Improved synthesis of the C-glucuronide/glycoside of 4-hydroxybenzylretinone (4-HBR)

Article abstract of DOI:10.1080/07328303.2016.1227831

Improvements in the synthesis of carbon-linked glucuronide/ glucoside conjugates of cancer chemopreventive retinoids have been achieved starting with 2,3,4,6-tetra-Obenzyl- D-glucopyranose. The revised approach demonstrates better yields, eliminates the use of an expensive, carcinogenic protecting group reagent, and avoids much painstaking chromatography. The new approach should allow synthesis of larger quantities of the agents for detailed animal and mechanistic studies.

Full text of DOI:10.1080/07328303.2016.1227831

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: http://www.tandfonline.com/loi/lcar20
Improved synthesis of the C-glucuronide/glycoside
of 4-hydroxybenzylretinone (4-HBR)
Kathryn R. Cavanaugh, Sureshbabu Narayanasamy, Joel R. Walker, Margaret
Clagett-Dame & Robert W. Curley, Jr.
To cite this article: Kathryn R. Cavanaugh, Sureshbabu Narayanasamy, Joel R. Walker, Margaret
Clagett-Dame & Robert W. Curley, Jr. (2016) Improved synthesis of the C-glucuronide/glycoside
of 4-hydroxybenzylretinone (4-HBR), Journal of Carbohydrate Chemistry, 35:5, 249-260, DOI:
10.1080/07328303.2016.1227831
To link to this article: http://dx.doi.org/10.1080/07328303.2016.1227831
Published online: 13 Oct 2016.
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Date: 03 November 2016, At: 13:24

JOURNAL OF CARBOHYDRATE CHEMISTRY
, VOL. , NO. , –
http://dx.doi.org/./..
Improved synthesis of the C-glucuronide/glycoside of
-hydroxybenzylretinone (-HBR)
Kathryn R. Cavanaugha, Sureshbabu Narayanasamya,b, Joel R. Walkera,
Margaret Clagett-Damec,d, and Robert W. Curley, Jr.a
aDivision of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University,
Columbus, OH, USA; bDepartment of Human Nutrition, The Ohio State University, Columbus, OH, USA;
cDepartment of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison,
Madison, WI, USA; dPharmaceutical Sciences Division, School of Pharmacy, University of
Wisconsin-Madison, Madison, WI, USA
ABSTRACT
ARTICLE HISTORY
Received  June 
Accepted  August 
Improvements in the synthesis of carbon-linked glu-
curonide/glucoside conjugates of cancer chemopreventive
retinoids have been achieved starting with 2,3,4,6-tetra-O-
benzyl-D-glucopyranose. The revised approach demonstrates
better yields, eliminates the use of an expensive, carcinogenic
protecting group reagent, and avoids much painstaking chro-
matography. The new approach should allow synthesis of larger
quantities of the agents for detailed animal and mechanistic
studies.
KEYWORDS
Chemopreventives;
C-Glucuronide; C-Glycoside;
Retinoid; Synthesis
GRAPHICAL ABSTRACT
Introduction
Drugs and xenobiotics are frequently metabolized by conjugation with glucuronic
acid. These conjugates typically have good water solubility and are relatively read-
ily eliminated in urine or bile. The vitamin A metabolite retinoic acid (RA; 1) is
known to form an O-acyl glucuronide metabolite.[1] RA and its analogs (retinoids)
CONTACT Robert W. Curley, Jr.
curley.@osu.edu
of Pharmacy, The Ohio State University, Columbus, OH, USA
Division of Medicinal Chemistry and Pharmacognosy, College
©  Taylor & Francis Group, LLC

250
K. R. CAVANAUGH ET AL.
have long been of interest as potential cancer chemopreventives or chemothera-
peutics because of the essential role for RA in the differentiation of epithelial tis-
sues.[2] It is rarely found that the glucuronide conjugates of drugs and hormones
retain the biological activity of the parent molecule.[3] In the case of retinoyl β-
glucuronide (2), it has been suggested that this might be an active antiproliferative
metabolite of RA.[4] The semisynthetic retinoid N-(4-hydroxyphenyl)retinamide (4-
HPR; 3) has generated interest as a less toxic analog of 1 showing good activity
in cancer chemoprevention and therapy.[5] Some evidence suggested that 3 might
also form a glucuronide conjugate (4) and that this might be an active mam-
mary tumor chemopreventive agent.[6] We prepared 4 and confirmed it is more
potent and less toxic than 3 as a mammary tumor chemopreventive/therapeutic.[7–9]
Since 4 is a substrate for β-glucuronidase and other hydrolytic processes, we pre-
pared a number of unhydrolyzable, carbon-linked analogs[10, 11] of this oxygen-
linked 4 and found that, in particular, the 4-HPR-C-glucuronide (5) showed
even better activity in a carcinogen-induced rat mammary tumor model.[12]
This strongly suggested that these glucuronide metabolites were active as intact
conjugates.
While 4-HPR is less toxic than 1, it is still possible for 3 to be hydrolyzed in vivo to
generate RA. Our evidence suggests that this hydrolysis does occur to some extent
and might account for the remaining toxicity, including some residual teratogenic-
ity of 3.[13] Therefore, we have also prepared the unhydrolyzable ketone analog of 3,
4-hydroxybenzylretinone (4-HBR; 6).[14] This ketone retains the tumor inhibitory
properties of 3 but had the hoped for reduction in toxicity, presumably since no
hydrolysis to RA can occur.[15] A compound combining these two structural themes
(an unhydrolyzable C-glucuronide and a ketone substitution for an amide) could
result in the most effective, least toxic analog in this series. Therefore, we prepared
4-HBR-C-glucuronide (4-HBRCG; 7).[16] This synthesis allowed us to prepare a
modest amount of 7 and preliminary experiments showed it to be relatively non-
toxic and effective in mammary tumor chemotherapy.[16] We also prepared a small
amount of the C-glucoside analog 8 as a model compound. To our surprise, this
analog showed some interesting preliminary growth inhibitory activity in vitro[17]
and thus a more robust synthesis of both 7 and 8 is needed to facilitate further
studies. We report here recent improvements in the preparation of these carbon-
linked analogs which feature modifications in the carbohydrate components of the
syntheses.
Results and discussion
The original synthesis of 7 is published[16] and only important elements are shown in
Scheme 1 to aid discussion. Key intermediate 10 was made by subjecting olefin 9 to
the hydroboration/Suzuki–Miyaura cross coupling sequence developed by Johnson
and co-workers for the synthesis of C-disaccharides.[18] While the sequence gener-
ally provided intermediates in good yields, a number of issues made it not amenable
for scale-up synthesis. These included the expense and toxicity of the chloromethyl

JOURNAL OF CARBOHYDRATE CHEMISTRY
251
Scheme . Reagents and conditions: (a) (i) -BBN-H, THF, reflux,  h; (ii) PdCl(dppf), M KPO, DMF,
-bromobenzyl alcohol,  h, %; (b) (i) NaH, THF, . h; (ii) CHI,  h, %; (c) (i)  N HCl, MeOH,  h;
(ii) TEMPO, NaClO, KBr, NaHCO,  °C,  min; (iii) CHI, DMF,  h; (iv) AcO, pyridine, DMAP,  h, %;
(d) HBr, AcOH,  h, %.
methyl ether needed to prepare precursors to 9. In addition, nearly all of the inter-
mediates in the synthetic scheme were oils which required careful chromatography,
even for those substances that eventually crystallized (e.g., 11 and 12).
Since the Petasis[19] and hydroboration/Suzuki sequence had previously been
successfully employed with benzyl-protected sugars,[20] we turned to the commer-
cially available 2,3,4,6-tetra-O-benzyl-D-glucopyranose (13) as starting material for
the revised synthesis of 7 and 8. Swern-type oxidation (DMSO, Ac2O) of 13 pro-
vides lactone 14 as the only oil in the revised synthesis, which was purified after
rapid “column filtration” through silica gel (Sch. 2). Subsequent products 15 and
16 were also purified in the same way unless they are prepared on a smaller scale
(<20 g), in which case both of these solids can be purified by recrystallization with-
out the need for removal of side products which on the larger scale hinder direct
crystallization. Lactone 14 is converted to olefin 15 using Petasis reagent much more
smoothly than using Tebbe’s reagent.[21] We do find that it is preferable to prepare
the Petasis reagent freshly for each use. This white, solid enol ether 15 is stable for
up to one month at room temperature. Hydroboration/Suzuki cross coupling of 15
with 4-bromotoluene provided the C-glucoside 16. However, unlike for the prepa-
ration of 10 from 9 (Sch. 1) in this case, when we used 4-iodotoluene instead of the
bromide, 16 was obtained in the expected higher yield. Previously, we and others
have shown that hydroboration with 9-BBN followed by the Pd-coupling provides
the β-stereochemistry at the former anomeric carbon center of the sugar.[16, 20, 21, 22]
All of the NMR data obtained for 16 supports the conclusion that the same is true
for this coupling reaction. Catalytic hydrogenolysis of 16 provided the tetrol analog
of 16 which was used as obtained. Conditions were developed which permitted this
process to be carried out at room temperature, with atmospheric pressure of hydro-
gen,[23] and without the use of acid catalysis which resulted in a cleaner product.
Selective, TEMPO-mediated oxidation of the 6-hydroxymethyl group of the
tetrol derived from 16, followed by reprotection provided the C-glucuronide 17 in a
manner analogous to the previous approach (see Sch. 1).[16] Bromination of 17 gave

252
K. R. CAVANAUGH ET AL.
Scheme. Reagentsandconditions:(a)AcO, DMSO, h, %;(b)CpTi(CH), PhCH, °C, h, %;
(c) (i) -BBN-H, THF, reflux, . h; (ii) PdCl(dppf), M KPO, DMF, -iodotoluene,  h, %; (d) (i) H,
% Pd/C; (ii) TEMPO, NaClO, KBr, NaHCO,  °C,  min; (iii) CHI, DMF,  h; (iv) AcO, pyridine, DMAP,
h, %;(e)NBS, benzoylperoxide, CCl, reflux, h, %;(f)(i)H, %Pd/C;(ii)AcO, pyridine, DMAP,
 h, %; (g) NBS, benzoyl peroxide, CCl, reflux,  h, %.
primary bromide 12 almost exclusively. Trace additional bromides/dibromides that
form can be substantially removed by crystallization. Analytically pure samples are
isolated by preparative HPLC, however, any trace impurities remaining after crystal-
lization, mainly dibromide, do not interfere with alkylation of umpolung-activated
retinal (18; Fig. 1) and isolation of that product. Alternatively, acetylation of the
tetrol provided C-glucoside 19 which was brominated to give 20 as for the forma-
tion of 12. Interestingly, these brominations seem to proceed more completely and
with fewer minor side products as the scale of the reaction is increased.
In summary, this paper describes more efficient syntheses of key C-glycoside
intermediates 12 and 20. It avoids the need for the highly toxic chloromethyl methyl
ether, most of the intermediates are crystallizable solids, bypasses much of the
tedious chromatography, and the cost is roughly one-third and two-thirds of the
previous method for the synthesis of the C-glucoside and C-glucuronide, respec-
tively. Alkylation of these bromides with the umpolung-activated aldehyde 18 as we
have previously done,[16] requires the relatively expensive polyene retinal (18). Our

JOURNAL OF CARBOHYDRATE CHEMISTRY
253
Figure . Structures of Retinoids.
recent improvements in the preparation of 18[24, 25] have further contributed to a
substantial decrease in the cost of the syntheses of these C-glucuronides/glycosides.
This should make larger scale study of the antitumor properties and mechanism(s)
of action of 7 and 8 feasible.
Experimental
General methods
1H and13C NMR spectra were recorded on a Bruker DRX400 instrument at 400
and 100 MHz, respectively. Melting points were measured on a Thomas-Hoover
capillary apparatus. Optical rotations were recorded on a Perkin-Elmer 343
polarimeter. Infrared spectra were collected on a Thermo-Nicolet 6700 FTIR. High-
resolution electrospray ionization/time of flight mass spectra were recorded at the
OSU Campus Chemical Instrument Center on a Bruker maXis 4G instrument.

254
K. R. CAVANAUGH ET AL.
TLC was performed on silica gel 60 F254 precoated aluminum-backed plates and
column “filtration”/chromatography was performed on silica gel 60, 70–230 mesh.
Analysis and separation by HPLC was conducted on a Beckman unit (model 127
pump, model 166 detector) using a Zorbax-Sil 4.6 × 250 mm column (4:1 hex-
ane/ethyl acetate at 2 mL/min) or Zorbax-Sil 9.4 × 250 mm column (3:1 hex-
ane/ethyl acetate at 5 mL/min), respectively, with monitoring at 265 nm. The
2,3,4,6-tetra-O-benzyl-D-glucopyranose was purchased from Alfa Aesar. The [1,1ꢀ-
Bis(diphenylphosphino)ferrocene]dichloropalladium(II), referred to as PdCl2(dppf),
was obtained from Frontier Scientific.
,,,-Tetra-O-benzyl-D-gluconic acid-δ-lactone ()[, ]
To an oven-dried flask under Ar was added 2,3,4,6-tetra-O-benzyl-D-glucopyranose
(13; 1.88 g; 3.49 mmol) and dissolved in 11 mL dry DMSO. Dry acetic anhydride
(7.3 mL) was added and the mixture stirred at rt overnight. The solution was poured
into ice water and extracted with ether (3 × 50 mL). The combined organic layer
was washed successively with saturated NaHCO3 and NaCl (brine) solutions, dried
(Na2SO4), filtered and solvent removed under reduced pressure. Product was puri-
fied via rapid filtration through silica gel using 15% ethyl acetate/hexanes. The
resulting oil was sparged with compressed air overnight to give clear oil 14 which
20
was used as obtained (1.25 g; 67% yield): [α]D +69.5 (c 0.14, CHCl3); 1H NMR
(CDCl3) δ 7.44–7.15 (m, 20H), 5.01 (d, 1H, J = 11.4 Hz), 4.76–4.45 (m, 7H), 4.45
(dd, 1H, J = 2.0, 13.9 Hz ), 3.93 (dd, 2H, J = 6.5, 10.6 Hz), 3.72 (dd, 2H, J = 2.2, 3.2
Hz); 13C NMR ((CD3)2CO) δ 170.17, 139.20, 139.10, 139.02, 138.67, 129.22, 129.19,
129.18, 129.04, 128.88, 128.72, 128.64, 128.58, 128.47, , 81.73, 78.94, 78.56, 76.81,
73.99, 73.82, 73.81, 73.76, 68.99; IR (cm−1) 3027, 2872, 1951, 1878, 1758.
Petasis reagent (dimethyltitanocene)[]
To an oven-dried, Al foil wrapped flask under Ar was added titanocene dichloride
(2.5 g, 10 mmol) and absolute ether (50 mL) and cooled to 10 °C . Methyl lithium
(1.6M in ether; 15 mL) was added dropwise. The cooling bath was then removed
and the solution was stirred at rt for 10 min. The reaction mixture was cooled in
an ice bath and ice cold water added. In the dark, the aqueous layer was extracted
3 × 50 mL with ether. The combined organic layer was dried (Na2SO4) and sparged
with Ar for 1 h. The product was filtered and concentrated in the dark at rt to give
an orange solid which was diluted with toluene (20 mL; 0.5 M) and used without
further purification.
,-Anhydro--deoxy-,,,-tetra-O-benzyl-D-gluco-hept--enitol () [, ]
To an oven-dried three-neck flask under Ar was added lactone 14 (1.08 g; 2 mmol)
in 10 mL toluene. The flask was wrapped in Al foil and 10 mL of 0.5 M Petasis
reagent solution in toluene added dropwise (or at once on larger scale) via an Al
foil wrapped syringe. The mixture was heated to 70 °C in an oil bath and stirred for
3–5 d in the dark with monitoring by TLC (20% ethyl acetate/hexanes). The reac-
tion mixture was poured into 2–2.5 volumes of hexanes and vacuum filtered through

JOURNAL OF CARBOHYDRATE CHEMISTRY
255
diatomaceous earth. The diatomaceous earth was washed with additional hexanes
and solvent removed under reduced pressure to give a bright yellow-orange oil that
solidifies upon standing. Crude product was purified by recrystallization (unless the
scale is larger than 20 g in which case filtering the yellow-orange solid loaded on sil-
ica gel through silica gel with hexanes then 5% ethyl acetate/hexanes solution gives a
yellow oil that solidifies upon standing). Product was then recrystallized from hex-
anes to give 15 as white needle crystals (0.75 g, 70% yield): m.p. 67–67.5°C (lit. m.p.
20
60–62°C); [α]D +52 (c 0.24, CHCl3); 1H NMR ((CD3)2CO) δ 7.31–7.22 (m, 20H),
4.79–4.46 (m, 10H), 3.99 (d, 1H, J = 4.5 Hz), 3.84 (m, 1H), 3.75–3.67 (m, 4H); 13
C
NMR ((CD3)2CO) δ 157.23, 139.27, 138.98, 138.93, 138.77, 129.24, 129.16, 129.09,
128.77, 128.76, 128.73, 128.58, 128.50, 128.40, 128.37, 128.32, , 93.92, 84.86, 79.22,
78.65, 78.46, 74.44, 73.99, 73.86, 72.39, 69.89; HRMS (ESI-TOF) m/z: [M+Na]+
Calcd for C35H36O5Na 559.2461; Found 559.2474 ; IR (cm−1) 3065, 2986, 2306.
,-Anhydro--deoxy--[-(methyl)phenyl]−,,,-tetra-O-benzyl-D-glycero-D-
gulo-heptitol ()[]
To a flame-dried flask under Ar was add enitol 15 (1.5 g; 2.8 mmol) in dry THF
(28 mL). A 0.5M solution of 9-BBN in THF (2.5 mmol; 14 mL) was added dropwise
and the mixture refluxed for 4.5 h. After cooling to rt and adding 2.2 mL 3M K3PO4
(2.4 eq) and stirring for 10 min, 4-iodotoluene (0.7 g; 3 mmol) and PdCl2(dppf)
(0.2 g, 0.22 mmol) dissolved in dry DMF (28 mL) were added dropwise and the
mixture stirred for 18 h. The mixture was diluted with ethyl acetate and the layers
separated. The aqueous layer was extracted 3 × 75 mL with ethyl acetate. The com-
bined organic layers were washed with water, brine and dried (MgSO4), filtered, and
concentrated to a brown solid which was recrystallized (unless the scale is greater
than 20 g in which case the solid was rapidly filtered through silica gel with 10% ethyl
acetate/hexanes to give white/yellow crystals). Recrystallization from hexanes gave
20
a white solid 16 (2.1 g, 77% yield); m.p. 88.5–90 °C; [α]D +25.6 (c 0.20, CHCl3);
1H NMR ((CD3)2CO) δ 7.35–7.25 (m, 20H), 7.15 (d, 4H, J = 7.9 Hz), 7.01 (d, 2H,
J = 7.8 Hz), 4.95–4.86 (m, 3H), 4.81 (d, 1H, J = 11.0 Hz), 4.71 (d, 1H, J = 11.2 Hz),
4.64 (d, 1H, J = 11.0 Hz), 4.52 (dd, 2H, J = 9.2, 12.2 Hz), 3.69 (m, 3H), 3.56 (dd,
1H, J = 9.6, 19.8 Hz), 3.48 (ddd, 1H, J = 2.2, 6.8, 9.1 Hz), 3.38 (dd, 1H, J = 2, 6.4
Hz), 3.29 (dd, 1H, J = 9.0, 18.3 Hz), 3.10 (dd, 1H, J = 1.8, 14.3 Hz), 2.81 (d, 1H, J =
5.4 Hz), 2.65 (dd, 1H, J = 5.4, 8.9 Hz), 2.24 (s, 3H); 13C NMR ((CD3)2CO) δ 140.07,
139.95, 139.85, 139.72, 136.93, 136.06, 130.36, 129.55, 129.16, 129.13, 129.10, 129.05,
128.67, 128.65, 128.38, 128.34, 128.23, 128.13, , 88.12, 82.82, 80.76, 79.95, 79.71,
75.87, 75.44, 75.33, 73.82, 70.22, 38.31, 21.12); HRMS (ESI-TOF) m/z: [M+Na]+
Calcd for C42H44O5Na 651.3087; Found 651.3112 ; IR (cm−1) 3018, 2917, 2404,
1954, 1881, 1815.
,-Anhydro--deoxy--[-(methyl)phenyl]-D-glycero-D-gulo-heptitol[]
To an oven-dried flask under Ar was add 1 g 10% Pd/C and the flask flushed with
argon and evacuated to remove O2. Benzyl protected 16 (6.68 g; 10.6 mmol) was
added in 53 mL dichloromethane under Ar and after using vacuum and Ar to fully

256
K. R. CAVANAUGH ET AL.
evacuate air, 53 mL of CH3OH was added slowly with stirring at rt. Vacuum and a H2
balloon was used alternately to charge the system with hydrogen, and stirring con-
tinued overnight or until the reaction was complete. When reaction was complete
(determined to be when Rf goes to zero by TLC in 20% ethyl acetate/hexanes) the
Pd/C was filtered off through diatomaceous earth and washed with CH3OH/H2O
and the filtrate concentrated. The debenzylated product tetrol was used without fur-
ther purification.
,-Anhydro--deoxy--[-(methyl)phenyl]−,,-tri-O-acetyl-L-glycero-L-gulo-
hetpinoic acid methyl ester ()
To a round-bottomed flask was added TEMPO (1.0 g; 6.4 mmol), KBr (0.75 g,
6.4 mmol), and 125 mL of saturated NaHCO3 and the mixture stirred at 0 °C for
20 min. Commercial grade bleach (3.5 mL) was added and the mixture stirred at 0
°C for 10 min. The debenzylated tetrol derived from 16 above (0.38 g; 1.42 mmol)
was dissolved in 7.5 mL CH3CN and along with 25 mL of saturated NaHCO3 was
added to the TEMPO solution and stirred for 45 min at 0 °C. At 25 min, a pH drop
of the reaction mixture was noted and an additional 7.5 mL of saturated NaHCO3
added. Ethanol (15 mL) was added and the mixture was washed with ether. The
aqueous layer was then concentrated to dryness and the resulting solid was stirred
with CH3OH overnight and the residue filtered and the alcohol concentrated. To
the residue was added 50 mL DMF and then iodomethane (1.2 mL; 19.3 mmol)
was added and stirring continued at rt under Ar for 24 h. Acetic anhydride (15 mL;
159 mmol) was added to the solution along with pyridine (7.5 mL; 92.9 mmol) and
5 mg of DMAP and the mixture was stirred for 48 h at rt. Liquids were evaporated
under a stream of air over 3 d and the residue partitioned between ethyl acetate and
water. The organic layer was washed with water, brine, dried (MgSO4), filtered, con-
centrated under reduced pressure, and chromatographed (2:1 then 1:1 hexanes/ethyl
acetate) to give an off-white solid which was recrystallized from hexanes to give
20
white solid 17 (0.514 g, 86% yield): m.p. 100–102 °C; [α]D −0.051 (c 0.07, CHCl3);
1H NMR ((CD3)2CO) δ 7.09 (d, 2H, J = 8.0 Hz), 7.06 (d, 2H, J = 7.9 Hz), 5.29 (dd,
1H, J = 9.3, 10.1 Hz), 5.05 (dd, 1H, J = 9.7, 10.3 Hz), 4.89 (dd, 1H, J = 9.6, 10.1
Hz), 4.15 (d, 1H, J = 10.0 Hz), 3.90 (m, 1H), 3.62 (s, 3H), 2.86 (dd, 1H, J = 3.2,
14.6 Hz), 2.72 (dd, 1H, J = 8.1, 14.5 Hz), 2.24 (s, 3H), 1.96 (s, 3H), 1.95 (s, 3H),
1.94 (s, 3H); 13C NMR ((CD3)2CO) δ 170.40, 170.16, 169.99, 168.50, 136.56, 135.21,
130.27, 129.66, 78.77, 76.44, 74.14, 72.57, 70.67, 52.77, 38.03, 21.07, 20.69, 20.62,
20.49; HRMS (ESI-TOF) m/z: [M+Na]+ Calcd for C21H26O9Na 445.1475; Found
445.1511 ; IR (cm−1) 3062, 2803, 1672.
,-Anhydro--deoxy--[-(bromomethyl)phenyl]−,,-tri-O-acetyl-L-glycero-L-
gulo-heptinoic acid methyl ester ()[]
To an oven-dried flask under Ar was added 127 mg (0.3 mmol) of 17 and dissolved
in 2.5 mL of dry CCl4. Recrystallized NBS (51 mg; 0.36 mmol) and benzoyl peroxide
(2.3 mg; 0.012 mmol) were added and the mixture refluxed for 2 h. After cooling to
rt, the mixture was filtered and the filtrate concentrated under reduced pressure. The

JOURNAL OF CARBOHYDRATE CHEMISTRY
257
resulting crude solid was chromatographed (3:2 hexanes/ethyl acetate) and further
purified by recrystallization from 20% ethyl acetate in hexanes to give a white solid
12 (88 mg, 74% yield) identical to our previously prepared 12.[16] Selected analytical
data: HPLC tR = 13.8 min (4:1 hexane/ethyl acetate); 1H NMR ((CD3)2CO) δ 7.39
(d, 2H, J = 8.1 Hz), 7.27 (d, 2H, J = 8.1 Hz), 5.32 (dd, 1H, J = 9.4, 11.3 Hz), 5.07
(dd, 1H, J = 9.4, 11.8 Hz), 4.93 (dd, 1H, J = 9.8, 10.4 Hz), 4.65 (s, 2H), 4.22 (d,
1H, J = 9.9 Hz), 3.97–4.06 (m, 1H), 3.68 (s, 3H), 2.94 (dd, 1H, J = 3.5, 14.6 Hz),
2.78–2.87 (m, 1H), 1.98 (s, 3H), 1.963 (s, 3H), 1.959 (s, 3H); 13C NMR ((CD3)2CO)
δ 170.39, 170.18, 170.01, 168.49, 138.78, 137.35, 130.79, 129.99, 78.52, 76.40, 74.12,
72.63, 70.66, 52.82, 38.20, 34.50, 20.72, 20.62, 20.51; HRMS (ESI) m/z: [M+H]+
Calcd for C21H26BrO9 507.07547; Found 507.07542.
,-Anhydro--deoxy--[-(methyl)phenyl]−,,,-tetra-O-acetyl-D-glycero-D-
gulo-heptitol ()
The debenzylated tetrol derived from 16 above (2.84 g; 10.6 mmol) was dissolved in
383 mL DMF. After addition of 32 mg DMAP, 85 mL acetic anhydride (899 mmol),
and 43 mL pyridine (532 mmol), the mixture was stirred for 18 h under Ar at rt. After
addition of cold water, the mixture was extracted with ethyl acetate (3 × 75 mL) and
the combined organic layer was washed with water, brine, dried (MgSO4), filtered,
and concentrated under reduced pressure to give crude solid which was recrystal-
lized twice from hexanes to give white solid 19 (3.74 g, 81% yield): m.p. 122–124°C;
20
[α]D −5.2 (c 0.06, CHCl3); 1H NMR ((CD3)2CO) δ 7.10 (d, 2H, J = 8.0 Hz ), 7.05
(d, 2H, J = 7.9 Hz), 5.22 (dd, 1H, J = 9.4, 9.9 Hz), 4.97 (dd, 1H, J = 9.8, 10.1 Hz),
4.85 (dd, 1H, J = 9.5, 9.8 Hz), 4.22 (dd, 1H, J = 5.9, 12.3 Hz), 4.00 (dd, 1H, J = 2.4,
12.2 Hz), 3.74–3.84 (m, 2H), 2.81 (m, 1H), 2.67 (dd, 1H, J = 8.5, 14.3 Hz), 2.25 (s,
3H), 1.98 (s, 3H), 1.97 (s, 3H), 1.96 (s, 3H), 1.93 (s, 3H); 13C NMR ((CD3)2CO) δ
170.65, 170.44, 170.21, 170.12, 136.43, 135.53, 130.30, 129.54, 78.76, 76.40, 76.07,
74.92, 72.83, 69.75, 63.04, 37.98, 21.03, 20.69, 20.68, 20.63, 20.60; HRMS (ESI-TOF)
m/z: [M+Na]+ Calcd for C22H28O9Na 459.1632; Found 459.1661; IR (cm−1) 2925,
2853, 1660.
,-Anhydro--deoxy--[-(bromomethyl)phenyl]−,,,-tetra-O-acetyl-D-
glycero-D-gulo-heptitol ()[]
To oven-dried glassware under Ar was added acetate 19 (3.2 g; 7.3 mmol) and
dissolved in 73 mL CCl4. NBS (1.6 g; 8.8 mmol) and benzoyl peroxide (0.07 g;
0.3 mmol) were added and the mixture refluxed for 2 h. After cooling to rt the
mixture was filtered and the filtrate concentrated under reduced pressure to give
crude solid which was chromatographed (3:2 hexanes/ethyl acetate) and recrystal-
lized from 40% ethyl acetate in hexanes to give white solid 20 (2.7 g, 71% yield):
20
m.p. 133–135 °C; [α]D −15.0 (c 0.22, CHCl3); HPLC tR = 14.4 min (4:1 hex-
ane/ethyl acetate); 1H NMR ((CD3)2CO) δ 7.35 (d, 2H, J = 8.1 Hz ), 7.22 (d, 2H,
J = 8.1 Hz), 5.2 (dd, 1H, J = 9.4, 18.9 Hz), 4.94 (dd, 1H, J = 9.8, 19.5 Hz), 4.84
(dd, 1H, J = 9.6, 19.2 Hz), 4.60 (s, 2H), 4.2 (dd, 1H, J = 5.9, 12.2 Hz), 3.96 (dd, 1H,
J = 2.3, 12.0 Hz), 3.85 (m, 2H), 2.84 (d, 1H, J = 3.1 Hz), 2.72 (dd, 1H, J = 3.0, 8.6

258
K. R. CAVANAUGH ET AL.
Hz), 2.00 (s, 3H), 1.99 (s, 3H), 1.97 (s, 3H), 1.95 (s, 3H); 13C NMR ((CD3)2CO) δ
170.47, 170.26, 170.05, 169.93, 138.86, 137.06, 130.61, 129.67, 78.32, 75.97, 74.75,
72.73, 69.63, 62.95, 37.99, 34.28, 20.76, 20.72, 20.63, 20.61; HRMS (ESI-TOF) m/z:
[M+Na]+ Calcd for C22H27BrO9Na 537.0736; Found 537.0724; IR (cm−1) 3018,
2952, 2401, 1755.
Acknowledgements
Mass spectra were obtained at the OSU-CCIC with the aid of NSF Instrument Award 1040302.
Funding
This work was supported by a grant from the National Institutes of Health- National Cancer
Institute (CA49837) which is gratefully acknowledged.
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