Regioselective benzoylation of glycopyranosides by benzoyl chloride in the presence of MoO2(acac)2

Article abstract of DOI:10.1080/07328303.2010.549258

Benzoylation of methyl and benzyl glycopyranosides by benzoyl chloride in the presence of MoO₂(acac)₂ as a catalyst resulted in 3-benzoates with good yield and high regioselectivity. Simple synthesis of the monobenzoates of some glyc

Full text of DOI:10.1080/07328303.2010.549258

Journal of Carbohydrate Chemistry, 29:369–378, 2010
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C
Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328303.2010.549258
Regioselective Benzoylation of
Glycopyranosides by Benzoyl
Chloride in the Presence
of MoO2(acac)2
E. V. Evtushenko
Pacific Institute of Bioorganic Chemistry, Far East Branch of the Russian Academy
of Sciences, Vladivostok, Russia
Benzoylation of methyl and benzyl glycopyranosides by benzoyl chloride in the presence
of MoO2(acac)2 as a catalyst resulted in 3-benzoates with good yield and high regiose-
lectivity. Simple synthesis of the monobenzoates of some glycopyranosides is suggested.
Keywords Glycopyranosides; Regioselective benzoylation; Molybdenum
INTRODUCTION
It is well known that carbohydrates play important roles in biological
processes. However, synthesis of carbohydrates on the base protection/
deprotection strategy is multistep and laborious. Selective transformation of
hydroxyl groups of carbohydrates is fundamental and until now an unresolved
problem of organic chemistry. Partially benzoylated sugars can be useful as
intermediate substances in the oligosaccharide synthesis. The enzymes, gen-
erally lipases, often have been used for regioselective acylation of carbohy-
drates. Primary hydroxyl groups of sugars demonstrated high reactivity.[1] Tin
organic compounds[2–11]; cuprum,[12–14] mercury,[12] and nickel[15] chelates; cer-
tain amines[16,17]; BOP-Cl[18]; Le BOP[19]; Lewis acids[20–22]; silver(I) oxide[23,24]
;
phase-transfer catalysis[25]; Mitsunobu reaction[26]; and organocatalysis[27,28]
are used for regioselective acylation of carbohydrates. Good results are accom-
plished in certain occasions, but regioselective acylation still is a challenge.
Received July 12, 2010; accepted December 6, 2010.
Address correspondence to Evgeny V. Evtushenko, Pacific Institute of Bioorganic Chem-
istry, Far East Branch of the Russian Academy of Sciences, Pr Stoletiya Vladivostoka
159, 690022, Vladivostok, Russia. E-mail: evt@piboc.dvo.ru
369

E. V. Evtushenko
370
RESULTS AND DISCUSSION
It is known that carbohydrates form complexes with transition metals.[29–31]
It can be assumed that the nucleophilicity of complexed hydroxyl groups will
depend on metal as well as the geometry of intermediate complexes. Thus,
the complexation of carbohydrates may increase discrimination of reactivity of
hydroxyl groups in nucleophilic reactions.
Earlier[22] we found that the acetylation of methyl glycosides of pen-
toses and 6-deoxy hexoses by acetic anhydride in the presence of MoCl5
as a catalyst gave 3-acetates with good yield and high regioselectivity. We
decided to extend this approach with benzoylation of carbohydrates by
benzoic anhydride. It was observed that neither MoCl5 nor other transi-
tion metal salts as catalysts have been active in this reaction. However,
the benzoylation of methyl α-L-rhamnopyranoside (1) by benzoyl chloride
in 1,4-dioxane in the presence symm-collidine and MoCl5 and especially
dioxo-bis(2,4-pentanedionato)molybdenum(VI) (MoO2(acac)2) resulted in good
yields and high regioselectivity of 3-benzoate (Table 1, entries 2 and 3). It is
interesting that cis-vicinal hydroxyl groups in methyl α-L-rhamnopyranoside
(1) were benzoylated predominatingly even without a catalyst (Table 1, entry
1), although with lower yield and regioselectivity. It might be supposed that
near cis-vicinal hydroxyl groups form among themselves hydrogen bonds that
enhance the nucleophilicity of hydroxyl groups.[32]
The results of regioselective benzoylation of some glycopyranosides in
the presence of MoO2(acac)2 are summarized in Table 2. Benzoylation of
glycosides without a catalyst proceeds slowly with low regioselectivity. The
exceptions are methyl β-L-rhamnopyranoside (3) (entry 6) and methyl β-D-
ribopyranoside (8) (entry 16), which demonstrated preferential substitution
Table 1: Effect of solvent and catalyst on benzoylation of methyl
α-L-rhamnopyranosidea
Benzoates,%
Entry
Catalyst
Solvent
HO-2
HO-3
HO-4
5
Parent
55
Di
1
2
3
4
5
6
7
no
dioxane
dioxane
dioxane
DME
13
4
25
87
90
28
60
76
85
2
9
7
MoCl5
MoO2(acac)2
MoO2(acac)2
MoO2(acac)2
MoO2(acac)2
MoO2(acac)2
3
2
70
35
THF
5
EtAc
11
3
13
12
CH3CN
aRatios determined by 1H NMR.

Regioselective Benzoylation of Glycopyranosides
371
Table 2: Regioselective benzoylation of glycopyranosides by benzoyl chloride in
the presence of MoO2(acac)2
Benzoates, %a
Di +
HO-4 Tri
Entry Glycopyranoside
Catalyst
HO-2
HO-3
1
2
MoO2(acac)2
no
3
13
90 (86)
25
7
4
1
3
4
MoO2(acac)2
no
2
10
91 (86)
16
7
6
2
3
5
6
MoO2(acac)2 83 (76)
11
14
6
9
no
2
16
2
7
8
MoO2(acac)2
no
91 (85)
8
4
5
6
9
10
MoO2(acac)2
no
93 (86)
16
7
11
12
MoO2(acac)2
no
4
2
86 (81)
6
3
4
11
11
13
14
MoO2(acac)2
no
84 (78)
6
5
3
7
8
15
16
MoO2(acac)2
no
5
83 (77)
43
12
8
12
4
17
18
MoO2(acac)2
no
7
92 (87)
6
10
9
19
20
MoO2(acac)2
no
11
93 (86)
9
7
9
6
10
11
21
22
MoO2(acac)2
no
4
88 (82)
6
3
5
(Continued on next page)

E. V. Evtushenko
372
Table 2: Regioselective benzoylation of glycopyranosides by benzoyl chloride in
the presence of MoO2(acac)2 (Continued)
Benzoates, %a
Di +
HO-4 Di + Tri
Entry Glycopyranoside
Catalyst
HO-2
HO-3
23
24
MoO2(acac)2
no
2
10
89 (83)
16
9
3
12
13
25
26
MoO2(acac)2
no
2
4
88 (81)
17
10
2
5
7
b
27
28
MoO2(acac)2
nob
1
5
97 (90)
42
14
aDetermined by 1H NMR analysis of monobenzoate fractions, isolated yields in parentheses.
bAcylation by AcCl.
at OH-3. As can be seen from Table 2, entry 5, the benzoylation of methyl
β-L-rhamnopyranoside (3) gave 2-benzoate predominantly, obviously as a con-
sequence of the ꢀ2-effect and high electronic density on O-2. Other exam-
ples demonstrated high formation of 3-benzoates, rising for α-(4) and β-(5)
D-fucopyranosides (entry 7 and 9) and 6-O-trityl methyl (9) and benzyl (10) α-
D-galactopyranosides (entry 17 and 19) to 91%–93% from total yield and 100%
from monobenzoates.
We have found that the primary hydroxyl group in methyl 2,3,4-tri-O-
acetyl-α-D-glucopyranoside, in spite of space accessibility, has substituted to
42% in this condition. At the same time, 2- and 3-methyl ethers of methyl β-
D-xylopyranoside and the same glycoside have not reacted in the conditions of
this reaction. This means that isolated secondary hydroxyl groups and trans-
vicinal hydroxyl groups probably do not make intermediate complexes with
molybdenum.
It is interesting that acetylation of methyl α-L-rhamnopyranoside (1) (entry
28) by acetyl chloride, even without catalyst content of 3-acetate, yielded 42%
of the total mixture or 78% of the monoacetate fraction. The acetylation of the
same glycoside in the presence of catalyst gave almost a quantitative yield of
3-acetate.
In conclusion, we have presented a new simple method of regioselec-
tive 3-benzoylation of some glycopyranosides containing cis-vicinal hydroxyl
groups.

Regioselective Benzoylation of Glycopyranosides
373
EXPERIMENTAL
General Methods
Melting points were determined on a Boethius micro hot-stage apparatus
and were uncorrected. Optical rotations were measured with a Perkin-Elmer
1
model 141. Chloroform was used as a solvent. H and 13C NMR spectra were
recorded on a Bruker WM-300 spectrometer. CDCl3 was used as a solvent.
Chemical shifts (δ) are reported in ppm related to Me4Si. TLC was performed
on silica gel L (5–40 µm; Chemapol) with 97:3 CHCl3-MeOH solvent and de-
tection by charring with sulfuric acid. Column chromatography was performed
on silica gel (100–160 µm; Chemapol).
General Procedure for the Monobenzoylation
of Glycopyranosides
The solution of glycopyranoside (0.5 mmol), symm-collidine (1 mmol), and
catalyst (0.01 mmol) in 1,4-dioxane (4 mL) was allowed to stir at rt for 6 h.
BzCl (0.75 mmol) was added to the solution in three portions. The reaction was
monitored by TLC. Chloroform (20 mL) was added to the solution. The organic
layer was washed with 2-N HCl, saturated aqueous sodium bicarbonate and
water, and concentrated to a small volume under reduced pressure at rt. The
product was isolated by flash chromatography on a column of silica gel using
gradient acetone in hexane.
Monoacetylation of Methyl α-L-Rhamnopyranoside (1)
The solution of methyl α-L-rhamnopyranoside (1) (0.5 mmol), symm-
collidine (1 mmol), catalyst (0.01 mmol) and AcCl (0.75 mmol) in 1,4-dioxane (4
mL) was allowed to stir at rt for 3 h. The reaction was monitored by TLC. Cold
water (1 mL) was added. The mixture was concentrated to a small volume un-
der reduced pressure at rt. The product was isolated by flash chromatography
on a column of silica gel using gradient acetone in hexane.
Methyl 3-O-benzoyl-α-L-rhamnopyranoside
Yield 121 mg (86%). Rf 0.45, mp 49–51◦C (from EtOAc-hexane), [α]D
20
−54.9◦ (c 0.6, CHCl3). Lit data[11]: mp 34–35◦C, [α]D −54.0◦. 1H NMR δ:
17
8.10–8.02 (m, 2H, PhH), 7.61–7.54 (m, 1H, PhH), 7.47–7.40 (m, 2H, PhH), 5.26
(dd, 1H, J2,3 = 3.2 Hz, J3,4 = 9.5 Hz, H-3), 4.70 (d, 1H, J1,2 = 2.0 Hz, H-1), 4.15
(dd, 1H, H-2), 3.79 (m, 2H, H-4, H-5), 3.40 (s, 3H, OCH3), 1.38 (d, 3H, J5,6
=
5.9 Hz, CH3). 13C NMR δ: 166.9, 133.4, 129.8, 129.6, 128.4, 100.6, 75.5, 71.3,
69.7, 68.4, 54.9, 17.5. Anal. Calcd. for C14H18O6: C, 59.57; H, 6.43. Found: C,
59.42; H, 6.51.

E. V. Evtushenko
374
Benzyl 3-O-benzoyl-α-L-rhamnopyranoside
Yield 154 mg (86%). Rf 0.56, mp 67–69◦С (from EtAc-hexane), [α]D −79.1◦
(c 0.6, CHCl3).1H NMR δ: 8.12–8.07 (m, 2H, PhH), 7.65–7.56 (m, 1H, PhH),
7.51–7.43 (m, 2H, PhH), 7.40–7.30 (m, 5H, PhH), 5.36 (dd, 1H, J2,3 = 3.2 Hz,
J3,4 = 9.5 Hz, H-3), 4.92 (d, 1H, J1,2 = 1.8 Hz, H-1), 4.78 и 4.58 (2d, 2H, J =
20
12.0 CH2PH), 4.22 (dd, 1H, H-2), 3.87 (m, 2H, H-4, H-5), 1.41 (d, 3H, J5,6
=
5.9 Hz, CH3). 13C NMR δ: 167.0, 137.0, 133.5, 130.1, 129.9, 129.5, 128.5, 128.1,
98.7, 75.0, 71.5, 69.9, 69.2, 68.9, 17.6. Anal. Calcd. for C20 H22O6: C, 67.03; H,
6.19. Found: C, 66.98; H, 6.11.
Methyl 2-O-benzoyl-β-L-rhamnopyranoside
Yield 107 mg (76%). Rf 0.46 mp 99–100◦С (from EtAc-hexane), [α]D
20
1
+82.5◦ (c 0.4, CHCl3). H NMR δ: 8.10–8.06 (2H, m, PhH), 7.60–7.52 (1H, m,
Ph-H), 7.47–7.37 (2H, m, PhH), 5.57 (dd, 1H, J1,2 = 0.7 Hz, J2,3 = 3.3 Hz, H-2),
4.52 (d, 1H, H-1), 3.76 (dd, 1H, J3,4 = 9.2 Hz, H-3), 3.54 (t, 1H, J4,5 = 9.0 Hz,
H-4), 3.50 (s, 3H, OCH3), 3.39 (m, 1H, H-5), 1.43 (d, 3H, J5,6 = 6.1 Hz, CH3).
13C NMR δ: 167.0, 133.3, 130.1, 128.4, 100.0, 73.5, 73.4, 72.2, 72.1, 57.1, 17.6.
Anal. Calcd. for C14H18O6: C, 59.57; H, 6.43. Found: C, 59.50; H, 6.38.
Methyl 3-O-benzoyl-α-D-fucopyranoside
Yield 120 mg (85%). Rf 0.47, [α]D +136.7◦ (c 0.8, CHCl3). H NMR δ:
8.12–8.07 (2H, m, Ph), 7.60–7.55 (m, 1H, PhH), 7.47–7.42 (m, 2H, PhH), 5.29
(dd, 1H, J2,3 = 10.3 Hz, J3,4 = 3.2 Hz, H-3), 4.85 (d, 1H, J1,2 = 3.9 Hz, H-1),
4.14 (dd, 1H, Н-2), 4.07 (m, 1H, J5,6 = 6.7 Hz, H-5), 3.98 (m, 1H, H-4), 3.46
(s, 3H, OCH3), 1.31 (d, 3H, CH3). 13C NMR δ: 166.5, 133.5, 130.0, 128.5, 99.8,
74.7, 71.0, 67.2, 65.8, 55.6, 16.1. Anal. Calcd. for C14H18O6: C, 59.57; H, 6.43.
Found: C, 59.52; H, 6.48.
20
1
Methyl 3-O-benzoyl-β-D-fucopyranoside
Yield 122 mg (86%). Rf 0.44, mp 142–143◦С (from EtAc-hexane), [α]D
20
1
+52.4◦ (c 0.6, CHCl3). H NMR δ: 8.12–8.06 (2H, m, Ph), 7.59–7.53 (m, 1H,
PhH), 7.46–7.41 (m, 2H, PhH), 5.00 (dd, 1H, J2,3 = 10.2 Hz, J3,4 = 3.2 Hz,
H-3), 4.22 (d, 1H, J1,2 = 7.8 Hz, H-1), 3.90 (m, 1H, Н-4), 3.88 (dd, 1H, H-2),
3.70 (m, 1H, H-5), 3.52 (s, 3H, OCH3), 1.28 (d, 3H, J5,6 = 6.3 Hz, H-6 CH3).
13C NMR δ: 166.5, 133.4, 129.9, 128.5, 104.2, 76.3, 70.6, 70.2, 69.4, 57.2, 16.2.
Anal. Calcd. for C14H18O6: C, 59.57; H, 6.43. Found: C, 59.46; H, 6.40.
Methyl 3-O-benzoyl-α-L-arabinopyranoside
Yield 108 mg (81%). Rf 0.33, mp 140–141◦С, (from EtAc-hexane), [α]D
20
1
+48.6◦ (c 0,7, CHCl3). H NMR δ: 8.14–8.06 (2H, m, Ph-H), 7.64–7.56 (m, 1H,
PhH), 7.51–7.42 (m, 2H, PhH), 5.14 (dd, 1H, J2,3 = 9.5 Hz, J3,4 = 3.4 Hz, H-3),
4.29 (d, 1H, J1,2 = 7.1 Hz, H-1), 4.21 (m, 1H, H-4), 4.08 (dd, 1H, J4,5a = 2.9 Hz,
J5a,5b = 12.7 Hz, H-5a) 4.02 (dd, 1H, H-2), 3.70 (dd, 1H, J4,5b = 1.5 Hz, H-5b),

Regioselective Benzoylation of Glycopyranosides
375
3.60 (s, 3H, OCH3). 13C NMR δ: 166.8, 133.7, 129.9, 129.6, 128.4, 104.4, 75.3,
69.7, 67.2, 66.0, 57.1. Anal. Calcd. for C13H16O6: C, 58.20; H, 6.01. Found: C,
58.08; H, 6.13.
Methyl 3-O-benzoyl-β-L-arabinopyranoside
Yield 104 mg (78%). Rf 0.43, [α]D +192.4◦ (c 0.7, CHCl3). Lit. data[5]:
20
[α]D −179◦ (for D-isomer). 1H NMR δ: 8.12–8.08 (2H, m, PhH), 7.62–7.56 (1H,
25
m, PhH), 7.49–7.42 (2H, m, PhH), 5.32 (dd, 1H, J2,3 = 10.1 Hz, J3,4 = 3.1 Hz,
H-3), 4.88 (d, 1H, J1,2 = 3.8 Hz, H-1), 4.19 (m, 1H, H-4), 4.16 (dd, 1H, H-2) 3.93
(dd, 1H, J4,5a = 1.3 Hz, J5a,5b = 12.6 Hz, H-5a), 3.76 (dd, 1H, J4,5b = 2.3 Hz,
H-5b), 3.49 (s, 3H, OCH3). 13C NMR δ: 166.3, 133.4, 129.8, 129.6, 128.4, 100.1,
73.6, 68.2, 67.5, 62.3, 55.6. Anal. Calcd. for C13H16O6: C, 58.20; H, 6.01. Found:
C, 58.12; H, 6.11.
Methyl 3-O-benzoyl-β-D-ribopyranoside
Yield 103 mg (77%). Rf 0.46, mp 104–105◦С (from EtAc-hexane), [α]D
20
1
−97.9◦ (c 0.6, CHCl3). H NMR δ: 8.13–8.05 (2H, m, Ph), 7.63–7.56 (m, 1H,
PhH), 7.50–7.41 (m, 2H, PhH), 5.28 (t, 1H, J2,3 = J3,4 = 3.2 Hz, H-3), 4.84 (d,
1H, J1,2 = 2.3 Hz, H-1), 4.19 (m, 1H, H-4), 4.04 (m, 1H, H-2), 3.98 (dd, 1H,
J4,5a = 1.7, J5a,5b = 12.5 Hz, H-5a), 3.85 (dd, 1H, J4,5b = 2.5 Hz, H-5b), 3.46 (s,
3H, OCH3). 13C NMR δ: 165.8, 133.5, 130.0, 128.5, 102.0, 69.8, 69.3, 68.6, 63.4,
55.5. Anal. Calcd. for C13H16O6: C, 58.20; H, 6.01. Found: C, 58.26; H, 6.10.
Methyl 3-O-benzoyl-6-О-trityl-α-D-galactopyranoside
Yield 235 mg (87%). Rf 0.63, mp 80–81◦С (from EtAc-hexane), [α]D +53.3◦
20
(c 0.6, CHCl3). 1H NMR δ: 8.14–8.10 (m, 2H, Ph-H), 7.65–7.60 (m, 1H, PhH),
7.51–7.42 (m, 8H, PhH), 7.37–7.23 (m, 9H, PhH), 5.29 (dd, 1H, J2,3 = 10.2 Hz,
J3,4 = 3.0 Hz, H-3), 4.94 (d, 1H, J1,2 = 3.9 Hz, H-1), 4.25 (bd, 1H, H-4), 4.23 (dd,
1H, H-2), 3.97 (bt, 1H, J5,6a = J5,6b = 5.4, H-5), 3.50 (s, 3H, OCH3), 3.45 (m, 2H,
H-6a, H-6b). 13C NMR δ: 166.5, 143.7, 133.2, 129.9, 128.6, 128.4, 128.0, 127.2,
99.8, 74.2, 69.1, 69.0, 67.4, 63.4, 55.5. Anal. Calcd. for C33H32O7: C, 73.32; H,
5.97. Found: C, 73.36; H, 6.05.
Benzyl 3-O-benzoyl-6-О-trityl-α-D-galactopyranoside
Yield 265 mg (86%). Rf 0.77, mp 84–85◦С (from EtAc-hexane), [α]D +94.7◦
20
(c 0.6, CHCl3). 1H NMR δ: 8.16–8.12 (m, 2H, PhH), 7.64–7.58 (m, 1H, PhH),
7.54–7.25 (m, 22H, PhH), 5.36 (dd, 1H, J2,3 = 10.2 Hz, J3,4 = 3.0 Hz, H-3), 5.21
(d, 1H, J1,2 = 4.0 Hz, H-1), 4.87 (d, 1H, Jgem = 11.7 Hz, CH2Ph), 4.68 (d, 1H,
CH2Ph), 4.30 (dd, 1H, H-2), 4.28 (bd, 1H, H-4), 4.08 (bt, 1H, J5,6a = J5,6b
=
5.2 Hz, H-5), 3.42 (m, 2H, H-6a, H-6b). 13C NMR δ: 166.4, 143.5, 136.8, 133.2,
129.8, 128.5, 128.3, 128.1, 128.0, 127.9, 127.1, 98.0, 74.1, 69.9, 69.2, 69.1, 67.3,
63.4. Anal. Calcd. for C39H36O7: C, 75.96; H, 5.88. Found: C, 76.02; H, 5.94.

E. V. Evtushenko
376
Methyl 3-O-benzoyl-6-О-trityl-β-D-galactopyranoside
Yield 221 mg (82%). Rf 0.66, mp 76–77◦С (from EtAc-hexane), [α]D +15.6◦
20
1
(c 0.6, CHCl3). H NMR δ: 8.05–8.01 (m, 2H, PhH), 7.53–7.46 (m, 1H, PhH),
7.42–7.33 (m, 6H, PhH), 7.27–7.13 (m, 11H, PhH), 5.01 (dd, 1H, J2,3 = 10.1
Hz, J3,4 = 3.2 Hz, H-3), 4.24 (d, 1H, J1,2 = 7.6 Hz, H-2), 4.20 (bd, 1H, H-4), 3.62
(dt, 1H, J4,5 = 0.8 Hz, J5,6a = J5,6b = 5.5 Hz, H-5), 3.53 (s, 3H, OCH3), 3.37
(m, 2H, H-6a, H-6b). 13C NMR δ: 166.2, 143.5, 133.2, 129.8, 129.6, 128.5, 128.3,
127.8, 127.1, 104.2, 75.7, 73.3, 69.5, 68.0, 62.8, 57.0. Anal. Calcd. for C33H32O7:
C, 73.32; H, 5.97. Found: C, 73.36; H, 6.02.
Methyl 3-O-benzoyl-6-О-trityl-α-D-mannopyranoside
Yield 224 mg (83%). Rf 0.65, mp 74–75◦С (from EtAc-hexane), [α]D +22.2◦
20
1
(c 0.6, CHCl3). H NMR δ: 8.13–8.07 (m, 2H, PhH), 7.62–7.43 (m, 9H, PhH),
7.37–7.23 (m, 9H, PhH), 5.35 (dd, 1H, J2,3 = 3.3 Hz, J3,4 = 9.7 Hz, H-3), 4.79
(d, 1H, J1,2 = 1.9 Hz, H-1), 4.16 (dd, 1H, H-2), 4.11 (t, 1H, J4,5 = 9.7 Hz, H-4),
3.84 (m, 1H, H-5), 3.52 (m, 2H, H-6a, H-6b), 3.46 (s, 3H, OCH3). 13C NMR δ:
166.4, 143.6, 133.2, 129.8, 128.6, 128.3, 127.9, 127.1, 100.5, 74.9, 70.7, 69.2,
67.7, 64.6, 54.9. Anal. Calcd. for C33H32O7: C, 73.32; H, 5.97. Found: C, 73.39;
H, 6.07.
Benzyl 3-O-benzoyl-6-О-trityl-α-D-mannopyranoside
Yield 250 mg (81%). Rf 0.75, [α]D +29.5◦ (c 0,6, CHCl3). 1H NMR δ:
20
7.24–8.12 (m, 25H, PhH), 5.44 (dd, 1H, J2,3 = 3.2 Hz, J3,4 = 9.7 Hz, H-3),
4.99 (d, 1H, J1,2 = 1.7 Hz, H-1), 4.84 (d, 1H, Jgem = 11.9 Hz, PhCH2), 4.62 (d,
1H, PhCH2), 4.23 (dd, 1H, H-2), 4.15 (t, 1H, J4,5 = 9.7 Hz, H-4), 3.95 (m, 1H,
H-5), 3.53 (m, 2H, H-6a, H-6b). 13C NMR δ: 166.4, 143.6, 133.5, 133.3, 129.8,
128.6, 128.4, 128.3, 128.0, 127.9, 127.1, 98.3, 75.0, 71.1, 69.5, 69.0, 67.9, 64.5.
Anal. Calcd. for C39H36O7: C, 75.96; H, 5.88. . Found: C, 76.05; H, 5.90.
Methyl 3-O-acetyl-α-L-rhamnopyranoside
Yield 99 mg (90%). The properties are as according to literature data.[22]
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