Reagents for stereoselective preparation of N-carbamyl β-d- glucuronides

Article abstract of DOI:10.1021/jo200238d

Carbamyl glucuronidation is an increasingly well-recognized route of metabolism for secondary amine drugs. Proper characterization of these metabolites requires the synthesis of authentic standards. O-Protected glucuronyl p-nitrophenyl carbonates can be p

Full text of DOI:10.1021/jo200238d

NOTE
pubs.acs.org/joc
Reagents for Stereoselective Preparation of N-Carbamyl
β-D-Glucuronides
William H. Bunnelle*
Abbott Laboratories, Neuroscience Research, Building AP9A, Department R4MN, 100 Abbott Park Road, Abbott Park,
Illinois 60064-6117, United States
S Supporting Information
b
ABSTRACT: Carbamyl glucuronidation is an increasingly well-recognized
route of metabolism for secondary amine drugs. Proper characterization of
these metabolites requires the synthesis of authentic standards. O-Pro-
tected glucuronyl p-nitrophenyl carbonates can be prepared with high
selectivity for the β-configuration at the anomeric center and efficiently
transfer the β-glucuronylcarbonyl group to secondary amines, constituting
an effective and versatile method for preparation of these metabolites.
onjugation to N-carbamyl β-D-glucuronides is an increas-
ingly well-recognized metabolic fate of many amine-contain-
p-nitrophenyl glucuronyl carbonate 4a as an 83:17 mix of R/β
epimers at the anomeric center.22 On the assumption that
a less-reactive acylating agent would favor capture of the
more nucleophilic β-anomeric hydroxyl group,23 the reaction
was repeated using bis(p-nitrophenyl)carbonate. Indeed, the
p-nitrophenyl glucuronyl carbonate 4a was formed with ca.
11:89 selectivity favoring the β-anomer. One recrystallization
of the crude product provided the protected p-nitrophenyl β-D-
glucuronyl carbonate with very high (>98:2) stereoselectivity,24
C
ing drugs.1 The transformation is considered to proceed by
reversible carboxylation of the amine with endogenous CO2,
followed by enzyme-mediated glucuronyl transfer to the inter-
mediate carbamic acid.1ꢀ4 Several isoforms of uridine dipho-
sphate β-D-glucuronyl tranferase (UDPGT) are known to be
competent for this process.5 Small quantities of carbamyl glucu-
ronides have been isolated and characterized from in vivo4,6ꢀ8 or
in vitro2,3,9 metabolic systems, but laboratory synthesis is most
practical for the larger amounts required for detailed studies of
the pharmacology and toxicology,10 distribution, recirculation,
and elimination of these metabolites. Good methods for direct,
stereocontrolled β-D-glucuronidation of alcohols, amines, and
carboxylic acids have been developed,11ꢀ14 but these are not
suitable for preparation of glucuronyl carbamates due to the
instability of the requisite carbamic acids. Activated ureas,15 like
carbamyl chlorides,16 form glucuronyl carbamates, but with poor
anomeric selectivity. On the other hand, it has been shown
(Scheme 1) that isocyanates react with excellent stereoselectively
with the anomeric hydroxyl of a suitably protected glucuronic
acids (e.g., 1a,17 and even less-protected versions18) providing a
route to β-D-glucuronyl carbamates of primary amines (2p).19
Leenders and Scheeren further exploited this finding to design
N-phenanthridinone O-β-D-glucuronyl carbamate (3) that effi-
ciently transfers the β-D-glucuronylcarbonyl group to primary or
secondary (2s) amines.20 The preparation of 3, though rather
efficient, requires five steps and may limit its availability and use.
Described here is methodology for stereoselective preparation of
mixed p-nitrophenyl β-D-glucuronyl carbonates 4a,b (Scheme 2)
that transfer the glucuronylcarbamyl moiety with excellent
stereochemical integrity, constituting a general method for
synthesis of β-D-glucuronyl carbamates.
as determined by 1H NMR (sugar H-1 resonance at δ 5.80, J1,2
=
6.1 Hz). Importantly, 4a reacts cleanly with amines to effect
transfer of the β-D-glucuronyl carbonyl group, with retention of
anomeric stereochemistry to form the protected amine β-D-
glucuronyl carbamate. This is illustrated by elaboration of ABT-
594 (5),25 a nicotinic agonist with demonstrated clinical efficacy
in treating chronic neuropathic pain,26 to its carbamyl β-D-
glucuronide 7, a putative human metabolite (Scheme 3). Thus,
addition of 4a to 5 provided the carbamate 6 in good yield after
chromatographic purification. Glucuronide deprotection was
accomplished with N,N-diisopropylethylamine in wet methanol
to provide the carbamyl glucuronide 7 after purification by
reversed-phase chromatography. The mild hydrolysis conditions
were essential to minimize formation of side products, in this case
resulting from methanolysis to form the methyl carbamate of 5
and elimination of the glucuronide 4-acetate providing the 4,5-
dehydro glucuronide.13 As expected, carbamate 7 was formed as
the β-anomer (sugar H-1 resonance at δ 5.34, J1,2 = 7.9 Hz),
indicating retention of configuration through the glucuronyl
transfer and deprotection steps.
In an effort to avoid hydrolysis side reactions in the sugar
deprotection, and thereby simplify isolation of the pure glucur-
onyl carbamate product, benzyl protection of the sugar was
investigated. Indeed, benzyl 2,3,4-tri-O-benzylglucuronate (1b,27
Reaction of methyl 2,3,4-tri-O-acetylglucuronate (1a)15,21
(as a ∼3:1 mix of R:β anomers in solution) with p-nitrophenyl
chloroformate in the presence of triethylamine provided the
Received: February 8, 2011
Published: May 20, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/jo200238d J. Org. Chem. 2011, 76, 5429–5432
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The Journal of Organic Chemistry
NOTE
Scheme 1. Stereoselective Methods for Preparation of
Glucuronylacabamates
Scheme 2. Stereoselective Preparation of p-Nitrophenyl β-D-
Glucuronyl Carbonates
sugar carbamates exhibited broad lines and split multiplets indicative of
slow interconversion of rotamers at room temperature. At 90 °C, the
signals coalesced and sharpened sufficiently to enable interpretation of
the proton spectra, but the larger dispersion (ΔHz) in the 13C NMR
made it impossible to obtain usable carbon spectra of 5, 6, 9, and 10. The
stereoselectivities for 4a and 4b were determined from integration of the
1H NMR signal for the anomeric proton for the β-glucuronide com-
pared to the chemical shift region for the R-anomer (δ 6.4ꢀ6.2 ppm).22
Methyl 2,3,4-Tri-O-acetyl-1-O-(4-nitrophenoxycarbonyl)-
β-D-glucopyranuronate (4a). A solution of bis(4-nitrophenyl)
carbonate (2.40 g, 7.88 mmol) in CH2Cl2 (35 mL) was added dropwise
over 20 min to a chilled (ꢀ5 to ꢀ10 °C) solution of methyl 2,3,4-tri-O-
acetyl-D-glucupyranuronate (1a)21 (2.51 g, 7.51 mmol) and triethyla-
mine (1.52 g, 15.02 mmol) in CH2Cl2 (60 mL) under a nitrogen
atmosphere. The resulting yellow solution was stirred for 30 min longer
and then washed successively with 5% Na2CO3 (aq) (1 ꢁ 200 mL, 1 ꢁ
80 mL) and 4% H2SO4 (aq) (180 mL). The organic phase was dried
(MgSO4) and concentrated under vacuum to leave an off-white, friable
foam (3.68 g). The residue was crystallized from ethyl ether (80 mL) to
provide a white, crystalline powder (2.89 g, 77%). If desired, further
purification can be accomplished by crystallization from methanol: mp
124.5ꢀ125.5 °C (lit.24 mp 132 °C); [R]2D0 = ꢀ20.0 (c 1.00, EtOAc)
(lit.24 [R]2D0 ꢀ4.4 (c 0.34, CHCl3); 1H NMR (400 MHz, CDCl3) δ 2.06
(s, 3 H), 2.07 (s, 3 H), 2.11 (s, 3 H), 3.77 (s, 3 H), 4.31 (d, J = 8.3 Hz, 1
H, H-5), 5.21 (dd, J = 8.7, 6.1 Hz, 1 H, H-2), 5.33 (t, J = 8.3 Hz, 1 H),
5.38 (t, J = 8.9 Hz, 1 H), 5.80 (d, J = 6.1 Hz, 1 H, H-1), 7.44 (d, J = 9.2 Hz,
2 H), 8.29 ppm (d, J = 8.6 Hz, 2 H); 13C NMR (101 MHz, CDCl3) δ
20.4 (q), 20.5 (q), 20.6 (q), 53.1 (q), 68.1 (d), 70.1 (d), 70.9 (d), 73.1
(d), 95.6 (d), 121.7 (d), 125.4 (d), 145.7 (s), 150.7 (s), 155.0 (s), 167.0
(s), 169.1 (s), 169.3 (s), 169.7 (s); HRMS m/z 737.27009 (M þ NH4
requires 737.27049). Anal. Calcd for (C20H21NO14): C, 48.10; H, 4.24;
N, 2.80. Found: C, 48.10; H, 4.14; N, 2.81.
Benzyl 2,3,4-Tri-O-benzyl-1-O-(4-nitrophenoxycarbonyl)-
β-D-glucopyranuronate (4b). Solid bis(4-nitrophenyl) carbonate
(210 mg, 0.691 mmol) was added to an ice-cooled solution of benzyl
2,3,4-tri-O-benzyl-D-glucupyranuronate (1b)27 (365 mg, 0.658 mmol)
in triethylamine (0.183 mL, 1.32 mmol) and CH2Cl2 (20 mL). After
2.5 h at 0 °C, the solution was diluted with CH2Cl2 (25 mL) and washed
successively with 5% Na2CO3 (aq) (2 ꢁ 20 mL) and 4% H2SO4 (aq)
(10 mL). The organic phase was dried (MgSO4) and concentrated
under vacuum. The residual pale oil (484 mg) was crystallized from ethyl
ether (5 mL) and hexanes (10 mL) to provide the title compound as fine
white needles (342 mg, 72%): mp 85.0ꢀ85.8 °C; [R]2D0 = ꢀ4.2 (c 1.00,
EtOAc); 1H NMR (300 MHz, CDCl3) δ 3.69ꢀ3.81 (m, 2 H), 3.92 (t, J =
9.0 Hz, 1 H), 4.17 (d, J = 9.5 Hz, 1 H, H-5), 4.47 (d, J = 10.5 Hz, 1 H), 4.71
(d, J = 10.9 Hz, 1 H), 4.75ꢀ4.88 (m, 4 H), 5.12ꢀ5.22 (m, 2 H), 5.65 (d, J =
6.8 Hz, 1 H, H-1), 7.12 (dd, J = 6.6, 3.2 Hz, 2 H), 7.21ꢀ7.37 (m, 20 H),
8.22ꢀ8.30 ppm (m, 2 H); 13C NMR (101 MHz, CDCl3) δ 67.7 (t), 75.0
(t), 75.1 (d), 75.5 (t), 78.7 (d), 80.3 (d), 83.2 (d), 98.2 (d), 121.7 (d), 125.3
(d), 127.76 (d), 127.82 (d), 127.85 (d), 128.0 (d), 128.35 (d), 128.44 (d),
128.49 (d), 128.55 (d), 128.57 (d), 128.59 (d), 134.7 (s), 137.4 (s), 137.6
found to exist as a ca. 2:1 ratio of R:β anomers in CDCl3
solution) reacted with bis(p-nitrophenyl)carbonate to provide
the mixed carbonate 4b with >95% β-anomeric selectivity.
Similar to 4a, the benzyl-protected glucuronyl carbonate 4b trans-
ferred the tetra-O-benzyl glucuronyl carbonyl group efficiently to
secondary amines. Thus, reaction with ABT-089 (8),28 a nicotinic
partial agonist tested clinically for treatment of ADHD,29 provided
the protected carbamate 9 in 89% yield after purification by flash
chromatography (Scheme 4). In fact, since reaction of 1b with
bis(p-nitrophenyl)carbonate proceeds with excellent β-anomeric
stereoselectivity, it was also possible to prepare 9 in a one-pot
reaction from 1b and triethylamine by sequential addition of bis(p-
nitrophenyl)carbonate and 8. Although related benzyl-protected
glucuronides have been reported to undergo full debenzylation
under mild conditions,30 catalytic hydrogenation of 9 proceeded
rather sluggishly once the benzyl ester was cleaved.31 After screening
a number of hydrogenolysis conditions (including different cata-
lysts, hydrogen pressures, and atom-transfer conditions), it was
found that full debenzylation could be accomplished using a high
loading of Pearlman’s catalyst, providing clean β-D-glucuronyl
carbamate 10 after 2 days’ reaction time with minimal workup.
This deprotection is not suitable for compounds with easily
hydrogenated functional groups (e.g., 7), but reagent 4b may be a
preferred alternative to the ester-protected analogue 4a when that is
not an issue. Use of a less-protected glucuronide might be preferred
in some cases, and allyl glucuronate (4c) has been reported18 to
undergo selective formation of β-glucuronyl carbamates and carbon-
ates on reaction with certain isocyanates and chloroformates, respec-
tively. Unfortunately, conditions could not be found to produce
the anomeric p-nitrophenylcarbonate of 4c or the related benzyl
glucuronate.
In summary, the protected glucuronyl carbonates 4a and 4b
are easily prepared in high stereochemical purity and function as
glucuronylcarbonyl transfer reagents, useful for the preparation
of β-D-glucuronyl carbamates.
’ EXPERIMENTAL SECTION
Melting ranges were determined with a capillary tube apparatus and
are uncorrected. Unless otherwise noted, reagents and solvents were
used as received from commercial suppliers. The 1H NMR spectra of the
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NOTE
Scheme 3
Scheme 4
(s), 137.9 (s), 145.6 (s), 151.0 (s), 155.0 (s), 168.1 ppm(s), one benzylic
CH2 and two phenyl CH signals not resolved; HRMS CI/NH3 m/z
737.27009 (M þ H requires 737.27049). Anal. Calcd for (C41H37NO11):
C, 68.42; H, 5.18; N, 1.95. Found: C, 68.58; H, 5.11; N, 1.86.
(d, J = 8.7 Hz, 1 H), 7.50 (dd, J = 8.7, 1.6 Hz, 1 H), 8.11 ppm (brd, J = 1.6
Hz, 1 H); HRMS (DCI/NH3) m/z 419.08520 (M þ H requires
419.08518). Anal. Calcd for (C16H19N2O9Cl 0.5TFA): C, 42.91; H,
3
4.13; N, 5.89. Found: C, 42.97; H, 4.25; N, 5.90.
Benzyl 2,3,4-Tri-O-benzyl-1-(2-(S)-[2-methylpyridin-3-
yloxymethyl]pyrrolidin-1-ylcarboxy)-β-D-glucopyranuro-
nate (9). Solid 8 (as the dihydrochloride salt)28 (95 mg, 0.358 mmol)
was added to a solution of 4b (100 mg, 0.139 mmol) in CH2Cl2 (3 mL).
The mixture was stirred at 20 °C as triethylamine (100 μL, 0.717 mmol)
was added, and the resulting bright yellow mixture was stirred at room
temperature for 2 h. The mixture was concentrated under vacuum, and
the residue was purified by flash chromatography (silica gel, eluted with
hexanesꢀEtOAc, 75:25ꢀ0:100) to provide a colorless glass (96 mg,
89%): [R]2D0 = ꢀ46.7 (c 1.01, EtOH); 1H NMR (400 MHz, DMSO-d6,
90 °C)32 δ 1.76ꢀ1.88 (m, 1 H), 1.90ꢀ2.05 (m, 3 H), 2.31 (s, 3 H), 3.27ꢀ
3.38 (m, 1 H), 3.38ꢀ3.50 (m, 1 H), 3.58 (dd, J = 8.4, 7.3 Hz, 1 H, H-2), 3.79
(t, J= 8.9 Hz, 1 H), 3.86 (t, J= 8.4 Hz, 1 H), 3.97ꢀ4.12 (m, 3 H), 4.25 (d, J=
9.2Hz, 1H,H-5),4.44(d,J=11.0Hz, 1H),4.60ꢀ4.68 (m, 3 H), 4.71 (d, J=
11.6 Hz, 1 H), 4.76 (d, J = 11.6 Hz, 1 H), 5.14 (s, 2 H), 5.71
(d, J = 7.3 Hz, 1 H, H-1), 7.06ꢀ7.14 (m, 4 H), 7.15ꢀ7.33 (m, 18 H),
7.99 (dd, J = 4.6, 1.2 Hz, 1 H); MS (ESI) m/z 413 (M þ H)þ. Anal.
Calcd for (C46H48N2O9): C, 71.49; H, 6.26; N, 3.62. Found: C, 71.26;
H, 6.05; N, 3.58.
One-Pot Preparation of Benzyl 2,3,4-Tri-O-benzyl-
1-(2-(S)-[2-methylpyridin-3-yloxymethyl]pyrrolidin-1-ylcarb-
oxy)-β-D-glucopyranuronate (9). A solution of 1b (270 mg, 0.487
mmol) in CH2Cl2 (15 mL) and triethylamine (0.117 mL, 0.84 mmol) was
stirred under nitrogen with ice cooling as a solution of bis(p-nitrophe-
nyl)carbonate (148 mg, 0.49 mmol) in CH2Cl2 (3mL) wasruninover30s.
The yellow solution was stirred with ice cooling for 3 h, a solution of 8 (192
mg, 1 mmol) in CH2Cl2 (4 mL) was added to the reaction mixture, and the
yellow solution was allowed to warm gradually to room temperature with
stirring overnight (13 h). The solution was diluted with CH2Cl2 (20 mL)
and washed with 20% Na2CO3 (aq) (2 ꢁ 15 mL). The organic phase was
concentrated under vacuum, and the residue was purified by flash chroma-
tography (SiO2, eluted with hexanesꢀEtOAc 80:20ꢀ60:40) to provide the
carbamate 9, identical to that described above (276 mg, 73% yield).
1-(2-(S)-[2-Methylpyridin-3-yloxymethyl]pyrrolidin-1-
ylcarboxy)-β-D-glucopyranuronic Acid (10). A solution of 9
(508 mg, 0.66 mmol) in ethanol (50 mL) was stirred under nitrogen
Methyl 2,3,4-Tri-O-acetyl-1-(2-(R)-[6-chloropyridin-3-
yloxymethyl]azetedin-1-ylcarboxy)-β-D-glucopyranuronate
(6). Solid 4a (99.3 mg, 0.199 mmol) was added at room temperature to a
solution of the p-toluenesulfonate salt of 5 (74.2 mg, 0.200 mmol) in
CH2Cl2 (5 mL) and triethylamine (0.1 mL, 0.7 mmol). The yellow
solution was stirred at room temperature for 75 min, diluted with CH2-
Cl2 (10 mL) and washed successively with 5% Na2CO3 (aq) (15 mL)
and 8% H2SO4 (aq) (10 mL). The organic phase was dried (Na2SO4)
and concentrated under vacuum to leave an off-white foam. The crude
material was purified by flash chromatography (silica gel, eluted with
hexanesꢀEtOAc, 50:50) to provide the title compound (98.4 mg, 88%
yield): [R]2D0 = þ33.1 (c 1.00, EtOH); 1H NMR (300 MHz, DMSO-d6,
90 °C)32 δ 1.87 (br s, 3 H), 1.94 (s, 3 H), 1.96 (s, 3 H), 2.15ꢀ2.28 (m, 1
H), 2.33ꢀ2.44 (m, 1 H), 3.65 (s, 3 H), 3.77ꢀ3.92 (m, 2 H), 4.17 (dd, J =
10.7, 3.3 Hz, 1 H), 4.27 (dd, J = 10.7, 4.4 Hz, 1 H), 4.57 (d, J = 9.5 Hz, 1
H, H-5), 4.56ꢀ4.63 (m, 1 H), 4.95 (dd, J = 9.3, 8.0 Hz, 1 H, H-2), 5.05
(t, J = 9.3 Hz, 1 H), 5.40 (t, J = 9.3 Hz, 1 H), 5.84 (d, J = 8.0 Hz, 1 H,
H-1), 7.37 (dd, J = 8.8, 0.7 Hz, 1 H), 7.46 (dd, J = 8.8, 1.9 Hz, 1 H), 8.12
ppm (dd, J = 1.9, 0.7 Hz, 1 H); MS (ESI) m/z 559/561 (M þ H)þ. Anal.
Calcd for (C23H27N2O12Cl): C, 49.43; H, 4.87; N, 5.01. Found: C,
49.48; H, 5.16; N, 4.84.
1-(2-(R)-[6-Chloropyridin-3-yloxymethyl]azetedin-1-
ylcarboxy)-β-D-glucopyranuronic Acid (7). A solution of 6 (92
mg, 0.16 mmol) in a mixture of methanol (5 mL) and water (1 mL) was
stirred with ice cooling as ethyldiisopropylamine (0.5 mL) was added at
once. The yellow solution was allowed to stir for 14 h, coming to room
temperature as the ice bath expired overnight. The solution was
concentrated under vacuum and the residue taken up in EtOAc
(5 mL) and concentrated under vacuum (repeated twice to remove
excess amine). The residue was purified by chromatography (Lobar
RP18 column, eluting with 0.1% trifluoroacetic acid(aq)ꢀCH3CN (9:1)
to provide the glucuronyl carbamate as an off-white solid (55.2 mg,
67%): [R]2D0 = þ49.7 (c 0.17, EtOH); 1H NMR (300 MHz, CD3OD)
δ 2.26ꢀ2.58 (m, 2 H), 3.37ꢀ3.60 (m, 3 H), 3.88 (br d, J = 9.1 Hz, 1 H,
H-5), 3.91ꢀ4.13 (m, 2 H), 4.21 (dd, J = 10.3, 2.8 Hz, 1 H), 4.40ꢀ4.53
(m, 1 H), 4.59ꢀ4.75 (m, 1 H), 5.34 (d, J = 7.9 Hz, 1 H, H-1), 7.35
5431
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NOTE
as 20% Pd(OH)2/C (500 mg) was added. The reaction flask was evacu-
ated and purged with nitrogen (four cycles), then with hydrogen (four
cycles), and the mixture was stirred at room temperature under hydro-
gen (1 atm) for 46 h. The flask was evacuated and purged with nitrogen
(four cycles), and the mixture was filtered through a pad of diatomac-
eous earth. The filter was rinsed with EtOH (15 mL), then water
(10 mL), and the filtrate was concentrated under vacuum. EtOAc
(20 mL) was added to the residue, and the mixture was concentrated
under vacuum to leave a white solid after drying under vacuum at 45 °C
(12) Kaspersen, F. M.; van Boeckel, C. A. A. Xenobiotica 1987,
17, 1451–1471.
(13) Engstom, K. M.; Daanen, J. F.; Wagaw, S.; Stewart, A. O. J. Org.
Chem. 1996, 71, 8378–8383.
(14) Stachulski, A. V.; Harding, J. R.; Lindon, J. C.; Maggs, J. L.; Park,
B. K.; Wilson, I. D. J. Med. Chem. 2006, 49, 6931–6945.
(15) Kasperson, F. M.; van Boeckel, C. A. A.; Delbressine, L. P. C.;
Koten, A.; Jacobs, P. L.; Funke, C. W. Carbohydr. Res. 1989,
190, c11–c13.
(16) In one experiment, the carbamyl chloride of 5, formed by
reaction with phosgene, reacted with 4a to produce, in low conversion,
a 1:1 mix of anomers of 6 among unidentified reaction side products.
(17) Leenders, R. G. G.; Ruytenbeek, R.; Damen, E. W. P.; Scheeren,
H. W. Synthesis 1996, 1309–1312.
(18) Thomas, M.; Gesson, J.-P.; Papot, S. SynLett 2007, 1966–1968.
(19) Cavalluzzi, M. M.; Lentini, G.; Lovece, A.; Bruno, C.; Catalano,
A.; Carocci, A.; Franchini, C. Tetrahedron Lett. 2010, 51, 5265–5268.
(20) Leenders, R. G. G.; Scheeren, H. W. Tetrahedron Lett. 2000,
41, 9173–9175.
(265 mg, 98% yield): [R]2D0 = ꢀ59.9 (c 0.55, EtOH); H NMR (400
1
MHz, D2O, 90 °C)32 δ 2.20ꢀ2.57 (m, 4 H), 2.87 (s, 3 H), 3.67ꢀ3.94
(m, 5 H), 4.09 (d, J = 9.4 Hz, 1 H, H-5), 4.55ꢀ4.73 (m, 3 H), 5.72 (d, J =
8.0 Hz, 1 H, H-1), 7.91 (br dd, J = 8.2, 5.5 Hz, 1 H), 8.13 (br d, J = 8.2 Hz,
1 H), 8.43 ppm (d, J = 5.5 Hz, 1 H); MS (ESI) m/z 413 (M þ H)þ;
HRMS (DCI/NH3) m/z 413.15558 (M þ H requires 413.15545). A
sample (20 mg) was dissolved in water (1.5 mL) and washed with
CH2Cl2 (2 ꢁ 2 mL). The aqueous phase was concentrated in a nitrogen
stream, and the residue was dried at 50 °C under vacuum: Anal. Calcd for
(21) Nudelman, A.; Herzig, J.; Gottlieb, H. E.; Keinan, E.; Sterling, J.
Carbohydr. Res. 1987, 162, 145–152.
(C18H24N2O9 H2O): C, 50.23; H, 6.09; N, 6.51. Found: C, 50.44; H,
3
5.81; N, 6.51.
(22) The ratio was determined by integration of the anomeric
proton signal in the 1H NMR: the R-anomer resonance appeared
downfield δ 6.37 ppm (d, J1,2 = 3.4 Hz) and exhibited smaller vicinal
coupling compared to the β anomer signal at δ 5.80 (d, J1,2 = 6.1 Hz).
(23) Schmidt, R. R.; Michel Tetrahedron Lett. 1984, 25, 821–824.
(24) A stereoselective preparation of compound 4a was previously
achieved by a kinetically-controlled capture of anomerically pure β-1a
with p-nitrophenyl chloroformate. See: Madec-Lougerstay, R.; Florent,
J.-C.; Monneret, C. J. Chem. Soc., Perkin Trans. 1 1999, 1369–1376.
(25) Holladay, M. W.; Wasicak, J. T.; Lin, N.-H.; He, Y.; Ryther,
K. B.; Bannon, A. W.; Buckley, M. J.; Kim, D. J. B.; Decker, M. W.;
Anderson, D. J.; Campbell, J. E.; Kuntzweiler, T.; Donnelly-Roberts,
D. L.; Piattoni-Kaplan, M.; Briggs, C. A.; Williams, M.; Arneric, S. P.
J. Med. Chem. 1998, 41, 407–412.
’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra for 4a,b, 6, 7, 9,
b
and 10. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: (847) 938-9765. Fax: (847) 937-9195. E-mail: william.h.
bunnelle@abbott.com.
(26) Rowbotham, M. C.; Duan, W. R.; Thomas, J.; Nothaft, W.;
Backonja, M.-M. Pain 2009, 146, 245–252.
’ ACKNOWLEDGMENT
(27) Kegleviꢀc, D.; Ljevakoviꢀc, D. Carbohydr. Res. 1978, 64, 319–322.
(28) Lin, N.-H.; Gunn, D. E.; Ryther, K. B.; Garvey, D. S.; Donnelly-
Roberts, D. L.; Decker, M. W.; Brioni, J. D.; Buckley, M. J.; Rodrigues,
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The assistance of Dr. Stephen Hannick of Abbott Laboratories
Pressure and Catalysis Group to identify improved debenzyla-
tion conditions is greatly appreciated.
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