Unexpected incorporation of bromine at a non-anomeric position during the synthesis of an O2-glycosylated diazeniumdiolate

Full text of DOI:10.1080/00304940902801968

Organic Preparations and Procedures International, 41:143–147, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print
DOI: 10.1080/00304940902801968
OPPI BRIEFS
Unexpected Incorporation of Bromine
at a Non-anomeric Position during the Synthesis
of an O2-Glycosylated Diazeniumdiolate
Joseph E. Saavedra,1 Keith M. Davies,2 Joseph J. Barchi, Jr.,3
and Larry K. Keefer4
1Basic Research Program, SAIC-Frederick, National Cancer Institute at
Frederick, Frederick, Maryland, USA
2Department of Chemistry, George Mason University, Fairfax, Virginia, USA
3Laboratory of Medicinal Chemistry, National Cancer Institute at Frederick,
Frederick, Maryland, USA
4Chemistry Section, Laboratory of Comparative Carcinogenesis, National
Cancer Institute at Frederick, Frederick, Maryland, USA
We recently reported that the novel NO-releasing O2-glycosylated diazeniumdiolates of
structure 1 showed promising anti-parasitic activity against Leishmania major.1 While
preparing some 2-deoxyglucose analogs for lead optimization, we have observed the
facile displacement of acetate by bromide from the 4-position of peracetylated 2-
deoxyglucose 2, as shown in Scheme 1, providing a convenient synthesis of 4-brominated
2,4-dideoxyglucose derivatives that would otherwise be difficult to access by currently
preferred, directed synthetic routes.
In an effort to prepare compound 4a, peracetylated 2-deoxyglucose 2 was treated with
HBr in glacial acetic acid. A tar assumed to be bromide 3 was formed and immediately
Submitted September 11, 2008.
Address correspondence to Joseph E. Saavedra, SAIC-Frederick, National Cancer Institute at
Frederick, Basic Research Program, Frederick, MD 21702. E-mail: saavj@mail.ncifcrf.gov
143

144
Saavedra et al.
Scheme 1
reacted with diazeniumdiolate salt 5 to generate a product expected to be 4a. However, this
easily crystallized, sharp-melting product was characterized by elemental analysis values
that were vastly different from our expectation. Further examination revealed the presence
of only two methyl singlets in the proton NMR, and mass spectrometry pointed to the
presence of a bromine atom in the molecular ion isotopic cluster. Detailed analysis of the
1H NMR spectral properties showed that the halide had replaced the C4 acetoxy group
with retention of configuration. Further work-up afforded 7a in 38% yield. The product
7a was deacetylated with methoxide in methanol to produce 7b. An alternate bromination
procedure using BiBr3 and trimethylsilyl bromide gave 4-α-bromo-2,4-dideoxyglucosyl
bromide diacetate 6, presumably the same glycosylating agent produced in the HBr/HOAc
reaction. The reaction with BiBr3 was rapid, efficient, and gave a higher yield of 6 than the
HBr procedure.
Diazeniumdiolates generate up to two moles of NO upon hydrolysis under various
conditions. Replacement of the C4 acetoxy group of compound 4b by bromine had little
effect (only about three-fold) on hydrolysis rates at pH values of 14, 7.4, and 3.8–4.6
(Table 1), a key predictor of anti-leishmanial activity.1
In conclusion, we have discovered a novel and simple BiBr3/TMS bromide-mediated
preparation of compound 6, an extremely useful intermediate in the preparation of the

Synthesis of an O2-Glycosylated Diazeniumdiolate
145
Table 1
Half-lives of Hydrolysis at 37◦C for Diazeniumdiolated Glycosides
of Structure Et2NN(O)=NOR
pH
R
14a
7.4b
3.8–4.6
β-(4-α-Bromo)-2,4-dideoxy-d-glucosyl (7b)
β-(2-Deoxy)-d-glucosyl (4b)1
72 min
23 min
1.5 days
0.5 days
1.8 daysc
1.2 daysd
a) 1.0 M NaOH.
b) 0.1 M phosphate.
c) 0.95 M citrate at pH 4.6.
d) 0.05 M citrate at pH 3.8.
2-deoxy sugars primed for further functionality at C4. In particular, compounds 7a and 7b
offer an electrophilic center at C4, making it potentially useful for further reaction with
nucleophiles, including peptide chains or additional saccharides.
Experimental Section
Starting materials were purchased from Aldrich Chemical Co. (Milwaukee, WI). NMR
spectra were obtained in chloroform-d or deuterium oxide on a Varian UNITY INOVA
spectrometer; chemical shifts (δ) are reported in parts per million (ppm) downfield from
tetramethylsilane or 3-(trimethylsilyl)propionic-2,2,3,3-d4 acid, sodium salt. Ultraviolet
(UV) spectra were recorded on an Agilent model 8453 or a Hewlett-Packard model 8451A
diode array spectrophotometer. ESI-MS analysis was performed on a Finnigan LCQ DECA
ion trap mass spectrometer. Elemental analyses were performed by Atlantic Microlab, Inc.
(Norcross, GA) and Midwest Microlab (Indianapolis, IN).
Isolation of O2-(3,6-Di-O-acetyl-4-[α-bromo]-2,4-dideoxy-β-D-glucopyranosyl)
1-(N,N-Diethylamino)diazen-1-ium-1,2-diolate (7a) (JS-33–45) from Deoxyglucose
Tetraacetate 2 with HBr in glacial Acetic Acid
2-Deoxy-D-glucose (Sigma-Aldrich) was acylated with acetic anhydride and pyridine using
the general method of Wolfrom and Thompson.2 The spectral properties of the product,
2, matched those in the published report. A solution of 6.0 g (0.018 mol) of 2 in 12 mL
of 30% HBr/acetic acid at 0◦C was allowed to warm to room temperature and stirred for
20 hours. The reaction mixture was diluted with 200 mL of dichloromethane and washed
with water. The organic layer was washed three times with aqueous 5% sodium bicarbonate
solution, dried over sodium sulfate, and filtered through a layer of anhydrous magnesium
sulfate. Evaporation of the solvent gave 3.60 g of 6 as a black tar. A 2.35 g portion of
the crude product 6 was dissolved in 25 mL of tetrahydrofuran. The resulting solution was
added dropwise to a cold slurry of 1.1 g (0.007 mol) of 53 in 20 mL of dimethyl sulfoxide
containing 200 mg of anhydrous sodium carbonate. After stirring at room temperature
under nitrogen for 72 hours, the solution was diluted with 200 mL of ether and filtered

146
Saavedra et al.
into a separatory funnel, washed with water, dried over sodium sulfate, and filtered through
a layer of magnesium sulfate. Evaporation of the solvent gave 2.09 g of a brown oil.
Purification was carried out on a 25-mm × 300-mm glass column packed with 70 g of
silica gel suspended in 10:1 dichloromethane:ethyl acetate. Elution was performed using
the same solvent system to give 1.12 g (38% based on 2.35 g of starting material) of 7a as
a colorless crystalline solid, mp 87.8◦C. ESI mass spectroscopy confirmed the presence of
bromide in the molecule (M+ 425 and 427); further NMR analysis using COSY and HSQC
acquisitions demonstrated that the bromide was at the C-4 equatorial position: UV (EtOH)
λmax (ε) 228 nm (10 mM−1 cm−1). 1H NMR (CDCl3): δ 1.11 (t, 6 H, J = 7.0 Hz, CH3CH2-),
2.09 (s, 3 H, CH3C=O), 2.12 (s, 3 H, CH3C=O), 2.43–2.52 (m, 1 H, H2), 2.71–2.76 (m, 1
H, H2ꢀ), 3.18 (q, 4 H, J = 7.1 Hz, CH3CH2-), 3.63–3.67 (m, 1 H, H5), 4.09–4.25 (m, 3 H,
H3, H6ꢀ and H6), 5.12 (t, 1 H, J = 9.9 Hz, H4), 5.25 (dd, 1 H, J = 2.2 and 10.1 Hz, H1).
13C NMR δ 11.50, 20.65, 20.68, 38.97, 45.26, 48.45, 62.40, 70.78, 74.40, 99.89, 169.30,
170.63.
Anal. Calcd for C14H25BrN3O7: C, 39.52; H, 5.69; N, 9.88. Found: C, 39.60; H, 5.67;
N, 9.81.
Bromination of 2 via BiBr3
The general procedure of Montero et al.4 was used to brominate compound 2. To a solu-
tion of 641 mg (1.93 mmol) of 2 in 10 mL of dichloromethane were added 90 mg (0.2
mmol) of bismuth tribromide (Sigma-Aldrich) and four equivalents (1.03 mL, 8 mmol) of
trimethylsilyl bromide under a nitrogen atmosphere. The solution was stirred at room tem-
perature for 2 hours, diluted with dichloromethane, washed with 5% sodium bicarbonate
solution, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 551 mg
of 6 as a gray-brown oil. The TLC and NMR of this crude product matched the TLC and
NMR of the over-brominated compound 6 described in the previous paragraph.
O2-[4-(α-Bromo)-2,4-dideoxy-β-D-glucopyranosyl] 1-(N,N-diethylamino)diazen-
1-ium-1,2-diolate (7b) (JS-33–48)
The general procedure of Wolfram and Thompson5 was used in the deacetylation step. A
solution of 936 mg (2.2 mmol) of 7a in 40 mL of methanol was treated with 150 µL of
25% methanolic sodium methoxide and stirred at room temperature. The progress of the
hydrolysis was followed on silica-gel TLC using 50:1 dichloromethane:methanol. After 2
hours, 1 g of pre-washed Dowex-50W resin was added to the reaction mixture and stirred
for 30 min. Filtration and evaporation of the filtrate gave a colorless solid that was purified
on silica gel, eluted with 5:1 dichloromethane:ethyl acetate. Pure 7b was isolated in 98%
yield (738 mg) mp 121–123 ◦C; UV (EtOH) λmax (ε) 226 nm (7.9 mM−1cm−1). 1H NMR
(D2O) δ 1.07 (t, 6 H, J = 7.1 Hz, CH3CH2-), 2.27–2.38 (m, 1 H, H2), 2.74–2.80 (m, 1 H,
H2ꢀ), 3.18 (q, 4 H, J = 7.1 Hz, CH3CH2-), 3.56–3.62 (m, 1 H, H5), 3.70 (t, 1 H, J = 9.7
Hz, H4), 3.82–3.95 (m, 3 H, H3, H6ꢀ, and H6), 4.17–4.26 (m, 1 H, H3ꢀ), 5.53 (dd, 1 H, J =
2.2 and 13.0 Hz, H1). 13C NMR (CDCl3) δ 11.50, 38.96, 48.37, 51.57, 62.50, 71.74, 77.48,
100.08.
1
Anal. Calcd for C10H20BrN3O5·4 CH2Cl2: C, 33.88; H, 5.69; N, 11.56. Found: C,
33.54; H, 5.57; N, 11.55.

Syntheses of C-1 Axial Derivatives of L-Menthol
147
Acknowledgments
This project has been funded in part with federal funds from the National Cancer Institute,
National Institutes of Health, under contract NO1-CO-2008–00001, and in part by the
Intramural Research Program of the NIH, National Cancer Institute, Center for Cancer
Research. The content of this article does not necessarily reflect the views or policies of the
Department of Health and Human Services, nor does mention of tradenames, commercial
products, or organizations imply endorsement by the U.S. Government.
References
1. C. A. Valdez, J. E. Saavedra, B. M. Showalter, K. M. Davies, T. C. Wilde, M. L. Citro, J. J. Barchi,
Jr., J. R. Deschamps, D. Parrish, S. El-Gayar, U. Schleicher, C. Bogdan and L. K. Keefer, J. Med.
Chem., 51, 3961 (2008).
2. M. L. Wolfrom and A. Thompson. Acetylation. In Methods in Carbohydrate Chemistry, pp. 211.
R. L. Whistler, M. L. Wolfrom, and J. N. BeMiller, eds., Academic Press, Inc., New York and
London, 1963.
3. R. S. Drago and B. R. Karstetter, J. Am. Chem. Soc., 83, 1819 (1961).
4. J.-L. Montero, J.-Y. Winum, A. Leydet, M. Kamal, A. A. Pavia and J.-P. Roque, Carbohydr. Res.,
297, 175 (1997).
5. M. L. Wolfrom and A. Thompson (1963) Deacetylation. In Methods in Carbohydrate Chemistry,
pp. 215. R. L. Whistler, M. L. Wolfrom, and J. N. BeMiller, eds., Academic Press, Inc., New York
and London, 1963.
Organic Preparations and Procedures International, 41:147–152, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print
DOI: 10.1080/00304940902802008
Syntheses of C-1 Axial Derivatives of L-Menthol
Debra K. Dillner
Department of Chemistry, United States Naval Academy, Annapolis,
Maryland, USA
Derivatives of menthol have interesting 1H NMR spectra and often, complete assignments of
the protons and determination of the configuration of substituents on the cyclohexane ring
are difficult. As part of a project to investigate the NMR properties of menthol derivatives,
several axially substituted menthanes (3–6) were prepared and their structures established.1
Submitted November 17, 2008.
Address correspondence to Debra K. Dillner, Department of Chemistry, United States Naval
Academy, Annapolis, MD 21402. E-mail: ddillner@usna.edu