Pentaric acids and derivatives from nitric acid-oxidized pentoses

Article abstract of DOI:10.1080/07328303.2012.745550

This report describes the preparation of the four stereoisomeric pentaric acids by nitric acid oxidation of d-xylose, d-arabinose, l-arabinose, and d-ribose, with xylaric, d-arabinaric, and l-arabinaric acids being made in a reactor under computer control. The pentaric acids were converted to their crystalline N,N′-dimethylpentaramides, derivatives that proved useful for isolation of the arabinaric acids from their respective oxidation mixtures. The N,N′-dimethylpentaramides were readily convertible to the corresponding pentaric acid disodium salts in aqueous sodium chloride. The 2,3,4-O-triacetyl-N,N′-dimethylpentaramides of xylaric, l-arabinaric, and ribaric acid were also prepared. Ribaric acid was isolated as crystalline 1,4(5,2)-ribarolactone and further characterized by x-ray crystallography.

Full text of DOI:10.1080/07328303.2012.745550

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Pentaric Acids and Derivatives from
Nitric Acid–Oxidized Pentoses
Michael R. Hinton a , Merilyn Manley-Harris b , Kenneth I. Hardcastle
c & Donald E. Kiely d
a Shafizadeh Rocky Mountain Center for Wood and Carbohydrate
Chemistry , The University of Montana , Missoula , MT , 59812 , USA
b Chemistry Department , University of Waikato , Hamilton , New
Zealand
c Emory University Crystallography Laboratory, Department of
Chemistry , Emory University , Atlanta , GA , 30322 , USA
d Department of Chemistry and Biochemistry , The University of
Montana , Missoula , MT , 59812 , USA
Published online: 11 Jan 2013.
To cite this article: Michael R. Hinton , Merilyn Manley-Harris , Kenneth I. Hardcastle & Donald
E. Kiely (2013) Pentaric Acids and Derivatives from Nitric Acid–Oxidized Pentoses, Journal of
Carbohydrate Chemistry, 32:1, 68-85, DOI: 10.1080/07328303.2012.745550
To link to this article: http://dx.doi.org/10.1080/07328303.2012.745550
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Journal of Carbohydrate Chemistry, 32:68–85, 2013
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Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328303.2012.745550
Pentaric Acids and Derivatives
from Nitric Acid–Oxidized
Pentoses
Michael R. Hinton,1 Merilyn Manley-Harris,2
Kenneth I. Hardcastle,3 and Donald E. Kiely4
1Shafizadeh Rocky Mountain Center for Wood and Carbohydrate Chemistry,
The University of Montana, Missoula, MT 59812, USA
2Chemistry Department, University of Waikato, Hamilton, New Zealand
3Emory University Crystallography Laboratory, Department of Chemistry,
Emory University, Atlanta GA, 30322, USA
4Department of Chemistry and Biochemistry, The University of Montana, Missoula,
MT 59812, USA
This report describes the preparation of the four stereoisomeric pentaric acids by ni-
tric acid oxidation of D-xylose, D-arabinose, L-arabinose, and D-ribose, with xylaric,
D-arabinaric, and L-arabinaric acids being made in a reactor under computer con-
trol. The pentaric acids were converted to their crystalline N,Nꢁ-dimethylpentaramides,
derivatives that proved useful for isolation of the arabinaric acids from their respec-
tive oxidation mixtures. The N,Nꢁ-dimethylpentaramides were readily convertible to
the corresponding pentaric acid disodium salts in aqueous sodium chloride. The 2,3,4-
O-triacetyl-N,Nꢁ-dimethylpentaramides of xylaric, L-arabinaric, and ribaric acid were
also prepared. Ribaric acid was isolated as crystalline 1,4(5,2)-ribarolactone and fur-
ther characterized by x-ray crystallography.
Keywords Nitric acid; Oxidation; Pentaric acids; Computer-controlled reaction; X-ray
crystal structure
INTRODUCTION
Nitric acid oxidation of aldoses to the corresponding aldaric acids represents an
old but relatively uncomplicated oxidation method.[1–4] Such aldaric acids are
Received August 16, 2012; accepted October 29, 2012.
Address correspondence to Donald E. Kiely, Department of Chemistry and Biochem-
istry, The University of Montana, Missoula, MT 59812, USA, or Rivertop Renewables,
1121 E. Broadway, Missoula MT, 59802, USA. E-mail: donald.kiely@umontana.edu,
don@rivertop.com
68

Pentaric Acids from Nitric Acid–Oxidized Pentoses
69
of interest as monomer diacid starting materials for the preparation of polyhy-
droxypolyamides (PHPAs)[5,6] and as useful chemical building blocks derived
from renewable carbohydrates.[7]
Synthetic polyhydroxypolyamides (PHPAs) derived from monomer aldaric
acids and alkylenediamines are of importance since they are derived in part
from renewable carbohydrates and readily break down in soil and serve as
a source of nitrogen for plant growth.[8,9] The stereoisomeric pentaric acids
meso-xylaric acid (1), D-arabinaric acid (D-lyxaric acid) (2), L-arabinaric acid
(L-lyxaric acid) (3), and meso-ribaric acid (4) (Fig 1) are among the aldaric acids
of interest and the subject of this report. Since the pentaric acids are not com-
mercially available, our first objective was to prepare representative amounts
of diacids 1–3 employing a modification of the long-known aldose nitric acid
method,[1–4] which was developed in this laboratory.[10]
A second objective was to establish a simple method to readily isolate indi-
vidual pentaric acids as suitable derivatives from the corresponding oxidation
reaction mixture without chromatographic purification. Among the pentaric
acids, only xylaric acid (1) can be readily crystallized from the oxidation mix-
ture,[1,11] while ribaric acid can be isolated as its crystalline 1,4(5,2)-lactone
(5).[1,2] Consequently, a pentaric acid derivative of choice should be easily con-
verted to the parent diacid and, while applicable to all of the pentaric acids,
COOR
H
COOR
OH
COOH
OH
COOR
OH
HO
H
H
H
HO
HO
H
HO
H
H
H
H
OH
OH
H
H
H
OH
OH
OH
COOR
COOR
COOH
COOR
4
8
R=H
R=Na
3
7
R=H
R=H
2
6
1
R=Na
R=Na
O
HO
O
H
H
O
H
HO
OH
5
Figure 1: Stereoisomeric xylaric (1), D-arabinaric (2, D-lyxaric), L-arabinaric (3, L-lyxaric) and
ribaric (4) acids, ribaro-1,4(5,2)-lactone (5), and disodium salts 6–8.

M. R. Hinton et al.
70
would be especially important for isolation of the stereoisomeric arabinaric
acids.
An additional objective of the study was to further characterize lactone 5
by way of its x-ray crystal structure.
RESULTS AND DISCUSSION
Nitric Acid Oxidations
Nitric acid oxidation of D-xylose, D-arabinose, and L-arabinose were carried
out in a computer-controlled reactor under an atmosphere of oxygen in a closed
2-L reaction flask to effect a catalytic oxidation process with oxygen as the
terminal oxidant. Because of its high cost and limited availability, D-ribose
was only oxidized on a small scale using conventional laboratory glassware.
Nitric acid oxidations of aldoses are characterized by an induction pe-
riod wherein the reaction mixture initially appears stable at rt but gradually
warms up and then undergoes a rapid temperature increase that is accompa-
nied by release of large amounts of gaseous, brown-colored nitrogen dioxide.
In order to control the highly exothermic oxidation of the pentoses, the experi-
mental protocols employed in this report were patterned after those described
for oxidation of D-glucose to D-glucaric acid[10] but designed for the individual
sugars 1–3. The use of a computer-controlled closed reactor for the D-glucose
oxidations provided control of reaction temperature while conserving the nitric
acid and using oxygen as the terminal oxidizing agent.[12] In effect, this oxida-
tion protocol is a catalytic reaction, with nitric acid being regenerated in situ.
The emphasis in carrying out oxidations of the pentoses was to evaluate this
oxidation methodology for these aldoses but without attempting to optimize
oxidation conditions.
Xylose oxidation
Nitric acid removal from oxidation mixtures was typically done by concen-
tration at reduced pressure. When the concentration step was applied to oxi-
dation of xylose, crystalline xylaric acid (1) was only obtained in a yield of 33%.
A shortcoming of the concentration step employed in the above example is that
during the concentration step, residual nitric acid becomes more concentrated
because it forms a reverse azeotrope with water, facilitating uncontrolled ox-
idation and production of added amounts of unwanted smaller organic acid
side products. In an effort to minimize side product formation, an alternative
procedure was applied to a representative D-xylose oxidation mixture. The con-
centration time of the nitric acid removal step was reduced, the reaction was
neutralized with sodium hydroxide, and resultant sodium nitrate was sepa-
rated from crude disodium xylarate, and minor coproduct organic acid sodium
salts, by nanofiltration.[10] The organic salt mixture was treated with an acid

Pentaric Acids from Nitric Acid–Oxidized Pentoses
71
form cation-exchange resin, the aqueous solution concentrated, and crystalline
xylaric acid isolated (46%). Although this latter xylaric acid isolation process is
clearly more complicated than crystallizing xylaric acid directly from the con-
centrated syrup, the difference in yields from the two procedures underscores
the importance of minimizing extended concentration of the reaction mixture
and the utility of nanofiltration in this application. This xylaric acid isolation
procedure is outlined in Scheme 1.
-
-
CO2H
OH
CO2 Na+
CO2 Na+
Nanofiltration
Purification
NaOH ,
Ice bath
H
HO
H
H
HO
H
OH
H
H
HO
H
OH
H
H
OH
OH
OH
CO2H
CO2-Na+
CO2-Na+
NaNO3
(crude)
crude
1
(permeate)
partially
purified -
retentate
disodium 2,2,3,3-tetra
hydroxybutanedioate (10)
H
resin
CO2H
OH
CO2H
OH
1. Concentrate
2. Seed
H
H
HO
H
H
HO
H
H
3. Stir with acetone
OH
OH
CO2H
CO2H
1
1
(partially purified)
Scheme 1: Isolation of xylaric acid employing a nanofiltration step.
During the course of the sodium hydroxide neutralization step in this latter
process, a white solid precipitated from the mixture at pH 4.5. The solid was re-
moved by filtration and subjected to GC-MS analysis as its per-O-trimethylsilyl
derivative. A mass fragmentation pattern of this derivative matched that of
per-O-trimethylsilyl-2,2,3,3-tetrahydroxybutanedioic acid (9, Fig. 2),[13] sug-
gesting that the isolated solid was disodium 2,2,3,3-tetrahydroxybutanedioate
(10).
The structure 10 was confirmed by comparison with authentic material,
synthesized from (2E-)-2,3-dihydroxy-2-butedioic acid (dihydroxyfumaric acid)
as reported by Burnett et al.[14] The GC retention time and the mass fragmen-
tation pattern of the per-O-trimethylsilyl derivatives from synthesized 10 and
the side product from nitric acid oxidations of D-xylose were the same. While

M. R. Hinton et al.
72
CO2TMS
OTMS
OTMS
CO2TMS
CO2
Na
OH
OH
Na
TMSO
TMSO
HO
HO
CO2
9
10
Figure 2: Per-O-trimethylsilyl-2,2,3,3-tetrahydroxybutanedioic acid (9) and disodium
2,2,3,3-tetrahydroxybutanedioate (10).
the exact oxidative pathway from D-xylose to 10 has not been established, 10 is
clearly a disalt of the dihydrate form of diketosuccinic (dioxobutanedioic) acid
formed in an overoxidation pathway. Disalt 10 (Fig. 2) has not been previously
reported from oxidation of an aldopentose.
L- and D-arabinose oxidations
D- and L-arabinose were both oxidized using the LabMax reactor, the aque-
ous acid solutions concentrated to syrups and the reaction mixtures neutral-
ized with sodium hydroxide. The target derivatives for isolation of D- and L-
arabinaric acids (2 and 3) were corresponding disodium salts 6 and 7 by way of
the water-insoluble N,Nꢁ-dimethyl-D- and L-arabinaramides, 12 and 13 (Fig. 3),
respectfully. Notable differences in the oxidation protocols for the arabinoses
compared to D-xylose oxidation stemmed from the lower water solubility of the
arabinoses and the decreased reactivity of the arabinoses to nitric acid oxi-
dation. A 62.5% D-xylose solution was added to the nitric acid and oxidation
carried out at no higher than 35◦C, while the arabinose solutions were added
as 50% solutions and the oxidation reactor temperature raised to 50◦C in order
to complete the oxidations.
CONHCH3
CONHCH3
CONHCH3
CONHCH3
OR
HO
H
H
H
OH
OH
H
RO
H
OR
H
OR
H
RO
RO
OR
H
H
H
H
H
OR
OR
CONHCH3
CONHCH3
CONHCH3
CONHCH3
11 R = H
15 R = Ac
12
14 R = H
17 R = Ac
13 R = H
16 R = Ac
Figure 3: N,Nꢁ-Dimethylpentaramides 11 - 14, and 2,3,4-tri-O-acetyl-N,Nꢁ-
dimethylpentaramides 15 - 17.

Pentaric Acids from Nitric Acid–Oxidized Pentoses
73
-
CO2H
OH
H
CO2 Na+
5M NaOH
Ice bath
MeOH / AcCl
Methanol
H
HO
HO
H
HO
HO
OH
H
H
esterified
L-arabinaric
acid
H
CO2H
CO2-Na+
NaCl
10
Crude 7
Crude 3
1. Methylamine
\EtOH
2. Filter
CONHCH3
CO2-Na+
H
HO
HO
OH
H
H
H
HO
HO
OH
H
H
NaOH
CONHCH3
CO2-Na+
13
7
Scheme 2: Preparation of N,Nꢁ-dimethyl-L-arabinaramide (13) and disodium L-arabinarate
(7).
Both D- and L-arabinose were subjected to the same oxidation protocol and
the crude arabinaric acid products treated as outlined in Scheme 2 for the L-
arabinose oxidation mixture.
The crude L-arabinaric acid product was made basic with sodium hydrox-
ide and the resulting crude disodium salt converted to a methanol-esterified
product in methanol/acetyl chloride. The esterified product was then treated
with methylamine/ethanol to yield N,Nꢁ-dimethyl-L-arabinarmide (13) as an
insoluble solid. This diamide was then directly converted to solid disodium L-
arabinarate (7, 47%) in aqueous sodium hydroxide. This same procedure was
applied to a D-arabinose oxidation mixture and solid disodium D-arabinarate
(6) isolated in 46% yield. Thus, formation of the diamide derivatives 13 and
12 proved to be an effective method to selectively remove the arabinaric acids
from their respective oxidation mixtures. As with D-xylose oxidations, basifica-
tion of the arabinose oxidation mixtures produced small amounts of insoluble
10 (3% to 6%).
D-Ribose oxidation
D-Ribose was oxidized on a small scale and the primary oxidation product,
ribaric acid, isolated as crystalline 1,4(5,2)-ribarolactone (5, 49.5%).[1,2] Lac-
tone 5 was readily converted to disodium ribarate (9) in aqueous sodium hy-
droxide, after drying and washing with methanol isolated in >95% yield based

M. R. Hinton et al.
74
Figure 4: The geometry of 5,2-ribarolactone (5) showing atom labeling and hydrogen
bonding (distances in angstroms) (color figure available online).
on 5. Overall, nitric acid oxidation of the four pentoses yielded diacid solid
products in the range of 46% to 50%, reasonable yields given the absence of
any protecting groups on the aldoses.
1,4(5,2)-Ribaro lactone (5) was further characterized by x-ray crystallog-
raphy, and the geometry of monoclinic crystalline 5, with atom labeling and
hydrogen bonding, is shown in Figure 4.
Monoclinic crystalline 5, which has a crystal density of 1.761 g cm–3, has
˚
one hydrogen bond acceptor [O5···H5-O3, 2.078A, 155.41º] bonded to the hy-
droxyl hydrogen of an adjacent molecule. The hydroxyl group oxygen of O(4)
˚
[O4-H6···O3, 1.942A, 167.50º] is acting as a hydrogen bond donor to the O(3)
hydroxyl group of an adjacent molecule. The carboxylic acid group hydrogen
˚
(H1) is hydrogen bonded [O6-H1···O1, 1.873A, 178.88º] to the carboxylic acid
group carboxyl oxygen of an adjacent molecule. All crystal structure graphics
were generated using ORTEP-3[15] or Mercury.[16] Crystal data and structure
refinement details for 1,4(5,2)-ribarolactone (5) are summarized in Table 1,
while full details and bond parameters are given in the supplementary infor-
mation.
2,3,4-tri-O-acetyl-N,Nꢁ-dimethylpentaramides 15–17
The diacids 1–4 were further characterized as their N,Nꢁ-dimethy
lpentaramides (11–14) and diacids 1, 3, and 4 as their N,Nꢁ-dimethyl-2,3,4-tri-
O-acetylpentaramides 15, 16, and 17, respectively. These diamides are also of
interest as solid-state model monomer diamide units of the corresponding poly-
hydroxypolyamides. The x-ray structures of all of these diamides have been
determined and are the subject of the following article in this issue.

Pentaric Acids from Nitric Acid–Oxidized Pentoses
75
Table 1: Crystal data and structure refinement for 1,4(5,2)-ribarolactone (5)
Identification code
Empirical formula
Formula weight
Temperature
1,4(5,2)-ribarolactone
C5 H6 O6
162.10
173(2) K
Wavelength
Crystal system
Space group
1.54178 Å
Monoclinic
P2(1)/c
Unit cell dimensions
a = 6.2642(7) Å
b = 5.3342(6) Å
c = 18.317(2) Å
α = 90◦.
β = 92.405(9)◦.
γ = 90◦.
Volume
611.51(12) Å3
4
Z
Density (calculated)
1.761 Mg/m3
1.490 mm−1
Absorption
coefficient
F(000)
336
Crystal size
0.39 × 0.29 × 0.09 mm3
Theta range for data
collection
4.83 to 61.24◦.
Index ranges
−6< = h< = 6, −5< =
k< = 5, −20< = l< =
20
Reflections collected
Independent
2050
847 [R(int) = 0.0127]
reflections
Completeness to
90.1%
theta = 61.24◦
Absorption correction
Semi-empirical from
equivalents
0.8776 and 0.5942
Max. and min.
transmission
Refinement method
Full-matrix least-squares
on F2
847 / 0 / 109
Data / restraints /
parameters
Goodness-of-fit on F2
Final R indices [I >
2sigma(I)]
1.109
R1 = 0.0279, wR2 =
0.0716
R indices (all data)
R1 = 0.0308, wR2 =
0.0739
Largest diff. peak and
hole
0.157 and −0.228 e.Å−3
EXPERIMENTAL
General Methods
Concentrations of solutions were carried out under reduced pressure. Dry-
ing of samples was carried out at reduced pressure using a Fischer Sci-
entific Isotemp Vacuum Oven Model 280A at rt. Elemental analyses were

M. R. Hinton et al.
76
performed by Atlantic Microlab, Inc. (Norcross, GA). Melting points were
obtained with a Fisher-Johns melting point apparatus and are reported
uncorrected.
Oxidations of D-xylose, D-arabinose, and L-arabinose were performed using
a Mettler Toledo RC-1 LabMax fitted with a Mettler Toledo PG5002-S Delta
Range top-loading balance, ProMinent Fluid Controls Inc. Model G/4b1201TT1
liquid feed pump; Sierra 830/840/860 Series Side-Trak & Auto-Trak Mass
Flow Meter and Controller flow valve; FTS Maxi Cool recirculation chiller;
and appropriate gas bubbler, pressure manifold with safety valves and gauges,
condenser, pH meter, stir rod, thermometer, and temperature-controlled jack-
eted reaction flask. The system is operator controlled through Camile TG
v1.2 software, enabling temperature and pressure control within the 2-L re-
action vessel. Concentration of nitric acid was carried out under reduced
pressure with a system consisting of a Buchi Rotovapor R-205, Buchi Vac-
uum Controller V-800, Buchi Heating Bath B-490, Brinkmann Model B-169
Vacuum Aspirator, and Thermo Haake compact refrigerated circulator DC30-
K20 in conjunction with a Thermo Haake EK45 immersion circulator cooling
coil.
GC-MS analyses were performed on an Agilent 6890N GC interfaced to an
Agilent 5973 MS detector. A Phenomenex ZB-5 GC column, 30 m × 0.25 mm ×
0.25 μm, composed of 5% phenyl 95% dimethylpolysiloxane, was used for
all GC-MS analysis. Samples for GC-MS analyses were prepared as per-O-
trimethylsilyl derivatives. Tri-Sil Reagent (1.0 mL) was added to dried sample
(5.0 mg) in a vial (7 mL) and the mixture heated at 50◦C for 60 min. The sample
was cooled to rt and heptane (6 mL) added. The mixture was centrifuged, the
liquid portion (3 mL) separated and diluted with heptane (3 mL), and aliquots
from the resulting solution taken for GC-MS analysis. The following tempera-
ture program was employed for sample analysis: begin 32◦C, + 12.5◦C/min to
250◦C, (hold 5 min), + 20◦/min to 300◦C (hold 5 min), total acquisition time of
30.10 min.
NMR spectra were recorded using a 400-MHz Varian Unity Plus spectrom-
eter, at 400 MHz for proton spectra and at 100 MHz for carbon spectra. NMR
spectra were processed using ACD/SpecManager 1D NMR software Version
9.13. Chemical shifts were expressed in parts per million relative to t-BuOH
(1.203 ppm) for D2O.
Nanofiltration was performed using reverse osmosis (RO) purified water
on a unit built in-house consisting of the necessary valves, pump, tubing,
pressure gauge, and fitted with a G.E. Water & Process Technologies Model
DL2540F1072 nanopore filter.
High-performance liquid chromatography (HPLC), employing a refractive
index (RI) detector, was performed on two Aminex HPX-87H columns in se-
ries. The first column was heated to 35◦C and the second column to 85◦C.

Pentaric Acids from Nitric Acid–Oxidized Pentoses
77
A 0.005-M H2SO4 eluent was heated to 70◦C under an argon atmosphere and
samples run isocratically at a 0.5-mL/min flow rate.
Nitric Acid Oxidations
Nitric acid oxidation of D-xylose
Nitric acid oxidation of D-xylose was carried out using the LabMax reactor.
The parameters were programmed in a series of stages for the oxidation. Stage
1: The reactor vessel temperature was set at 25◦C and the stirring rod speed at
200 rpm. Concentrated nitric acid (70%, 3 mol, 187 mL) was added, the vessel
was closed to the atmosphere, and time set for 3 min. Stage 2: Oxygen was
added to the reaction vessel to increase the pressure to 0.25 bar. Stage 3: D-
xylose [181.2 g of an aqueous 62.5% solution containing sodium nitrite (1.16 g,
16.8 mmol)] was added over 120 min. Stage 4: A 1-min stabilization period was
employed with no change in reaction conditions. Stage 5: The reactor temper-
ature was raised to 35◦C and the pressure raised by addition of oxygen to 0.5
bar over 60 min. Stage 6: The reaction mixture was held at 35◦C and 0.5 bar
of pressure for 210 min. Stage 7: The reaction mixture was cooled to 25◦C over
10 min and the vessel opened to the atmosphere.
Isolation of xylaric acid (1)—concentration method
A D-xylose oxidation mixture, taken directly from the Mettler Toledo Lab-
Max reactor, was concentrated to a thick syrup at 50◦C. Water (200 mL) was
added to dissolve the syrup and the resulting solution concentrated to a syrup.
This concentration process was repeated twice; the resulting syrup was seeded
with xylaric acid and then left undisturbed at rt for 3 d. Cold acetone (300 mL)
was added to the semisolid mixture and the mixture stirred at rt for 12 h. The
mixture was cooled (ice bath) and white solid xylaric acid was obtained by fil-
tration. (1, 44.6 g, 247.5 mmol, 33.00% yield): mp 144–145◦C (Lit. 145.5◦C,[1]
151-2◦C,[11] 1H NMR (D2O) δ 4.45 (d, 2H, J = 4.33 Hz, H-1, H-3) δ 4.22 (t, 1H,
H-2); Anal. Calcd for C5H8O7 (180.11): C, 33.34; H, 4.48. Found C, 33.31; H,
4.34.
Isolation of xylaric acid (1)—nanofiltration method
A D-xylose oxidation mixture, taken directly from the LabMax reactor,
was concentrated to a thick syrup at 50◦C. Water (200 mL) was added to
dissolve the syrup, the solution cooled (ice bath), and sodium hydroxide (5
M) added with stirring to bring the mixture to pH 4.5. A white precipitate
formed, then removed by filtration, and characterized as disodium 2,2,3,3-
tetrahydroxybutanedioate (10, 8.39 g, 37.1 mmol, 4.94% yield), mp (dec.)
142◦C. The filtrate was cooled (ice bath) and sodium hydroxide (5 M) added

M. R. Hinton et al.
78
with stirring to bring the solution to pH 10. The solution was concentrated un-
der reduced pressure at 50◦C to give a brown solid to which absolute ethanol
(300 mL) was added and the mixture stirred at rt for 12 h. The solid was re-
moved by filtration and dried to yield crude disodium xylarate (156.9 g) as
a brown solid. The solid was dissolved in RO water (3,500 mL) and the solu-
tion subjected to nanofiltration. When the permeate volume reached 1,000 mL,
RO water (1,000 mL) was added to the feedstock. The typical rate of per-
meate flow was 48 mL/min. After 2,000 mL of permeate had been removed,
another 1,000 mL of RO water was added to the feedstock. This was re-
peated until 4,000 mL of RO water had been added to the feedstock. Fil-
tration continued until the permeate flow slowed to a trickle. The reten-
tate contained predominantly organic acid sodium salts and the permeate
predominately inorganic sodium nitrate, as determined by HPLC analyses.
The retentate was concentrated at 50◦C to 200 mL and treated with an ex-
cess of Amberlite IR-120H+ resin (1.32 L, 2.5 mol, 3 h). The resin was re-
moved by filtration and rinsed with water (500 mL), and the combined fil-
trate and rinse concentrated at 50◦C to a thick syrup. The syrup was seeded
with xylaric acid and allowed to remain undisturbed at rt for 3 d. Cold ace-
tone (300 mL) was added to the near-solid product and the mixture stirred
at rt for 12 h. The mixture was cooled (ice bath) and white solid xylaric
acid was separated by filtration (1, 67.10 g, 372.6 mmol, 49.67% yield): mp
138–140◦C (lit. 145.5◦C),[1] 1H NMR (D2O) δ 4.45 (d, 2H, H-1, H-3) δ 4.22
(t, 1H, H-2).
Disodium L-arabinarate (7) from nitric acid oxidation of L-arabinose
The oxidation of L-arabinose was carried out using the LabMax reactor em-
ploying a procedure patterned after that used for D-xylose oxidation. The fol-
lowing reaction parameters for the oxidation were programmed into the Recipe
Menu accessed on the LabMax Camile TG v1.2 software in the following se-
ries of stages. Stage 1: The reactor vessel temperature was set at 25◦C and
the stirring rod speed at 200 rpm. Concentrated nitric acid (70%, 5.13 mol,
320 mL) was added and the vessel was closed to the atmosphere. Stage 2: Oxy-
gen was added to the reaction vessel to increase the pressure to 0.25 bar. Stage
3: L-Arabinose [226.6 g of an aqueous 50.0% solution containing sodium nitrite
(1.76 g, 25.5 mmol)] was added over 90 min. Stage 4: A 1-min stabilization pe-
riod was employed with no changes in reaction conditions. Stage 5: The reactor
temperature was raised to 50◦C and the pressure raised by addition of oxygen
to 0.5 bar over 45 min. Stage 6: The reaction was held at 50◦C and 0.5 bar of
pressure for 180 min. Stage 7: The reaction mixture was cooled to 25◦C over
10 min and the vessel opened to the atmosphere. The L-arabinose oxidation
mixture was taken directly from the LabMax reactor, concentrated to a syrup
at 50◦C, and dissolved in cold (ice bath) water (200 mL). Sodium hydroxide

Pentaric Acids from Nitric Acid–Oxidized Pentoses
79
(5 M) was added with stirring to bring the mixture to pH 4.5. A white precipi-
tate that formed was removed by filtration and identified as disodium 2,2,3,3-
tetrahydroxybutanedioate (10, 7.95 g, 35.2 mmol, 4.69%, mp (dec.) 142◦C). The
filtrate was cooled (ice bath) and sodium hydroxide (5 M) added with stirring
to bring the mixture to pH 10. The solution was concentrated at 50◦C to give
a brown solid, which was stirred with absolute ethanol (300 mL) at rt for
12 h. The solid was removed by filtration and dried, to yield crude disodium
L-arabinarate (148.8 g) as a brown solid. Acetyl chloride (119 g, 1.52 mol) was
added with stirring to a mixture of crude solid 3 and cold (ice bath) methanol
(100 mL). The reaction mixture was stirred at rt (4 h), after which white, insol-
uble sodium chloride was removed by filtration. The filtrate was concentrated
to a thick syrup at 40◦C, which was then dissolved in methanol (100 mL). A
solution of methylamine in ethanol (33% b/w, 87.0 g, 265 mL, 2.80 mol) was
added dropwise to the cold (ice bath) methanol solution, and the resulting re-
action mixture stirred at rt (24 h). White solid N,Nꢁ-dimethyl-L-arabinaramide
(13) was removed by filtration and used directly in the next step. An analytical
sample of 13 was prepared by recrystallization from ethanol, mp 193◦C; Anal.
Calcd for C7H14N2O5 (206.2): C, 40.77; H, 6.84; N, 13.58. Found C, 41.07; H,
6.87; N, 13.54.
Aqueous sodium hydroxide (2 M, 0.760 mmol, 380.1 mL) was added at
rt to solid 13, the reaction mixture was stirred for 3 d and concentrated at
40◦C, and the resultant solid stirred with absolute ethanol (300 mL). The solid
was removed by filtration and the stirring/filtration process with ethanol was
repeated three times to give a final white amorphous solid of disodium L-
1
arabinarate (7, 79.9 g, 356.5 mmol, 47.5%); [α]20D –3.68 (c 0.217, water); H
NMR (D2O) δ 4.15 (d, 1H, J = 1.47 Hz) δ 4.03 (d, 1H) δ 3.99 (d, 1H). 13C NMR
(D2O): 180.60, 180.05, 74.20, 74.16, 72.94 ppm. GC-MS of salt 7 as its per-
O-TMS derivative (ESI) m/z Calcd for [M – 15, C19H45O7Si5+] 525.2. Found
1
525. The H NMR spectrum of 7 supported a single disalt structure with no
evidence of epimerized product(s).
Disodium D-arabinarate (6) from nitric acid oxidation of D-arabinose
The oxidation of D-arabinose was carried out in the LabMax reactor using
the procedure described for oxidation of L-arabinose. The D-arabinose oxida-
tion mixture was taken directly from the LabMax reactor, concentrated to a
syrup at 50◦C, and dissolved in cold (ice bath) water (200 mL). Sodium hy-
droxide (5 M) was added with stirring to bring the mixture to pH 4.5. White
solid disodium 2,2,3,3-tetrahydroxybutanedioate (6.25 g, 27.7 mmol, 3.69%, mp
(dec.) 142◦C) precipitated and was then removed by filtration. The filtrate was
cooled (ice bath) and sodium hydroxide (5 M) added with stirring to bring the
mixture to pH 10. The solution was concentrated at 50◦C to give a brown solid,
which was stirred with absolute ethanol (300 mL) at rt for 12 h. The solid
was removed by filtration and dried to yield crude disodium D-arabinarate as

M. R. Hinton et al.
80
a brown solid (142.45 g). Acetyl chloride (119 g, 1.52 mol) was added with stir-
ring to a mixture of crude solid disodium D-arabinarate and cold (ice bath)
methanol (100 mL). The reaction mixture was stirred at rt for 4 h, white insol-
uble sodium chloride was removed by filtration, and the filtrate concentrated
to a thick syrup at 40◦C. The syrup was dissolved in methanol (100 mL), a
solution of methylamine in ethanol (33% b/w, 87.0 g, 265 mL, 2.80 mol) was
added dropwise to the cold (ice bath) solution, and the resulting reaction mix-
ture stirred at rt (24 h). White solid N,Nꢁ-dimethyl-D-arabinaramide (12) was
removed by filtration and used directly in the next step. An analytical sample
of 12 was prepared by recrystallization from ethanol, mp 195◦C; Anal. Calcd
for C7H14N2O5 (206.2): C, 40.77; H, 6.84; N, 13.58. Found C, 40.91; H, 6.70; N,
13.35.
Aqueous sodium hydroxide (2M, 0.760 mmol, 380 mL) was added at rt to
solid 12, the reaction mixture was stirred for 3 d and concentrated at 40◦C,
and the resultant solid was stirred with absolute ethanol (300 mL) and then
removed by filtration. The ethanol stirring/filtration processes were repeated
three times to give a final white amorphous solid of disodium D-arabinarate
1
(6), 77.3 g, 345.2 mmol, 46.02%); [α]20D 4.46 (c 0.213, water); H NMR (D2O)
δ 4.15 (d, 1H, J = 1.47 Hz) δ 4.03 (d, 1H) δ 3.99 (d, 1H). 13C NMR (D2O):
180.60, 180.05, 74.20, 74.16, 72.94 ppm. GC-MS of salt 6 as its per-O-TMS
derivative (ESI) m/z Calcd for [M – 15, C19H45O7Si5+] 525.2. Found 525. The
1H NMR spectrum of 6 supported a single disalt structure with no evidence of
epimerized product(s).
Ribaro-5,2(1,4)-lactone (5)—nitric acid oxidation of D-ribose
Solid D-ribose (30.4 g, 202.3 mmol) and solid sodium nitrite (<1 mg) were
added to nitric acid (70%, 75 mL, 1.80 mol) in a 500-mL round-bottom flask.
The flask was immediately fitted with a water-cooled Liebig condenser and
the resulting solution warmed with stirring in an oil bath (65◦C, 4 h). Within
1 min the solution warmed to boiling and brown gases violently evolved. At
the end of the reaction process the resulting solution was concentrated under
reduced pressure to yield a white solid, which was dissolved in water (100 mL)
and the solution concentrated to dryness. The dissolution/concentration pro-
cesses were then repeated twice. The solid product was triturated by stirring
with ethyl ether (300 mL, 1 h), to remove nitric acid,[17] and then isolated by
filtration.
The trituration/filtration process was repeated five times and after each
filtration step the filtrate was tested for acidity using pH paper, the fifth filtrate
having a neutral pH. The white solid was dried under vacuum overnight to
yield ribaro-5,2(1,4-lactone) (5, 16.3 g, 100 mmol, 49.5% yield). 1H NMR (D2O)
δ 5.01 (s, 1H) δ 4.66 (d, 1H) δ 4.62 (d, 1H), mp 163–166◦C, lit mp 170–171◦C.[1]
Anal. Calcd for C5H6O6 (162.10): C, 37.05; H, 3.73. Found C, 36.87; H, 3.71.

Pentaric Acids from Nitric Acid–Oxidized Pentoses
81
Disodium ribarate (8)
Aqueous sodium hydroxide (5 M, 30.0 mL, 150 mmol) was added dropwise,
with stirring at rt to a solution of ribaro-5,2(1,4)-lactone (5, 10.0 g, 61.8 mmol)
in water (50 mL). The solution was stirred at rt for 12 h and then concen-
trated at 35◦C to a white solid. The solid was washed by stirring with methanol
(100 mL, 1 h), the white solid isolated by filtration, and the methanol wash
procedure repeated three times. The resulting white solid was dried to yield
1
disodium ribarate (8, 13.2 g, 59.1 mmol, 95.65%). H NMR (D2O) δ 4.062 (s,
H2,3,4). 13C NMR (D2O): 179.84, 75.42, 74.03 ppm. GC-MS of 7 as its per-
O-TMS derivative (ESI) m/z Calcd for C20H48O7Si5 [M – 15, C19H45O7Si5]+
1
525.2. Found 525. The H NMR spectrum of 8 supported a single disalt struc-
ture with no evidence of epimerized product(s).
Disodium 2,2,3,3-tetrahydroxybutanedioate (10)
Disalt 10 was prepared by a modified procedure described by Burnett
et al. [13] and based on the early reports of Fenton.[18,19] Glacial acetic acid
(1 mL) dissolved in cold (ice bath) water (1 mL) was added to a solution of
dihydroxyfumaric acid (0.19 g, 1.30 mmol) in water (5 mL). Bromine (0.28 g,
1.73 mmol) was added dropwise with stirring to cold (ice bath) glacial acetic
acid (1.5 mL) and the bromine/glacial acetic acid solution was added drop-
wise over 3 h to the cooled dihydroxyfumaric acid/acetic acid solution. Solid
sodium bicarbonate was added until bubble formation stopped and a precipi-
tate that formed was removed by filtration. The solid was washed with ace-
tone (3 × 2 mL), isolated by filtration, and dried to give disodium 2,2,3,3-
tetrahydroxybutanedioate dihydrate (10, 0.24 g, 0.92 mmol, 70.4%): mp (dec.)
142◦C. Anal. Calcd for C4H8Na2O10 (262.08): C, 18.33; H, 3.08. Found C, 18.12;
H, 3.07.
N,Nꢁ-dimethylxylaramide (11)
Acetyl chloride (0.34 g, 2.85 mmol) was added to a solution of xylaric acid
(1, 2.06 g, 11.4 mmol) in cold methanol (10 mL) and the solution stirred for 3 h.
The reaction mixture was concentrated to a syrup and the syrup was dissolved
in cold (ice bath) methanol (15 mL) to which methylamine 10.5 M (5.21 g,
0.17 mmol) in ethanol was added dropwise. The solution was stirred for 3 h
and a white solid was removed by filtration and rinsed with cold methanol (2
× 5 mL); yield N,Nꢁ-dimethylxylaramide (11, 1.74 g, 8.43 mmol, 73.8%): mp
191–194◦C; 1H NMR (D2O) δ 4.266–4.256 (d, 2H, J = 3.66 Hz), 4.097–4.079 (t,
1H), 2.749 (s, 6H); 13C NMR (D2O): 175.55, 73.34, 26.58 ppm. Analytical-grade
crystals of 11 were obtained by dissolving the white solid in water and allowing
the water to slowly evaporate. Anal. Calcd for C7H14N2O5 (206.2): C, 40.77; H,
6.84; N, 13.59. Found C, 40.69; H, 6.84; N, 13.40.

M. R. Hinton et al.
82
2,3,4-Tri-O-acetyl-N,Nꢁ-dimethylxylaramide (15)
Acetic anhydride (5.0 mL, 52.9 mmol) was added to 11 (0.24 g, 1.18 mmol)
in pyridine (4 mL) and the solution warmed at 50◦C for 3 h. Cold water (7 mL)
was added with stirring to the reaction mixture and the mixture extracted
with chloroform (3 × 4 mL). The chloroform solutions were combined and
concentrated under a stream of nitrogen and then dried at reduced pressure
overnight to yield crystalline 2,3,4-tri-O-acetyl-N,Nꢁ-dimethylxylaramide (15,
1
0.27 g, 0.58 mmol, 85.3%): mp 171◦C; H NMR (CDCl3) δ 6.26 (s, 2H), 5.70
(t, 1H, J = 5.11 Hz), 5.40–5.38 (d, 2H, J = 5.53 Hz), 2.81 (s, 3H), 2.80 (s, 3H),
2.16 (s, 6H), 2.05 (s, 3H); 13C NMR (CDCl3): 169.44, 166.85, 71.86, 70.43, 26.15,
20.65, 20.43 ppm. Analytical-grade crystals of 15 were obtained by dissolving
the crystalline product described in water and allowing acetone to diffuse into
the aqueous solution. Anal. Calcd for C13H20N2O8 (332.31): C, 46.99; H, 6.07;
N, 8.43. Found C, 46.93; H, 6.12; N, 8.33.
2,3,4-Tri-O-acetyl-N,Nꢁ-dimethyl L-arabinaramide (16)
Acetic anhydride (5.0 mL, 52.9 mmol) was added dropwise to N,Nꢁ-
dimethyl-L-arabinaramide (13, 0.35 g, 1.69 mmol) in pyridine (4 mL) and the
solution warmed to 50◦C for 3 h. Cold (ice bath) water (7 mL) was added drop-
wise to the solution and the mixture concentrated under a stream of nitrogen
and then at reduced pressure overnight. The resulting solid was stirred with
water (1.5 mL) for 30 min, isolated by filtration, and dried to yield 2,3,4-tri-
O-acetyl-N,Nꢁ-dimethyl-L-arabinaramide (16, 0.35 g, 1.06 mmol, 62.74%): mp
1
209–210◦C; H NMR (CDCl3) δ 6.74 (s, 1H), 6.46 (s, 1H), 5.67–5.64 (d, 1H),
5.48–5.46 (d, J = 7.99 Hz, 1H), 5.35–5.34 (d, 1H, J = 4.79 Hz), 2.85–2.83
(q, 6H), 2.21 (s, 3H), 2.12 (s, 3H), 2.06 (s, 3H); 13C NMR (CDCl3): 169.48,
169.27, 168.65, 166.91, 166.81, 71.71, 70.57, 70.50, 26.18, 26.09. Analytical-
grade crystals of 16 were obtained by dissolving the crystalline product in
warm methanol and allowing the diffusion of acetone into the methanol so-
lution. Anal. Calcd for C13H20N2O8 (332.31): C, 46.99; H, 6.07; N, 8.43. Found
C, 47.03; H, 6.07; N, 8.41.
N,Nꢁ-Dimethylribaramide (14)
Acetyl chloride (4.61 mL, 5.09 g, 64.8 mmol) was added to a solution of
disodium ribarate (8, 4.84 g, 21.6 mmol) in cold (ice bath) methanol (30 mL)
and the reaction mixture stirred for 3 h. A white solid was removed by filtra-
tion, the filtrate was concentrated, and the syrupy residue dissolved in cold (ice
bath) methanol (10 mL). Methylamine (10.5 M, 11.0 mL, 86.4 mmol) in ethanol
was added dropwise to the methanol solution and the reaction mixture stirred
overnight at rt. A white solid was removed by filtration, dried at reduced pres-
sure overnight, stirred with methanol (5 mL), separated by filtration, rinsed
with methanol (2 × 1 mL), and dried to yield N,Nꢁ-dimethylribaramide (14,

Pentaric Acids from Nitric Acid–Oxidized Pentoses
83
1
1.58 g, 7.67 mmol, 35.5%): mp 165–168◦C; H NMR (D2O) δ 4.233 (d, 1H,
J = 5.13 Hz), 4.112 (t, 2H, J = 5.13 Hz), 2.73 (s, 6H); 13C NMR (D2O): 175.48,
74.37, 73.04, 26.55 ppm. Evaporation of water from an aqueous solution of 14
gave analytical-grade product. Anal. Calcd for C7H14N2O5 (206.2): C, 40.77; H,
6.84; N, 13.59. Found C, 40.86; H, 6.83; N, 13.58.
2,3,4-Tri-O-acetyl-N,Nꢁ-dimethylribaramide (17)
Acetic anhydride (11.8 mL, 125 mmol) was added dropwise to N,Nꢁ-
dimethylribaramide (14, 1.25 g, 6.23 mmol) in pyridine (5 mL) and the so-
lution stirred overnight. Cold (ice bath) water (15 mL) was added dropwise
and the mixture stirred for 30 min. The solvent was removed under a stream
of nitrogen, the residue dissolved in water (3 mL), and the aqueous solution
extracted with chloroform (3 × 10 mL). The chloroform extracts were com-
bined, concentrated under a stream of nitrogen, and dried at reduced pres-
sure overnight to yield 2,3,4-tri-O-acetyl-N,Nꢁ-dimethylribaramide (17, 2.05 g,
1
6.16 mmol, 79.9%): mp 166–169◦C; H NMR (CDCl3) δ 6.33 (s, 2H), 5.66 (t,
1H, J = 5.86 Hz), 5.45 (d, 2H, J = 5.86 Hz), 2.81 (s, 3H), 2.80 (s, 3H), 2.13
(s, 6H), 2.03 (s, 3H); 13C NMR (CDCl3): 169.23, 166.73, 71.18, 70.65, 26.11,
20.68 ppm. Anal. Calcd for C10H14N2O11 (332.31): C, 46.99; H, 6.07; N, 8.43.
Found C, 47.17; H, 5.97; N, 8.54.
Crystal Structure Analysis
A suitable crystal of 1,4(5,2)-ribarolactone (5) was coated with Paratone
N oil, suspended in a small fiber loop, and placed in a cooled nitrogen gas
stream at 173 K on a Bruker D8 APEX II CCD sealed tube diffractometer with
˚
graphite monochromated CuKα (1.54178 A) radiation. Data were measured us-
ing a series of combinations of phi and omega scans with 10-s frame exposures
and 0.5◦ frame widths. Data collection, indexing, and initial cell refinements
were all carried out using APEX II[20] software. Frame integration and final
cell refinements were done using SAINT[21] software.
The structure was solved using direct methods and difference Fourier tech-
niques (SHELXTL, V6.12).[22] Hydrogen atoms were placed in their expected
chemical positions using the HFIX command and were included in the final
cycles of least squares with isotropic Uij related to the atom’s ridden upon
except for the hydrogens on O2 and O3 that were located in a diff map and
refined. All nonhydrogen atoms were refined anisotropically. Scattering fac-
tors and anomalous dispersion corrections are taken from the International
Tables for X-ray Crystallography.[23] Structure solution, refinement, graphics,
and generation of publication materials were performed by using SHELXTL,
v6.12 software. Additional details of data collection and structure refinement
are given in Table 1.

M. R. Hinton et al.
84
Supplementary Information
The Supplementary Tables give crystal data and refinement details, bond
lengths, bond angles, selected torsion angles, and H-bonding details for 1–7.
Crystallographic data for the structural analyses have been deposited with
the Cambridge Crystallographic Data Center, CCDC Nos. 865172-865178 for
compound 5. Copies of this information may be obtained free of charge from
the Director, CCDC, 12 Union Road, Cambridge, CB2 1 EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.ac.uk).
1H NMR spectra of compounds prepared are included as additional supplemen-
tary information.
ACKNOWLEDGMENTS
This work was funded in part from USDA Cooperative State Research, Edu-
cation and Extension Service award nos. 2005-34463-15561 and 2006-34463-
16886.
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