%;
t
(d) trans-2-phenylvinyl boronic acid, BuNH2, EtOH, rt, 24 h; (e) (Boc)2O, Et3N, DMAP, THF, rt, 12 h, 40% over two steps; (f) Grubbs second
generation catalyst (10 mol %), DCM, reflux, 24 h, 51%; (g) TFA, DCM, 2 h then H2O, 1 h, 85%.
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Note
a
Scheme 3. Formal Synthesis of (−)-Conduramine E 29
a
Reagent and conditions: (a) I2, acetone, rt, 24 h, 80% ; (b) Ph3PCH3Br, tBuOK, THF, −20 °C, 4 h, 85%; (c) TBDPSCl, imidazole, DMF, rt, 24 h,
87%; (d) 80% AcOH, rt, 6 h, 75%; (e) NaIO4, THF/H2O (9:1), 0 °C to rt, 1.5 h; (f) TBAF, EtOH, 30 min then trans-2-phenylvinyl boronic acid,
tBuNH2, 80 °C, 24 h; (g) (Boc)2O, Et3N/DMAP (3:1), 0 °C to rt, 12 h, 21% from 21; (h) Grubbs second generation catalyst (10 mol %), DCM,
reflux, 24 h, 48%; (i) TFA, DCM, 2 h then H2O, 91%.
(neat, cm−1) 3336, 2864, 1639, 1222, 1076, 770; 1H NMR (300 MHz,
= +66.0 (c 0.24, CHCl3) for 25}. Ring-closing metathesis of
CDCl3) δ 1.28 (s, 3H), 1.44 (s, 3H), 2.83 (s, 1H, OH), 3.11 (m, 1H,
diene 25 in the presence of Grubbs second generation catalyst
OH), 3.39 (s, 3H), 3.72−3.76 (m, 2H), 3.82−3.89 (m, 1H), 3.97−
under refluxing condition furnished the required carbocyclic
3.99 (m, 3H), 4.17−4.18 (m, 2H), 4.71 (d, J = 3.6 Hz, 1H); 13C NMR
core of (−)-conduramine E 26 (Scheme 3). Finally, the
(50 MHz, CDCl3) δ 26.2, 28.0, 55.8, 62.7, 68.4, 69.9, 74.1, 76.6, 99.1,
isopropylidene protection in 26 was easily cleaved by treating it
110.0; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for C10H19O6
with TFA to furnish the diol 27 in 91% yield, from which the
235.1182, found 235.1174.
(−)-conduramine E 29 could be obtained via 28 by following
the procedure reported by Russell et al.26 Here, it was worth
mentioning that 26 and 27 were the enantiomers of 13 and 14,
respectively. The values for their optical rotations were close in
Compound 3. 2,3-O-Isopropylidine-methyl-α-D-galactopyranoside
2 (500 mg, 2.14 mmol), PPh3 (840 mg, 3.2 mmol) and imidazole (435
mg, 6.4 mmol) were taken in a round-bottom flask in dry toluene (15
mL). The reaction mixture was stirred at room temperature with I2
(815 mg, 3.2 mmol). The dark brown reaction mixture was heated at
80 °C for 3 h. After completion of the reaction, the reaction mixture
was quenched with MeOH (2 mL), and the whole mixture was then
concentrated to a residue. Saturated aqueous solution of Na2S2O3 was
added to it. The entire solution was stirred until the reaction mixture
became colorless. Afterward, it was extracted with DCM (2 × 20 mL),
and the combined organic layer was dried over Na2SO4 and
concentrated under reduced pressure to a residue which on column
chromatographic purification afforded iodide 3 (600 mg, 1.75 mmol,
82%).
Eluent for column chromatography: EtOAc/hexane (2/5, v/v);
[α]28D = +130.3 (c 0.74, CHCl3); Rf = 0.32 (1/3, EtOAc/hexane); IR
(neat, cm−1) 3133, 3077, 2542, 1384, 1215, 1021, 781; 1H NMR (300
MHz, CDCl3 + CD3OD) δ 1.35 (s, 3H), 1.50 (s, 3H), 3.33−3.38 (m,
2H), 3.48−3.49 (m, 3H), 3.73−3.74 (m, 1H), 4.127−4.134 (m, 1H),
4.19−4.23 (m, 1H), 4.33−4.40 (m, 3H), 4.71 (m, 1H); 13C NMR (50
MHz, CDCl3 + CD3OD) δ 6.1, 29.7, 31.5, 59.4, 72.6, 73.3, 77.7, 80.2,
103.5, 113.3; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for
C10H18IO5 345.0199, found 345.0191.
General Procedure for Preparation of Aldehyde 4. To a
magnetically stirred suspension of Zn dust (680 mg, 10.4 mmol) and
NH4Cl (560 mg, 10.38 mmol) in dry methanol (20 mL) was added
cyanocobalamine (7 mg, 0.005 mmol), and the resulting mixture was
allowed to stir for 15 min. Afterward, a solution of 3 (150 mg, 0.44
mmol) in dry methanol (5 mL) was added to it, and the resulting
solution was further stirred for 5 min. The reaction mixture was
filtered through a Celite bed, and the filtrate was evaporated under
reduced pressure. The residue obtained was dissolved in ethyl acetate
(25 mL) and washed with a mixture of brine and water (1:1 v/v, 10
mL each). The organic layer was dried over Na2SO4 and concentrated
to give the crude aldehyde 4, which unfortunately decomposed rapidly.
Compound 5. To a stirred solution of compound 3 (345 mg, 1
mmol) in dry DCM (5 mL) were added imidazole (135 mg, 2 mmol)
and TBDPSCl (412 mg, 0.39 mL, 1.5 mmol), and the reaction mixture
was allowed to stir for another 6 h. Water (10 mL) was added to the
reaction mixture and extracted with DCM (2 × 10 mL). The
combined organic layer was evaporated under reduced pressure to give
a residue that on purification by column chromatography gave 5 as
clear oil (495 mg, 0.85 mmol, 85%).
magnitude but opposite in sign {[α]28 = +124.2 (c 0.125,
D
CHCl3) for 13 and [α]26 = −134.0 (c 0.112, CHCl3) for
D
26}{[α]28D = +78.5 (c 0.23, CHCl3) for 14 and [α]26D = −73.7
(c 0.16, CHCl3) for 27}.
Here, it is worth mentioning that in our present approach the
syn-β-amino alcohol motif of conduramine E was installed via
an intermolecular Petasis-Borono-Mannich reaction, whereas
Norsikian et al. disclosed a novel approach to synthesize anti-β-
amino alcohol motif of conduramine C-4 and ent-conduramine
A-1 by utilizing intramolecular Petasis-Borono-Mannich re-
action.28 Carbohydrates were utilized as a starting material in
both the cases.
In summary, we developed a convenient chiron approach to
the formal synthesis of both the enantiomers of conduramine E.
The commercially available monosaccharides were utilized as
starting material to complete the synthesis of key oxazolidinone
fused carbocyclic intermediates (13 and 26) involving highly
diastereoselective Petasis-Borono-Mannich (PBM) and ring-
closing metathesis (RCM) reactions. Several aminocytitols
could also be synthesized by using this flexible approach
starting from carbohydrates.
EXPERIMENTAL SECTION
■
Compound 2. To a stirred suspension of methyl-α-D-galactopyr-
anoside 1 (500 mg, 2.57 mmol) in dry acetone (10 mL) was added I2
(130 mg, 0.5 mmol) at room temperature, and the reaction was
allowed to stir at same temperature for 4 h. After completion of the
reaction, excess iodine was quenched with saturated aqueous solution
of Na2S2O3 and the resulting mixture was concentrated. The reaction
mixture was then extracted with EtOAc (3 × 20 mL) and the
combined organic layer was dried over Na2SO4 and concentrated
under reduced pressure to a residue that on purification by column
chromatography gave 2,3-O-isopropylidine-methyl-α-D-galactopyrano-
side 2 (420 mg, 1.8 mmol, 70%).
Eluent for column chromatography: EtOAc/hexane (2/1, v/v);
[α]27 = +156.7 (c 0.8, CHCl3); Rf = 0.25 (2/1, EtOAc/hexane); IR
D
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Note
Eluent for column chromatography: EtOAc/hexane (1/19, v/v);
D
mg, 11.52 mmol) were taken in a round-bottom flask, and dry toluene
(20 mL) was added to it. The reaction mixture was stirred at room
temperature with I2 (1.46 g, 5.76 mmol). The dark brown reaction
mixture was then heated at 80 °C for 3 h. After completion of the
reaction (TLC control), the reaction mixture was quenched with
MeOH (2 mL), and the resulting solution was concentrated to a
residue. A saturated aqueous solution of Na2S2O3 was added to it. The
stirring of the solution was continued until it became colorless.
Afterward, it was extracted with DCM (2 × 25 mL), and the combined
organic layer was dried over Na2SO4 and concentrated under reduced
pressure to a residue that on column chromatographic purification
afforded the iodide 11 (1.22 g, 3.3 mmol, 86%).
[α]28 = +84.2 (c 1.23, CHCl3); Rf = 0.54 (1/6, EtOAc/hexane); IR
(neat, cm−1) 3017, 2361, 1372, 1215, 763; 1H NMR (300 MHz,
CDCl3) δ 1.12 (s, 9H), 1.24 (s, 3H), 1.33 (s, 3H), 3.23−3.34 (m, 5H),
3.73−3.77 (m, 1H), 4.08−4.13 (m, 1H), 4.26−4.37 (m, 3H), 7.36−
7.44 (m, 6H), 7.71−7.77 (m, 4H); 13C NMR (50 MHz, CDCl3) δ 3.2,
19.6, 26.7, 27.3, 28.2, 55.6, 86.4, 72.2, 74.3, 77.4, 128.0, 130.1, 133.1,
134.7, 136.1, 136.5; HRMS (ESI TOF (+)) calcd for C26H35IO5SiNa
[M + Na]+ 605.1196, measured 605.1208.
Compound 8. To a magnetically stirred suspension of Zn dust
(1.56 mg, 23.9 mmol) and NH4Cl (1.3 g, 23.9 mmol) in dry methanol
(30 mL) was added cyanocobalamine (16 mg, 0.012 mmol), and
stirring was continued for another 15 min. After that, a solution of 5
(580 mg, 0.1 mmol) in dry methanol (5 mL) was added, and the
resulting solution was further stirred for 5 min. The reaction mixture
was filtered through a Celite bed. The filtrate was evaporated under
reduced pressure. The residue obtained was dissolved in ethyl acetate
(25 mL) and washed with a mixture of brine and water (1:1 v/v, 10
mL each). The organic layer was dried over Na2SO4 and concentrated
to give the crude aldehyde 6 (430 mg), which was used immediately
for the next step.
Eluent for column chromatography: EtOAc/hexane (1/4, v/v);
[α]28 = −56.8 (c 0.71, CHCl3); Rf = 0.66 (1/3, EtOAc/hexane); IR
D
1
(neat, cm−1) 3333, 2979, 2906, 1380, 1258, 1069; H NMR (300
MHz, CDCl3) δ 1.26−1.27 (m, 6H), 1.36 (s, 3H), 1.46 (s, 3H), 3.10−
3.14 (m, 1H), 3.21−3.26 (m, 1H), 3.86−3.89 (m, 1H), 4.22−4.23 (m,
1H), 4.31−4.34 (m, 1H), 4.53−4.55 (m, 1H); 13C NMR (75 MHz,
CDCl3) δ 8.6, 30.8, 31.2, 32.25, 32.3, 75.2, 82.9, 83.4, 83.8, 103.0,
115.1, 115.8; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for
C12H20IO5 371.0355, measured 371.0345.
To a stirred solution of aldehyde 6 in EtOH (10 mL) was added
TBAF (1 mL, 1 M solution in THF), and the reaction mixture was left
stirring at room temperature. After 30 min, trans-2-phenylvinyl
General Procedure for Preparation of Compound 12. To a
magnetically stirred suspension of Zn dust (680 mg, 10.4 mmol) and
NH4Cl (560 g, 10.38 mmol) in dry methanol (20 mL) was added
cyanocobalamine (7 mg, 0.005 mmol). The stirring was allowed to
continue for another 10 min. After that, a solution of 11 (370 mg, 1
mmol) in dry methanol (5 mL) was added, and the resulting solution
was further stirred for 15 min. The reaction mixture was filtered
through a Celite bed. The filtrate was evaporated under reduced
pressure. The residue obtained was dissolved in ethyl acetate (30 mL)
and washed with a mixture of brine and water (1:1 v/v, 10 mL each).
The organic layer was dried over Na2SO4 and concentrated to give the
hemiacetal 12 as a mixture of α and β anomer (220 mg, 0.9 mmol,
90%), which was directly used for the next step.
t
boronic acid (149 mg, 1 mmol) and BuNH2 (0.5 mL) were added,
and the reaction mixture was left stirring under refluxing condition.
After completion of the reaction (24 h, TLC control), the reaction
mixture was concentrated to a residue that on column chromato-
graphic purification afforded amine 7 with some unidentified
impurities. The impure amine 7 was used directly for the next step.
To a stirred solution of amine 7 in dry THF (5 mL) were added
Et3N (0.42 mL, 3 mmol) and DMAP (170 mg, 1 mmol) at room
temperature. The resulting reaction mixture was cooled to 0 °C.
(Boc)2O (1.5 mmol) was then added to it. The stirring was continued
for overnight without further cooling. After completion of the reaction,
the reaction mixture was concentrated to a residue that on column
chromatographic purification furnished the oxazolidinone 8 (59 mg,
0.15 mmol, 15% from 5) with simultaneous Boc protection followed
by oxazolidinone ring formation.
Compound 8 from Compound 12. To a stirred solution of
hemiacetal 12 (245 mg, 1 mmol) in EtOH (6 mL) were added trans-2-
t
phenylvinyl boronic acid (149 mg, 1 mmol) and BuNH2 (0.5 mL),
and the reaction mixture was left stirring. After completion of the
reaction (24 h, TLC control), the reaction mixture was concentrated
to a residue that on column chromatographic purification afforded
amine 7 with some unidentified impurities.
To a stirred solution of amine 7 in THF (5 mL) were added Et3N
(0.42 mL, 3 mmol) and DMAP (170 mg, 1 mmol), and the resulting
solution was cooled to 0 °C. (Boc)2O (1.5 mmol) was added to it ,and
the stirring was continued for 12 h. Afterward, the reaction mixture
was concentrated under reduced pressure to a residue that on column
chromatographic purification furnished the oxazolidinone 8 (155 mg,
0.4 mmol, 40% from 12).
Compound 13. To a 100 mL two necked oven-dried round-
bottom flask fitted with a reflux condenser and septum was added
Grubbs second generation catalyst (22 mg, 0.026 mmol) under argon
atmosphere. Dry degassed CH2Cl2 (25 mL) was added to it through a
syringe, and the resulting solution was left stirring. Compound 8 (100
mg, 0.26 mmol) in DCM (5 mL) was added through a syringe to the
stirring solution. The septum was replaced with a glass stopper while
the stirring was continued. The solution was refluxed for 24 h. The
temperature of the mixture was cooled slowly to room temperature.
The organic solvent was evaporated under reduced pressure to give a
black residue that on column chromatographic purification gave 13 as
a semisolid compound (37 mg, 0.133 mmol, 51%).
Eluent for column chromatography: EtOAc/hexane (1/9, v/v);
[α]28D = +124.2 (c 0.125, CHCl3); Rf = 0.29 (1/3, EtOAc/hexane); IR
(neat, cm−1) 3026, 2791, 1745, 1216, 766; 1H NMR (300 MHz,
CDCl3) δ 1.36−1.37 (m, 6H), 1.46 (s, 9H), 4.23 (d, J = 5.9 Hz, 1H),
4.57 (brm, 2H), 4.74 (d, J = 6.6 Hz, 1H), 5.72−5.84 (m, 2H); 13C
NMR (75 MHz, CDCl3) δ 27.0, 28.3, 28.9, 51.7, 54.2, 69.7, 70.9, 71.4,
110.3, 123.3, 129.0, 155.4; HRMS (ESI TOF (+)) m/z [M + H]+
calcd for C14H22NO4 268.1549, measured 268.1544.
Eluent for column chromatography: EtOAc/hexane (1/2, v/v);
[α]26 = −80.0 (c 0.28, CHCl3); Rf = 0.33 (1/3, EtOAc/hexane); IR
D
1
(neat, cm−1) 3342, 1740, 1219, 769; H NMR (300 MHz, CDCl3) δ
1.31 (s, 3H), 1.40 (s, 9H), 1.53 (s, 3H), 4.25−4.30 (m, 1H), 4.36−
4.50 (m, 3H), 5.37−5.43 (m, 2H), 5.89−6.01 (m, 1H), 6.25 (dd, J =
9.0, 15.9 Hz, 1H), 6.52 (d, J = 16.0 Hz, 1H), 7.32−7.39 (m, 5H); 13C
NMR (75 MHz, CDCl3) δ 25.7, 28.1, 28.6, 54.8, 60.9, 76.5, 76.8, 78.3,
110.1, 120.4, 126.0, 127.0, 129.1, 129.3, 134.5, 135.0, 135.7, 155.8;
HRMS (ESI TOF (+)) m/z [M + H]+ calcd for C22H30NO4 372.2175,
measured 372.2169.
Compound 10. To a stirred suspension of D-galactose 9 (5 g,
27.75 mmol) in dry acetone (200 mL) was added I2 (1.5 g, 5.9 mmol)
at room temperature, and the reaction was allowed to stir at same
temperature. After 24 h, excess iodine was quenched with aqueous
saturated solution of Na2S2O3, and the resulting mixture was
concentrated. The reaction mixture was then extracted with EtOAc
(3 × 100 mL), and the combined organic layer was dried over Na2SO4
and concentrated under reduced pressure to a residue that on
purification by column chromatography gave 1,2;3,4-di-O-isopropyli-
dine-α-D-galactopyranoside 10 (5.77 g, 22.2 mmol, 80%).
Eluent for column chromatography: EtOAc/hexane (1/4, v/v);
[α]28 = −55.3 (c 0.77, CHCl3); Rf = 0.29 (1/2, EtOAc/hexane); IR
D
1
(neat, cm−1) 3532, 3462, 2989, 2930, 1380, 1170; H NMR (300
MHz, CDCl3) δ 1.30 (s, 6H), 1.41 (s, 3H), 1.49 (s, 3H), 2.61 (s, 1H,
OH), 3.69−3.82 (m, 3H), 4.22−4.31 (m, 2H), 4.56−4.59 (m, 1H),
5.52 (d, J = 4.95 Hz, 1H); 13C NMR (50 MHz, CDCl3) δ 24.6, 25.2,
26.2, 26.3, 62.4, 68.6, 70.9, 71.0, 71.7, 96.6, 109.0, 109.7; HRMS (ESI
TOF (+)) m/z [M + H]+ calcd for C12H21O6 261.1338, measured
261.1328.
Compound 11. 1,2;3,4-di-O-isopropylidine-α-D-galactopyranoside
10 (1.0 g, 3.84 mmol), PPh3 (1.51 g, 5.76 mmol), and imidazole (785
Compound 14. To a 50 mL round-bottom flask compound 13 (30
mg, 0.11 mmol) was taken in DCM (4 mL), and TFA (1 mL) was
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Note
added to it at 0 °C. The mixture was allowed to stir without further
cooling. After 2 h, it was cooled to 0 °C, and water (1 mL) was added
to it. The resulting solution was further left stirring for 1 h. After that,
the reaction mixture was concentrated and coevaporated with toluene
under reduced pressure to get a residue that on column chromato-
graphic purification gave the diol 14 (22 mg, 0.095 mmol, 85%).
Eluent for column chromatography: EtOAc/hexane (2/1, v/v);
chromatographic purification furnished diol 21 (342 mg, 0.75 mmol,
75%).
Eluent for column chromatography: EtOAc/hexane (1/2, v/v);
[α]28 = +19.4 (c 0.88, CHCl3); Rf = 0.56 (2/5, EtOAc/hexane); IR
D
(neat, cm−1) 3033, 2961, 1641, 1216, 762; 1H NMR (300 MHz,
CDCl3) δ 1.09 (s, 9H), 1.15 (s, 3H), 1.25 (s, 3H), 2.36 (s, 1H, OH),
2.71 (s, 1H, OH), 3.67−3.78 (m, 3H), 3.93 (dd, J = 3.3, 7.9 Hz, 1H),
4.17−4.22 (m, 1H), 4.35−4.39 (m, 1H), 5.06 (d, J = 10.1 Hz, 1H),
5.15 (d, J = 16.9 Hz, 1H), 5.47−5.59 (m, 1H), 7.36−7.44 (m, 6H),
7.70−7.75 (m, 4H); 13C NMR (50 MHz, CDCl3) δ 20.0, 25.5, 27.5,
27.9, 63.7, 72.8, 74.3, 78.9, 79.3, 108.8, 119.6, 127.5, 127.9, 129.8,
130.1, 133.7, 134.0, 134.5, 136.5; HRMS (ESI TOF (+)) m/z [M +
Na]+ calcd for C26H36O5SiNa 479.2224, measured 479.2231.
Compound 25. To the diol 21 (500 mg, 1.1 mmol) dissolved in
THF/H2O (9:1, 15 mL) was added NaIO4 (320 mg, 1.5 mmol) at 0
°C, and the mixture was stirred for 1.5 h without further cooling. The
reaction mixture was quenched with saturated Na2S2O3 solution (5
mL) at 0 °C and extracted with EtOAc (2 × 10 mL). The combined
organic layer was dried over Na2SO4 and concentrated under reduced
pressure to give the crude aldehyde 22, which was immediately used
for the next step.
[α]28 = +78.5 (c 0.23, CHCl3); Rf = 0.30 (4/1, EtOAc/hexane); IR
D
(neat, cm−1) 3211, 3140, 1740, 1654, 1261, 804; 1H NMR (300 MHz,
CDCl3) δ 1.37 (s, 9H), 4.24−4.29 (m, 2H), 4.37 (brm, 1H), 4.57−
4.60 (m, 1H), 5.75 (m, 2H); 13C NMR (50 MHz, CDCl3) δ 28.7, 52.6,
54.4, 64.2, 67.5, 73.5, 124.8, 131.7, 156.6; HRMS (ESI TOF (+)) m/z
[M + H]+ calcd for C11H18NO4 228.1236, measured 228.1224.
Compound 19. To a stirred suspension of D-mannose 17 (5 g,
27.75 mmol) in dry acetone (200 mL) was added I2 (1.5 g, 5.9 mmol),
and the reaction was allowed to stir at room temperature. After 24 h,
excess iodine was quenched with an aqueous saturated solution of
Na2S2O3, and the resulting mixture was concentrated under vacuum.
The aqueous portion was extracted with EtOAc (3 × 100 mL), and the
combined organic layer was dried over Na2SO4 and concentrated
under reduced pressure to a residue that on purification by column
chromatography gave 1,2;5,6-di-O-isopropylidine-α-D-mannofurano-
side 18 (5.78 g, 22.2 mmol, 80%).
To a stirred solution of aldehyde 22 in EtOH (10 mL) was added
TBAF (1.3 mL, 1 M solution in THF), and the reaction mixture was
left stirring at room temperature. After 30 min, trans-2-phenylvinyl
boronic acid (165 mg, 1.1 mmol) and tBuNH2 (0.5 mL) were added to
the reaction mixture, and it was refluxed for 24 h. Solvent was removed
under reduced pressure, and the resulting oil was purified by flash
chromatography to yield amino alcohol 24 with some unidentified
impurities (TLC).
To the stirring solution of amine 24 in dry THF (5 mL) were added
Et3N (0.42 mL, 3 mmol) and DMAP (170 mg, 1 mmol) at room
temperature. The resulting mixture was cooled to 0 °C. (Boc)2O (1.5
mmol) was added to it, and the mixture was stirred overnight without
further cooling. After 12 h, the reaction mixture was concentrated to a
residue that on column chromatographic purification furnished the
oxazolidinone 25 (89 mg, 0.23 mmol, 21% from 21).
To a 250 mL two necked dry round-bottom flask were added
methyltriphenylphosphonium bromide (Ph3PCH3Br) (39.6 g, 111
t
mmol) and BuOK (9.95 g, 88.8 mmol) under nitrogen atmosphere.
Dry THF (100 mL) was added at 0 °C, and the stirring was continued
without further cooling. After 1 h, the reaction mixture was again
cooled to 0 °C, and the compound 18 (5.78 g, 22.2 mmol) in THF
(25 mL) was added to it through a syringe. The solution was stirred
until the reaction was completed (TLC control, 4 h). Afterward, the
reaction mixture was quenched with an aqueous solution of NH4Cl
(25 mL). It was extracted with EtOAc (3 × 50 mL), and the combined
organic layer was evaporated under reduced pressure to give a residue
that on column chromatographic purification afforded the olefin 19 as
a clear oil (4.87 g, 18.87 mmol, 85%).
Eluent for column chromatography: EtOAc/hexane (1/9, v/v);
D
Eluent for column chromatography: EtOAc/hexane (1/13, v/v);
[α]26 = +66.0 (c 0.24, CHCl3); Rf = 0.3 (1/3, EtOAc/hexane); IR
[α]28 = −35.7 (c 1.0, CHCl3); Rf = 0.54 (1/4, EtOAc/hexane); IR
D
(neat, cm−1) 3026, 2761, 1745, 1216, 770; 1H NMR (300 MHz,
CDCl3) δ 1.31 (s, 3H), 1.40 (s, 9H), 1.53 (s, 3H), 4.25−4.30 (m, 1H),
4.35−4.49 (m, 3H), 5.37−5.43 (m, 2H), 5.89−6.01 (m, 1H), 6.25 (dd,
J = 9.1, 16.0 Hz, 1H), 6.52 (d, J = 16.0 Hz, 1H), 7.32−7.39 (m, 5H);
13C NMR (50 MHz, CDCl3) δ 25.8, 28.1, 28.6, 54.8, 60.9, 76.6, 76.8,
78.4, 110.1, 120.4, 126.0, 127.0, 129.1, 129.3, 134.5, 135.0, 135.7,
155.8; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for C22H30NO4
372.2175, measured 372.2167.
1
(neat, cm−1) 3235, 1634, 1217, 764; H NMR (300 MHz, CDCl3) δ
1.29 (s, 3H), 1.33 (s, 3H), 1.35 (s, 3H), 1.48 (s, 3H), 2.21 (d, J = 8.0
Hz, 1H), 3.41 (dd, J = 6.7, 7.7 Hz, 1H), 3.91−4.05 (m, 3H), 4.33 (dd,
J = 1.09, 7.44 Hz, 1H), 4.64 (t, J = 7.5 Hz, 1H), 5.25−5.37 (m, 2H),
5.99−6.10 (m, 1H); 13C NMR (50 MHz, CDCl3) δ 24.8, 25.6, 26.9,
27.0, 67.4, 70.8, 76.3, 77.0, 79.4, 108.9, 109.5, 119.7, 134.6; HRMS
(DART TOF (+)) m/z [M + H]+ calcd for C13H23O5 259.1545,
measured 259.1542.
Compound 20. To a stirred solution of compound 19 (260 mg, 1
mmol) in DMF (2 mL) were added imidazole (275 mg, 4 mmol) and
TBDPSCl (412 mg, 0.39 mL, 1.5 mmol), and the reaction mixture was
allowed to stir for 24 h. Water (10 mL) was added to it, and the entire
solution was extracted with EtOAc (2 × 10 mL). The combined
organic layer was evaporated under reduced pressure to give a residue
that on purification by column chromatography afforded the silyl ether
20 as clear oil (432 mg, 0.87 mmol, 87%).
Compound 26. To a 50 mL two necked oven-dried round-bottom
flask fitted with a reflux condenser and septum was added Grubbs
second generation catalyst (11 mg, 0.013 mmol, 10 mol %) under
argon atmosphere. Dry degassed CH2Cl2 (15 mL) was added to it, and
the reaction mixture was left stirring. Compound 25 (50 mg, 0.13
mmol) in DCM (5 mL) was added through a syringe to the stirring
solution. The septum was replaced with a glass stopper, and the
solution was refluxed with stirring for 24 h. The temperature of the
mixture was cooled slowly to room temperature. The organic solvent
was evaporated under reduced pressure to give a black residue that on
column chromatographic purification afforded 26 as a semisolid
compound (17 mg, 0.062 mmol, 48%).
Eluent for column chromatography: EtOAc/hexane (1/9, v/v);
[α]28D = −134.0 (c 0.112, CHCl3); Rf1= 0.3 (1/3, EtOAc/hexane); IR
(neat, cm−1) 3069, 1745, 1217, 765; H NMR (300 MHz, CDCl3) δ
1.36−1.38 (m, 6H), 1.46 (s, 9H), 4.24 (d, J = 5.4 Hz, 1H), 4.57 (brm,
2H), 4.75 (d, J = 6.3 Hz, 1H), 5.72−5.84 (m, 2H); 13C NMR (75
MHz, CDCl3) δ 27.0, 28.3, 28.9, 51.7, 54.2, 69.7, 70.8, 71.4, 110.3,
123.3, 129.0, 155.4; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for
C14H22NO4 268.1549, measured 268.1545.
Eluent for column chromatography: EtOAc/hexane (1/30, v/v);
[α]28 = +37.2 (c 1.47, CHCl3); Rf = 0.5 (1/6, EtOAc/hexane); IR
D
(neat, cm−1) 2938, 2796, 1374, 1217, 765; 1H NMR (300 MHz,
CDCl3) δ 1.07 (s, 9H), 1.11 (s, 3H), 1.14 (s, 3H), 1.31 (s, 3H), 1.32
(s, 3H), 3.82 (t, J = 7.2 Hz, 1H), 3.97−4.10 (m, 4H), 4.40−4.44 (m,
1H), 5.02−5.16 (m, 2H), 5.42−5.54 (m, 1H), 7.35−7.42 (m, 6H),
7.71−7.76 (m, 4H); 13C NMR (50 MHz, CDCl3) δ 20.1, 25.3, 25.5,
26.4, 27.4, 28.0, 67.5, 72.8, 77.2, 79.1, 79.9, 108.1, 109.4, 118.5, 127.3,
127.6, 129.4, 129.7, 134.1, 134.8, 135.1, 136.4, 136.6; HRMS (ESI
TOF (+)) m/z [M + Na]+ calcd for C29H40O5SiNa 519.2537,
measured 519.2543.
Compound 21. To a 100 mL round-bottom flask was added
compound 20 (500 mg, 1 mmol) dissolved in 80% AcOH (10 mL),
and the solution was allowed to stir at room temperature. After 6 h,
the reaction mixture was concentrated and coevaporated with toluene
under reduced pressure to obtain an oily residue that on column
Compound 27. To a solution of compound 26 (30 mg, 0.11
mmol) in DCM (4 mL) was added TFA (1 mL) at 0 °C, and the
reaction was allowed to stir without further cooling. After 2 h, the
reaction mixture was again cooled to 0 °C, and water (1 mL) was
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Note
added. The resulting solution was left stirring for another 1 h. After
that, the reaction mixture was concentrated and coevaporated with
toluene under reduced pressure to obtain a residue that on column
chromatographic purification afforded the diol 27 (23 mg, 0.1 mmol,
91%).
(16) Angelaud, R.; Babot, O.; Charvat, T.; Landais, Y. J. Org. Chem.
1999, 64, 9613−9624.
́
(17) Ovva, H.; Codee, J. D. C.; Lastdrager, B.; Overkleeft, H. S.; van
der Marel, G. A.; van Boom, j. H. Tetrahedron Lett. 1999, 40, 5063−
5066.
Eluent for column chromatography: EtOAc/hexane (2/1, v/v);
D
(18) Spielvogel, D.; Kammerer, J.; Keller, M.; Prinzbach, H.
[α]28 = −73.7 (c 0.16, CHCl3); Rf = 0.29 (4/1, EtOAc/hexane); IR
Tetrahedron Lett. 2000, 41, 7863−7867.
(neat, cm−1) 3420, 2926, 1723, 1219, 768; 1H NMR (300 MHz,
CDCl3) δ 1.42 (s, 9H), 3.65 (brs, 1H), 4.08 (brs, 1H), 4.29−4.32 (m,
2H), 4.40 (brm, 1H), 4.63 (dd, J = 4.2, 5.8 Hz, 1H), 5.79 (brm, 2H);
13C NMR (50 MHz, CDCl3) δ 28.7, 52.6, 54.3, 64.2, 67.3, 73.6, 124.6,
131.8, 156.6; HRMS (ESI TOF (+)) m/z [M + H]+ calcd for
C11H18NO4 228.1236, measured 228.1231.
(19) Łysek, R.; Favre, S.; Vogel, P. Tetrahedron 2007, 63, 6558−6572.
(20) Łysek, R.; Schutz, C.; Vogel, P. Bioorg. Med. Chem. Lett. 2005,
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15, 3071−3075.
(21) Alegret, C.; Benet-Buchholz, J.; Riera, A. Org. Lett. 2006, 8,
3069−3072.
(22) Pandey, G.; Tiwari, K. N.; Puranik, V. G. Org. Lett. 2008, 10,
3611−3614.
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ASSOCIATED CONTENT
* Supporting Information
■
4281.
S
(24) Trost, B. M.; Malhotra, S.; Olson, D. E.; Maruniak, A.; Bois, J.
D. J. Am. Chem. Soc. 2009, 131, 4190−4191.
(25) Jana, C. K.; Grimme, S.; Studer, A. Chem.Eur. J. 2009, 15,
9078−9084.
General experimental details, full characterization and copies of
1HNMR and 13CNMR spectra of compounds 2, 3, 5, 8, 10, 11,
13, 14, 19, 20, 21, 25, 26, and 27 are provided. This material is
available free of charge via the Internet at http://pubs.acs.org.
(26) Chappell, D.; Drew, M. G. B.; Gibson, S.; Harwood, L. M.;
Russell, A. T. Synlett 2010, 517−520.
(27) Lu, P.-H.; Yang, C.-S.; Devendar, B.; Liao, C.-C. Org. Lett. 2010,
12, 2642−2645.
AUTHOR INFORMATION
Corresponding Author
*E-mail: akshaw55@yahoo.com.
■
́
(28) Norsikian, S.; Soule, J.-F.; Cannillo, A.; Guillot, R.; Dau, M.-E.
T. H.; Beau, J.-M. Org. Lett. 2012, 14, 544−547.
(29) Ducatti, D. R. B.; Massi., A.; Noseda, M. D.; Duarte, M. E. R.;
Dondoni, A. Org. Biomol. Chem. 2009, 7, 576−588.
(30) Ghosal, P.; Kumar, V.; Shaw, A. K. Tetrahedron 2010, 66, 7504−
7509.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(31) Ghosal, P.; Kumar, V.; Shaw, A. K. Carbohydr. Res. 2010, 345,
We are thankful to Sophisticated Analytical Instrument Facility,
CDRI for providing spectral data, DST (Project SR/SI/OC-
17/2010) for financial support and Mr. A.K. Pandey for
technical assistance. P. G. thanks CSIR for awarding Senior
Research Fellowship. CDRI communication no. 8302.
41−44.
(32) Reddy, L. V. R.; Swamy, G. N.; Shaw, A. K. Tetrahedron:
Asymmetry 2008, 19, 1372−1375.
(33) Reddy, L. V. R.; Reddy, P. V.; Shaw, A. K. Tetrahedron:
Asymmetry 2007, 18, 542−546.
(34) Pal, P.; Shaw, A. K. Tetrahedron 2011, 67, 4036−4047.
(35) Kumar, V.; Das, P.; Ghosal, P.; Shaw, A. K. Tetrahedron 2011,
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