Synthesis of C-disaccharide analogues of the α-D-arabinofuranosyl- (1→5)-α-D-arabinofuranosyl motif of mycobacterial cell walls via alkynyl intermediates

Article abstract of DOI:10.1016/j.tetlet.2005.03.017

Two C-glycosides related to the recurrent α-D-arabinofuranosyl- (1→5)-α-D-arabinofuranosyl structural motif of mycobacterial arabinan have been prepared by routes involving acetylenic intermediates.

Full text of DOI:10.1016/j.tetlet.2005.03.017

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 3249–3252
Synthesis of C-disaccharide analogues of the
a-D-arabinofuranosyl-(1!5)-a-D-arabinofuranosyl motif
of mycobacterial cell walls via alkynyl intermediates
Tashfeen Aslam, Michael G. G. Fuchs, Adeline Le Formal and Richard H. Wightman*
Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK
Received 27 August 2004; revised 23 February 2005; accepted 3 March 2005
Available online 25 March 2005
Abstract—Two C-glycosides related to the recurrent a-D-arabinofuranosyl-(1!5)-a-D-arabinofuranosyl structural motif of myco-
bacterial arabinan have been prepared by routes involving acetylenic intermediates.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Tuberculosis remains one of the major infectious dis-
eases worldwide, responsible for around two million
deaths annually, particularly in the developing world.1
Additionally, the synergism of the disease with HIV
and the appearance of multi-drug resistant strains of
the causative agent, Mycobacterium tuberculosis, raises
the prospect that tuberculosis may become prevalent
as a disease only curable with great difficulty in devel-
oped nations.2
binofuranosyl-1-monophosphoryldecaprenol is inhib-
ited by one major anti-tuberculosis agent in clinical
use, ethambutol.7
The most common recurrent structural motif in myco-
bacterial arabinan is the a-D-arabinofuranosyl-(1!5)-
a-D-arabinofuranosyl unit 1. C-Glycosides are close
analogues of oligosaccharide structures, which are resis-
tant to chemical and enzymic degradation.8 We here de-
scribe direct routes for the synthesis of two C-glycosides
2 and 3 related to motif 1, by the use of acetylenic inter-
mediates. An alternative route to 2 using a Wittig-based
approach had recently been reported,9 whilst a synthesis
of 3 using the Henry reaction as a key step has been
claimed.10
In a search for new drug targets, the mycobacterial cell
envelope3 is attractive. Major components of the cell
wall are two polysaccharide structures, lipoarabino-
mannan (LAM) and arabinogalactan (AG), this latter
structure being covalently linked to the bacterial
peptidoglycan and esterified as the non-reducing termini
of the arabinan component with long-chain fatty acids
(mycolic acids).
For the synthesis of 2 (see Scheme 1) the lactone 4,
prepared by oxidation11 of commercially available tri-
O-benzyl-D-arabinofuranose, was treated with lithio(tri-
methylsilyl)ethyne at low temperature to give the lactol 5
(66%). Treatment of this with triethylsilane and BF3Æ
Et2O gave the separable isomers 6a (60%) and 6b
(13%).12 That the major isomer 6a was the expected13
isomer in which hydride delivery had occurred cis to
the vicinal benzyloxy group was confirmed by the obser-
vation of an NOE interaction between H-10 and H-30,
which was absent in the spectrum of 6b, which however
showed a strong interaction between H-10 and H-20.
Desilylation of 6a gave 7 (97%), which again showed
an NOE interaction between H-10 and H-30, confirming
the stereochemistry of this material. The synthesis could
then be completed by an iterative route. Treatment of 7
with n-BuLi, followed by addition of lactone 4 gave the
In seeking to block the biosynthesis of AG4 and/or
LAM,5 the glycosyl transferases responsible for assem-
bly of the arabinan components of both these polymers6
are appealing targets for inhibitor design, given that the
D-arabinose units are exclusively in their furanose form,
and the xenobiotic status of the furanose form of
D-arabinose. It is known that arabinofuranosyl transfer
to the growing arabinan from the sugar donor b-D-ara-
Keywords:
C-Glycosides;
author.
r.h.wightman@hw.ac.uk
C-Disaccharides;
Tel.: +44 131
Arabinofuranosyl;
4518039; e-mail:
Alkynes.
*
Corresponding
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.03.017

3250
T. Aslam et al. / Tetrahedron Letters 46 (2005) 3249–3252
OH
O
O
O
O
O
R
O
O
OH
HO
OH
HO
OH
HO
OH
HO
2
R = CH2OH
3 R = OMe
1
OBn
BnO
OBn
OBn
OBn
O
O
O
H
OH
O
H
O
1'
a
b
1'
3'
+
2'
BnO
OBn Tms
OBn
O
OBn
Tms
BnO
OBn
BnO
Tms
6α
6β
4
5
c
OBn
H
d
OBn
O
H
O
1'
BnO
OBn
HO
3'
OBn
H
OBn
BnO
OBn
BnO
8
7
b
OH
HO
OBn
8
O
H
O
12
e
10
O
1
O
5
BnO
OBn
OH
OH
OBn
3
H
OH
HO
BnO
OBn
2
9
Scheme 1. Reagents and conditions: (a) TMS–acetylene, n-BuLi, THF, ꢀ78 ꢁC; (b) BF3ÆEt2O, Et3SiH, DCM, ꢀ78 ꢁC; (c) K2CO3, MeOH; (d) BuLi,
THF, ꢀ78 ꢁC, then 4; (e) Pd(OH)2/C, H2 (1 atm), MeOH–EtOAc (5:1).
hemiacetal 8 (85%), which on reduction with Et3SiH and
BF3ÆEt2O gave the disubstituted alkyne 9 (83%) as the
major product. The stereochemistry of 9 was clear from
its NMR spectra,14 which indicated C2 symmetry, and
the observation of NOEs between H-5/8 and both H3/
10 and (weakly) H-1/12. Reduction–hydrogenolysis of
9 then gave the C-disaccharide 215 in near-quantitative
yield.
uct 14b showed an NOE between H-7 and H-10. Addi-
tionally, the signal for C-8 in 14b was significantly
shielded (d 83.4) as compared with the equivalent signal
for 14a (d 88.8), a correlation, which was also found for
alkynes 6a and 6b,12 and for 7 and its b-isomer. Both
14a and 14b showed C-3 in the region of d 88. For 14a,
the signals for H-8 (d 4.23), and to a smaller extent,
H-10 (d 4.25), were also deshielded by the anisotropic
effect of the alkyne as compared with the equivalent
signals for 14b (d 4.00 and 4.06, respectively). It should
also be noted that alkyne 9 showed signals for positions
4/9 at dC 88.8 and dH 4.23.
For the synthesis of the methyl glycoside 3 (see Scheme
2), methyl 2,3-di-O-benzyl-a-D-arabinofuranoside (10)16
was prepared by modifications of the original route.17
Swern oxidation of 10, followed by treatment of the
aldehyde with CBr4–Ph3P gave the dibromoalkene 11
(73% overall), which on treatment with n-BuLi gave
alkyne 12 (75%).18 Reaction of the lithio-derivative of 12
with lactone 4 gave hemiacetal 13 (87%), which on treat-
ment with Et3SiH and BF3ÆEt2O gave 14a (66%) and 14b
(20%),19 separable by chromatography. The stereochem-
istry of the major product 14a was indicated by an NOE
between H-7 and H-9; by comparison, the minor prod-
Catalytic hydrogenation of 14a gave the C-disaccharide
3 in quantitative yield. The data for 320 was similar to,
but significantly different from, that noted in the previ-
ous report10 on the synthesis of this compound. How-
1
ever, in the H NMR data of 3, NOEs were observed
between the multiplet for H-5/6 and both H-8 and H-
3, in support of its stereostructure. Given these discrep-
ancies, 14a was subjected to diimide reduction to give

T. Aslam et al. / Tetrahedron Letters 46 (2005) 3249–3252
Br
3251
Br
OBn
BnO
OH
O
O
O
O
OMe
OMe
O
OMe
a
b
OBn
BnO
OBn
BnO
OBn
OBn
BnO
4
12
11
10
c
OBn
BnO
OBn
BnO
O
OBn
H
OH
O
8
7
H
7
10
9
8
d
O
O
+
OBn
O
OBn
OMe
BnO
OBn
OMe
O
OMe
3
H
H
H
BnO
OBn
BnO
OBn
BnO
OBn
13
14α
14β
f
e
OBn
BnO
OH
O
O
6
6
8
8
5
5
O
O
OMe
OMe
OBn
HO
OH
3
3
OBn
BnO
OH
HO
15
3
Scheme 2. Reagents and conditions: (a) i. DMSO, (COCl)2, DCM, ꢀ78 ꢁC, then Et3N; ii. CBr4, Ph3P, DCM, 0 ꢁC; (b) n-BuLi, THF, ꢀ78 to 0 ꢁC;
(c) n-BuLi, THF, ꢀ78 ꢁC, then 4; (d) BF3ÆEt2O, Et3SiH, DCM, ꢀ78 ꢁC; (e) Pd(OH)2/C, H2 (1 atm), MeOH; (f) dipotassium azodicarboxylate,
MeOH–pyridine, then HOAc.
the saturated compound 1521 (83%), which had also
2. Basso, L. A.; Blanchard, J. S. In Resolving the Antibiotic
been reported by the previous workers.10 This com-
pound, as prepared here, had spectroscopic data in full
Paradox; Resistance to Antitubercular Drugs; Rosen, B. P.,
Mobashery, S., Eds.; Plenum: New York, 1998; p 115.
3. Brennan, P. J.; Nikaido, H. Annu. Rev. Biochem. 1995, 64,
agreement with its structure, but at considerable vari-
29; Chatterjee, D. Curr. Opin. Chem. Biol. 1997, 1, 579.
1
ance from the data reported earlier.10 In the H NMR
4. Crick, D. C.; Mahapatra, S.; Brennan, P. J. Glycobiology
data of 15, NOEs were again observed between H-5/6
2001, 11, 107R.
and both H-8 and H-3. We thus must question the pre-
5. Besra, G. S.; Brennan, P. J. Biochem. Soc. Trans. 1997, 25,
845, and references cited therein.
6. Lee, R. E.; Brennan, P. J.; Besra, G. S. Glycobiology 1997,
7, 1121.
vious report on the synthesis of 3, and suggest that our
work constitutes the first definitive synthesis of this
compound.
7. Lee, R. E.; Mikusova, K.; Brennan, P. J.; Besra, G. S.
J. Am. Chem. Soc. 1995, 117, 11829.
8. For reviews of C-glycoside synthesis, see: (a) Levy, D. E.;
Tang, C. The Chemistry of C-Glycosides; Pergamon:
Oxford, 1995; (b) Postema, M. H. D. C-Glycoside
Synthesis; CRC: Boca Raton, FL, 1995; (c) Postema, M.
H. D.; Calimente, D. In Glycochemistry: Principles,
Synthesis and Applications; Wang, P. G., Bertozzi, C.,
Eds.; Marcel Dekker: New York, 2000; Chapter 4.
9. Dondoni, A.; Marra, A. Tetrahedron Lett. 2003, 44, 4067.
10. Gurjar, M. K.; Nagaprasad, R.; Ramana, C. V. Tetrahe-
dron Lett. 2002, 43, 7577.
Acknowledgements
We thank the EPSRC (T.A.) and the EU Socrates Pro-
gramme (A.Le F., M.G.G.F.) for financial support. We
also thank the EPSRC for access to the National Mass
Spectrometry Service Centre, University of Wales,
Swansea, and Dr. Alan Boyd (Heriot-Watt University)
for assistance with NMR data.
11. Rabinsohn, Y.; Fletcher, H. G. J. Org. Chem. 1967, 32,
3452.
References and notes
12. Selected data: 6a: [a]D +43.4 (c 1.0, CHCl3); dH (400 MHz,
CDCl3): 0.20 (9H, s, SiMe3), 3.58 (1H, dd, J 10.6, 4.9, H-
50a), 3.63 (1H, dd, J 10.6, 4.3, H-50b), 4.04 (1H, dd, J 5.8,
3.5, H-30), 4.20–4.27 (2H, m, H-20, H-40), 4.49–4.60 (5H,
1. Recent reviews: Stewart, G. R.; Robertson, B. D.; Young,
D. B. Nat. Rev. Microbiol. 2003, 1, 97; Raviglione, M. C.
Tuberculosis 2003, 83, 4.

3252
T. Aslam et al. / Tetrahedron Letters 46 (2005) 3249–3252
m, OCH2Ph), 4.68 (1H, d, J 11.6, OCH2Ph), 4.70 (1H, d, J
128.4 (Ph), 137.29 (Ph, q); m/z (ES) 356.1847 [(M+NH4)+;
C21H26NO4 requires 356.1856].
4.2, H-10), 7.20–7.40 (15H, m, Ph); dC (100 MHz, CDCl3):
ꢀ0.2 (SiMe3), 69.7 (C-50), 72.05, 72.1 (2 · OCH2Ph), 72.3
(C-10), 73.4 (OCH2Ph), 81.2 (C-40), 84.2 (C-30), 88.8 (C-
20), 91.8, 102.8 (alkyne), 127.6–128.4 (Ph), 137.4, 137.9.
138.1 (Ph, q). Compound 6b: [a]D ꢀ39.8 (c 1.3, CHCl3); dH
(400 MHz, CDCl3): 0.10 (9H, s, SiMe3), 3.59 (1H, dd, J
10.0, 6.6, H-50a), 3.69 (1H, dd, J 10.0, 5.9, H-50b), 3.93
19. Selected data: 14a: dH (400 MHz, CDCl3): 3.37 (3H, s,
OCH3), 3.59 (1H, dd, Jgem 10.6, J11a,10 5.0, H-11a), 3.63
(1H, dd, Jgem 10.6, J11b,10 5.0, H-11b), 3.94 (1H, dd, J2,3
3.5, J2,1 = 1.5, H-2), 4.02 (1H, dd, J9,10 5.9, J9,8 3.2, H-9),
4.09 (1H, ddd, J3,4 7.1, J3,2 3.5, J3,1 0.6, H-3), 4.23 (1H, t,
J8,7 ꢁ J8,9 ꢁ 3.2, H-8), 4.25 (1H, t, J10,9 ꢁ J10,11 ꢁ 5.0, H-
10), 4.44–4.65 (10H, m, Bn), 4.67 (1H, dd, J4,3 7.1, J4,7 1.5,
H-4), 4.80 (1H, dd, J7,8 3.5, J7,4 1.5, H-7), 4.92 (1H, dd,
J1,2 1.5, J1,3 0.5, H-1), 7.22–7.36 (25H, m, Ph); dC
(100 MHz, CDCl3): 55.2 (OCH3), 69.7 (C-11), 70.8 (C-
4), 72.0, 72.1 (OCH2Ph), 72.2 (C-7), 72.6, 73.4 (OCH2Ph),
81.6 (C-10), 83.8 (alkyne), 84.2 (C-9), 84.4 (alkyne), 87.9
(C-3), 88.2 (C-2), 88.8 (C-8), 107.2 (C-1), 127.6–128.5 (Ph),
137.35, 137.43, 137.47, 137.8, 138.1 (Ph, q); m/z (ES)
758.3693 [(M+NH4)+; C47H52NO8 requires 758.3687].
Compound 14b: dH (400 MHz, CDCl3): 3.36 (3H, s,
OCH3), 3.59 (1H, dd, Jgem 10.0, J11a,10 6.8, H-11a), 3.68
(1H, dd, Jgem 10.0, J11b,10 5.9, H-11b), 3.93–3.96 (2H, m,
H-2 and H-9), 4.00 (1H, dd, J8,7 4.1, J8,9 2.1, H-8), 4.06
(1H, dt, J10,11a ꢁ J10,11b ꢁ 6.2, J10,9 3.8, H-10), 4.12 (1H,
ddd, J3,4 6.8, J3,2 3.5, J3,1 0.6, H-3), 4.44–4.68 (10H, m,
Bn), 4.71 (1H, dd, J4,3 6.8, J4,7 1.5, H-4), 4.76 (1H, dd, J7,8
4.1, J7,4 1.5, H-7), 4.91 (1H, dd, J1,2 1.5, J2,3 0.6, H-1),
7.21–7.36 (25H, m, Ph); dC (100 MHz, CDCl3): 55.1
(OCH3), 70.4 (C-11), 71.0 (C-4), 71.4 (C-7), 71.7, 72.1,
72.3, 72.4, 73.3 (OCH2Ph), 82.1 (alkyne), 82.3 (C-10), 83.4
(C-8), 84.3 (C-9), 84.8 (alkyne), 87.6 (C-3), 88.1 (C-2),
107.2 (C-1), 127.6–128.4 (Ph), 137.44, 137.45, 137.6, 137.7,
138.1 (C).
20. Selected data for 3: dH (400 MHz, D2O): 1.76–1.85 (4H, m,
H-5, H-6), 3.42 (3H, s, OCH3), 3.70 (1H, dd, Jgem 12.3,
J11a,10 5.8, H-11a), 3.77 (1H, dd, Jgem 12.3, J11b,10 3.4, H-
11b), 3.84 (1H, ddd, J3,4 6.0, J3,2 3.3, J3,1 0.4, H-3), 3.86–
3.90 (1H, m, H-7), 3.89–3.93 (1H, m, H-10), 3.94 (1H, dd,
J8,7 6.7, J8,9 5.7, H-8), 3.40–4.01 (1H, m, H-4), 4.04 (1H,
dd, J9,10 6.5, J9,8 5.8, H-9), 4.05 (1H, dd, J2,3 3.3, J2,1 1.6,
H-2), 4.91 (1H, dd, J1,2 1.6, J1,3 0.4, H-1); dC (100 MHz,
D2O) 28.8 (CH2), 28.9 (CH2), 55.2 (OCH3), 61.7 (C-11),
77.3 (C-9), 80.4 (C-3), 80.7 (C-8), 81.5 (C-2), 82.1 (C-7),
82.6 (C-10), 83.5 (C-4), 108.4 (C-1); m/z (ES) 312.1658
[(M+NH4)+; C12H26NO8 requires 312.1653].
(1H, dd, J3 ;4 3.7, J3 ;2 1.9, H-30), 3.98 (1H, dd, J2 ;1 4.1,
0
0
0
0
0
0
J2 ;3 1.8, H-20), 4.02 (1H, ddd, J 6.6, 6.0, 3.7, H-40), 4.40–
4.62 (5H, m, OCH2Ph), 4.68 (1H, d, J 4.1, H-10), 4.69
(1H, d, J 12.4, OCH2Ph), 7.20–7.40 (15H, m, Ph); dC
(100 MHz, CDCl3): ꢀ0.3 (SiMe3), 70.3 (C-50), 71.66
(OCH2Ph), 71.7 (C-10), 72.0, 73.3 (2 · OCH2Ph), 82.3
(C-40), 83.3 (C-20), 84.6 (C-30), 93.0, 100.1 (alkyne), 127.6–
128.4 (Ph), 137.6, 137.9, 138.2 (Ph, q).
0
0
13. Calzada, E.; Clarke, C. A.; Roussin-Bouchard, C.; Wig-
htman, R. H. J. Chem. Soc., Perkin Trans. 1 1995,
517.
14. Selected data for 9: dH (400 MHz, CDCl3): 3.59 (2H, dd,
Jgem 10.6, J1a,2/J12a,11 5.0, H-1a/12a), 3.70 (2H, dd, Jgem
10.6, J1b,2/J12b,11 4.4, H-1b/12b), 4.03 (2H, dd, J3,2/J10,11
5.6, J3,4/J10,9 2.9, H-3/10), 4.23 (2H, t, J4,3/J9,10 ꢁ J4,5
/
/
J9,8 ꢁ 3.2, H-4/9), 4.26 (2H, dt, J2,3/J11,10 5.6, J2,1a
J11,12a ꢁ J2,1b/J11,12b ꢁ 4.9, H-2/11), 4.48 (2H, d, J 11.7,
OCH2Ph), 4.49 (2H, d, J 12.1, OCH2Ph), 4.53 (2H, d, J
12.1, OCH2Ph), 4.54 (2H, s, OCH2Ph), 4.56 (2H, s,
OCH2Ph), 4.61 (2H, d, J 11.7, OCH2Ph), 4.78 (2H, d, J
3.2, H-5/8), 7.23–7.36 (30H, m, Ph); dC (100 MHz,
CDCl3): 69.7 (C-1/12), 72.0 (OCH2Ph), 72.1 (OCH2Ph),
72.2 (C-5/8), 73.4 (OCH2Ph), 81.5 (C-2/11), 84.20 (C-3/10),
84.24 (C-6/7), 88.8 (C-4/9), 127.5–128.40 (Ph), 137.38,
137.81, 138.05 (Ph, q); m/z (ES) 848.4150 [(M+NH4)+;
C54H58NO8 requires 848.41].
15. Selected data for 2: dH (400 MHz, D2O): 1.78 (4H, m, H-6/
7), 3.69 (2H, dd, Jgem 12.3, J1a,2/J12a,11 5.9, H-1a/12a), 3.75
(2H, dd, Jgem 12.3, J1b,2/J12b,11 3.5, H-1b/12b), 3.83–3.90
(2H, br m, H-5/8), 3.89 (2H, td, J2,3/J11,10 ꢁ J2,1a
/
J11,12a ꢁ 6.2, J2,1b/J11,12b 3.5, H-2/11), 3.93 (2 · 1H, t,
J4,5/J9,8 ꢁ J2,3/J9,10 ꢁ 6.2, H-4/9), 4.03 (2H, t, J3,2
/
J10,11 ꢁ J3,4/J10,9 6.2, H-3/10); dC (100 MHz, D2O): 28.68
(C-6/7), 61.65 (C-1/12), 77.24 (C-3/10), 80.67 (C-4/9), 82.20
(C-5/8), 82.55 (C-2/11); m/z (ES) 295.1387 [(M+H)+;
C12H23O8 requires 295.1387].
21. Selected data for 15: dH (400 MHz, CDCl3): 1.62–1.89
(4H, m, H-5, H-6), 3.35 (3H, s, OMe), 3.52 (1H, dd, Jgem
10, J11a,10 5.9, H-11a), 3.59 (1H, dd, Jgem 10, J11b,10 5.6, H-
11b), 3.63 (1H, dd, J3,4 6.8, J3,2 2.9, H-3), 3.81 (1H, dd,
J 4.1, 2.6, H-8), 3.93 (1H, dd, J2,3 2.9, J2,1 0.9, H-2),
3.98–4.03 (3H, m, H-7, H-9, H-4), 4.19 (1H, dt,
J10,11a ꢁ J10,11b ꢁ 5.3, J10,9 4.1, H-10), 4.45–4.60 (10H,
m, 5 · OCH2Ph), 4.88 (1H, s, H-1), 7.22–7.38 (25H, m,
Ph); dC (100 MHz, CDCl3): d 29.39 (CH2), 29.45 (CH2),
54.6 (OCH3), 70.3 (C-11), 71.7, 71.8 (OCH2Ph), 72.0, 72.2,
73.3 (OCH2Ph), 80.5 (C-4), 81.2 (C-10), 82.1 (C-9), 85.4
(C-7), 87.2 (C-3), 87.8 (C-8), 88.6 (C-2), 106.7 (C-1),
127.6–128.42 (Ph), 137.6, 137.8, 137.91, 137.94, 138.2
(Ph, q); m/z (ES) 762.4002 [(M+NH4)+; C47H56NO8
requires 762.4000].
16. Montgomery, J. A.; Shortnacy, A. T.; Thomas, H. J. Med.
Chem. 1974, 17, 1197; Yin, H.; DꢀSousa, F. W.; Lowary,
T. L. J. Org. Chem. 2002, 67, 892.
17. Glaudemans, C. P. J.; Fletcher, H. G. J. Am. Chem. Soc.
1965, 87, 4637.
18. Selected data for 12: [a]D +60.8 (c 1.085, DCM); dH
(200 MHz, CDCl3): 2.62 (1H, d, J 2.1, H-6), 3.40 (3H, s,
OCH3), 3.98 (1H, dd, J2,3 3.3, J2,1 1.2, H-2), 4.15 (1H, dd,
J3,4 6.6, J3,2 3.3, H-3), 4.48 (1H, d, J 11.6, Bn), 4.55 (1H, d,
J 11.6, Bn), 4.60 (1H, d, J 11.6, Bn), 4.65 (1H, dd, J4,3 6.6,
J4,6 2.1, H-4), 4.71 (1H, d, J 11.6, Bn), 4.96 (1H, d, J 1.2,
H-1), 7.25–7.45 (10H, m, Ph); dC (50 MHz, CDCl3): 55.2
(OCH3), 70.6 (C-6), 72.0 (OCH2Ph), 72.5 (OCH2Ph), 75.1
(C-5), 80.7 (CH), 87.8 (CH), 87.9 (CH), 107.2 (C-1), 127.8,