Role of the side chain stereochemistry in the α-glucosidase inhibitory activity of kotalanol, a potent natural α-glucosidase inhibitor. Part 2

Bioorganic & Medicinal Chemistry 20 (2012) 6321–6334

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Bioorganic & Medicinal Chemistry

journal homepage: w ww.elsevier.com/locate/bmc

Role of the side chain stereochemistry in the

a-glucosidase inhibitory activity of

kotalanol, a potent natural

a

-glucosidase inhibitor. Part 2

Genzoh Tanabe ^a, Kanjyun Matsuoka ^a, Masahiro Yoshinaga ^a, Weijia Xie ^b,, Nozomi Tsutsui ^a,

⇑

Mumen F. A. Amer ^a, Shinya Nakamura ^a, Isao Nakanishi ^a, Xiaoming Wu ^b, Masayuki Yoshikawa ^c,

Osamu Muraoka ^a,

⇑

^aSchool of Pharmacy, Kinki University, 3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502, Japan

^bDepartment of Medicinal Chemistry, China Pharmaceutical University, 24 Tongjia Xiang, Nanjing, Jiang Su 210009, People’s Republic of China

^cKyoto Pharmaceutical University, 1 Shichono-cho, Misasagi, Yamashina-ku, Kyoto 607-8412, Japan

a r t i c l e i n f o

a b s t r a c t

Article history:

To examine the role of the side chain of kotalanol (2), a potent natural

a-glucosidase inhibitor isolated

Received 1 August 2012

Revised 1 September 2012

Accepted 5 September 2012

Available online 13 September 2012

from Salacia reticulata, on inhibitory activity, four diastereomers (11a–11d) with reversed conﬁguration

(S) at the C-4⁰position in the side chain were synthesized and evaluated. Two of the four (11b and 11d)

signiﬁcantly lost their inhibitory activity against both maltase and sucrase, while the other two (11a and

11c) sustained the inhibitory activity to a considerable extent, showing distinct activity in response to the

change of stereochemistry of the hydroxyls at the 5⁰and 6⁰positions. Different activities were rationalized

with reference to in silico docking studies on these inhibitors with hNtMGAM. Against isomaltase, all four

analogs showed potent inhibitory activity as well as 2, and 11b and 11d exhibited enzyme selectivity.

Keywords:

Salacinol

Kotalanol

a-Glucosidase inhibitor sulfonium salts

In silico docking study

1. Introduction

OH OH OH

OH

3'S

5'R

OH

6'S

1' 2'S

4'R

OH

In the late 1990s the highly potent

a-glucosidase inhibitor,

S⁺OR

OH

salacinol (1), was isolated from Salacia reticulata, a traditional

Ayurvedic medicine that has been used for the treatment of diabe-

tes in Sri Lanka and the southern region of India.¹The structure of

1, established by X-ray crystallographic analysis, was quite unique.

Speciﬁcally, the ring sulfonium ion was stabilized by the sulfate

counter anion through spirobicyclic-like conﬁguration comprised

HO

OH

HO

-

salacinol (1) : R = SO₃

kotalanol (2) : R = SO₃

neosalacinol (5) : R = H

neokotalanol (6) : R = H

of 1-deoxy-4-thio-

D

-arabinofranosyl cation and 1-deoxy-

L-erythro-

syl-3-sulfate anion.¹The

a

-glucosidase inhibitory activity of 1 was

OH

OH OH

potent and was revealed to be as strong as that of voglibose and

acarbose, which have been widely used clinically.¹The related

sulfonium sulfate, kotalanol (2), was subsequently isolated from

Salacia extracts and was shown to possess even higher inhibitory

OH

S⁺OR

HO

S⁺

OH

OR

HO

power against

a

-glucosidases.²Human clinical trials, conducted

OH

salaprinol (4) : R = SO₃

HO

OH

ponkoranol (3) : R = SO₃

HO

with a Salacia reticulata extract on patients with type-2 diabetes

have shown effective treatment with minimal side effects.³There-

after, the side chain analogues, ponkolanol⁴(3) and salaprinol⁴(4),

as well as the de-O-sulfonated analogues, neosalacinol⁵(5), neok-

otalanol⁶(6), neoponkoranol⁷(7), and neosaraprinol⁷(8), were also

isolated from the same plant genus (Fig. 1). Other than 4 and 8,

-

neosalaprinol (8) : R = H

neoponkoranol (7) : R = H

Figure 1. Thiosugar sulfonium salts as a new class of a-glucosidase inhibitors.

these sulfonium salts (3, 5, 6, and 7) were shown to have

sidase inhibitory activities similar to 1 and 2.^4–7

a-gluco-

⇑

Because of sulfonium salts’ intriguing structures and high

-glucosidase inhibitory activities, intensive structure–activity

Corresponding authors.

E-mail address: muraoka@phar.kindai.ac.jp (O. Muraoka).

a

http://dx.doi.org/10.1016/j.bmc.2012.09.006

6322

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

OH OH OH

O

S

O

OMOM

5'

OH

6'

4'R

S⁺

S

OH

-

OSO₃

HO

OMOM

O

HO

11

O

OH

HO

OH

HO

13

12

9

a : 5'α-OMOM, 6'α-OMOM b : 5'β-OMOM, 6'β-OMOM

c : 5'α-OMOM, 6'β-OMOM d : 5'β-OMOM, 6'α-OMOM

a : 5'α-OH, 6'α-OH

c : 5'α-OH, 6'β-OH d : 5'β-OH, 6'α-OH

Scheme 1. The key step for the synthesis of 11a–11d.

OH OH OH

3'R

3'S

5'

OH

HO

5'

OH

6'

4'S

followed by the reduction of sodium borohydride of the resulting

S⁺

OH

keto sugar to give a desired epimer of 16, 5-O-tert-butyldimethylsi-

-

OSO₃

HO

lyl-1,2-O-isopropylidene-a-D

-ribofuranose¹³(17), in good yield.

The TBS moiety of 17 was selectively hydrolyzed with diluted

hydrochloric acid and subsequent dibenzylation of the resulting

diol with benzyl (Bn) bromide gave 3,5-di-O-benzyl-1,2-O-isopro-

OH

HO

OH

HO

10

11

pylidene-a-D

-ribofuranose^12b,14(18) in 81% yield from 16. The ace-

a : 5'α-OH, 6'α-OH b : 5'β-OH, 6'β-OH

c : 5'α-OH, 6'β-OH d : 5'β-OH, 6'α-OH

tal moiety of 18 was removed by the action of 0.5% aqueous sulfuric

acid in 1,4-dioxane to give 14 as a ca. 1:1.5 anomeric mixture.

Figure 2. Kotalanol (2) and its side chain diastereomers.

Next, the mixture of two anomers (

tert-butoxycarbonylmethylenetriphenylphosphorane to give tert-

butyl (E)-5,7-di-O-benzyl-2,3-dideoxy- -ribo-hept-2-enoate (E-

a and b-14) was treated with

D

relationship (SAR) studies have been conducted.⁸Heterocyclic ana-

logues, six-membered ring analogues, and those with different

thiosugar stereochemistry, as well as their side chain stereoiso-

mers, were extensively synthesized, by replacing the sulfonium

center by a selenonium or an ammonium ion, and evaluated.

Important structural determinants for the inhibitory activities

have been revealed by this work.⁸The exact stereo-structure of

the side chains of 1, 3, and 4 were elucidated soon after their iso-

lation by total syntheses⁹and/or through the SAR studies^8l–nde-

scribed above; that of 2 was recently clariﬁed by total synthesis

performed by Pinto and co-workers.¹⁰In that process, side chain

diastereomers (9a, 9c, and 9d) of 2 were synthesized and some

important stereo-structural factors of the side chain activity were

revealed.^8d,8f

19), and its Z-isomer (Z-19) in 73% and 15% yields, respectively.

The major 1,3-diol E-19 was then converted to the corresponding

acetal, tert-butyl (E)-5,7-di-O-benzyl-2,3-dideoxy-4,6-O-isopropyl-

idene-D-ribo-hept-2-enoate (E-20), by treatment with 2,2-dimet-

oxypropane. Subsequent reduction of the crude products with

diisopropyl aluminum hydride (DIBAL) gave E-allyl alcohol, (E)-

5,7-di-O-benzyl-2,3-dideoxy-4,6-O-isopropylidene-D-ribo-hept-2-

enitol (E-21), in 93% yield from enoate E-19. In a similar manner,

the minor enoate Z-19 was converted to the corresponding Z-allyl

alcohol (Z-21) in good yield. With compounds E- and Z-21 in hand,

osmium tetroxide catalyzed dihydroxylation was performed in the

presence of N-methylmorphorine N-oxide (NMO). Upon reaction

with E-allyl alcohol E-21, a ca. 3:1 mixture of two triols, 1,3-di-O-

benzyl-2,4-O-isopropylidene-D-glycero-

L-allo-heptitol (22a) and

In the course of our independent efforts to elucidate the struc-

ture of 2, a group of diastereomers (10a, 10b, 10c, and 10d), which

have reversed stereochemistry to 2 at both C-3⁰and C-4⁰positions,

were also synthesized. SAR studies on the diastereomers had con-

ﬁrmed the known stereo-structural factors of the side chain activ-

ity.¹¹In this continuing study, we synthesized and evaluated four

sulfonium sulfates (11a, 11b, 11c, and 11d) in which stereochem-

istry at C-4⁰is diverted to S as a common feature (Fig. 2). Evaluation

5,7-di-O-benzyl-4,6-O-isopropylidene-

D

-glycero- -gluco-heptitol

D

(22b), was obtained. Newly developed threo stereochemistry of tri-

ols 22a and 22b was conﬁrmed after leading them to the known

heptitols,

D-glycero-L D-glycero-D-gluco-

-allo-heptitol¹⁵(23a) and

heptitol¹⁵(23b). Dihydroxylation of Z-isomer Z-21 in a similar

manner gave a ca. 1:1 mixture of 5,7-di-O-benzyl-4,6-O-isopropyl-

idene-

D

-glycero-

D-allo-heptitol (22c) and 5,7-di-O-benzyl-4,6-O-

isopropylidene-

D

-glycero- -manno-heptitol (22d). The erythro ste-

D

and comparison of the a-glucosidase inhibitory activities of these

reochemistry at the 5 and 6 positions of 22c and 22d was also con-

ﬁrmed after derivatization to 23c¹⁵and 23d,¹⁵respectively.

(Scheme 2)

A mixture of triols 22a and 22b was then treated with chloro-

methyl methyl ether (MOMCl) to give 1,3-di-O-benzyl-2,4-O-iso-

sulfonium sulfates with those of 2 and related diastereomers pro-

vided additional stereo-structural factors for the inhibitory activ-

ity. This suggested another binding mode and/or binding sites

between the inhibitors and enzymes.

propylidene-5,6,7-tri-O-methoxymethyl-

and

D

-glycero-

5,7-di-O-benzyl-4,6-O-propylidene-1,2,3-tri-O-methoxy-

-glycero- -gluco-heptitol (24b) in 68% and 23% yields from

mixture of 22c and 22d was

converted to 5,7-di-O-benzyl-4,6-O-isopropylidene-1,2,3-tri-O-

methoxymethyl- -glycero- -allo-heptitol (24c) and 5,7-di-O-

benzyl-4,6-O-isopropylidene-1,2,3-tri-O-methoxymethyl- -glycero-

-manno-heptitol (24d) in 42% and 45% yields from Z-21,

L-allo-heptitol (24a)

2. Results and discussion

methyl-

D

2.1. Preparation of cyclic sulfates

E-21,respectively. Similarly, a

The target compounds (11a–11d) were prepared by the regiose-

lective ring-opening reaction of cyclic sulfates (12a–12d) with a

D

thiosugar, 1,4-dideoxy-1,4-epithio-

reaction (Scheme 1).⁹A common synthon for the four cyclic

sulfates (12a–12d), 3,5-di-O-benzyl-

-ribofuranose¹²(14) was se-

lected and prepared by conversion of the C-3 stereochemistry

starting from commercially available -xylose (15).

Thus, 5-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-

xylofuranose^8m(16) was subjected to Swern oxidation. This was

D

-arabinitol (13), as the key

D

respectively. The tri-MOM ethers (24a–24d) obtained were then

subjected to hydrogenolysis in the presence of a small amount of

sodium hydrogen carbonate, which was added to avoid

undesirable deprotection of acid-labile protecting groups by a

contaminated acid arising from the Pd–C catalysts,¹⁶to give

corresponding diols: 2,4-O-isopropylidene-5,6,7-tri-O-methoxy-

D

a-D-

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6323

O

OH

O

OH

R¹O

O

BnO

e

TBSO

HO

O

a,b

O

lit.8m

OH

D-xylose (15)

HO

R²O

17 : R¹= TBS, R²= H

HO

BnO

14

16

c,d

: R¹= R²= Bn

18

O

OH OH

g

CO₂^tBu

R

i

OBn OBn

: R = CO₂^tBu

: R = CH₂OH

-19

E

E-20

E

j

O

OH

OH OH OH

h

-21

f

OH

5

3

OH

1

7

2

+

OBn OBn OH

OH OH OH

i

23

CO₂^tBu

22

O

R

OH OH

g

c

a

: 5'α-OH, 6'β-OH

: 5'α-OH, 6'α-OH

d : 5'β-OH, 6'α-OH

b : 5'β-OH, 6'β-OH

OBn OBn

: R = CO₂^tBu

-20

Z

Z-19

h

Z-21 : R = CH₂OH

Scheme 2. Reagents and conditions: (a) (COCl)₂, DMSO, CH₂Cl₂, –60 to –30 °C, then NEt₃; (b) NaBH₄, EtOH, H₂O, –30 to 10 °C; (c) 0.2% aq HCl, THF, rt; (d) BnBr, NaH, DMF,

0 °C; (e) 0.5% aq H₂SO₄, 1,4-dioxane, reﬂux; (f) Ph₃P@CHCO₂^tBu, CH₂Cl₂, reﬂux; (g) (CH₃)₂C(OCH₃)₂, p-TsOH, acetone, rt; (h) 1 M soln. of DIBAL in toluene, THF, –60 °C to rt; (i)

OsO₄, NMO, acetone, H₂O, reﬂux, (j) H₂, Pd–C, 80% aq AcOH, 60 °C.

the diols (25a–25d) were converted to the desired cyclic sulfates

(12a–12d) by cyclic sulfation in 43–75% yields (Scheme 3).

OR¹

O

The spectroscopic properties of these cyclic sulfates were very

similar. All the products (12a–12d) showed protonated molecu-

lar-ion [M+H]⁺peaks at m/z 447 in their fast atom bombardment

(FAB) mass spectra. In their ¹H NMR spectra, highly deshielded sig-

nals due to C-1 methylene and C-3 methine protons were observed

at around d 4.5–4.9 [i.e., for 12a: d_H4.46 (H-1_eq), 4.60 (H-1_ax), and

d_H4.87 (H-3)], supporting the cyclic sulfate formation. Large vici-

nal coupling constants (J_2,3= 9.8 and J_3,4= 9.8 Hz) were observed

for 12a, which indicated that three protons at C-2, C-3, and C-4

were in axial orientation. With regard to compound 12b, ﬁne single

crystals were obtained, and structural conﬁrmation was also estab-

lished based on X-ray crystallographic analysis (Fig. 3).

OR¹

O

S

O

OMOM

3

1

c

OR²OR²OR¹

5

OMOM

7

2

22 : R¹= H, R²= Bn

24 : R¹= MOM, R²= Bn

25 : R¹= MOM, R²= H

a

b

O

OMOM

O

12

a : 2α-OH, 3α-OH

b : 2β-OH, 3β-OH

c : 2α-OH, 3β-OH

d : 2β-OH, 3α-OH

i

Scheme 3. Reagents and conditions: (a) MOMCl, Pr₂NEt, DMF, 60 °C; (b) H₂, Pd-C,

NaHCO₃, 1,4-dioxane, 60 °C; (c) SOCl₂, NEt₃, CH₂Cl₂, 0 °C, then NaIO₄, RuCl₃ꢀn-H₂O,

NaHCO₃, CH₃CN, CCl₄, H₂O, 0 °C.

2.2. Preparation of kotalanol analogues (11a, 11b, 11c, and 11d)

The coupling reaction of thiosugar 13 and the cyclic sulfates

(12a–12d) proceeded at 60 °C in 1,1,1,3,3,3-hexaﬂuoroisopropanol

(HFIP) to give corresponding sulfoniums (26a–26d) in 91, 90, 86,

and 92% yield, respectively (Scheme 4). The spectral properties of

the products (26a–26d) were similar. In the FAB mass spectra

run in a positive mode the peaks observed at m/z 597 corresponded

to the protonated molecular-ion [M+H]⁺. In the ¹H NMR spectrum,

downﬁeld signal shifts associated with sulfonium ion formation,

were observed due to C-1 methylene (around d_H3.8) and C-4

methine (around d_H4.0) protons. A pair of one-proton doublet of

doublets, which appeared at around d_H4.0 due to methylene pro-

tons

a to the sulfur atom in the side chain, also supported the sul-

fonium ion formation. The relative stereochemistry between the

side chain and the methanol moiety at C-4 of all the coupled prod-

ucts (26a–26d) was determined to be in trans on the basis of nucle-

ar Overhauser effect (NOESY) experiments, as shown in Scheme 4.

Deprotection of 26a, 26b, 26c, and 26d, by the action of 30% aque-

ous triﬂuoroacetic acid, gave the target sulfonium salts 11a, 11b,

11c, and 11d in 78, 82, 92, and 95% yields, respectively. All the

compounds showed protonated molecular-ion peaks [M+H]⁺at

m/z 425; their molecular formula C₁₂H₂₄O₁₂S₂was conﬁrmed by

the HR–FAB mass spectra. The ¹³C NMR spectroscopic properties

of the products are shown in Table 1.

Figure 3. Perspective view of compound 12b.

methyl-

tri-O-methoxymethyl-

propylidene-1,2,3-tri-O-methoxymethyl-

(25c), and 4,6-O-isopropylidene-1,2,3-tri-O-methoxymethyl-

cero- -manno-heptitol (25d) in approximately 95% yield. Finally,

D

-glycero-

L

-allo-heptitol (25a), 4,6-O-isopropylidene-1,2,3-

-glycero- -gluco-heptitol (25b), 4,6-O-iso-

-glycero- -allo-heptitol

-gly-

D

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G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

OMOM

MOMO

O

OH

6'S

O

OH OH

OH

6'R

OMOM

-

3'S

5'S

OH

3'S

5'S

4'S

2'S

OH

OMOM

-

4'S

2'S

b

3'

OSO₃

b

S⁺

OH

O

H

2'

1'

S⁺

OH

-

OSO₃

OH

11c

HO

-

S⁺

OSO₃

H

S⁺

HO

Ha

Hb

1

HO

H ₅

4

HO

OH

11a

HO

26c

OH

3

a

H

HO

OH

NOE

S

26a

HO

OMOM

MOMO

OH

HO

MOMO

13

O

a

OMOM

-

a

OH

OH OH

5'R

O

OMOM

-

3'S

OH

6'S

OSO₃

4'S

2'S

6'R

b

3'S

5'R

b

OSO₃

OH

S⁺

OH

4'S

2'S

S⁺

-

OSO₃

HO

S⁺

OH

HO

-

OSO₃

OH

11b

HO

OH

11d

HO

OH

HO

OH

HO

26d

Scheme 4. Reagents and conditions: (a) cyclic sulfate 12a, 12b, 12c or 12d, HFIP, K₂CO₃, 60 °C; (b) 30% aq TFA, 50 °C.

26b

Table 1

¹³C NMR data for kotalanol (2), 11a, 11b, 11c and 11d

diastereomers (10a–10d), as shown in Table 2. In addition to the

fundamental requirements for the thiosugar moiety, based on the

intensive SAR studies, several important determinants with respect

to the length and stereostructure of the side chain have been

revealed: (a) 2⁰S-OH is essential for the activity; (b) a polyhydroxy-

lated side chain longer than four carbons does not signiﬁcantly

enhance the inhibitory activity; (c) the cooperative role of 2⁰S-OH

and 4⁰-OH is critical for onset of strong inhibition; and the R

conﬁguration of OH at C4⁰is imperative to inhibitors bearing a side

chain of more than four carbons.

2^b

11a^a

11b^a

11c^b

11d^a

C-1

C-2

C-3

C-4

C-5

C-1⁰

C-2⁰

C-3⁰

C-4⁰

C-5⁰

C-6⁰

C-7⁰

51.1

79.0

79.9

73.0

60.8

53.3

67.8

79.0

69.9

70.5

71.8

65.1

51.5

79.2

79.7

73.3

61.0

52.7

68.0

81.9

72.6

72.2

71.8

64.7

51.7

79.3

79.6

73.1

60.9

51.7

69.3

80.2

73.2

70.8

74.8

64.0

51.5

79.2

79.7

73.3

61.0

52.5

67.9

81.0

73.9

73.8

74.3

64.4

51.7

79.3

79.6

73.2

60.9

51.6

69.7

79.9

70.9

71.2

72.4

65.1

As shown in Table 2, all four diastereomers (11a–11d) synthe-

sized in this study showed less activity than kotalanol (2) against

maltase and sucrase. In particular, two (11b and 11d) lost consid-

erable activity against these two enzymes, which is consistent with

the previously known determinants [(a), (b), (c)]. However, it is

noteworthy that among the eight diastereomers (10a–10d, 11a–

11d) with 4⁰S-OH conﬁguration, two isomers (11a and 11c), which

have the reverse stereochemistry at the C5⁰position (5⁰S-OH) to 2,

retained moderate activity against maltase and sucrase. The other

six isomers lost considerable activity. The present results suggest

that the OH groups at the C5⁰and C6⁰positions play a role in bind-

ings with these enzymes and/or contribute to conformational sta-

bilization of the polyhydroxylated chain by any intramolecular

hydrogen bonding, although the previous SAR studies suggested

that polyhydroxylated side chains longer than four carbons do

not enhance inhibitory activity signiﬁcantly (determinant b).

In humans, family GH31 glycoside hydrolases maltase-glucoam-

ylase (MGAM) and sucrase-isomaltase (SI) are responsible for the

digestion of terminal starch products left after the action of R-

amylase. These membrane-bound enzymes are known to contain

two catalytic subunits: an N-terminal subunit (ntMGAM and ntSI),

which is proximal to the membrane-bound end and a C-terminal

luminal subunit (ctMGAM and ctSI). Rat intestinal maltase is known

to be homologous to hNtMGAM.¹⁷The substrate speciﬁcities of the

catalytic subunits vary and overlap to include maltose, isomaltose,

sucrose, and small linear and branched oligosaccharides.¹⁸

a

Measured at 125 MHz.

Measured at 150 MHz, in CD₃OD.

b

Table 2

IC₅₀values (lM) of thiosugar sulfonium sulfate inner salts against disaccharidases

Entry

Compd

Maltase

Sucrase

Isomaltase

1

2

3

4

5

6

7

8

9

10

1^a

5.2

7.2

1.6

0.75

1.3

5.7

16

20

21

58

1.6

11

6.5

16

2^a

10a

10b

10c

10d

11a

11b

11c

11d

>236 (25)^b

>236 (32)^b

>236 (45)^b

134

>236 (8)^b

>236 (28)^b

>236 (34)^b

55

49

67

136

32

214

>236 (42)^b

58

>236 (44)^b

a

Lit.4.

b

Values in parentheses indicate inhibition (%) at 100 lg/ml [236 lM, (MW for

10a–10d and 11a–11d: 424)].

2.3. a-Glucosidase inhibitory activity

The glycosidase inhibitory activities of the synthesized com-

pounds (11a–11d) against rat small intestinal -glucosidases

were tested in vitro and compared with those of 2 and related

a

The binding features of these sulfonium type inhibitors to the

subunit have been revealed by a recent X-ray crystallographic

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6325

study on the complex of 2 with human ntMGAM^19aand an in silico

docking study of 1 with the subunit.^19bWith the aid of an in silico

docking study, we recently found that introduction of a monosub-

stituted benzyl group (27) at the C3⁰position of neosalacinol (5)

enhanced the inhibitory activity against maltase ca. 40-fold. This

enhancement was caused by the different binding modes of the

substituent to the surrounding amino acid residues.²⁰

OH

Cl^-

OH

S⁺

O

X

HO

OH

27

X = CH₃, Cl, CF₃, NO₂

HO

The different activities of 11a and 11d were reasonably ratio-

nalized based on the results of an in silico docking simulation

study. Calculations indicated that the binding modes of C2⁰-OH,

C4⁰-OH, and C6⁰-OH in both 11a and 11d with ntMGAM were quite

similar; four hydrogen bonds were detected with surrounding ami-

no acid residues, as shown in Figure 4 (A and B, blue dotted line b,

c, d, e). It is noteworthy that in 11d, the 5⁰R-OH group is shown to

make a rather ﬂexible 8-membered ring by forming an intramolec-

–

ular hydrogen bonding with one of the oxygen atom in SO₃at C3⁰

(Fig. 4B, blue dotted line a). In contrast, 5⁰S-OH in 11a was found to

form a stable 6 membered ring (C3⁰–C4⁰–C5⁰–C5⁰O–H–C3⁰O–C3⁰),

which would contribute to the more efﬁcient formation of the

two hydrogen bondings (Fig. 4A, b and c) than the ﬂexible 8-mem-

bered ring (Fig. 4B, b and c). Additionally, in 11a, van der Waals

interactions were detected between the oxygen atom at C5⁰and

the hydrophobic parts of Trp406 and Phe450 (Fig. 4A, green arrows

f and g); however, these afﬁnity factors were not observed in 11d.

The compound (11a) is less potent than kotalanol (2) although

the quantitative contributions of the intermolecular hydrogen

bonds (i.e. four hydrogen bonds indicated by b, c, d and e in Fig-

ure 4) are the same between them. The less activity of 11a would

be caused by the intramolecular conformational strain induced by

the two hydroxyls (2⁰S-OH and the 4⁰S-OH) in 11a. Both the 4⁰S-OH

and the 6⁰S-OH in 11a and 2 are forming the hydrogen bonds with

Asp203 as shown by b and c. In order to maximize the interactions

to ntMGAM involving these interactions, the 2⁰S-OH and 4⁰S-OH in

11a are compelled to be arranged in parallel as shown in Figure 4A,

causing slight electrostatic repulsion between these two moieties,

which is not observed in kotalanol (2). These unfavorable confor-

mational deformations in 11a would reduce the quality of hydro-

gen bonds with the protein, and caused the differences in the

inhibitory activities.

As far as isomaltase is concerned, the four compounds (11a–

11d) showed efﬁcient activities. Two (11b and 11d) selectively

inhibited isomaltase. It is known that relatively small structural

changes in a compound can result in signiﬁcant changes in its abil-

ity to selectively inhibit one enzyme unit over others. For example,

salacinol is a 4 to 5-fold better inhibitor of ctSI compared to the N-

terminal enzymes and ctMGAM-N2. De-O-sulfonation of kotalanol

resulted in a 10-fold change in activity against ntMGAM, with little

effect on the other enzyme units.²¹Acarbose, an oral anti-diabetic

medicine currently in use, shows a stronger level of inhibition

against ctMGAM than ntMGAM.²²The diastereomers of 2 with

small stereostructural changes (10a–10d, 11a–11d) and the previ-

ously synthesized isomers (9a, 9c, 9d) would be useful in further

study to rationalize the different selectivity observed among them.

In summary, four diastereomers (11a–11d) of 2 with 4⁰C-S ste-

reochemistry as the common structure were synthesized system-

Figure 4. Superposition of 11a [A], 11d [B], and kotalanol (2) [C] in the hNtMGAM

active site. The blue dotted lines show hydrogen bonding, and the double-headed

green arrows show the van der Waals interactions of the oxygen atom with the

amino acid residues (distances of f: 3.98 Å, g: 3.62 Å).

atically by the coupling reaction of thiosugar (13) and cyclic

sulfates (12) with appropriate stereochemistry. SAR studies based

on the precise stereo-structural modiﬁcation suggested an addi-

tional stereostructural factor with respect to the side chain proper-

ties of 2 in addition to the previously revealed requirements for

this type of inhibitors to exert the activity. All the synthesized dia-

stereomers were found to be potent inhibitors against isomaltase.

These diastereomers of 2, including those previously reported (9a,

9c, 9d, and 10a–10d) would be useful in the study of the selectivity

6326

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

of these sulfonium type inhibitors against subunits of

a

-glucosi-

8.0, H-3), 4.57 (1H, dd, J = 5.0, 3.8, H-2), 5.81 (1H, d, J = 3.8, H-1).

t

dases. Further SAR studies, including in silico methods, to develop

more potent inhibitors and to elucidate the factors that control the

selectivity of these sulfoniums are in progress.

¹³C NMR (125 MHz, CDCl₃) d: –5.38/–5.34 [Si(CH₃)₂Bu], 18.4

[SiMe₂C(CH₃)₃], 25.9 [SiMe₂C(CH₃)₃], 26.57/26.59 [C(CH₃)₂],

61.8 (C-5), 71.3 (C-3), 78.7 (C-2), 81.2 (C-4), 104.2 (C-1), 112.6

[C(CH₃)₂].

3. Experimental

3.2. 3,5-Di-O-benzyl-1,2-O-isopropylidene-a-D-ribo-furanose

(18)

Mps were determined on a Yanagimoto MP-3S micromelting

point apparatus, and mps and bps are uncorrected. IR spectra were

measured on either a Shimadzu IR-435 grating spectrophotometer

or a Shimadzu FTIR-8600PC spectrophotometer. NMR spectra were

recorded on a JEOL JNM-ECA 500 (500 MHz ¹H, 125 MHz ¹³C) or a

JEOL JNM-ECA 600 (600 MHz ¹H, 150 MHz ¹³C) spectrometer. Low-

resolution and high-resolution mass spectra were recorded on a

JEOL JMS-HX 100 spectrometer. Optical rotations were determined

with a JASCODIP-370 digital polarimeter. Column chromatography

was effected over Fuji Silysia silica gel BW-200. All the organic ex-

tracts were dried over anhydrous sodium sulfate prior to

evaporation.

A mixture of the crude alcohol 17 (23.6 g), tetrahydrofuran

(650 ml), and 0.2% hydrochloric acid (500 ml) was stirred at room

temperature for 2.5 h. After the reaction was quenched with so-

dium hydrogen carbonate, the resulting mixture was condensed

in vacuo, and the resulting brown solid was washed with n-hexane.

The n-hexane insoluble material was extracted with methanol

(150 ml), and the brown methanol solution was treated with active

charcoal. After ﬁltration, the ﬁltrate was condensed to give the cor-

responding diol, 1,2-O-isopropylidene-a-D

-ribofuranose^14,24as a

pale yellow solid (15.6 g), which was used in the next step without

puriﬁcation. For analytical purpose a small portion was puriﬁed by

means of column chromatography (n-hexane–AcOEt, 1/2) to give

the diol as a colorless needles (from CH₂Cl₂). Mp. 85.0–87.0 °C,

3.1. 5-O-(tert-Butyldimethylsilyl)-1,2-O-isopropylidene-a-D-

ribofuranose (17)

lit.^14b86–87.5 °C, lit.²⁴86–87 °C. ½a ²_D¹

ꢁ

= +42.7 (c = 1.32, CHCl₃),

lit.²⁴

½

a ²_D⁵= +37 (c = 0.59, CHCl₃). ¹H NMR (500 MHz, CDCl₃) d:

ꢁ

A solution of 5-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-

-D

-xylofuranose^8m(16, 48 g, 158 mmol) in dichloromethane

1.38/1.58 [each 3H, s, C(CH₃)₂], 1.89 (1H, br dd-like, J = ca. 7.8,

4.0, OH), 2.41 (1H, d, J = 10.6, OH), 3.76 (1H, ddd, J = 12.1, 7.8, 3.8,

H-5a), 3.85 (1H, ddd, J = 8.9, 3.8, 3.0, H-4), 3.96 (1H, ddd, J = 12.1,

4.0, 3.0, H-5b), 4.01 (1H, ddd, J = 10.6, 8.9, 5.1, H-3), 4.59 (1H, dd,

J = 5.1, 4.0, H-2), 5.83 (1H, d, J = 4.0, H-1). ¹³C NMR (125 MHz,

CDCl₃) d: 26.49/26.54 [C(CH₃)₂], 60.9 (C-5), 70.9 (C-3), 78.7 (C-2),

80.7 (C-4), 104.0 (C-1), 112.8 [C(CH₃)₂].

a

(65 ml) was added dropwise to a mixture of oxalyl chloride

(20.5 ml, 240 mmol), dimethyl sulfoxide (34.1 ml, 480 mmol),

and dichloromethane (200 ml) at –60 °C, and the reaction mixture

was stirred for 1 h at –60 °C and another 30 min at –30 °C. After

addition of a solution of triethylamine (78 ml, 561 mol) in dichlo-

romethane (35 ml) at –30 °C, the reaction mixture was poured into

water, and the resulting mixture was extracted with dichlorometh-

ane. The extract was washed with brine, and condensed to give the

corresponding pentofuranos-3-ulose^13,23(47.5 g) as an orange oil,

which was used in the next step without puriﬁcation. For analyti-

cal purpose a small portion was puriﬁed by means of column chro-

matography (n-hexane–AcOEt, 20/1) to give the ulose as colorless

A solution of the crude 1,2-O-isopropylidene-a-D-ribofuranose

(15.5 g) in DMF (50 ml) was added dropwise to a mixture of so-

dium hydride (7.2 g, 180 mmol, 60% in liquid parafﬁn, washed with

benzene), benzyl bromide (20.3 ml, 171 mmol), and DMF (50 ml)

at 0 °C. After being stirred at 0 °C for 2 h, the mixture was poured

into ice-water (400 ml) and extracted with a mixture of diethyl

ether and n-hexane (1/2). The extract was washed with brine

and condensed to give a colorless oil (29.3 g), which on distillation

at reduced pressure gave title compound 18 (23.0 g, 81% from 16).

needles (from n-hexane). Mp. 38–39.5 °C, lit.²³40–43 °C. ½a _D²⁴

ꢁ

+120.1 (c = 4.78, CHCl₃), lit.¹³

½

a ²_D⁰= +114 (c = 10.0, CHCl₃). ¹H

ꢁ

t

NMR (600 MHz, CDCl₃) d: 0.03/0.06 (each 3H, s, Si(CH₃)₃Bu), 0.86

[9H, s, SiMe₂C(CH₃)₃], 1.45/1.46 [each 3H, s, C(CH₃)₂], 3.82 (1H,

dd, J = 10.8, 2.2, H-5a), 3.88 (1H, dd, J = 10.8, 2.0, H-5b), 4.28

(1H, dd, J = 4.4, 1.1, H-2), 4.36 (1H, ddd, J = 2.2, 2.0, 1.1, H-4),

6.13 (1H, d, J = 4.4, H-1). ¹³C NMR (150 MHz, CDCl₃) d: –5.7/–5.5

3.2.1. Compound 18

Colorless oil. bp. 196–198 °C/1 mmHg, lit.^14bbp. 178–182 °C/

0.025 mmHg.

½

a ²_D¹

ꢁ

= +86.6 (c = 2.66, CHCl₃), lit.^14a

½

a ²_D⁵

= +84.5

ꢁ

(c = 0.65, CHCl₃). ¹H NMR (500 MHz, CDCl₃) d: 1.36/1.59 [each

3H, s, C(CH₃)₂], 3.56 (1H, dd, J = 11.2, 3.9, H-5a), 3.76 (1H, dd,

J = 11.2, 2.0, H-5b), 3.86 (1H, dd, J = 9.0, 4.5, H-3), 4.18 (1H, ddd,

J = 9.0, 3.9, 2.0, H-4), 4.55 (1H, dd, J = 4.5, 3.8, H-2), 4.49/4.56 (each

2H, d, J = 12.3, PhCH₂), 4.54/4.73 (each 2H, d, J = 12.0, PhCH₂), 5.75

(1H, d, J = 3.8, H-1), 7.25–7.35 (10H, m, arom.). ¹³C-NMR

(125 MHz, CDCl₃) d: 26.5/26.8 [C(CH₃)₂], 67.9 (C-5), 72.2/73.4

(PhCH₂), 77.1 (C-3), 77.3 (C-2), 77.9 (C-4), 104.1 (C-1), 112.8

[C(CH₃)₂], 127.6/127.7/127.9/128.0/128.3/128.4 (d, arom.), 137.6/

138.0 (s, arom.).

t

[SiC(CH₃)₃Bu], 18.1 [SiMe₂C(CH₃)₃], 25.7 [SiMe₂C(CH₃)₃], 27.2/27.7

[C(CH₃)₂], 63.9 (C-5), 77.1 (C-2), 81.7 (C-4), 103.8 (C-1), 114.1

[C(CH₃)₂], 211.0 (C-3).

To a solution of the crude ulose (47.3 g) in a mixture of ethanol

(270 ml) and water (30 ml) was added sodium borohydride (11.8 g,

311 mmol) in small portions at –30 °C, and the reaction mixture

was stirred at –10 °C for 2.5 h. After concentration of the mixture,

the residue was diluted with water (500 ml) and extracted with

dichloromethane. The extract was washed with brine, and con-

densed to give 17 as a colorless oil (47.8 g), which was used in

the next step without puriﬁcation. For analytical purpose a small

portion was puriﬁed by means of column chromatography (n-hex-

ane–AcOEt, 10/1) to give title compound 17.¹³

3.3. 3,5-Di-O-benzyl-a- and b-D-ribofuranose (a-14 and b-14)

A mixture of 18 (22.9 g, 61.9 mmol), 1,4-dioxane (170 ml) and

0.5% aqueous sulfuric acid (510 ml) was heated under reﬂux for

3 h. After the 1,4-dioxane was evaporated at the reduced pressure,

the resulting aqueous residue was extracted with dichlorometh-

ane. The extract was washed with brine and condensed to give a

3.1.1. Compound 17

Colorless oil. bp. 95–98 °C/0.004 mmHg. ½a _D²⁴

ꢁ

= +31.8 (c = 1.46,

a _D= +25.7 (c = 4.1, CHCl₃). IR (neat): 3479, 1254,

CHCl₃), lit.¹³

½

ꢁ

1219, 1126, 1076, 1022 cm^ꢂ1

.

¹H NMR (500 MHz, CDCl₃) d: 0.07/

ca 1.5:1 anomeric mixture of a

- and b-14¹²(20.5 g) as a colorless

t

0.08 [each 3H, s, Si(CH₃)₂Bu], 0.90 [9H, s, SiMe₂C(CH₃)₂], 1.37/

1.57 [each 3H, s, C(CH₃)₂], 2.37 (1H, d, J = 9.7, OH), 3.79–3.84 (2H,

m, H-4, H-5a), 3.89–3.93 (1H, m, H-5b), 4.00 (1H, ddd, J = 9.7, 5.0,

oil, which was used in the next step without puriﬁcation. For ana-

lytical purpose a small portion was recrystallized from n-hexane-

diethyl ether to give a mixture of a- and b-14.

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6327

A mixture of

Et₂O). Mp. 78.0–79.0 °C, lit.^12amp 84–86 °C, lit.^12cmp 78–79 °C.

+ 50.3 (c = 1.13, CHCl₃), lit.^12a

= +47.3 (c = 0.55, CH₂Cl₂).

¹H NMR (500 MHz, CDCl₃) d: 2.71 (0.4H, d, J = 3.2, OH_b), 2.91

(0.6H, d, J = 7.7, OH ), 3.41 (0.4H, br d-like, J = ca. 7.2, OH_b), 3.46

a

- and b-14: Colorless needles (from n-hexane-

3.5. tert-Butyl (E)-5,7-Di-O-benzyl-2,3-dideoxy-4,6-O-

isopropylidene- -ribo-hept-2-enoate (E-20)

D

½

a ²_D¹

ꢁ

½ ꢁ

a ²_D⁰

A mixture of E-19 (12.0 g, 28 mmol), 2,2-dimethoxypropane

(34.3 ml, 280 mmol), p-toluenesulfonic acid (24 mg), and acetone

(120 ml) was stirred at room temperature for 1.5 h. After the reac-

tion was quenched by the addition of aqueous sodium hydrogen

carbonate (30 ml), the acetone was evaporated. The residual solu-

tion was diluted with water (30 ml) and extracted with dichloro-

methane. The extract was washed with brine and condensed to

give a colorless solid (14.3 g), which was pure enough for further

reaction. For analytical purpose a small portion was recrystallized

from n-hexane to give title compound E-20.

a

(0.4H, dd, J = 10.4, 3.2, H-5a_b), 3.47 (0.6H, dd, J = 10.3, 4.0, H-5a ),

a

3.53 (0.6H, dd, J = 10.3, 4.0, H-5b ), 3.64 (0.4H, dd, J = 10.4, 3.2, H-

a

5b_b), 3.67 (0.6H, d, J = 9.8, OH ), 3.97 (0.6H, dd, J = 5.7, 4.0, H-3 ),

a

4.03 (0.4H, br dd-like, J = 4.9, 3.2, H-2_b), 4.14 (0.6H, ddd, J = 7.7,

5.7, 4.3, H-2 ), 4.19 (0.4H, ddd, J = 6.0, 3.2, 3.2, H-4_b), 4.25 (0.6H,

a

ddd, J = 4.0, 4.0, 4.0, H-4 ), 4.27 (0.4H, dd, J = 6.0, 4.9, H-3_b), 4.46–

a

4.63 (4H, m, PhCH₂), 5.23 (0.4H, br d, J = 7.2, H-1_b), 5.27 (0.6H, dd,

J = 9.8, 4.3, H-1 ), 7.25–7.39 (10H, m, arom.). ¹³C NMR (125 MHz,

a

CDCl₃,

a/b) d: 69.6/69.7 (C-5), 70.6/74.5 (C-2), 72.98/73.04/73.5/

73.6 (PhCH₂), 77.9/78.2 (C-3), 80.2/81.0 (C-4), 97.1/102.5 (C-1),

127.6/127.8/127.9/128.1/128.3/128.36/128.42/128.56/128.64/

128.7 (d, arom.), 136.9/137.0/137.1/ 137.8 (s, arom.).

3.5.1. Compound E-20

Colorless needles (from n-hexane). mp. 73–74 °C. ½a _D²⁴

ꢁ

– 29.2

(c = 1.01, CHCl₃). IR (CHCl₃): 1709, 1654, 1454, 1369, 1312, 1211,

1153, 1096 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.48/1.494 [each

.

3.4. tert-Butyl (E)- and (Z)-5,7-Di-O-benzyl-2,3-dideoxy-

hept-2-enoate (E-19 and Z-19)

D

-ribo-

3H, s, C(CH₃)₂], 1.491 [9H, s, C(CH₃)₃], 3.30 (1H, dd, J = 9.7, 9.7, H-

5), 3.63 (1H, dd, J = 10.9, 1.9, H-7a), 3.72 (1H, dd, J = 10.9, 4.3, H-

7b), 3.91 (1H, ddd, J = 9.7, 4.3, 1.9, H-6), 4.34 (1H, ddd, J = 9.7, 5.1,

1.5, H-4), 4.39/4.49 (each 1H, d, J = 10.6, PhCH₂), 4.55/4.66 (each

1H, d, J = 12.2, PhCH₂), 6.09 (1H, dd, J = 15.6, 1.5, H-2), 6.97 (1H,

dd, J = 15.6, 5.1, H-3), 7.15–7.37 (10 H, m, arom.). ¹³C NMR

(150 MHz, CDCl₃) d: 19.2/29.3 [(CH₃)₂C], 28.1 [C(CH₃)₃], 69.2 (C-

7), 72.3 (C-4), 73.2 (C-6), 73.5/74.8 (PhCH₂), 74.5 (C-5), 80.4

[C(CH₃)₃], 98.9 [C(CH₃)₂], 124.2 (C-2), 127.7/127.9/128.1/128.2/

128.4/ 128.5 (d arom.), 137.2/138.1 (s arom.), 143.1 (C-3), 165.5

(C-1). FABMS m/z: 469 [M+H]⁺(pos.), FABHRMS m/z: 469.2571

(C₂₈H₃₇O₆requires 469.2590).

A solution of a crude mixture of a- and b-14 (9.9 g), tert-butoxy-

carbonylethylenetriphenylphosphorane (14.8. g, 39.4 mmol) in

dichloromethane (30 ml) was heated under reﬂux for 1 h. After re-

moval of the solvent, the oily residue was triturated with a mixture

of n-hexane and diethyl ether (5:1), and the deposited precipitates

were ﬁltered off and washed with a mixture of n-hexane and

diethyl ether (5:1). The combined ﬁltrate and washings were con-

densed to give a pale yellow oil (20.0 g), which on column chroma-

tography (n-hexane–Et₂O, 2/1) gave title compounds E-19 (9.3 g,

73% from 18) and Z-19 (1.9 g, 15% from 18).

3.6. tert-Butyl (Z)-5,7-Di-O-benzyl-2,3-dideoxy-4,6-O-

isopropylidene-D-ribo-hept-2-enoate (Z-20)

3.4.1. Compound E-19

Colorless needles (from n-hexane–Et₂O). mp. 58–59 °C. ½a _D²⁴

ꢁ

–

Following the method used for acetalization of diol E-19, Z-19

(1.7 g, 4.0 mmol) was treated with dimethoxypropane (4.9 ml,

40 mmol) in acetone (30 ml). Work-up gave a colorless solid

(1.87 g), which was pure enough for further reaction. For analytical

purpose a small portion was recrystallized from n-hexane to give

title compound Z-20.

5.74 (c = 1.30, CHCl₃). IR (CHCl₃): 3526, 1705, 1655, 1454, 1393,

1369, 1315, 1226, 1215, 1157, 1088 cm^ꢂ^{1 1}H NMR (500 MHz,

.

CDCl₃) d: 1.48 [9H, s, C(CH₃)₃], 2.69 (1H, br d, J = 5.5, OH), 3.15

(1H, br d, J = 4.0, OH), 3.53 (1H, dd, J = 7.2, 5.4, H-5), 3.60 (1H, dd,

J = 9.8, 5.5, H-7a), 3.67 (1H, dd, J = 9.8, 3.7, H-7b), 3.91 (1H, dddd,

J = 7.2, 5.5, 5.5, 3.7, H-6), 4.51/4.56 (each 1H, d, J = 11.8, PhCH₂),

4.51/4.62 (each 1H, d, J = 11.2, PhCH₂), 4.55 (1H, dddd, J = 5.4, 5.2,

4.0, 1.7, H-4), 6.06 (1H, dd, J = 15.8, 1.7, H-2), 6.99 (1H, dd,

J = 15.8, 5.2, H-3), 7.23–7.38 (10H, m, arom.). ¹³C NMR (125 MHz,

CDCl₃) d: 28.1 [C(CH₃)₃], 70.6 (C-7), 71.7 (C-6), 72.3 (C-4), 73.5/

74.1 (PhCH₂) 80.4 [C(CH₃)₃], 81.4 (C-5), 123.6 (C-2), 127.9/

127.99/128.04 /128.1/128.5 (d, arom.), 137.46/137.52 (s, arom.),

145.1 (C-3), 165.6 (C-1). FABMS m/z: 429 [M+H]⁺(pos.), FABHRMS

m/z: 429.2293 (C₂₅H₃₃O₆requires 429.2277).

3.6.1. Compound Z-20

Colorless needles (from n-hexane). mp. 58–59 °C. ½a _D²⁴

ꢁ

+ 96.6

(c = 4.60, CHCl₃). IR (CHCl₃): 1717, 1651, 1454, 1369, 1207, 1157,

1096 cm^ꢂ^{1 1}H NMR (500 MHz, CDCl₃) d: 1.43 [9H, s, (CH₃)₃C],

.

1.46/1.57 [each 3H, s, (CH₃)₂C], 3.32 (1H, br dd, J = 9.8, 9.5, H-5),

3.62 (1H, dd, J = 10.9, 2.0, H-7a), 3.71 (1H, dd, J = 10.9, 4.3, H-7b),

3.96 (1H, ddd, J = 9.8, 4.3, 2.0, H-6), 4.35/4.47 (each 1H, d, J = 10.6,

PhCH₂), 4.55/4.65 (each 1H, d, J = 12.3, PhCH₂), 5.61 (1H, dd,

J = 9.5, 8.9, H-4), 5.86 (1H, d, J = 11.5, H-2), 5.98 (1H, dd, J = 11.5,

8.9, H-3), 7.11–7.38 (10H, m, arom.). ¹³C NMR (125 MHz, CDCl₃)

d: 19.6/29.4 [C(CH₃)₂], 28.1 [C(CH₃)₃], 68.2 (C-4), 69.4 (C-7), 72.8

(C-6), 73.5/74.2 (PhCH₂), 73.9 (C-5), 80.8[C(CH₃)₃], 98.8 [C(CH₃)₂],

125.6 (C-2), 127.6/127.7/127.9/128.2/128.3 (d, arom.), 137.7/

138.2 (s, arom.), 142.7 (C-3), 164.7 (C-1). FABMS m/z: 469 [M+H]⁺

(pos.), FABHRMS m/z: 469.2617 (C₂₈H₃₇O₆requires 469.2590).

3.4.2. Compound Z-19

Colorless needles (from n-hexane). mp. 61–62 °C. ½a _D²⁴

ꢁ

+ 2.73

(c = 1.20, CHCl₃). IR (CHCl₃): 3430, 1697, 1651, 1454, 1416, 1369,

1227, 1207, 1157, 1092 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.48

.

[9H, s, C(CH₃)₃], 3.23 (1H, d, J = 5.0, OH), 3.62 (1H, dd, J = 9.8, 5.5,

H-7a), 3.69 (1H, dd, J = 9.8, 3.0, H-7b), 3.71 (1H, d, J = 5.1, OH),

3.77 (1H, dd, J = 7.7, 4.0, H-5), 3.85 (1H, dddd, J = 7.7, 5.5, 5.0, 3.0,

H-6), 4.52/4.57 (each 1H, d, J = 11.8, PhCH₂), 4.64/4.76 (each 1H,

d, J = 11.3, PhCH₂), 5.26 (1H, dddd, J = 7.2, 5.1, 4.0, 1.5, H-4), 5.83

(1H, dd, J = 11.9, 1.5, H-2), 6.34 (1H, dd, J = 11.9, 7.2, H-3), 7.25–

7.36 (10H, m, arom.). ¹³C NMR (150 MHz, CDCl₃) d: 28.1

[C(CH₃)₃], 69.0 (C-4), 70.7 (C-6), 70.9 (C-7), 73.4/73.7 (PhCH₂),

81.5 [C(CH₃)₃], 81.7 (C-5), 122.9 (C-2), 147.4 (C-3), 127.7/127.76/

127.84/128.1/128.4 (d, arom.), 138.0/138.2 (s, arom.), 166.7 (C-1).

FABMS m/z: 429 [M+H]⁺(pos.), FABHRMS m/z: 429.2302

(C₂₅H₃₃O₆requires 429.2277).

3.7. (E)-5,7-di-O-Benzyl-2,3-dideoxy-4,6-O-isopropylidene-

ribo-hept-2-enitol (E-21)

D-

To a solution of a crude acetonide E-20 (14.2 g) in tetrahydrofu-

ran (190 ml) was added dropwise a 1 M solution of DIBAL in tolu-

ene (64 ml, 64 mmol) at –78 °C. After being stirred at –78 °C for

1 h, the reaction mixture was allowed to reach room temperature,

and stirred for 6 h. The reaction was quenched with water

(150 ml). The deposited gel was ﬁltered off through celite and

6328

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

washed with tetrahydrofuran. The combined ﬁltrate and washings

were condensed to give a colorless solid (11.6 g), which on recrys-

tallization from a mixture of n-hexane and ethyl acetate gave title

compound E-21 (9.2 g, 83% from E-19). Column chromatography

(CHCl₃) of the mother liquid gave E-21 (1.1 g, 10% from E-19).

¹H NMR spectrum. Analytical samples of both diastereomers were

obtained by means of column chromatography (n-hexane-acetone,

3/1).

3.9.1. Compound 22a

Colorless oil. ½a _D²⁴

ꢁ

– 2.1 (c = 1.13, CHCl₃). IR (neat): 3418, 1454,

3.7.1. Compound E-21

1384, 1265, 1203, 1169, 1107, 1030 cm^ꢂ^{1 1}H NMR (600 MHz,

.

Colorless needles (from n-hexane–AcOEt). mp. 92–93 °C.

CDCl₃) d: 1.45/1.49 [each, 3H, s, C(CH₃)₂], 2.25 (1H, dd, J = 7.4, 4.8,

OH), 3.11 (1H, dd, J = 3.6, OH), 3.19 (1H, d, J = 6.5, OH), 3.53 (1H,

ddd, J = 11.7, 7.4, 4.5, H-7a), 3.59 (1H, dd, J = 9.8, 9.2, H-3), 3.61

(1H, ddd, J = 11.7, 4.8, 4.5, H-7b), 3.66 (1H, dd, J = 11.2, 2.1, H-1a),

3.75 (1H, ddd, J = 6.5, 3.8, 1.6, H-5), 3.79 (1H, dd, J = 11.2, 3.6, H-

1b), 3.86 (1H, ddd, J = 4.5, 4.5, 1.6, H-6), 3.88 (1H, ddd, J = 9.2, 3.6,

2.1, H-2), 3.99 (1H, dd, J = 9.8, 3.8, H-4), 4.45/4.52 (each 1H, d,

J = 11.0, PhCH₂), 4.58/4.71 (each 1H, d, J = 12.0, PhCH₂), 7.16–7.39

(10H, m, arom.). ¹³C NMR (150 MHz, CDCl₃) d: 19.0/29.3

[C(CH₃)₂], 64.7 (C-1), 69.1 (C-7), 69.9 (C-6), 71.3 (C-5), 71.7 (C-3),

73.3 (C-2), 73.7/73.9 (PhCH₂), 75.6 (C-4), 99.2 [C(CH₃)₂], 127.8/

128.1/128.2/128.3/128.4/128.6 (d, arom.), 137.0/137.8 (s, arom).

FABMS m/z: 433 [M+H]⁺(pos.), FABHRMS m/z: 433.2213

(C₂₄H₃₃O₇requires 433.2226).

½

a ²_D⁴

ꢁ

+ 9.1 (c = 1.22, CHCl₃). IR (nujol): 3479, 1651, 1203, 1169,

1111, 1096, 1054, 1029 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.35

.

(1H, br t-like, J = ca. 4.3, OH), 1.47/1.51 [each 3H, s, C(CH₃)₂], 3.30

(1H, dd, J = 8.0, 8.0, H-5), 3.65 (1H, dd, J = 9.1, 1.7, H-7a), 3.72 (1H,

dd, J = 9.1, 3.6, H-7b), 3.89 (1H, ddd, J = 8.0, 3.6, 1.7, H-6), 4.12

(2H, br t-like, J = ca. 4.3, H-1a and H-1b), 4.21, (1H, br dd, J = 8.0,

5.8, H-4), 4.40/4.48 (each 1H, d, J = 10.8, PhCH₂), 4.56/4.67 (each

1H, d, J = 12.3, PhCH₂), 5.72 (1H, ddt, J = 12.9, 5.8, 1.3, H-3), 6.00

(1H, dtd, J = 12.9, 4.3, 0.7, H-2), 7.14–7.39 (10H, m, arom.). ¹³C

NMR (150 MHz, CDCl₃) d: 19.4/29.4 [C(CH₃)₂], 62.9 (C-1), 69.3 (C-

7), 73.0 (C-6), 73.5/74.4 (PhCH₂), 73.7 (C-4), 74.4 (C-5), 98.7

[C(CH₃)₂], 127.6/127.9/128.0/128.2/128.3/128.4 (d. arom.), 128.8

(C-3), 133.3 (C-2), 137.7/138.2 (s, arom.). FABMS m/z: 399 [M+H]⁺

(pos.), FABHRMS m/z: 399.2180 (C₂₄H₃₁O₅requires 399.2171).

3.9.2. Compound 22b

3.8. (Z)-5,7-di-O-Benzyl-2,3-dideoxy-4,6-O-isopropylidene-

ribo-hept-2-enitol (Z-21)

D

-

Colorless plates (from n-hexane–AcOEt). mp. 121–122 °C.

½

a ²_D⁴

ꢁ

+ 11.7 (c = 1.09, CHCl₃). IR (CHCl₃): 3526, 1451, 1384, 1215,

1204, 1165, 1092, 1042 cm^ꢂ^{1 1}H NMR (500 MHz, CDCl₃) d: 1.46/

.

Following the method used for reduction of E-20, a crude aceto-

nide Z-20 (1.8 g) was treated with 1 M solution of DIBAL in toluene

(9.5 ml, 9.5 mmol). Work-up gave quantitatively the title com-

pound Z-21 (1.53 g) as a pale yellow solid, which was used in

the next step without puriﬁcation. For analytical purpose a small

portion was recrystallized from a mixture of n-hexane and ethyl

acetate to give Z-21.

1.50 [each, 3H, s, C(CH₃)₂], 2.24 (1H, t, J = 6.0, OH), 2.67 (1H, dd,

J = 9.5, OH), 3.13 (1H, d, J = 1.2, OH), 3.63 (1H, dd, J = 10.9, 2.0, H-

7a). 3.68 (1H, dd, J = 10.9, 4.6, H-7b), 3.70 (2H, dd-like, J = ca. 6.0,

5.4, H-1a and H-1b), 3.76 (1H, dd, J = 9.7, 9.7, H-5), 3.80–3.88

[3H, m, H-2, H-3, including one-proton double multiplets due to

H-4 at d 3.83 (J = 9.7)], 3.90 (1H, ddd, J = 9.7, 4.6, 2.0, H-6), 4.49/

4.62 (each 1H, d, J = 10.9, PhCH₂), 4.56/4.64 (each 1H, d, J = 12.1,

PhCH₂), 7.17–7.39 (10H, m, arom.). ¹³C NMR (125 MHz, CDCl₃) d:

19.4/29.3 [C(CH₃)₂], 64.0 (C-1), 68.6 (C-2), 69.3 (C-7), 69.6 (C-5),

73.1 (C-6), 73.4 (C-3), 73.5/74.6 (PhCH₂), 75.7 (C-4), 99.0

[(CCH₃)₂], 127.7/127.97/128.03/128.4/128.5 (d, arom.), 137.6/

138.0 (s, arom.). FABMS m/z: 433 [M+H]⁺(pos.), FABHRMS m/z:

433.2239 (C₂₄H₃₃O₇requires 433.2226).

3.8.1. Compound Z-21

Colorless needles (from n-hexane–AcOEt). mp. 75–76 °C.

½

a ²_D⁴

ꢁ

+ 76.5 (c = 2.37, CHCl₃). IR (CHCl₃): 3472, 1650, 1219, 1165,

1096, 1030 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.47/1.53 [each

.

3H, s, C(CH₃)₂], 1.99 (1H, br t-like, J = ca. 6.4 Hz, OH), 3.34 (1H,

dd, J = 9.7, 9.7, H-5), 3.64 (1H, dd, J = 11.0, 2.0, H-7a), 3.73 (1H,

dd, J = 11.0, 4.3, H-7b), 3.91 (1H, ddd, J = 9.7, 4.3, 2.0, H-6), 4.15

(1H, dddd, J = 13.0, 6.4, 6.4, 1.4, H-1a), 4.18 (1H, dddd, J = 13.0,

6.4, 6.4, 1.4, H-1b), 4.44/4.50 (each 1H, d, J = 10.7, PhCH₂), 4.57/

4.67 (each 1H, d, J = 12.2, PhCH₂), 4.63 (1H, ddd, J = 9.7, 8.3, 0.9,

H-4), 5.57 (1H, ddt, J = 11.2, 8.3, 1.4, H-3), 5.89 (1H, dtd, J = 11.2,

6.4, 0.9, H-2), 7.13–7.38 (10H, m, arom). ¹³C NMR (150 MHz, CDCl₃)

d: 19.4/29.4 [C(CH₃)₂], 59.2 (C-1), 69.3 (C-7), 69.4 (C-4), 73.1 (C-6),

73.5/74.7 (PhCH₂), 74.3 (C-5), 98.8 [C(CH₃)₂], 127.7/127.9/128.1/

128.2/128.4/128.5 (d arom.), 129.9 (C-3), 133.5 (C-2), 137.2/138.1

(s arom.). FABMS m/z: 399 [M+H]⁺(pos.), FABHRMS m/z:

399.2184 (C₂₄H₃₁O₅requires 399.2171).

Following the method used for oxidation of E-21, a mixture of a

crude oleﬁnic alcohol Z-21 (1.5 g), 0.045 M aqueous osmium

tetroxide (4.2 ml, 0.19 mmol), N-methylmorphorine N-oxide

(887 mg, 7.5 mmol), and acetone (10 ml) was heated under reﬂux

for 30 min. Work-up gave a ca. 1:1 mixture of 5,7-di-O-benzyl-

4,6-O-isopropylidene-

D-glycero-

D-allo-heptitol (22c) and 5,7-di-O-

benzyl-4,6-O-isopropylidene-

D

-glycero-

D-manno-heptitol (22d) as

a pale yellow oil (1.68 g), which was used in the next step without

puriﬁcation. Analytical samples of both diastereomers were ob-

tained by means of column chromatography (n-hexane-acetone,

2/1).

3.9.3. Compound 22c

3.9. Dihydroxylation of oleﬁnic alcohols E-21 and Z-21

Colorless needles (from n-hexane–AcOEt). mp. 82–83 °C.

½

a ²_D⁴

ꢁ

+ 4.2 (c = 1.38, CHCl₃). IR (CHCl₃): 3533, 1520, 1454, 1223,

A mixture of E-21 (6.2 g, 15.6 mmol), 0.045 M aqueous osmium

tetroxide (17.2 ml, 0.78 mmol), N-methylmorphorine N-oxide

(3.65 g, 31.2 mmol), acetone (55 ml), and water (5 ml) was heated

under reﬂux for 2.5 h. After the reaction was quenched by the addi-

tion of sodium sulﬁte (3.9 g, 31.2 mmol), the resulting mixture was

diluted with water (200 ml), and extracted with diethyl ether. The

extract was washed with brine and condensed to give a ca. 3:1

1204, 1092 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.45/1.50 [each

.

3H, s, C(CH₃)₂], 2.31 (1H, br s, OH), 2.79 (1H, br d, J = 2.2, OH),

2.94 (1H, br d, J = 3.7, OH), 3.68 (1H, dd, J = 11.2, 2.2, H-7a), 3.71

(1H, br dm, J = ca. 10.5, H-1a), 3.73–3.78 (1H, m, H-2), 3.78–3.84

[4H, m, H-1b, H-3, including two one-proton doublet of doublets

due to H-7b and H-5 at d 3.79 (J = 11.2, 3.7) and d 3.81 (J = 9.6,

9.6), respectively], 3.89 (1H, ddd, J = 9.6, 3.7, 2.2, H-6), 3.93 (1H,

dd, J = 9.6, 4.4, H-4), 4.56/4.59 (each 1H, d, J = 10.8, PhCH₂), 4.57/

4.70 (each 1H, d, J = 12.2, PhCH₂), 7.16–7.39 (10H, m, arom). ¹³C

NMR (150 MHz, CDCl₃) d: 19.3/29.2 [C(CH₃)₂], 64.2 (C-1), 69.3 (C-

7), 71.8 (C-2), 72.3 (C-5), 73.3 (C-3 and C-4), 73.7/74.2 (PhCH₂),

73.9 (C-6), 98.9 [C(CH₃)₂], 127.8/128.06/128.13/128.3/128.4/128.7

mixture of 1,3-di-O-benzyl-2,4-O-isopropylidene-

heptitol (22a) and 5,7-di-O-benzyl-4,6-O-isopropylidene-

ro- -gluco-heptitol (22b) as a pale yellow oil (6.9 g), which was

D

-glycero-

L-allo-

-glyce-

D

used in the next step without puriﬁcation. The ratio of products

22a and 22b in the mixture was determined on the basis of the

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6329

(d arom.), 136.8/ 137.8 (s arom.). FABMS m/z: 433 [M+H]⁺(pos.),

FABHRMS m/z: 433.2200 (C₂₄H₃₃O₇requires 433.2226).

(5H, m, H-2, H-3, H-4). ¹³C NMR (125 MHz, D₂O) d: 63.9 (C-1 and

C-7), 73.4 (C-2 and C-6), 73.7 (C-3 and C-5), 74.0 (C-4).

Following the method used for the deprotection of 22a, triol

22d (86 mg, 0.2 mmol) was hydrogenated in 80% aqueous acetic

acid (4 ml) at 60 °C. Work-up gave a colorless oil (62 mg), which

on column chromatography (AcOEt–MeOH–H₂O, 20/4/1) gave

3.9.4. Compound 22d

Colorless prisms (from n-hexane–AcOEt). mp. 91–92 °C.

½

a ²_D⁴

ꢁ

+ 8.5 (c = 2.46, CHCl₃). IR (CHCl₃): 3479, 1520, 1423, 1223,

1092, 1045 cm^ꢂ^{1 1}H NMR (600 MHz, CDCl₃) d: 1.45/1.51 [each

.

D-glycero-D

-manno-heptitol 22d (41 mg, 97%). ¹³C NMR spectroscopic

3H, s, C(CH₃)₂], 2.04/2.37/2.48 (each 1H, br s, OH), 3.64 (1H, dd,

J = 11.0, 2.2, H-7a), 3.70 (1H, dd, J = 11.0, 4.5, H-7b), 3.71 (1H, dd,

J = 9.8, 9.8, H-5), 3.72–3.76 (3H, m, H-1a, H-2, H-3), 3.79 (1H, dm,

J = ca. 10.5, H-1b), 3.92 (1H, ddd, J = 9.8, 4.5, 2.2, H-6), 4.01 (1H,

d, J = 9.8, H-4), 4.49/4.59 (each 1H, d, J = 11.0, PhCH₂), 4.56/4.64

(each 1H, d, J = 12.2, PhCH₂), 7.17–7.38 (10H, m, arom). ¹³C NMR

(150 MHz, CDCl₃) d: 19.5/29.2 [C(CH₃)₂], 64.2 (C-1), 69.27 (C-2),

69.33 (C-7), 69.7 (C-5), 72.1 (C-4), 72.2 (C-3), 73.2 (C-6), 73.5/

74.6 (PhCH₂), 98.9 [C(CH₃)₂], 127.7/127.96/128.00/128.4/128.5 (d

arom.), 137.6/138.0 (s arom.). FABMS m/z: 433 [M+H]⁺(pos.), FAB-

HRMS m/z: 433.2239 (C₂₄H₃₃O₇requires 433.2226).

properties of 22d were in good accordance with those reported.¹⁵

3.10.4. Compound 22d

Colorless amorphous. ¹H NMR (500 MHz, D₂O) d: 3.51 (1H, dd,

J = 11.8, 6.0, H-1a), 3.54 (1H, dd, J = 12.0, 7.7, H-7a), 3.60 (1H, ddd,

J = 8.8, 6.0, 2.6, H-2), 3.65 (1H, dd, J = 8.8, 1.0, H-3), 3.66 (1H,

dd, J = 8.3, 4.9, H-5), 3.67 (1H, dd, J = 12.0, 2.9, H-7b), 3.71

(1H, dd, J = 11.8, 2.6, H-1b), 3.75 (1H, dd, J = 8.3, 1.0, H-4), 3.79 (1H,

ddd, J = 7.7, 4.9, 2.9, H-6). ¹³C NMR (125 MHz, D₂O) d: 63.4 (C-7),

64.6 (C-1), 70.9 (C-3), 71.0 (C-4), 72.1 (C-2), 72.8 (C-5), 74.2 (C-6).

3.11. Methoxymethylation of triols 22a, 22b, 22c and 22d

3.10. Identiﬁcation of triols 23a, 23b, 23c and 23d

A mixture of a crude triols 22a and 22b (6.9 g), methoxymeth-

ylchloride (MOMCl, 14.6 ml, 192 mmol), diisopropylethylamine

(55.6 ml, 319 mmol), and dimethylformamide (200 ml) was heated

at 60 °C for 1 h. After being cooled, the reaction mixture was neu-

tralized by addition of aqueous sodium hydrogen carbonate

(140 ml), and the resulting mixture was extracted with diethyl

ether. The extract was washed with brine and condensed to give

a pale yellow oil (8.3 g), which on column chromatography (n-hex-

ane–Et₂O, 2/1) gave 1,3-di-O-benzyl-2,4-O-isopropylidene-5,6,7-

A suspension of 10% palladium-on-carbon (130 mg) in 80%

aqueous acetic acid (2 ml) was pre-equilibrated with hydrogen.

To the suspension was added a solution of 22a (130 mg, 0.3 mmol)

in 80% aqueous acetic acid (4 ml), and the mixture was hydroge-

nated at 60 °C under atmospheric pressure until the uptake of

hydrogen ceased. The catalyst was ﬁltered off, and the ﬁltrate

was concentrated in vacuo. The residue (80 mg) was puriﬁed by

means of column chromatography (AcOEt–MeOH–H₂O, 20/4/1) to

give

D-glycero-

L

-allo-heptitol 23a (59 mg, 93%). ¹³C NMR spectro-

tri-O-methoxymethyl-

E-21) and 5,7-di-O-benzyl-4,6-O-isopropylidene-1,2,3-tri-O-

-glycero- -gluco-heptitol 24b (2.0 g, 23% from

D-glycero-L-allo-heptitol 24a (6.0 g, 68% from

scopic properties of 23a were in good accordance with those

reported.¹⁵

methoxymethyl-

D

E-21).

3.10.1. Compound 23a

Colorless oil. ¹H NMR (500 MHz, D₂O) d: 3.51 (1H, dd, J = 10.0,

7.0 Hz, H-7a), 3.52 (1H, dd, J = 8.3, 3.4, H-1a), 3.54 (1H, dd,

J = 10.0, 5.5, H-7b), 3.66 (1H, dd, J = 5.5, 1.8, H-5), 3.67 (1H, dd,

J = 8.3, 3.4, H-1b), 3.73 (1H, dd, J = 7.0, 3.5, H-3), 3.74 (1H, dd,

J = 5.5, 3.5, H-4), 3.79 (1H, ddd, J = 7.0, 3.4, 3.4, H-2), 3.82 (1H,

ddd, J = 7.0, 5.5, 1.8, H-6). ¹³C NMR (125 MHz, D₂O) d: 64.0 (C-1),

64.4 (C-7), 72.0 (C-6), 72.1 (C-5), 72.9 (C-3), 73.3 (C-2), 74.2 (C-4).

Following the method used for the deprotection of 22a, triol

22b (130 mg, 0.3 mmol) was hydrogenated in 80% aqueous acetic

acid (6 ml) at 60 °C. Work-up gave a colorless oil (78 mg), which

on column chromatography (AcOEt–MeOH–H₂O, 20/4/1) gave

3.11.1. Compound 24a

Colorless oil. Bp. 239–243 °C/0.004 mHg. ½a _D²⁴

ꢁ

+ 37.9 (c = 1.90,

¹H

CHCl₃). IR (neat): 1454, 1381, 1258, 1207, 1150, 1026 cm^ꢂ1

.

NMR (600 MHz, CDCl₃) d: 1.45/1.48 [each 3H, s, C(CH₃)₂], 3.32/

3.39/3.44 (each 3H, s, OCH₂OCH₃), 3.66 (1H, dd, J = 11.0, 2.2, H-

1a), 3.720 (1H, dd, J = 9.5, 9.5, H-3), 3.722 (1H, dd, J = 10.8, 6.5, H-

7a), 3.73 (1H, dd, J = 11.0, 4.5, H-1b), 3.77 (1H, dd, J = 10.8, 4.0, H-

7b), 3.88 (1H, ddd, J = 9.5, 4.5, 2.2, H-2), 3.98 (1H, ddd, J = 7.2,

6.5, 4.0, H-6), 4.01 (1H, dd, J = 9.5, 1.0, H-4), 4.07 (1H, dd, J = 7.2,

1.0, H-5), 4.44/4.67 (each 1H, d, J = 10.8, PhCH₂), 4.57/4.66 (each

1H, d, J = 12.2, PhCH₂), 4.59/4.60 (each 1H, d, J = 6.4, OCH₂OCH₃),

4.73/4.828 (each 1H, d, J = 6.7, OCH₂OCH₃), 4.812/4.826 (each 1H,

d, J = 7.0 Hz, OCH₂OCH₃), 7.17–7.38 (10H, m, arom.). ¹³C NMR

(150 MHz, CDCl₃) d: 19.0/29.4 [C(CH₃)₂], 55.4/55.6/56.0

(OCH₂OCH₃), 67.9 (C-7), 69.6 (C-1), 70.7 (C-3), 73.47 (C-2), 73.52/

73.8 (PhCH₂), 74.0 (C-4), 76.6 (C-6), 77.3 (C-5), 96.7/97.1/97.4

(OCH₂OCH₃), 98.7 [C(CH₃)₂], 127.6/127.7/127.88/127.93/128.3/

128.4 (d, arom.), 137.7/138.2 (s, arom.). FABMS m/z: 565 [M+H]⁺

(pos.), FABHRMS m/z: 565.2983 (C₃₀H₄₅O₁₀requires 565.3012).

D

-glycero-D

-gluco-heptitol 23b (61 mg, 96%). ¹³C NMR spectroscopic

properties of 23b were in good accordance with those reported.¹⁵

3.10.2. Compound 23b

Colorless amorphous. ¹H NMR (600 MHz, D₂O) d: 3.45 (1H, dd,

J = 11.8, 6.2 Hz, H-1a), 3.51 (1H, dd, J = 11.8, 7.4, H-7a), 3.57 (1H,

dd, J = 11.8, 3.4, H-1b), 3.58 (1H, dd, J = 7.0, 1.9, H-4), 3.64 (1H,

dd, J = 11.8, 3.1, H-7b), 3.65 (1H, dd, J = 7.0, 5.0, H-5), 3.68 (1H,

ddd, J = 6.2, 6.2, 3.4, H-2), 3.70 (1H, dd, J = 6.2, 1.9, H-3), 3.76 (1H,

ddd, J = 7.4, 5.0, 3.1, H-6). ¹³C NMR (150 MHz, D₂O) d: 63.5 (C-7),

63.8 (C-1), 71.3 (C-3), 72.8 (C-4), 73.0 (C-5), 73.9 (C-6), 74.3 (C-2).

Following the method used for the deprotection of 22a, triol 22c

(130 mg, 0.3 mmol) was hydrogenated in 80% aqueous acetic acid

(6 ml) at 50 °C. Work-up gave a colorless oil (78 mg), which on col-

3.11.2. Compound 24b

Colorless oil. Bp. 245–248 °C/0.005 mHg. ½a _D²⁴

ꢁ

– 3.0 (c = 1.53,

CHCl₃). IR (neat): 1454, 1381, 1257, 1204, 1150, 1110,

1034 cm^ꢂ^{1 1}H NMR (500 MHz, CDCl₃) d: 1.47/1.48 [each 3H, s,

.

C(CH₃)₂], 3.33/3.34/3.41 (each 3H, s, OCH₂OCH₃), 3.64 (1H, dd,

J = 11.2, 5.8, H-1a), 3.68 (1H, dd, J = 10.9, 2.0, H-7a), 3.74 (1H, dd,

J = 9.7, 9.7, H-5), 3.77 (1H, dd, J = 10.9, 4.3, H-7b), 3.81 (1H, dd,

J = 11.2, 2.1, H-1b), 3.90 (1H, ddd, J = 9.7, 4.3, 2.0, H-6), 3.96 (1H,

dd, J = 9.7, 0.9, H-4), 4.02 (1H, ddd, J = 6.9, 5.8, 2.1, H-2), 4.08 (1H,

dd, J = 6.9, 0.9, H-3), 4.49/4.71 (each 1H, d, J = 10.8, PhCH₂), 4.56/

4.68 (each 1H, d, J = 12.2, PhCH₂), 4.62/4.64 (each 1H, d,

J = 6.4 Hz, OCH₂OCH₃), 4.730/4.89 (each 1H, d, J = 6.6 Hz,

umn chromatography (AcOEt–MeOH–H₂O, 20/4/1) gave D-glycero-

D

-allo-heptitol 23c (58 mg, 91%). ¹³C NMR spectroscopic properties

of 23c were in good accordance with those reported.¹⁵

3.10.3. Compound 23c

Colorless amorphous. ¹H NMR (500 MHz, D₂O) d: 3.51 (2H, dd,

J = 11.8, 6.6, H-1a), 3.66 (2H, dd, J = 11.8, 2.9, H-1b), 3.70–3.77

6330

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

OCH₂OCH₃), 4.732/4.77 (each 1H, d, J = 6.6 Hz, OCH₂OCH₃), 7.17–

7.38 (10H, m, arom.). ¹³C NMR (125 MHz, CDCl₃) d: 19.0/29.5

[C(CH₃)₂], 55.4/55.7/56.0 (OCH₂OCH₃), 68.2 (C-1), 69.87 (C-5),

69.96 (C-7), 71.2 (C-4), 73.5/73.6 (PhCH₂), 73.7 (C-6), 76.6 (C-3),

78.3 (C-2), 96.7/97.4/98.4 (OCH₂OCH₃), 98.5 [C(CH₃)₂], 127.56/

127.65/127.72/127.9/128.28/128.30 (d, arom.), 138.2/138.3 (s,

arom.). FABMS m/z: 565 [M+H]⁺(pos.), FABHRMS m/z: 565.3013

(C₃₀H₄₅O₁₀requires 565.3012).

Following the method described above, a mixture of triols 22c

and 22d (925 mg) was treated with MOMCl (2 ml, 26 mmol) in

DMF (30 ml) at 60 °C. Work-up gave a pale yellow oil (1.15 g),

which on column chromatography (n-hexane–Et₂O, 2/1) gave

5,7-di-O-benzyl-4,6-O-isopropylidene-1,2,3-tri-O-methoxy-

and the ﬁltrate was concentrated in vacuo. The residue (1.98 g)

was washed with n-hexane to give a practically pure 2,4-O-isopro-

pylidene-5,6,7-tri-O-methoxymethyl-D-glycero-L-allo-heptitol 25a

(1.87 g, 96%).

3.12.1. Compound 25a

Colorless oil. Bp. 176–179 °C/0.004 mmHg. ½a _D²⁴

ꢁ

+ 37.6 (c = 2.89,

CHCl₃). IR (neat): 3418, 1454, 1384, 1265, 1207, 1151, 1108,

1034 cm^ꢂ^{1 1}H NMR (500 MHz, CDCl₃) d: 1.39/1.50 [each 3H, s,

.

C(CH₃)₂], 2.17 (1H, dd-like J = ca. 7.0, 6.0, OH), 3.38/3.41/3.44 (each

3H, s, OCH₂OCH₃), 3.66 (1H, ddd, J = 8.6, 8.6, 2.3, H-3), 3.68 (1H, dd,

J = 10.3, 7.2, H-7a), 3.72–3.79 [3H, m, H-1a H-2, including one-pro-

ton doublet of doublets due to H-7b at d 3.76 (J = 10.3, 5.7)], 3.82

(1H, d, J = 2.3, OH), 3.83–3.88 (1H, m, H-1b), 3.89 (1H, dd, J = 8.6,

6.0, H-4), 3.91 (1H, dd, J = 6.0, 2.6, H-5), 3.97 (1H, ddd, J = 7.2, 5.7,

2.6, H-6), 4.65 (2H, s-like, OCH₂OCH₃), 4.74/4.76 (each 1H, d,

J = 6.7, OCH₂OCH₃), 4.78/4.85 (each 1H, d, J = 6.0, OCH₂OCH₃). ¹³C

NMR (125 MHz, CDCl₃) d: 19.4/29.3 [(CH₃)₂C], 55.6/56.0/56.4

(OCH₂OCH₃), 63.2 (C-1), 66.2 (C-3), 67.3 (C-7), 72.0 (C-4), 72.9

(C-2), 76.5 (C-6), 81.0 (C-5), 97.0/97.6/98.67 (OCH₂OCH₃), 98.70

[C(CH₃)₂]. FABMS m/z: 385 [M+H]⁺(pos.), FABHRMS m/z:

385.2072 (C₁₆H₃₃O₁₀requires 385.2074).

methyl-

5,7-di-O-benzyl-4,6-O-isopropylidene-1,2,3-tri-O-methoxy-

methyl- -glycero- -glycero- -manno-heptitol 24d (527 mg, 45%

from Z-19).

D-glycero-D-allo-heptitol 24c (489 mg, 42% from Z-19) and

D

3.11.3. Compound 24c

Colorless oil½a _D²⁴

ꢁ

+ 14.1 (c = 1.40, CHCl₃). IR (neat): 1454, 1381,

1258, 1207, 1150, 1107, 1034 cm^ꢂ1

.

¹H NMR (500 MHz, CDCl₃) d:

1.46/1.50 [each 3H, s, C(CH₃)₂], 3.352/3.354/3.41 (each 3H, s,

OCH₂OCH₃), 3.63 (1H, dd, J = 10.9, 2.0, H-7a), 3.70 (1H, dd,

J = 10.9, 4.6, H-7b), 3.72 (1H, dd, J = 10.9, 4.9, H-1a), 3.75 (1H, dd,

J = 9.8, 9.8, H-5), 3.87 (1H, ddd, J = 9.8, 4.6, 2.0, H-6), 3.94 (1H, dd,

J = 10.9, 2.3, H-1b), 4.01 (1H, ddd, J = 7.2, 4.9, 2.3, H-2), 4.10 (1H,

dd, J = 7.2, 1.2, H-3), 4.12 (1H, dd, J = 9.8, 1.2, H-4), 4.46/4.68 (each

1H, d, J = 10.9, PhCH₂), 4.55/4.64 (each 1H, d, J = 12.2, PhCH₂), 4.64/

4.66 (each 1H, d, J = 6.3, OCH₂OCH₃), 4.72/4.755 (each 1H, d, J = 6.6,

OCH₂OCH₃), 4.764/4.79 (each 1H, d, J = 6.3, OCH₂OCH₃), 7.20–7.38

(10H, m, arom). ¹³C NMR (125 MHz, CDCl₃) d: 19.0/29.4

[(CH₃)₂C], 55.3/55.9/56.0 (OCH₂OCH₃), 68.2 (C-1), 69.6 (C-7), 71.2

(C-5), 73.4/74.1 (PhCH₂), 73.6 (C-6), 74.5 (C-4), 76.1 (C-3), 76.7

(C-2), 96.8/97.0/97.1 (OCH₂OCH₃), 98.8 [(CH₃)₂C], 127.6/127.7/

127.8/ 128.30/ 128.34 (d arom.), 138.0/138.3 (s arom.). FABMS

m/z: 565 [M+H]⁺(pos.), FABHRMS m/z: 565.3026 (C₃₀H₄₅O₁₀re-

quires 565.3013).

Following the method described above, 24b (864 mg, 1.53

mmol), 24c (275 mg, 0.49 mmol), and 24d (287 mg, 0.51 mmol)

were converted to 4,6-O-isopropylidene-1,2,3-tri-O-methoxy-

methyl-

pylidene-1,2,3-tri-O-methoxymethyl-

(170 mg, 91%) and 4,6-O-isopropylidene-1,2,3-tri-O-methoxymethyl-

-glycero- -manno-heptitol 25d (179 mg, 92%), respectively.

D

-glycero-

D

-gluco-heptitol 25b (567 mg, 96%), 4,6-O-isopro-

D

-glycero- -allo-heptitol 25c

D

3.12.2. Compound 25b

Colorless plates (from n-hexane–Et₂O). Mp. 64.5–65 °C. bp.

173–175 °C/0.005 mmHg. ½a _D²⁴

ꢁ

– 59.2 (c = 1.27, CHCl₃). IR (neat):

3422, 1454, 1384, 1261, 1204, 1152, 1109, 1034 cm^ꢂ1

.

¹H NMR

(500 MHz, CDCl₃) d: 1.42/1.49 [each 3H, s, C(CH₃)₂], 2.14 (1H, dd-

like ca. 7.8, 4.6, OH), 3.41/3.42/3.46 (each 3H, s, OCH₂OCH₃), 3.63

(1H, dd, J = 11.2, 3.2, H-1a), 3.72–3.82 [5H, m, H-5, H-6, H-7a,

and OH, including one-proton doublet of doublets due to H-1b at

d 3.75 (J = 11.2, 2.3)], 3.82–3.86 (2H, m, H-4 and H-7b), 3.97 (1H,

ddd, J = 8.3, 3.2, 2.3, H-2), 4.06 (1H, dd, J = 8.3, 2.9, H-3), 4.66/

4.67 (each 1H, d, J = 6.6 Hz, OCH₂OCH₃), 4.76 (2H, br d, J = ca. 6.8,

OCH₂OCH₃), 4.48 (1H, d, J = 6.9, OCH₂OCH₃), 4.87 (1H, d, J = 6.3,

OCH₂OCH₃). ¹³C NMR (125 MHz, CDCl₃) d: 19.2/29.2 [C(CH₃)₂],

55.6/55.7/56.2 (OCH₂OCH₃), 63.1 (C-7), 63.3 (C-5), 67.1 (C-1),

73.0 (C-4), 73.1 (C-6), 77.3 (C-3), 77.5 (C-2), 96.9/97.0/99.5

(OCH₂OCH₃), 99.2 [C(CH₃)₂]. FABMS m/z: 385 [M+H]⁺(pos.), FAB-

HRMS m/z: 385.2085 (C₁₆H₃₃O₁₀requires 385.2074).

3.11.4. Compound 24d

Colorless oil. ½a _D²⁴

ꢁ

+ 4.45 (c = 1.37, CHCl₃). IR (neat): 1458, 1381,

1258, 1204, 1151, 1108, 1034 cm^ꢂ1

.

¹H NMR (600 MHz, CDCl₃) d:

1.48 [6H, s, C(CH₃)₂], 3.36/3.39/3.40 (each 3H, s, OCH₂OCH₃), 3.68

(1H, dd, J = 11.0, 2.0, H-7a), 3.73 (1H, dd, J = 11.2, 4.5, H-1a), 3.76

(1H, dd, J = 11.0, 4.3, H-7b), 3.77 (1H, dd, J = 9.7, 9.7, H-5), 3.86

(1H, ddd, J = 6.9, 4.5, 2.5, H-2), 3.91 (1H, ddd, J = 9.7, 4.3, 2.0, H-6),

3.92 (1H, dd, J = 11.2, 2.4, H-1b), 3.97 (1H, dd, J = 9.7, 1.2, H-4),

4.11 (1H, dd, J = 6.9, 1.2, H-3), 4.50/4.76 (each 1H, d, J = 11.2 Hz,

PhCH₂), 4.56/4.67 (each 1H, d, J = 12.2, PhCH₂), 4.65/4.66 (each

1H, d, J = 6.4, OCH₂OCH₃), 4.71/4.72 (each 1H, d, J = 6.7, OCH₂OCH₃),

4.74/4.91 (each 1H, d, J = 6.7, OCH₂OCH₃), 7.21–7.38 (10H, m,

arom). ¹³C NMR (150 MHz, CDCl₃) d: 19.1/29.5 [(CH₃)₂C], 55.3/

55.7/55.9 (OCH₂OCH₃), 67.8 (C-1), 69.96 (C-7), 70.02 (C-5), 71.9

(C-4), 73.55/73.6 (PhCH₂), 73.57 (C-6), 76.6 (C-3), 77.3 (C-2), 96.8/

97.1/98.1 (OCH₂OCH₃), 98.5 [(CH₃)₂C], 127.56/127.62/127.9/

128.27/128.30 (d arom.), 138.3/138.4 (s arom.). FABMS m/z: 565

[M+H]⁺(pos.), FABHRMS m/z: 565.3002 (C₃₀H₄₅O₁₀requires

565.3013).

3.12.3. Compound 25c

Colorless oil. ½a _D²⁴

ꢁ

+ 22.4 (c = 3.30, CHCl₃). IR (neat): 3421, 1458,

1385, 1261, 1207, 1151, 1108, 1034 cm^ꢂ1

.

¹H NMR (600 MHz,

CDCl₃) d: 1.39/1.49 [each 3H, s, C(CH₃)₂], 2.19 (1H, br t-like, J = ca

5.3, OH), 3.37/3.42/3.43 (each 3H, s, OCH₂OCH₃), 3.648 (1H, ddd,

J = 9.1, 9.1, 2.1, H-5), 3.650 (1H, dd, J = 10.5, 6.9, H-1a), 3.71–3.78

[3H, m, H-6, H-7a including one-proton doublet of doublets due

to H-1b at d 3.73 (J = 10.5, 4.7)], 3.85 (1H, ddd, J = 7.2, 5.3, 5.3, H-

7b), 3.88 (1H, dd, J = 9.1, 4.4, H-4), 3.98 (1H, dd, J = 4.4, 3.1, H-3),

4.112 (1H, ddd, J = 6.9, 4.7, 3.1, H-2), 4.114 (1H, d, J = 2.1, OH),

4.63/4.64 (each 1H, d, J = 6.7, OCH₂OCH₃), 4.77/4.80 (each 1H, d,

J = 6.7, OCH₂OCH₃), 4.78/4.83 (each 1H, d, J = 6.4, OCH₂OCH₃). ¹³C

NMR (150 MHz, CDCl₃) d: 19.3/29.2 [C(CH₃)₂], 55.3/55.8/56.1

(OCH₂OCH₃), 63.4 (C-7), 64.6 (C-5), 67.5 (C-1), 72.2 (C-4), 73.0 (C-

6), 76.3 (C-2), 79.3 (C-3), 96.6/96.87/96.93 (OCH₂OCH₃), 98.6

[C(CH₃)₂]. FABMS m/z: 385 [M+H]⁺(pos.), FABHRMS m/z:

385.2090 (C₁₆H₃₃O₁₀requires 385.2074).

3.12. Hydrogenolysis of MOM ethers 24a, 24b, 24c and 24d

A suspension of 10% palladium-on-carbon (2.0 g) and sodium

hydrogen carbonate (400 mg) in 1,4-dioxane (20 ml) was pre-

equilibrated with hydrogen. To the suspension was added a solu-

tion of 24a (2.85 g, 5.05 mmol) in 1,4-dioxane (25 ml), and the

mixture was hydrogenated at 60 °C under atmospheric pressure

until the uptake of hydrogen ceased. The catalyst was ﬁltered off,

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6331

3.12.4. Compound 25d

propylidene-1,2,3-methoxymethyl-D-glycero-D-manno-heptitol

5,7-cyclic sulfate 12d (134 mg, 75%), respectively.

Colorless oil. ½a _D²⁴

ꢁ

– 9.1 (c = 3.16, CHCl₃). IR (neat): 3420, 1458,

1384, 1261, 1204, 1153, 1108, 1030 cm^ꢂ1

.

¹H NMR (600 MHz,

CDCl₃) d: 1.43/1.48 [each 3H, s, C(CH₃)₂], 2.16 (1H, br dd-like ca.

7.2, 4.0, OH), 3.39/3.42/3.49 (each 3H, s, OCH₂OCH₃), 3.55 (1H, d,

J = 4.8, OH), 3.71 (1H, dd, J = 11.0, 3.1, H-1a), 3.72 (1H, ddd,

J = 9.6, 9.6, 4.8, H-5), 3.76–3.87 [4H, m, H-6, H-7a, H-7b, including

one-proton doublet of doublet of doublets due to H-2 at d 3.85

(J = 8.4, 3.1, 2.4)], 3.90 (1H, dd, J = 11.0, 2.4, H-1b), 3.95 (1H, dd,

J = 9.6, 2.4, H-4), 4.07 (1H, dd, J = 8.4, 2.4, H-3), 4.68/4.700 (1H, d,

J = 6.5, OCH₂OCH₃), 4.69/4.74 (1H, d, J = 6.5, OCH₂OCH₃), 4.702/

4.85 (1H, d, J = 6.5, OCH₂OCH₃). ¹³C NMR (150 MHz, CDCl₃) d:

19.4/29.4 [C(CH₃)₂], 55.6/55.7/56.8 (OCH₂OCH₃), 63.0 (C-7), 63.4

(C-5), 67.5 (C-1), 72.5 (C-4), 73.1 (C-6), 76.17 (C-3), 76.22 (C-2),

97.0/97.6/99.0 (OCH₂OCH₃), 99.1 [C(CH₃)₂]. FABMS m/z: 385

[M+H]⁺(pos.), FABHRMS m/z: 385.2097 (C₁₆H₃₃O₁₀requires

385.2074).

3.13.2. Compound 12b

Colorless prisms (from n-hexane–AcOEt). mp. 79–80 °C.½a _D²⁴

ꢁ

–

29.4 (c = 2.50, CHCl₃). IR (CHCl₃): 1416, 1231, 1200, 1150, 1107,

1018 cm^ꢂ^{1 1}H NMR (500 MHz, CDCl₃) d: 1.46/1.56 [each 3H s,

.

C(CH₃)₂], 3.38/3.40/3.46 (each 3H, s, OCH₂OCH₃), 3.60 (1H, dd,

J = 11.5, 6.0, H-1a), 3.81 (1H, dd, J = 11.5, 2.6, H-1b), 3.94 (1H, dd,

J = 6.6, 1.7, H-3), 4.01 (1H, dd, J = 6.6, 6.0, 2.6, H-2), 4.25 (1H, ddd,

J = 10.6, 9.5, 4.9, H-6), 4.26 (1H, dd, J = 9.5, 1.7, H-4), 4.47 (1H, dd,

J = 10.6, 4.9, H-7 eq), 4.61 (1H, dd, J = 10.6, 10.6, H-7ax), 4.63/4.65

(each 1H, d, J = 6.6, OCH₂OCH₃), 4.71 (1H, dd, J = 9.5, 9.5, H-5), 4.74

(2H, d, J = 6.6, OCH₂OCH₃), 4.78 (1H, d, J = 6.6, OCH₂OCH₃), 4.81

(1H, d, J = 6.6, OCH₂OCH₃). ¹³C NMR (125 MHz, CDCl₃) d: 19.1/28.8

[C(CH₃)₂], 55.4/55.8/56.5 (OCH₂OCH₃), 64.6 (C-6), 68.0 (C-1), 69.6

(C-4), 73.1 (C-7), 73.5 (C-3), 76.5 (C-5), 77.2 (C-2), 96.8/97.3/98.2

(OCH₂OCH₃), 101.3 [C(CH₃)₂]. FABMS m/z: 447 [M+H]⁺(pos.), FAB-

HRMS m/z: 447.1545 (C₁₆H₃₁O₁₂S requires 447.1537).

3.13. Preparation of cyclic sulfates 12a, 12b, 12c and 12d

A

solution of freshly distilled thionyl chloride (250

l

l,

3.13.3. compound 12c

3.4 mmol) in dichloromethane (20 ml) was added dropwise to a

stirred mixture of diol 25a (1.0 g, 2.6 mmol), triethylamine

(0.9 ml, 6.5 mmol) and dichloromethane (20 ml) at 0 °C. After

being stirred at 0 °C for 30 min, the mixture was poured into ice-

cooled and vigorously stirred aq. sodium hydrogen carbonate

(40 ml), and extracted with dichloromethane. The extract was

washed with brine, and condensed to give the corresponding sul-

ﬁte (1.3 g) as a pale yellow oil, which was immediately used in

the next step without puriﬁcation.

To a well stirred mixture of the crude sulﬁte (1.3 g), sodium

hydrogen carbonate (800 mg, 9.5 mmol), carbon tetrachloride

(20 ml), acetonitrile (20 ml), and water (20 ml) was added drop-

wise a brown mixture of sodium metaperiodate (1.67 g, 7.8 mmol),

ruthenium chloride n-hydrate (100 mg), and water (13 ml) at 0 °C.

After being stirred at 0 °C for 30 min, the reaction was quenched by

the addition of aqueous sodium thiosulfate–sodium hydrogen car-

bonate (20 ml). The resulting purple mixture was extracted with

diethyl ether. The extract was washed with brine, and condensed

to give a colorless oil (1.27 g), which on column chromatography

(CH₂Cl₂–AcOEt, 5/1) gave 2,4-O-isopropylidene-5,6,7-methoxy-

Colorless oil.½a _D²⁴

ꢁ

– 12.5 (c = 5.68, CHCl₃). IR (neat): 1458, 1420,

1252, 1204, 1152, 1114, 1026 cm^ꢂ1

.

¹H NMR (600 MHz, CDCl₃) d:

1.43/1.56 [each 3H, s, C(CH₃)₂], 3.38 (3H, s, OCH₂OCH₃), 3.43 (6H,

s, OCH₂OCH₃), 3.69 (1H, dd, J = 10.5, 4.0, H-1a), 3.85 (1H, ddd,

J = 7.7, 4.0, 2.8, H-2), 3.87 (1H, ddd, J = 10.5, 2.8, H-1b), 3.97 (1H,

dd, J = 7.7, 2.0, H-3), 4.24 (1H, ddd, J = 10.5, 9.8, 4.8, H-6), 4.43

(1H, dd, J = 9.8, 2.0, H-4), 4.47 (1H, dd, J = 10.5, 4.8, H-7 eq), 4.60

(1H, dd, J = 10.5, 10.5, H-7ax), 4.66 (2H, s, OCH₂OCH₃), 4.74/4.78

(each 1H, d, J = 6.5, OCH₂OCH₃), 4.77 (2H, s, OCH₂OCH₃), 4.83

(1H, dd, J = 9.8, 9.8, H-5). ¹³C NMR (150 MHz, CDCl₃) d: 19.1/28.7

[(CH₃)₂C], 55.4/56.0/56.4 (OCH₂OCH₃), 64.3 (C-6), 66.9 (C-1), 71.1

(C-4), 73.0 (C-7), 75.8 (C-2), 76.1 (C-3), 77.9 (C-5), 96.7/96.9/97.9

(OCH₂OCH₃), 101.2 [(CH₃)₂C]. FABMS m/z: 447 [M+H]⁺(pos.), FAB-

HRMS m/z: 447.1549 (C₁₆H₃₁O₁₂S requires 447.1537).

3.13.4. Compound 12d

Colorless oil. ½a _D²⁴

ꢁ

– 9.9 (c = 6.00, CHCl₃). IR (neat): 1458, 1420,

1253, 1204, 1153, 1112, 1034 cm^ꢂ1

.

¹H NMR (600 MHz, CDCl₃) d:

1.47/1.55 [each 3H, s, C(CH₃)₂], 3.39/3.42/3.46 (each 3H, s,

OCH₂OCH₃), 3.72 (1H, dd, J = 11.2, 3.6, H-1a), 3.80 (1H, ddd,

J = 7.8, 3.6, 2.4, H-2), 3.91 (1H, dd, J = 11.2, 2.4, H-1b), 3.97 (1H,

dd, J = 7.8, 1.6, H-3), 4.26 (1H, ddd, J = 10.3, 9.8, 4.8, H-6), 4.29

(1H, dd, J = 9.8, 1.6, H-4), 4.49 (1H, dd, J = 10.3, 4.8, H-7 eq), 4.62

(1H, dd, J = 10.3, 10.3, H-7ax), 4.68 (2H, s, OCH₂OCH₃), 4.71/4.73

(each 1H, d, J = 6.7, OCH₂OCH₃), 4.71 (1H, dd, J = 9.8, 9.8, H-3),

4.72/4.80 (1H, d, J = 6.2, OCH₂OCH₃). ¹³C NMR (150 MHz, CDCl₃)

d: 19.2/28.8 [C(CH₃)₂], 55.5/55.8/56.5 (OCH₂OCH₃), 64.5 (C-6),

67.0 (C-1), 70.0 (C-4), 73.1 (C-7), 73.6 (C-3), 75.9 (C-2), 76.8 (C-

5), 96.9/97.2/98.6 (OCH₂OCH₃), 101.4 [C(CH₃)₂]. FABMS m/z: 447

methyl-

51%).

D-glycero-L-allo-heptitol 1,3-cyclic sulfate 12a (593 mg,

3.13.1. Compound 12a

Colorless oil. ½a _D²²

ꢁ

+ 5.02 (c = 2.57, CHCl₃). IR (neat): 1454, 1416,

1250, 1203, 1151, 1110, 1026 cm^ꢂ1

.

¹H NMR (600 MHz, CDCl₃) d:

1.45/1.56 [each 3H, s, C(CH₃)₂], 3.38/3.41/3.43 (each 3H, s,

OCH₂OCH₃), 3.74 (1H, dd, J = 11.0, 5.0, H-7a), 3.77 (1H, dd,

J = 11.0, 3.4, H-7b), 3.92–3.77 (2H, m, H-5 and H-6), 4.22 (1H,

ddd, J = 10.3, 9.8, 4.8, H-2), 4.25 (1H, dd, J = 9.8, 2.7, H-4), 4.46

(1H, dd, J = 10.3, 4.8, H-1 eq), 4.60 (1H, dd, J = 10.3, 10.3, H-1ax),

4.64/4.66 (each 1H, d, J = 6.7, OCH₂OCH₃), 4.74/4.77 (each 1H, d,

J = 6.7, OCH₂OCH₃), 4.75/4.78 (each 1H, d, J = 6.7, OCH₂OCH₃),

4.87 (1H, dd, J = 9.8, 9.8 Hz, H-3). ¹³C NMR (150 MHz, CDCl₃) d:

19.1/28.7 [C(CH₃)₂], 55.5/55.8/56.2 (OCH₂OCH₃), 64.3 (C-2), 68.0

(C-7), 71.0 (C-4), 73.0 (C-1), 76.5/76.6 (C-5 and C-6), 78.1 (C-3),

96.8/97.1/97.9 (OCH₂OCH₃), 101.2 [C(CH₃)₂]. FABMS m/z: 447

[M+H]⁺(pos.), FABHRMS m/z: 447.1561 (C₁₆H₃₁O₁₂S₁requires

447.1537).

Following the method described above, 25b (539 mg,

1.4 mmol), 25c (148 mg, 0.38 mmol), and 25d (154 mg, 0.4 mmol)

were converted to 4,6-O-isopropylidene-1,2,3-tri-O-methoxy-

methyl-

57%), 4,6-O-isopropylidene-1,2,3-tri-O-methoxy-methyl-

-allo-heptitol 5,7-cyclic sulfate 12c (74 mg, 43%), and 4,6-O-iso-

[M+H]⁺(pos.), FABHRMS m/z: 447.1559 (C₁₆H₃₁O₁₂

447.1537).

S requires

3.14. Coupling reaction between cyclic sulfates (12a, 12b, 12c,

and 12d) and Thiosugar 13

According to the literature,^9ca mixture of cyclic sulfate 12a

(200 mg, 0.45 mmol), thiosugar^8m13 (51.7 mg, 0.35 mmol), potas-

sium carbonate (15 mg, 0.11 mmol), and 1,1,1,3,3,3-hexaﬂuoroiso-

propanol (HFIP, 0.5 ml) in a sealed tube was stirred at 60 °C for

42 h. After removal of the solvent, the residue was triturated with

diethyl ether to give a yellow amorphous (272 mg), which on col-

umn chromatography (CHCl₃? CHCl₃–MeOH, 10/1?5/1) gave

1,4-dideoxy-1,4-{(S)-[(2S,3S,4S,5S,6R)-2,4-O-isopropylidene-5,6,7-

D

-glycero-

D

-gluco-heptitol 5,7-cyclic sulfate 12b (356 mg,

D-glycero-

tri-O-methoxymethyl-3-(sulfooxy)heptyl]episulfoniumylidene}-

arabinitol inner salt 26a (187 mg, 91%).

D-

D

6332

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

3.14.1. Compound 26a

J = 13.8, 4.6, H-1⁰a), 4.08 (1H, ddd, J = 6.4, 6.0, 1.9, H-6⁰), 4.13 (1H,

dd, J = 13.8, 3.2, H-1⁰b), 4.18 (1H, dd, J = 6.4, 1.2, H-5⁰), 4.24 (1H,

dd, J = 9.6, 1.2, H-4⁰), 4.38 (1H, ddd, J = 9.6, 4.6, 3.2, H-2⁰), 4.43

(1H, d-like, J = 2.2, H-3), 4.48 (1H, dd, J = 9.6, 9.6, H-3⁰), 4.60–4.63

(1H, m, H-2), 4.62/4.67 (each 1H, d, J = 6.5, OCH₂OCH₃), 4.70/4.92

(each 1H, d, J = 6.3, OCH₂OCH₃), 4.74/4.75 (each 1H, d, J = 6.7,

OCH₂OCH₃). ¹³C NMR (150 MHz, CD₃OD) d: 19.2/29.2 [(CH₃)₂C],

50.5 (C-1⁰), 51.4 (C-1), 55.6/56.3/56.5 (OCH₂OCH₃), 60.9 (C-5),

69.7 (C-7⁰), 70.9 (C-3⁰), 71.4 (C-2⁰), 73.5 (C-4), 74.8 (C-4⁰), 77.8 (C-

6⁰), 78.0 (C-5⁰), 79.2 (C-2), 80.1 (C-3), 97.8/97.9/98.7 (OCH₂CH₃),

101.1 [(CH₃)₂C]. FABMS m/z: 597 [M+H]⁺(pos.), FABHRMS m/z:

597.1890 (C₂₁H₄₁O₁₅S₂requires 597.1887).

Following the method described above, cyclic sulfate 12d

(130 mg, 0.29 mmol) was treated with thiosugar 13 (37 mg,

0.25 mmol) at 60 °C for 72 h. Work-up gave a pale orange amor-

phous (215 mg), which on column chromatography (CHCl₃?

CHCl₃–MeOH, 10/1?5/1) gave 1,4-dideoxy-1,4-{(S)-[(2S,3S,4S,5R,

6 R )-2,4-O-isopropylidene-5,6,7-tri-O-methoxymethyl-3-(sulfoxy)

Colorless prisms (from MeOH–Et₂O). mp. 160–161 °C.

+ 17.7 (c = 0.84, CH₃OH). IR (nujol): 3344, 1265, 1211, 1150,

1103, 1030 cm^ꢂ^{1 1}H NMR (500 MHz, CD₃OD) d: 1.47/1.54 [each

½ ꢁ

a ²_D²

.

3H, s, C(CH₃)₂], 3.36/3.39/3.41 (each 3H s, OCH₂OCH₃), 3.78 (1H,

dd, J = 12.8, 3.8, H-1a), 3.81 (2H, d-like, J = ca. 4.5, H-7⁰a and H-

7⁰b), 3.85 (1H, dd, J = 12.8, 1.8, H-1b), 3.94 (1H, dd, J = 10.6, 1.7,

H-5a), 3.98 (1H, dd, J = 10.6, 4.6, H-5b), 3.98–4.02 (1H, m, H-4),

4.06 (1H, dd, J = 13.8, 4.9, H-1⁰a), 4.08 (1H, dd, J = 6.9, 1.5, H-5⁰),

4.14 (1H, dd, J = 13.8, 3.2, H-1⁰b), 4.18 (1H, dd, J = 9.5, 1.5, H-4⁰),

4.24 (1H, dt-like, J = 6.9, 4.5, H-6⁰), 4.40 (1H, ddd, J = 9.5, 4.9, 3.2,

H-2⁰), 4.43 (1H, br d, J = 2.0, H-3), 4.50 (1H, dd, J = 9.5, 9.5, H-3⁰),

4.60–4.63 (1H, br m, H-2), 4.63/4.65 (each 1H, d, J = 6.3,

OCH₂OCH₃), 4.70/4.76/4.89 (each 1H, d, J = 6.6, OCH₂OCH₃, a signal

due to one of the methylene protons in MOM groups overlapped

with that of CD₃OH). ¹³C NMR (125 MHz, CD₃OD) d: 19.3/29.2

[(CH₃)₂C], 50.5 (C-1⁰), 51.4 (C-1), 55.7/56.1/56.4 (OCH₂OCH₃), 60.9

(C-5), 69.9 (C-7⁰), 70.8 (C-3⁰), 71.3 (C-2⁰), 73.4 (C-4), 74.5 (C-4⁰),

78.7 (C-6⁰), 78.8 (C-5⁰), 79.2 (C-2). 80.1 (C-3), 97.8/98.7/98.8

(OCH₂OCH₃), 101.1 [(CH₃)₂C]. FABMS m/z: 597 [M+H]⁺(pos.), FAB-

HRMS m/z: 597.1863 (C₂₁H₄₁O₁₅S₂requires 597.1887).

heptyl]episulfoniumylidene}-D-arabinitol inner salt 26d (135 mg,

92%).

Following the method described above, cyclic sulfate 12b

(300 mg, 0.67 mmol) was treated with thiosugar 13 (78 mg,

3.14.4. Compound 26d

Colorless amorphous. ½a _D²⁵

ꢁ

+ 29.7 (c = 4.20, CH₃OH). IR (nujol):

0.52 mmol) at 60 °C for 54 h. Work-up gave

a

colorless oil

3391, 1255, 1207, 1157, 1103, 1022 cm^ꢂ^{1 1}H NMR (500 MHz,

.

(394 mg), which on column chromatography (CHCl₃? CHCl₃–

MeOH, 10/1?5/1) gave 1,4-dideoxy-1,4-{(S)-[(2S,3S,4S,5R,6S)-2,4-

O-isopropylidene-5,6,7-tri-O-methoxymethyl-3-(sulfooxy)heptyl]-

CD₃OD) d: 1.46/1.55 [each 3H, s, C(CH₃)₂], 3.36/3.39/3.44 (each

3H, s, OCH₂OCH₃), 3.72 (1H, dd, J = 10.9, 5.4, H-7a⁰), 3.77–3.82

[2H, m, H-6⁰, including one-proton doublet of doublets due to H-

1a at d 3.79 (J = 12.6, 3.7)], 3.84 (1H, dd, J = 12.6, 1.6, H-1b), 3.90

(1H, dd, J = 10.9, 2.3, H-7b⁰), 3.93–3.99 (2H, m, H-4 and H-5a),

4.00 (1H, dd, J = 10.4, 4.0, H-5b), 4.04 (1H, dd, J = 13.5, 5.2, H-1a⁰),

4.11 (1H, dd, J = 9.5, 0.9, H-4⁰), 4.15 (1H, dd, J = 13.5, 2.9, H-1b⁰),

4.18 (1H, dd, J = 6.6, 0.9, H-5⁰), 4.41 (1H, dm, J = ca. 9.5, H-2⁰),

4.43 (1H, br d, J = 2.3, H-3), 4.48 (1H, dd, J = 9.5, 9.5, H-3⁰), 4.60–

4.62 (1H, m, H-2), 4.62/4.64 (each 1H, d, J = 6.6 Hz, OCH₂OCH₃),

4.70/4.72 (each 1H, d, J = 6.6, OCH₂OCH₃), 4.88/4.90 (each 1H, d,

J = 6.3, OCH₂OCH₃). ¹³C NMR (125 MHz, CD₃OD) d: 19.5/29.1

[C(CH₃)₂], 50.6 (C-1⁰), 51.3 (C-1), 55.7/56.2/56.6 (OCH₂OCH₃),

60.9 (C-5), 68.9 (C-7⁰), 70.3 (C-3⁰), 71.2 (C-2⁰), 72.3 (C-4⁰), 73.5

(C-4), 77.0 (C-5⁰), 78.6 (C-6⁰), 79.2 (C-2), 80.0 (C-3), 97.8/

98.0/100.3 (OCH₂CH₃), 101.1 [C(CH₃)₂]. FABMS m/z: 597

[M+H]⁺(pos.), FABHRMS m/z: 597.1912 (C₂₁H₄₁O₁₅S₂requires

597.1887).

episulfoniumylidene}-D-arabinitol inner salt 26b (278 mg, 90%).

3.14.2. Compound 26b

Colorless prisms (from MeOH–Et₂O). Mp. 153–154 °C.

+ 40.8 (c = 1.15, CH₃OH). IR (nujol): 3420, 3329, 1261, 1207,

1149, 1103, 1038 cm^ꢂ^{1 1}H NMR (500 MHz, CD₃OD) d: 1.45/1.55

½ ꢁ

a ²_D⁴

.

[each 3H, s, C(CH₃)₂], 3.35/3.400/3.402 (each 3H, s, OCH₂OCH₃),

3.55 (1H, dd, J = 11.5, 7.8, H-7⁰a), 3.78 (1H, dd, J = 12.9, 3.8, H-1a),

3.83 (1H, dd, J = 12.9, 2.3, H-1b), 3.88 (1H, dd, J = 11.5, 1.5, H-7⁰b),

3.94 (1H, br dd, J = 7.2, 6.6, H-4 and 1H, dd, J = 8.0, 6.6, H-5a),

3.99 (1H, dd, J = 8.0, 7.2, H-5b), 4.02 (1H, dd, J = 13.8, 4.6, H-1⁰a),

4.12 (1H, dd, J = 13.8, 3.2, H-1⁰b), 4.15–4.20 [3H, m, H-4⁰, H-5⁰

and H-6⁰], 4.35 (1H, dd, J = 9.5, 9.5, H-3⁰), 4.40 (1H, ddd, J = 9.5,

4.6, 3.2, H-2⁰), 4.44 (1H, br d, J = 1.8, H-3), 4.59–4.61 (1H, m, H-

2), 4.60/4.63 (each 1H, d, J = 6.6, OCH₂OCH₃), 4.68/4.77 (each 1H,

d, J = 6.6, OCH₂OCH₃), 4.74/5.01 (each 1H, d, J = 6.9, OCH₂OCH₃).

¹³C NMR (125 MHz, CD₃OD) d: 19.3/29.1 [(CH₃)₂C], 50.5 (C-1⁰),

51.3 (C-1), 55.6/56.2/56.5 (OCH₂OCH₃), 60.9 (C-5), 69.7 (C-3⁰),

69.9 (C-7⁰), 70.9 (C-4⁰), 71.4 (C-2⁰), 73.5 (C-4), 77.5 (C-6⁰), 79.1 (C-

2), 79.6 (C-5⁰), 80.1 (C-3), 97.6/98.3/100.7 (OCH₂CH₃), 101.0

[(CH₃)₂C]. FABMS m/z: 597 [M+H]⁺(pos.), FABHRMS m/z:

597.1861 (C₂₁H₄₁O₁₅S₂requires 597.1887).

3.15. Preparation of kotalanol analogs 11a, 11b, 11c and 11d

A solution of coupled product 26a (158 mg, 0.27 mol) in 30%

aqueous triﬂuoroacetic acid (15 ml) was stirred at 50 °C for 2 h. Re-

moval of the solvent in vacuo left a colorless oil (156 mg), which on

column chromatography (CHCl₃–MeOH–H₂O, 10/5/1) gave 1,4-

dideoxy-1,4-{(S)-[(2S,3S,4S,5S,6R)-2,4,5,6,7-pentahydroxy-3-(sul-

Following the method described above, cyclic sulfate 12c

(73 mg, 0.16 mmol) was treated with thiosugar 13 (21 mg,

0.14 mmol) at 60 °C for 54 h. Work-up gave a pale orange oil

(96.4 mg), which on column chromatography (CHCl₃?CHCl₃–

MeOH, 20/1?10/1) gave 1,4-dideoxy-1,4-{(S)-[(2S,3S,4S,5S,6S)-

2,4-O-isopropylidene-5,6,7-tri-O-methoxymethyl-3-(sulfooxy)

fooxy)heptyl]episulfoniumylidene}-D-arabinitol inner salt 11a

(88 mg, 78%).

3.15.1. Compound 11a

Colorless viscous oil. ½a _D²⁴

ꢁ

+ 12.4 (c = 0.97, H₂O). IR (neat): 3380,

heptyl]episulfoniumylidene}-

86%).

D-arabinitol inner salt 26c (72 mg,

1297, 1271, 1238, 1215, 1135, 1108, 1065, 1025 cm^ꢂ^{1 1}H NMR

.

(500 MHz, CD₃OD) d: 3.62 (1H, dd, J = 10.5, 6.5, H-7⁰a), 3.64 (1H,

dd, J = 10.5, 5.8, H-7⁰b), 3.76 (1H, dd, J = 8.3, 2.0, H-5⁰), 3.84 (2H,

d-like, J = ca. 2.6, H-1a and H-1b), 3.88–3.93 [2H, m, H-1⁰a, includ-

ing one-proton broad doublet of doublets due to H-6⁰at d 3.91

(J = 6.5, 5.8)], 3.93 (1H, dd, J = 8.6, 5.7, H-5a), 3.95–4.00 [2H, m,

H-4, including one-proton doublet of doublets due to H-1⁰b at d

3.99 (J = 13.5, 4.0)], 4.03 (1H, dd, J = 8.6, 3.5, H-5b), 4.16 (1H, dd,

J = 8.3, 2.6, H-4⁰), 4.38 (1H, d-like, J = ca. 2.6, H-3), 4.54 (1H, ddd,

J = 6.3, 6.3, 4.0, H-2⁰), 4.59 (1H, dt-like, J = ca. 2.6, 2.6, H-2),

4.73 (1H, dd, J = 6.3, 2.6, H-3⁰). ¹³C NMR spectrum of 11a was

3.14.3. Compound 26c

Colorless amorphous. ½a _D²⁶

ꢁ

– 10.5 (c = 3.38, CH₃OH). IR (nujol):

¹H NMR (600 MHz,

3383, 1262, 1211, 1150, 1103, 1022 cm^ꢂ1

.

CD₃OD) d: 1.47/1.55 [each 3H, s, C(CH₃)₂], 3.35/3.40/3.42 (each

3H, s, OCH₂OCH₃), 3.65 (1H, dd, J = 11.0, 6.0, H-7⁰a), 3.77 (1H, dd,

J = 12.7, 3.6, H-1a), 3.84 (1H, dd, J = 12.7, 1.6, H-1b), 3.94 (1H, dd,

J = 8.1, 4.9, H-5a), 3.97 (1H, dd, J = 11.0, 1.9, H-7⁰b), 3.97–3.99

(1H, m, H-4), 3.99 (1H, dd, J = 8.1, 3.6, H-5b), 4.06 (1H, dd,

G. Tanabe et al. / Bioorg. Med. Chem. 20 (2012) 6321–6334

6333

summarized in Table 1. FABMS m/z: 425 [M+H]⁺(pos.), FABHRMS

m/z: 425.0795 (C₁₂H₂₅O₁₂S₂requires 425.0788).

[M+H]⁺(pos.), FABHRMS m/z: 425.0760 (C₁₂H₂₅O₁₂S₂requires

425.0788).

Following the method described above, 26b (112 mg,

0.19 mmol) was hydrolyzed with 30% aqueous TFA (11 ml) at

50 °C for 2 h. Work-up gave a colorless oil (114 mg), which on col-

umn chromatography (CHCl₃–MeOH–H₂O, 10/5/1) gave 1,4-dide-

oxy-1,4-{(S)-[(2S,3S,4S,5R,6S)-2,4,5,6,7-pentahydroxy-3-(sulfooxy)

3.16. X-Ray crystallographic analysis

Data of compound 12b were taken on a Rigaku RAXIS RAPID

imaging plate area detector with graphite monochromated Mo-

heptyl]episulfoniumylidene}-

82%).

D

-arabinitol inner salt 11b (65.3 mg,

Ka radiation. The structure of 12b was solved by direct methods

with SIR97 and SHELXL97. Full-matrix least-squares reﬁnement

was employed with anisotropic thermal parameters for all non-

hydrogen atoms. All calculations were performed using the Crystal

Structure (Ver. 3.6, Rigaku/MSC) crystallographic software pack-

age. ORTEP drawing of compound 12b is shown in Figure 3. The

data of 12b have been deposited with the Cambridge Crystallo-

graphic Data Centre as supplementary publication number CCDC

884491.

3.15.2. Compound 11b

Colorless amorphous. ½a _D²⁴

ꢁ

– 8.1 (c = 1.13, H₂O). IR (nujol): 3390,

¹H NMR

1260, 1235, 1205, 1162, 1107, 1060, 1016 cm^ꢂ1

.

(500 MHz, CD₃OD) d: 3.61 (1H, dd, J = 11.2, 6.2, H-7⁰a), 3.68 (1H,

dd, J = 11.2, 4.5, H-7⁰b), 3.79 (1H, ddd, J = 6.2, 4.6, 4.5, H-6⁰), 3.84

(2H, d-like, J = ca. 2.6, H-1a and H-1b), 3.89 (1H, dd, J = 4.6, 1.7,

H-5⁰), 3.90–3.99 [3H, m, H-4, including one-proton doublet of dou-

blets due to H-1⁰a at d 3.92 (J = 13.5, 3.7) and one-proton doublet of

doublets due to H-5a at d 3.94 (J = 10.0, 8.0)], 3.98 (1H, dd, J = 13.5,

8.1, H-1⁰b), 3.99 (1H, dd, J = 6.9, 1.7, H-4⁰), 4.03 (1H, dd, J = 10.0, 4.9,

H-5b), 4.38 (1H, dd, J = 2.6, 1.5, H-3), 4.47 (1H, dd, J = 6.9, 4.6, H-3⁰),

4.53 (1H, ddd, J = 8.1, 4.6, 3.7, H-2⁰), 4.60 (1H, dt-like, J = ca. 2.6, 2.6,

H-2). ¹³C NMR spectrum of 11b was summarized in Table 1. FABMS

m/z: 425 [M+H]⁺(pos.), FABHRMS m/z: 425.0809 (C₁₂H₂₅O₁₂S₂re-

quires 425.0788).

3.17. Crystal data for cyclic sulfate 12b

Monoclinic, space group C2, a = 30.63(3), b = 8.98(1),

c = 19.50(2) Å, b = 125.50(3)°, V = 4350(7) Å³, Z = 8,

l

(Mo-

) = 2.07 cm^ꢂ1, F(000) = 1904, D_c= 1.363 g/cm³, crystal dimen-

sions: 0.24 ꢃ 0.30 ꢃ 0.32 mm. A total of 19,955 reﬂections (9450

unique) were collected using the -2h scan technique to a maxi-

mum 2h value of 55°, and 1400 reﬂections with I > 2 (I) were used

Ka

x

r

Following the method described above, 26c (41 mg,

0.069 mmol) was hydrolyzed with 30% aqueous TFA (4 ml) at

50 °C for 1 h. Work-up gave a colorless oil (43 mg), which on

column chromatography (CHCl₃–MeOH–H₂O, 10/5/1) gave 1,4-

dideoxy-1,4-{(S)-[(2S,3S,4S,5S,6S)-2,4,5,6,7-pentahydroxy-3-(sulfo-

in the structure determination. Final R and R_wvalues were 0.048

and 0.140, respectively. The maximum and minimum peaks in

the difference map were 0.51 e^ꢂÅ^ꢂ3and –0.40 e^ꢂÅ^ꢂ3, respectively.

3.17.1. Enzyme inhibition assays

Rat small intestinal brush border membrane vesicles were pre-

pared and its suspension in 0.1 M maleate buffer (pH 6.0) was used

oxy)-heptyl]episulfoniumylidene}-

27 mg, 92%).

D-arabinitol inner salt (11c,

as small intestinal

a-glucosidases of maltase and sucrase. A test

3.15.3. Compound 11c

compound was dissolved in dimethyl sulfoxide (DMSO), and the

resulting solution was diluted with 0.1 M maleate buffer to prepare

the test compound solution (concentration of DMSO: 10%). A sub-

strate solution in the maleate buffer (maltose: 74 mM, sucrose:

Colorless solid. ½a _D²⁴

ꢁ

+ 4.4 (c = 2.31, H₂O). IR (nujol): 3391, 1262,

1215, 1108, 1061 cm^ꢂ1. ¹H NMR (500 MHz, CD₃OD) d: 3.65 (1H, dd,

J = 11.2, 5.2, H-7⁰a), 3.77 (1H, dd, J = 11.2, 3.2, H-7b⁰), 3.77–3.82

(2H, m, H-5⁰and H-6⁰), 3.84 (2H, d-like, J = ca. 2.6, H-1a and H-

1b), 3.92 (1H, dd, J = 13.5, 6.9, H-1a⁰), 3.95 (1H, dd, J = 9.7, 7.5, H-

5a), 3.97–4.03 [2H, m, H-4, including one-proton doublet of dou-

blets due to H-1⁰b at d ca. 4.00 (J = ca. 13.5, 3.8)], 4.03 (1H, dd,

J = 9.7, 4.9, H-5b), 4.23 (1H, dd, J = 6.0, 2.9, H-4⁰), 4.39 (1H, dd,

J = 2.6, 1.2, H-3), 4.54 (1H, ddd, J = 6.9, 6.0, 3.8, H-2⁰), 4.60 (1H,

dt-like, J = ca. 2.6, 2.6, H-2), 4.72 (1H, dd, J = 6.0, 2.9, H-3⁰). ¹³C

NMR spectrum of 11c was summarized in Table 1. FABMS m/z:

425 [M+H]⁺(pos.), FABHRMS m/z: 425.0760 (C₁₂H₂₅O₁₂S₂requires

425.0788).

74 mM, 100

solution (50

l

l), a test compound solution (50

ll), and an enzyme

ll) were mixed and incubated at 37 °C for 30 min. After

incubation, the solution was mixed with water (0.8 ml) and imme-

diately heated by boiling water for 2 min to stop the reaction. Glu-

cose concentration was then determined by the glucose-oxidase

method. Final concentration of DMSO in test solution was 2.5%

and no inﬂuence of DMSO was detected on the inhibitory activity.

Acknowledgements

Following the method described above, 26d (78 mg, 0.13 mmol)

was hydrolyzed with 30% aqueous TFA (7 ml) at 50 °C for 2 h.

Work-up gave a pale yellow oil (71 mg), which on column chroma-

tography (CHCl₃–MeOH–H₂O, 10/5/1) gave 1,4-dideoxy-1,4-{(S)-

[(2S,3S,4S,5R,6R)-2,4,5,6,7-pentahydroxy-3-(sulfoxy)-heptyl]epis-

This work was supported by ‘High-Tech Research Center’ Pro-

ject for Private Universities: matching fund subsidy from MEXT

(Ministry of Education, Culture, Sports. Science and Technology),

2007–2011 (OM) and also supported by a grant-in aid for scientiﬁc

research by JSPS (the Japan Society for the Promotion of Science)

(GT).

ulfoniumylidene}-D-arabinitol inner salt 11d (53 mg, 95%).

3.15.4. Compound 11d

Colorless solid. ½a _D²⁴

ꢁ

– 9.6 (c = 2.64, H₂O). IR (nujol): 3368, 1260,

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Article Doi

Role of the side chain stereochemistry in the α-glucosidase inhibitory activity of kotalanol, a potent natural α-glucosidase inhibitor. Part 2

DOI: 10.1016/j.bmc.2012.09.006

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