Synthesis of 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol derivatives applying titanium-mediated reaction conditions

Article abstract of DOI:10.1016/j.tet.2011.12.024

The titanium-mediated cyclopropanation reaction using Ti(O ⁱPr)₃Me/EtMgBr/BF₃·OEt₂ has been applied to various 2-cyanopyrrolidines for the synthesis of functionalized 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol d

Full text of DOI:10.1016/j.tet.2011.12.024

Tetrahedron 68 (2012) 1802e1809
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol derivatives applying
titanium-mediated reaction conditions
,
a
b
c
Delphine Declerck a, Albert Nguyen Van Nhien a , Solen Josse , Jan Szymoniak , Philippe Bertus ,
*
,
Claudia Bello d, Pierre Vogel d, Denis Postel a
*
a
ꢀ
ꢀ
Laboratoire des glucides UMR6219, Universite de Picardie Jules Verne, Faculte des Sciences, 33 rue Saint-Leu, 80039 Amiens, France
Universite de Reims Champagne-Ardenne, UMR-CNRS 6229, Institut de Chimie Moleculaire de Reims, BP 1039, 51687 Reims Cedex 02, France
Universite du Maine, UMR-CNRS 6011, Unite de Chimie Organique Moleculaire et Macromoleculaire, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France
Laboratoire de glycochimie et de synthese asymetrique (LGSA), Ecole Polytechnique Federale de Lausanne (EPFL), Batochime, CH 1015 Lausanne, Switzerland
b
c
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
d
ꢁ
ꢀ
ꢀ ꢀ
a r t i c l e i n f o
a b s t r a c t
The titanium-mediated cyclopropanation reaction using Ti(OiPr)3Me/EtMgBr/BF3$OEt2 has been applied
to various 2-cyanopyrrolidines for the synthesis of functionalized 2-(1-aminocyclopropyl)pyrrolidine-
3,4-diol derivatives (dideoxyiminoalditols). Under the same experimental conditions the trans-5-azi-
domethyl-2-cyanopyrrolidine derivative was not cyclopropanated but reduced into the corresponding 5-
amino-2-cyano derivative. After polyol deprotection 2-(1-aminocyclopropyl)pyrrolidine-3,4-diols were
obtained and their inhibitory activity towards 13 glycosidases has been evaluated. (2S,3S,4R,5S)-2-(1-
Article history:
Received 11 October 2011
Received in revised form 5 December 2011
Accepted 10 December 2011
Available online 24 December 2011
Keywords:
a-L-Fucosidase inhibition
2-Cyanopyrrolidine
Dideoxyiminoalditols
Cyclopropylamine
Titanium
Aminocyclopropyl)-5-methylpyrrolidine-3,4-diol (38), which has the same absolute configuration as
fucose, is a moderate (IC50¼44 M), but selective, inhibitor of -fucosidase from human placenta.
Ó 2011 Elsevier Ltd. All rights reserved.
L-
m
a-L
Kulinkovich reaction
1. Introduction
Ki¼135 nM). When made more membrane permeable through ad-
equate derivation, such as in compound 6, promising anti-
proliferative activities on human glioblastoma and melanoma cells
were observed for these inhibitors.12 Other 2-(aminomethyl)pyrro-
lidine derivatives complexed with platinum (cisplatin derivatives)
are used in cancer chemotherapy.15 Sitafloxacin (7) is a potent an-
tibacterial agent (DU-6859) that possesses a 3-aminopyrrolidine ring
and two cyclopropyl groups.16 The cyclopropane ring was identified
Dideoxyiminoalditols(iminosugars) are monosaccharidemimetics
with an amino moiety instead of an oxygen moiety in their ring. Under
physiological conditions they are protonated into ammonium species
that imitate the transition structures or intermediates of the
glycosidase-catalyzed hydrolysis of O-saccharides, and thuscan inhibit
these enzymes strongly. These inhibitors1,2 can be polyhydroxylated
pyrrolidine,3e5 piperidine6,7 or azepane derivatives.8,9 We present
here the synthesis of a new kind of pyrrolidine-3,4-diol derivatives
that possess a 2-(1-aminocyclopropyl) substituent.
R
N
OH
OH
HO
H
N
combinatorial
chemistry
Several 2-(aminomethyl)pyrrolidine-3,4-diol derivatives have
been reported for their promising biological activities (Fig. 1). For
instance, Wong and co-workers identified compound
NHAc
NH2
+
RCOOH
HO
OH
OH
2
1
R = H, CH3,
R = -(CH2)7-NH2, 2
(Ki¼2.6 nM) as a significantly more potent inhibitor than the sim-
pler iminosugar 1 (Ki¼24 nM) of N-acetyl-
b
-hexosaminidase (rel-
O
O
evant to osteoarthritis treatment).10,11
F
Ph
H
N
H
NHBn
OH
Gerber-Lemaire and co-workers12e14 have shown that pyrroli-
N
OR
R
N
N
N
H
dine-3,4-diols 3e5 are selective and competitive inhibitors of
mannosidase from jack bean (3, Ki¼7.4 M; 4, Ki¼1.2 M; 5,
a-
Cl
HO OH
m
m
HO OH
H2N
F
R = H, 3
R = CH2OH,
5
R = H,
4
* Corresponding authors. Fax: þ33
3
22827568; e-mail addresses: albert.
R = -CO-Ph-pBr, 6
Sitafloxacin 7
nguyen-van-nhien@u-picardie.fr (A. Nguyen Van Nhien), denis.postel@u-picardie.fr
(D. Postel).
Fig. 1. Few substituted pyrrolidine with biological activities.
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.12.024

D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
1803
RO
RO
as a prominent pharmacophore that induces essential binding in-
teractions with the biological receptor. This has inspired us to con-
struct iminosugars that incorporate such moiety and has led us to
prepare polyhydroxylated 1-azaspirocyclopropane derivatives. Some
of them are moderate glycosidase inhibitors.17e21 We describe here
the synthesis of 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol de-
Bn
N
Bn
N
NH2
CN
i, ii
O
O
O
O
12
, R = Bn
14, R = Bn (57%)
13, R = Bz
15, R = Bz + 16, R = H (65%)
rivatives based on
a titanium-mediated transformation of 2-
iii
cyanopyrrolidines. The new iminoalditols obtained after amine and
polyol deprotection have been evaluated for their inhibitory activity
towards 13 commercially available glycosidases.
Scheme 3. Ti mediated reductivecyclopropanation. Reagents and conditions: (i) 1.5 equiv
Ti(OiPr)3Me, 1.5 equiv EtMgBr, THF; (ii) 2 equiv BF3$OEt2. (iii) NH3eMeOH 7 M (68%).
Titanium-mediated aminocyclopropanation of nitriles22e25 is
a very convenient reaction that has been studied by some of us for
several years.25 In a preliminary communication,26 we have dis-
closed the synthesis of aminocyclopropyl iminosugars applying this
reaction to carbohydrate-derived carbonitriles (Scheme 1). The
presumed mechanism involves a cyclic titanium iminate in-
termediate in the aminocyclopropanation step. The latter is thought
to undergo a ring contraction into the corresponding cyclopropane
ring. Usually this process requires the addition of BF3$OEt2.25
yields (37%e45%) than in the cases of the cis-carbonitriles 12 and 13
(57e65%) (Scheme 4).
BnO
BnO
Bn
N
Bn
N
NH2
CN
i, ii
BnO
17
OBn
BnO
OBn
(37%)
Bn NH2
20
BnO
BnO
Bn
N
Bn
N
Bn
N
N
Ti(OiPr)2
N
BF3 OEt
⋅
EtMgBr
Ti(OiPr)3Me
2
CN
N
i, ii
(OR)n
(OR)n
BnO
18
OBn
BnO
21
OBn
(45%)
F3B
NH2
Bn
Bn
N
N
Ti(OiPr)2
N
O
O
Bn
N
Bn
N
NH2
H2O
CN
(OR)n
(OR)n
O
O
i, ii
Scheme 1. General approach to the synthesis of protected 2-(1-aminocyclopropyl)
pyrrolidine derivatives.
O
O
O
O
19
22
(44%)
2. Results and discussions
Scheme 4. Reagents and conditions: (i) 1.5 equiv Ti(OiPr)3Me, 1.5 equiv EtMgBr, THF;
(ii) 2 equiv BF3$OEt2.
The 2,3-cis (2R) 2-cyanopyrrolidine 12 and 13 were obtained ster-
eoselectively in two steps27 from 5-O-benzyl-2,3-O-isopropylidene-
D-
The same trend was observed for the reductive cyclopropanation
of cis-(23)27 and trans-2-cyano-5-methylpyrrolidine (24)27 de-
rivatives (Scheme 5), which led to cyclopropylamines 25 and 26 in 57
and 38% yield, respectively.
ribofuranose 828 and 5-O-benzoyl-2,3-O-isopropylidene-
D-ribofur-
anose 927,29 using our modified Strecker reaction,30 followed by
a spontaneous cyclization via the mesylation of the secondary alcohol
in 84% and 56% yield, respectively (Scheme 2).
Bn
N
RO
RO
RO
Bn
N
Bn
N
OH NHBn
CN
NH2
O
OH
CN
ii
i
CN
i, ii
O
O
O
O
O
O
O
O
O
O
8
10, R = Bn (86%)
11, R = Bz (59%)
12, R = Bn (84%)
13, R = Bz (56%)
, R = Bn
9, R = Bz
23
25
(57%)
Scheme 2. Conversion of D-ribofuranose into the corresponding 2-cyanopyrrolidines.
Reagents and conditions: (i) (a) 2 equiv Ti(OiPr)4, MeOH, 2 equiv HCOOꢀ þNH3Bn, (b)
1.2 equiv TMSCN; (ii) 5 equiv MsCl, pyr., 80 ꢁC.
Bn
N
Bn
N
NH2
The reductive cyclopropanation of the carbonitriles (Scheme 3)
uses Ti(OiPr)3Me and EtMgBr, followed by in situ addition of
BF3$OEt2.31 This converts 12 into cyclopropylamine 14. When the
O-benzoyl derivative 13 was submitted to the same conditions,
a mixture of compound 15 and the debenzoylated derivative 16 was
obtained in 65% and 11% yield, respectively. Aminoalcohol 16
probably resulted from an unwanted Kulinkovich ester hydrolysis
of the benzoate protecting group.32 Upon treatment with a solution
of NH3eMeOH (7 M), 15 afforded 16 in 68% yield.
Next, we investigated analogous reactions of the 2,5-trans imi-
nosugars 17,27 1827 and 1927 obtained in a similar way as 12 and 13
(Scheme 2). Under standard reaction conditions, the cyclopropyl-
amine derivatives 20, 21 and 22 were obtained in somewhat lower
CN
i, ii
O
O
O
O
24
26 (38%)
Scheme 5. Reductive cyclopropanation of cis- and trans-2-cyano-5-methylpyrrolidine
derivatives. Reagents and conditions: (i) 1.5 equiv Ti(OiPr)3Me, 1.5 equiv EtMgBr, THF;
(ii) 2 equiv BF3$OEt2.
Applying the above reaction conditions to trans-5-azidomethyl-
2-cyanopyrrolidine derivative 2727 (Scheme 6) the 5-aminomethyl

1804
D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
Table 1
derivative 28, resulting from the reduction of the azide group, was
obtained in 46% yield, instead of the expected cyclopropylamine
derivative. This unexpected result can be interpreted in terms of the
non-formation of the cyclic titanium iminate, which would have
led, after ring contraction, to the cyclopropane ring. We presumed
that EtMgBr reacts with the azide faster than with the methyl-
Experimental results for Staudinger aza-Wittig reaction
Entry
1
Conditions
31 Yield (%)
30 Yield (%)
EtMgBr (1.5 equiv)
BF3$OEt2 (2 equiv)
Ti(OiPr)3Me (1.5 equiv)
BF3$OEt2 (2 equiv)
Ti(OiPr)3Me (1.5 equiv)
EtMgBr (1.5 equiv)
EtMgBr (1.5 equiv)
MeMgBr (1.5 equiv)
BF3$OEt2 (2 equiv)
36
8
2
3
da
d
d
titanium triisopropoxide leading to 28 through a
b
-hydrogen
22
transfer and aqueous work-up (Scheme 6).
4
5
d
da
74
d
N3
Bn
N
N3
Bn
N
NH2
CN
i, ii
a
No reaction.
O
O
O
O
27
i, ii
N
H
-
BrMg
H
N
O
H
-
H
Bn
N
O
i
H
H2N
Bn
Bn
N
Bn
N
BrMg
N
N
H
CN
N
30
29
(74%)
N
N
BrMg
N
N
N
H
CN
CN
CN
O
O
O
O
O
O
O
O
28
(46%)
Scheme 8. Reagents and conditions: (i) 1.5 equiv EtMgBr.
Scheme 6. Possible mechanism for the azide reduction. Reagents and conditions: (i)
1.5 equiv Ti(OiPr)3Me, 1.5 equiv EtMgBr, THF; (ii) 2 equiv BF3$OEt2.
In full agreement with our hypothesis concerning the reduction
of the azide by the Grignard reagent, replacement of EtMgBr by
MeMgBr (entry 5) did not lead to any product of reduction.
As demonstrated in a precedent work,30 cyclic amidines could
be obtained in quantitative yield via a Staudinger aza-Wittig (SAW)
reaction. Unfortunately, treatment of 29 with PMe3 (Scheme 9, step
(i)) exclusively afforded the reduced compound 30. Replacement of
PMe3 by PPh3 gave similar results (Scheme 9).
Under our standard reaction conditions the 2,5-cis-isomer 2927
was converted into the six-membered amidine 31 in 15% yield. The
expected amine 30 was not observed. Apparently, after the b-hydride
transfer from EtMgBr, the resulting magnesium adduct undergoes
nucleophilic addition onto the cis-cyano group activated by BF3$OEt2.
The reaction is accompanied by a highly exergonic N2 elimination.
This type of process has no precedent in the literature. From
a mechanistic point of view, it can be viewed as a Staudinger aza-
Wittig reaction between an azide and a cyano group (Scheme 7).30
i
29
30
(>99%)
BrMg
MgBr
ii
N
H
N
Bn
N
-
N3
Bn
N
H
Bn
N
i, ii
N
CN
N
N
N N
CN
Ph3P
iii
O
O
BF3
O
O
O
O
N
Bn
N
CN
29
O
O
N
NH2
H2N
Bn
N
Bn
N
CN
32 (88%)
O
O
Scheme 9. Reagents and conditions: (i) PMe3, THF; (ii) PPh3 (1 equiv), MgBr2$OEt2
(1 equiv), THF, (iii) NH3eMeOH 7 N, >99%.
O
O
30
31
(15%)
With these results in hand, and in order to favour the SAW re-
action under cyano group electrophilic activation conditions,
BF3$OEt2 was added along with PMe3 (entry 1, Table 2). This led
exclusively to amine 30, whereas the use of PPh3 (entry 2) led to
Scheme 7. Reagents and conditions: (i) 1.5 equiv Ti(OiPr)3Me, 1.5 equiv EtMgBr, THF;
(ii) 2 equiv BF3$OEt2.
Several experiments were carried out to confirm the mechanism
proposed above. In the absence of Ti(OiPr)3Me (entry 1, Table 1) the
expected amidine 31 was obtained in 36% yield together with
amine 30 (8%). By removing the Grignard reagent (entry 2), no
reaction was observed and without BF3$OEt2 (entry 3), only amine
30 was obtained in 22% yield after aqueous work-up. Therefore
both EtMgBr and BF3$OEt2 are required for the reduction of the
azide and the formation of the amidine.
Table 2
Experimental results for SAW reaction using phosphine reagent
Entry
1
Conditions
31 Yield (%)
30 Yield (%)
41a
32 Yield (%)
PMe3 (1 equiv)
d
d
BF3$OEt2 (2 equiv)
PPh3 (1.1 equiv)
BF3$OEt2 (2 equiv)
MgBr2$OEt2 (1 equiv)
PPh3 (1 equiv)
2
3
4
da
d
71
d
48
29
88
d
Indeed, in the absence of BF3$OEt2 and MeTi(OiPr)3, (entry 4) the
reaction of 29 with EtMgBr in THF led to 30 in 74% yield (Scheme 8).
The intramolecular addition of the magnesium amide intermediate
onto the cis-cyano group does not occur without electrophilic ac-
tivation by BF3$OEt2.
MgBr2$OEt2 (1 equiv)
PMe3 (1 equiv)
d
a
Starting material (25%) has been recovered.

D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
1805
a total conversion of the starting material giving 30 in only 71%
yield and the iminophosphorane 32 isolated in 29% yield. Because
the amidine formation seems to be favoured in the presence of
magnesium derivatives via a hypothetic cyclic transition state in-
volving a complex between magnesium, cyano and azide groups,
several experiments with added Mg2þ salts were conducted. When
MgBr2$OEt2 was used instead of BF3$OEt2 (entry 3), compound 32
was obtained in 88% yield whereas, when mixed with PMe3 (entry
4), 30 was obtained in 48% yield.
Surprisingly, when a mixture of PPh3, BF3$OEt2 and MgBr2$OEt2
was used, no cyclic amidine was formed, and the brominated
compound 33 was isolated instead in 31% yield (Scheme 10). To the
best of our knowledge, this azide substitution by a halide has not
been described in the literature. For the moment we do not have
any mechanism to explain this displacement reaction. Neverthe-
less, we need to mention that when using MgCl2 instead of
MgBr2$OEt2, the chloride derivative 34 was obtained in 38% yield.
The new compounds 14, 20, 21 and 25 were submitted to acidic
hydrogenolysis and provided the corresponding unprotected 2-(1-
aminocyclopropyl)pyrrolidine-3,4-diols in the form of bis-
hydrochlorides 35, 36, 37 and 38, respectively, in moderate to
good yield (38e99%) (Scheme 11).
1 mM; IC50¼44
m
M). Compound 35 is a weaker inhibitor of the same
enzyme (64% inhibition at 1 mM). Compound 36 was an even weaker
inhibitor of -fucosidase (27%). All other glycosidases assayed
were not inhibited at 1 mM concentration of compounds 35e38,
except for 36 that showed to be a weak inhibitor of -glucosidase from
almonds (Table 3). Among pyrrolidine-3,4-diols (3S,4R,5S)-5-methyl-
1-pyrroline3,4-diol, (3S,4R,5S)-5-methylpyrrolidine-3,4-diol,33,34
(2S,3S,4R,5S)-2-(hydroxymethyl)-5-methylpyrrolidine-3,4-diol35 and
(2S,3S,4R,5S)-2-(2-hydroxyethyl)-5-methylpyrrolidine-3,4-diol are
low nanomolar inhibitors of
-fucosidases from bovine kidney.33 Upon
a-L
b
D
L
substitution of (3S,4R,5S)-5-methylpyrrolidine-3,4-diol (Ki¼50 nM)
by a (2S)-(p-biphenylaminomethyl) group a slight increase of in-
hibitory activity (Ki¼40 nM)36 has been observed. In our case the ex-
change of the (2S)-(p-biphenylaminomethyl) group by a (2S)-2-(1-
aminocyclopropyl) group decreases the inhibitory activity by a factor
of about 1000! Apparently the cyclopropyl group has difficulty to find
room in the active site of the enzyme, more so then a slimmer N-
arylated aminomethyl, a hydroxymethyl or a 2-hydroxyethyl group. As
reported on many occasions, when the 5-methyl group is replaced by
a larger group, such as a hydroxymethyl group, the inhibitory activity
towards
paring the activities of 36 versus 38.
deoxy- -fucose and 1-deoxy- -fuconojirimycin are low nanomolar
inhibitors of a-L-fucosidases. Even more potent inhibitors are obtained
L
-fucosidases is reduced.3 This is also the case when com-
-Fuconojirimycin 5-amino-5-
L
L
L
upon substitution at C(1) by N-acetyl 1-aminomethyl groups.37e39
R
Bn
N
CN
i or ii
29
Table 3
O
O
Inhibition data of compounds 35e38 towards glycosidases
Enzyme
-Fucosidase EC 3.2.1.51
25-Human placenta
-Galactosidase EC 3.1.1.22
2-Coffee bean
-Galactosidase EC 3.2.1.23
38
37 35
36
a-L
33, R = Br 31%
95%eIC50¼44
m
M
d
d
64% 27%
34
, R = Cl 38%
a
d
d
d
Scheme 10. Reagents and conditions: (i) MgBr2$OEt2 (1 equiv), PPh3 (1 equiv),
BF3$OEt2 (2 equiv); (ii) MgCl2 (1 equiv), PPh3 (1 equiv), BF3$OEt2 (2 equiv).
b
5-Escherichia coli
8-Aspergillus orizae
d
d
d
d
d
d
d
d
a
-Glucosidase EC 3.2.1.20
i, ii
H
N
Bn
N
NH2
NH2
10-Yeast
11-Rice
Amyloglucosidase EC 3.2.1.3
13-Aspergillus niger
d
d
d
d
d
d
d
d
n(HO)
n(HO)
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
substrate
14
product
H.HCl
yield (%)
35 (38%)
b
-Glucosidase EC 3.2.1.21
15-Almonds
-Mannosidase EC 3.2.1.24
16-Jack beans
-Mannosidase EC 3.2.1.25
18-Snall
-Xylosidase EC 3.2.1.37
19-Aspergillus niger
-N-Acetylglucosaminidase EC 3.2.1.30
HO
NH2.HCl
15%
d
N
a
HO
OH
b
d
HO
HO
H.HCl
N
NH2.HCl
NH2.HCl
NH2.HCl
20
21
36 (68%)
37 (99%)
b
d
b
HO
HO
OH
H.HCl
21-Jack beans
22-Bovine kidney
d
d
d
d
d
d
d
d
N
Inhibition values are expressed as % of inhibition at 1 mM concentration.
OH
H.HCl
25
38 (50%)
N
4. Conclusion
HO
OH
,
Reagents and conditions: i) H Pd/C, MeOH, HCl 1M; ii) HCl 3M.
Iminosugars of the type 2-(1-aminomethyl)pyrrolidine-3,4-diol
have been obtained applying a modified Kulinkovich protocol using
EtMgBr, Ti(OiPr)3Me and BF3$OEt2 on 2-cyanopyrrolidine derivatives.
Under these conditions, 5-azidomethyl-2-cyanopyrrolidine de-
rivatives were reduced into the corresponding 5-aminomethyl-2-
Scheme 11. Obtention of polyhydroxycyclopropylamines.
3. Enzymatic assays
cyanopyrrolidines through a b-hydride transfer from the ethyl
Grignard reagent. The replacement of the Grignard reagent by MgX2
salts (X¼Cl, Br) led to the substitution of the azido group by halide X.
Fully deprotected 2-(1-aminocyclopropyl)pyrrolidine-3,4-diols
35e38 (iminosugars) have been prepared and assayed towards 13
glycosidases. Compound 38 (2S,3S,4R,5S)-2-(1-aminocyclopropyl-5-
The iminosugars 35e38 have been evaluated for their inhibitory
activities towards
wards 12 other commercially available glycosidases. Compound 38 is
a moderate but selective inhibitor of -fucosidase (95% inhibition at
a-L-fucosidase from human placenta as well as to-
a-L

1806
D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
methylpyrrolidine-3,4-diol) that has the same configuration as
cose is the most promising inhibitor and showed a 95% inhibition of
-fucosidase from human placenta concentration at 1 mM con-
M). It is a selective inhibitor of this enzyme as it
L
-fu-
(NCH2Ph), 50.0 (C-1), 26.8, 24.5 (2ꢃ CH3). HRMS: C23H28N2O4Na
calcd 419.1947, found 419.1939.
a-L
centration (IC50¼44
m
5.3.2. (1R)-5-O-Benzoyl-1-N-benzylamino-1-C-cyano-1-deoxy-2,3-
O-isopropylidene-D-ribose (11). To a solution of 9 (3.0 g, 10.3 mmol)
did not inhibit any of the 12 other glycosidases assayed.
in MeOH was added HCOONH3Bn (3.15 g, 20.61 mmol) and
Ti(OiPr)4 (6.2 mL, 20.61 mmol). After stirring at room temperature
for 24 h, TMSCN (1.7 mL, 12.36 mmol) was added and the reaction
mixture stirred overnight. A few drops of water were added until
oxidation of titanium then EtOAc was added to dilute. After elimi-
nation of the solvent under vacuum, the crude was filtered through
a silica pad and eluted with EtOAc. After usual workup, the residue
was flash chromatographed (EtOAc/cyclohexane, 20/80) to afford
5. Experimental part
5.1. Materials and methods
Melting points are uncorrected. Optical rotations were recorded
in CHCl3 or MeOH solutions. 1H NMR (300.13 MHz) and 13C NMR
(75.47 MHz) spectra were recorded in CDCl3, DMSO-d6 or MeOD-d4
(internal Me4Si). TLC was performed on Silica F254 and detection by
UV light at 254 nm or by charring with phosphomolybdiceH2SO4
reagent. FTIR spectra were obtained on an AVATARÔ 320 neat using
ATR and are reported in cmꢀ1. Mass spectral data were acquired on
a WATERS Micromass ZQ spectrometer or a WATERS Micromass Q-
TOFF spectrometer. Column chromatographies were effected on
Silica Gel 60 (230 mesh). Cyclohexane and ethyl acetate were dis-
tilled before use.
11 (2.5 g, 59%) as a slight yellow syrup; ½a D20
ꢀ40 (c 0.29, CH2Cl2);
ꢂ
1H NMR (CDCl3, 300 MHz)
d
7.53e7.29 (m, 10H, 2ꢃ C6H5), 4.67 (dd,
J4,5a¼2.3 Hz, J5a,5b¼11.5 Hz, 1H, H-5a), 4.49 (m, 2H, H-2, H-4), 4.37
(dd, J4,5b¼6.0 Hz, 1H, H-5b), 4.21 (dd, J2,3¼6.4 Hz, J3,4¼9.3 Hz, 1H, H-
3), 4.16 (d, JA,B¼12.7 Hz, 1H, H-A NCH2Ph), 4.10 (d, J1,2¼2.6 Hz, 1H,
H-1), 3.86 (d, 1H, H-B NCH2Ph), 1.54 (s, 3H, CH3), 1.40 (s, 3H, CH3);
13C NMR (CDCl3, 75 MHz)
d
167.1 (C]O), 137.4, 133.3e127.9 (2ꢃ
C6H5), 118.3 (CN), 109.5 [OC(CH3)2], 76.4, 76.3 (C-2, C-3), 68.1 (C-4),
67.2 (C-5), 51.6 (NCH2Ph), 49.2 (C-1), 27.0, 24.7 (2ꢃ CH3). HRMS:
C23H26N2O5Na calcd 433.1739, found 433.1739.
5.2. General method for the cyclopropanation reaction (A)
To a solution of azasugar (1 equiv) and Ti(OiPr)3Me (1.5 equiv) in
THF, was slowly added at room temperature EtMgBr (1.5 equiv, 2 M
solution in Et2O). After stirring for 1 h, BF3$OEt2 (2 equiv) was
added, and the reaction mixture further stirred for 1 h at room
temperature. A solution of HCl 1 M was added until two clear
phases were formed. Then, a solution of NaOH (2 M) was added
until pH of aqueous layer was basic. The organic layer was extracted
with ethyl acetate and dried over Na2SO4. The solvent was evapo-
rated under vacuum and the residue was purified by column
chromatography.
5.3.3. (2R,3S,4R,5S) 1-N-Benzyl-5-benzyloxymethyl-2-cyano-3,4-O-
isopropylidenepyrrolidine-3,4-diol (12). To a solution of 10 (1.51 g,
3.82 mmol) in pyridine (10 mL) heated at 80 ꢁC MsCl (1.47 mL,
19.1 mmol) was added dropwise. After 1 h, water and CH2Cl2 were
added. The reaction mixture was extracted. The organic layer was
dried over Na2SO4, filtered and evaporated to dryness. After flash
chromatography (EtOAc/cyclohexane, 20/80), compound 12 (1.22 g,
84%) was isolated as a slight orange solid; mp¼73e75 ꢁC; ½a D20
ꢀ28
ꢂ
(c 0.36, CHCl3); 1H NMR (CDCl3, 300 MHz)
d
7.39e7.29 (m, 10H, 2ꢃ
C6H5), 4.68e4.52 (m, 4H, H-3, H-4, OCH2Ph), 4.18 (d, JA,B¼14.7 Hz,
1H, H-A NCH2Ph), 4.02 (d, 1H, H-B NCH2Ph), 3.88 (dd, J5,6a¼5.2 Hz,
J6a,6b¼9.9 Hz, 1H, H-6a), 3.76 (dd, J5,6b¼5.2 Hz, 1H, H-6b), 3.26 (d,
J2,3¼4.9 Hz,1H, H-1), 2.78 (m, J4,5¼5.2 Hz,1H, H-5),1.63 (s, 3H, CH3),
5.3. General method for debenzylation (B)
To a solution of cyclopropylamine azasugar (1 equiv) in MeOH
was added Pd/C (3 equiv, 10% w/w) and a few drop of HCl 1 M. The
reaction mixture was placed under atmospheric pressure of H2.
After 12e36 h and filtration, the solvent was eliminated under re-
duced pressure. After dissolution with HCl 3 M (3 equiv), the re-
action mixture was stirred overnight at room temperature. After
evaporation, the deprotected cyclopropylamine was obtained in the
hydrochloride form.
1.38 (s, 3H, CH3); 13C NMR (CDCl3, 75 MHz)
d 138.0, 133.5,
130.2e127.8 (2ꢃ C6H5), 115.9 (CN), 113.3 [OC(CH3)2], 80.0, 77.5 (C-3,
C-4), 73.6 (OCH2Ph), 68.8 (C-5), 63.3 (C-6), 57.5 (C-2), 53.1
(NCH2Ph), 26.2, 25.7 (2ꢃ CH3). HRMS: C23H26N2O3Na calcd
401.1841, found 401.1844.
5.3.4. (2R,3S,4R,5S)-5-Benzoyloxymethyl-1-N-benzyl-2-cyano-3,4-
O-isopropylidenepyrrolidine-3,4-diol (13). To a solution of 11 (2.2 g,
5.36 mmol) in pyridine (30 mL) heated at 80 ꢁC MsCl (1.47 mL,
19.1 mmol) was added dropwise. After 2 h, water and CH2Cl2 were
added. The reaction mixture was extracted. The organic layer was
dried over Na2SO4, filtered and evaporated to dryness. After flash
chromatography (EtOAc/cyclohexane, 35/65), compound 13 (1.15 g,
5.3.1. (1R)-5-O-Benzyl-1-N-benzylamino-1-C-cyano-1-deoxy-2,3-O-
isopropylidene- -ribose (10). To a solution of 8 (1.8 g, 6.45 mmol) in
D
MeOH was added HCOONH3Bn (1.97 g, 12.9 mmol) and Ti(OiPr)4
(3.85 mL, 12.9 mmol). After stirring at room temperature for 24 h,
TMSCN (1.03 mL, 7.74 mmol) was added and the reaction mixture
stirred overnight. A few drops of water were added until oxidation
of titanium then the reaction mixture was diluted with EtOAc. After
elimination of the solvent under vacuum, the crude was filtered
through a silica pad and eluted with EtOAc. After usual workup, the
residue was flash chromatographed (EtOAc/cyclohexane, 20/80) to
56%) was isolated as a slight orange solid; mp¼73e75 ꢁC; ½a D20
ꢀ28 (c
ꢂ
0.36, CHCl3); 1H NMR (CDCl3, 300 MHz)
d
8.09, 7.61e7.34 (m,10H, 2ꢃ
C6H5), 4.78e4.58 (m, 4H, H-2, H-4, H-6a, H-6b), 4.16 (d, JA,B¼14.8 Hz,
1H, H-A NCH2Ph), 4.09 (d, 1H, H-B NCH2Ph), 3.36 (d, J2,3¼5.0 Hz, 1H,
H-2), 2.93 (dd, J4,5¼4.9 Hz, J5,6a¼11.4 Hz, 1H, H-5), 1.67 (s, 3H, CH3),
1.42 (s, 3H, CH3); 13C NMR (CDCl3, 75 MHz)
d 166.2 (C]O),
afford 10 (2.21 g, 86%) as a slight yellow syrup; ½a D20
ꢂ
ꢀ5 (c 0.2,
133.7e128.1 (2ꢃ C6H5),115.7 (CN),113.6 [OC(CH3)2], 79.7, 77.5 (C-3, C-
4), 62.9 (C-5), 62.4 (C-6), 58.0 (C-2), 53.7 (NCH2Ph), 26.3, 25.8 (2ꢃ
CH3). HRMS: C23H24N2O4Na calcd 415.1634, found 415.1641.
CH2Cl2); 1H NMR (CDCl3, 300 MHz)
d
7.38 (m, 10H, 2ꢃ C6H5), 4.63
(dd, JA,B¼11.9 Hz, 1H, H-A OCH2Ph), 4.58 (d, 1H, H-B OCH2Ph), 4.48
(dd, J1,2¼2.7 Hz, J2,3¼6.5 Hz, 1H, H-2), 4.40 (ddd, 1H, H-4), 4.26 (dd,
J2,3¼6.5 Hz, J3,4¼8.5 Hz, 1H, H-3), 4.15 (d, 1H, H-1), 4.12 (d,
JA,B¼12.8 Hz, 1H, H-A NCH2Ph), 3.84 (d, 1H, H-B NCH2Ph), 3.77 (dd,
J4,5a¼2.7 Hz, J5a,5b¼9.8 Hz, 1H, H-5a), 3.63 (dd, J4,5b¼5.3 Hz, 1H, H-
5b), 1.54 (s, 3H, CH3), 1.40 (s, 3H, CH3); 13C NMR (CDCl3, 75 MHz)
5.3.5. (2R,3S,4R,5S)-2-(1-Aminocyclopropyl)-1-N-benzyl-5-
benzyloxymethyl-3,4-O-isopropylidenepyrrolidine-3,4-diol
(14). Following the general method A, 12 (0.50 g, 1.32 mmol),
Ti(OiPr)3Me (480
and BF3$OEt2 (300
chromatography (EtOAc) compound 14 (0.30 g, 57%) as a syrup;
mL,1.98 mmol), EtMgBr (900
mL,1.98 mmol, 2.2 M)
d
137.9, 137.8, 128.7e127.7 (2ꢃ C6H5), 118.6 (CN), 109.1 [OC(CH3)2],
m
L, 2.64 mmol) in THF (30 mL) gave after flash
76.9 (C-2, C-3, C-4), 73.5, 72.0 (2ꢃ OCH2Ph), 68.3 (C-5), 51.6

D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
1807
½
a 1D6
ꢂ
ꢀ3 (c 1.04, CHCl3); 1H NMR (CDCl3, 300 MHz)
d
7.35e7.24 (m,
EtMgBr (3.6 mL, 5.79 mmol, 2.2 M) and BF3$OEt2 (1.0 mL,
7.74 mmol) in THF (50 mL) gave after flash chromatography (EtOAc/
10H, C6H5), 4.67e4.59 (m, 2H, H-6a, H-A OCH2Ph), 4.43 (d,
J¼12.0 Hz 1H, H-A NCH2Ph), 4.33 (d, 1H, H-B NCH2Ph), 3.90e3.74
(m, 3H, H-2, H-3, H-6b), 3.48 (dd, J4,5¼6.1 Hz, J3,4¼9.5 Hz, 1H, H-4),
2.73 (dt, J5,6¼4.9 Hz, 1H, H-5), 2.51 (br s, 2H, NH2), 1.61 (d,
JA,B¼4.3 Hz, 1H, OCH2Ph), 1.55 (s, 3H, CH3), 1.35 (s, 3H, CH3),
0.78e0.74 (m, 1H, CH2D), 0.54e0.50 (m, 1H, CH2D), 0.42e0.40 (m,
cyclohexane, 3/7) compound 21 (0.85 g, 45%) as a syrup; ½a D16
ꢀ16
ꢂ
(c 1.04, CHCl3); 1H NMR (CDCl3, 300 MHz)
d 7.47e7.17 (m, 20H,
C6H5), 4.90 (d, J¼12.4 Hz, 1H, CH2Ph), 4.64e4.45 (m, 6H, OCH2Ph),
3.99e3.90 (m, 1H, H-6a), 3,90 (t, J3,4¼J4,5¼2.9 Hz, 1H, H-4), 3.77 (t,
J2,3¼2.9 Hz, 1H, H-3), 3.46 (br s, 2H, NH2), 3.03 (d, J¼13.5 Hz, 1H,
OCH2Ph), 2.98 (dd, J5,6b¼4.4 Hz, J6a,6b¼10.8 Hz, H-6b), 2.50 (t,
J5,6a¼10.8 Hz, 1H, H-5), 1.89 (d, J2,3¼2.9 Hz, 1H, H-2), 0.94e0.88 (m,
1H, CH2D), 0.74e0.69 (m, 1H, CH2D), 0.65e0.57 (m, 1H, CH2D),
2H, CH2D); 13C NMR (CDCl3, 75 MHz):
(C6H5), 110.8 [OC(CH3)2], 81.3 (C-3), 78.6 (C-4), 75.0 (C-2), 73.3
(OCH2Ph), 69.1 (C-6), 68.6 (C-5), 56.3 (NCH2Ph), 31.4 (C ), 26.1
d 140.3e138.3, 128.4e126.8
D
(CH3), 24.6 (CH3), 16.8 (CH2D), 10.1 (CH2D); HRMS C25H33N2O3:
0.27e0.21 (m, 1H, CH2D); 13C NMR (CDCl3, 75 MHz)
d 138.8e137.3,
calcd 409.2491, found 409.2482.
128.7e126.9 (C6H5), 79.7 (C-3), 75.2 (C-5), 74.1 (OCH2Ph), 73.0 (C-
4), 72.7 (OCH2Ph), 71.4 (NCH2Ph), 65.1 (C-2), 58.7 (OCH2Ph), 49.7
5.3.6. (2R,3S,4R,5S)-2-(1-Aminocyclopropyl)-5-benzoyloxymethyl-1-N-
benzyl-3,4-O-isopropylidenepyrrolidine-3,4-diol (15) and (2R,3S,4R,5S)-
2-(1-aminocyclopropyl)-1-N-benzyl-5-hydroxymethyl-3,4-O-iso-
propylidenepyrrolidine-3,4-diol (16). Following the general method A,
13 (0.91 g, 2.32 mmol), Ti(OiPr)3Me (1 mL, 3.48 mmol), EtMgBr
(C-6), 34.1 (CD), 17.9 (CH2D), 10.3 (CH2D); HRMS C36H41N2O3: calcd
549.3117, found 549.3119.
5.3.9. (2S,3R,4S,5S,6R)-2-(1-Aminocyclopropyl)-1-N-benzyl-5-(2,2-
dimethyl-1,3-dioxolan-4-yl)-3,4-O-isopropylidenepyrrolidine-3,4-
diol (22). Following the general method A, 19 (0.5 g, 1.39 mmol),
Ti(OiPr)3Me (0.50 mL, 2.09 mmol), EtMgBr (0.80 mL, 2.09 mmol,
2.2 M) and BF3$OEt2 (0.36 mL, 2.78 mmol) in THF (20 mL) gave after
flash chromatography (EtOAc) compound 22 (0.24 g, 44%) as
(2.2 mL, 3.48 mmol, 2.2 M) and BF3$OEt2 (735 mL, 4.64 mmol) in THF
(45 mL) gave after flash chromatography (EtOAc) compound 15
(0.63 g, 65%) followed by 16 (81 mg, 11%) (EtOAc/MeOH, 80/20).
a 20
Compound 15: syrup; ½ ꢂD ꢀ8 (c 0.95, CHCl3); 1H NMR (CDCl3,
300 MHz)
d
8.01e7.98 (m, 2H, C6H5), 7.55e7.25 (m, 8H, C6H5),
a syrup; ½a 1D6
ꢂ
þ15 (c 0.98, CHCl3); 1H NMR (CDCl3, 300 MHz)
4.71e4.66 (m, 2H, H-3, H-4), 4.55 (dd, J5,6a¼7.6, J6a,6b¼11.1 Hz, 1H, H-
6a), 4.43 (dd, J5,6b¼4.7 Hz, 1H, H-6b), 4.01 (d, JA,B¼15.3 Hz, 1H, H-A
CH2Ph), 3.78 (d, 1H, H-B CH2Ph), 2.92e2.90 (m, 1H, H-5), 2.51 (br s,
2H, NH2), 1.71 (d, J2,3¼3.9 Hz, 1H, H-2), 1.60 (s, 3H, CH3), 1.37 (s, 3H,
CH3), 0.82e0.79 (m, 1H, CH2D), 0.60e0.56 (m, 1H, CH2D), 0.47e0.45
d
7.33e7.25 (m, 5H, C6H5), 4.55 (dd, J3,4¼4.8 Hz, J2,3¼6.5 Hz, 1H, H-
3), 4.34 (dd, J4,5¼6.5 Hz, 1H, H-4), 4.05e3.95 (m, 4H, H-7a, H-7b,
CH2Ph), 3.83 (dd, J5,6¼6.5 Hz, J6,7a¼8.2 Hz, 1H, H-6), 3.21 (dd,
J4,5¼4.8 Hz, J5,6¼6.5 Hz, 1H, H-5), 2.28 (d, J2,3¼4.8 Hz, 1H, H-2), 1.46
(s, 3H, CH3), 1.44 (s, 3H, CH3), 1.32 (s, 3H, CH3), 1.27 (s, 3H, CH3),
0.58e0.53 (m, 2H, CH2D), 0.46e0.37 (m, 2H, CH2D); 13C NMR
(m, 2H, CH2D); 13C NMR (CDCl3, 75 MHz)
d
166.2 (CO), 139.8,
132.9e127.2 (C6H5), 111.3 [OC(CH3)2], 81.4 (C-3), 78.4 (C-4), 75.2 (C-2),
67.8 (C-5), 60.3 (C-6), 56.4 (CH2Ph), 31.5 (C ), 26.1 (CH3), 24.7 (CH3),
(CDCl3, 75 MHz)
[OC(CH3)2], 81.2 (C-3), 79.8 (C-4), 77.5 (C-2), 77.4 (C-5), 71.4 (C-6),
66.2 (C-7), 57.4 (CH2Ph), 32.9 (C ), 27.6 (CH3), 26.5 (CH3), 25.6
d 139.7, 128.6e127.1 (C6H5), 112.6 [OC(CH3)2], 109.5
D
16.9 (CH2D), 10.3 (CH2D); HRMS C25H31N2O4: calcd 423.2284, found
D
423.2290. Compound 16: syrup; ½a D16
ꢂ
ꢀ7 (c 1.00, CHCl3); 1H NMR
(CH3), 24.8 (CH3), 16.8 (CH2D), 8.6 (CH2D); HRMS C22H33N2O4: calcd
389.2440, found 389.2442.
(CDCl3, 300 MHz)
d
7.40e7.20 (m, 5H, C6H5), 4.69e4.61 (m, 2H, H-3,
H-4), 3.86 (d, JA,B¼14.9 Hz, 1H, H-A CH2Ph), 3.76 (dd, J5,6a¼7.5 Hz,
J6a,6b¼11.2 Hz, 1H, H-6a), 3.65 (d, 1H, H-B CH2Ph), 3.60 (dd,
J5,6b¼3.6 Hz, 1H, H-6b), 3.56 (br s, 2H, NH2), 2.67e2.63 (m, 1H, H-5),
1.73 (d, J2,3¼4.4 Hz 1H, H-2), 1.55 (s, 3H, CH3), 1.33 (s, 3H, CH3),
0.85e0.81 (m, 1H, CH2D), 0.65e0.61 (m, 1H, CH2D), 0.46e0.44 (m, 2H,
5.3.10. (2R,3S,4R,5S)-2-(1-Aminocyclopropyl)-1-N-benzyl-3,4-O-iso-
propyliden-5-methylpyrrolidine-3,4-diol (25). Following the general
method A, 23 (1.0 g, 3.67 mmol), Ti(OiPr)3Me (1.3 mL, 5.51 mmol),
EtMgBr (3.7 mL, 5.51 mmol, 2.2 M) and BF3$OEt2 (0.93 mL,
7.34 mmol) in THF (50 mL) gave after flash chromatography (EtOAc)
CH2D); 13C NMR (CDCl3, 75 MHz)
d
139.4, 128.4e127.2 (CH, C6H5),
111.1 [OC(CH3)2], 81.3 (C-3), 79.3 (C-4), 73.6 (C-2), 68.6 (C-5), 60.6 (C-
6), 55.9 (CH2Ph), 31.4 (C ), 25.9 (CH3), 24.2 (CH3), 16.0 (CH2D), 9.2
compound 25 (0.63 g, 57%) as a syrup; ½a D16
ꢂ
ꢀ11 (c 1.01, CHCl3); 1H
D
NMR (CDCl3, 300 MHz) d 7.44e7.19 (m, 5H, C6H5), 4.74 (s, 2H, NH2),
(CH2D); HRMS C18H27N2O3: calcd 319.2022, found 319.2032.
4.60 (dd, J2,3¼4.7 Hz, J3,4¼6.5 Hz, 1H, H-3), 4.43 (dd, J4,5¼5.1 Hz, 1H,
H-4), 3.78 (d, JA,B¼15.1 Hz, 1H, H-A CH2Ph), 3.63 (d, 1H, H-B CH2Ph),
2.53e2.49 (m, 1H, H-5), 1.58 (d, J2,3¼4.7 Hz, 1H, H-2), 1.57 (s, 3H,
CH3), 1.34 (s, 3H, CH3), 1.14 (d, JH,CH3¼6.4 Hz, 3H, CHCH3), 0.88e0.83
(m, 1H, CH2D), 0.66e0.61 (m, 1H, CH2D), 0.46e0.44 (m, 2H, CH2D);
5.3.7. (2S,3R,4R,5S)-2-(1-Aminocyclopropyl)-1-N-benzyl-3,4-di-O-
benzyl-5-benzyloxymethylpyrrolidine (20). Following the general
method A, 17 (1.0 g, 1.93 mmol), Ti(OiPr)3Me (700
mL, 2.89 mmol),
EtMgBr (1.9 mL, 2.89 mmol, 2.2 M) and BF3$OEt2 (500 L,
m
13C NMR (CDCl3, 75 MHz)
d
140.0, 128.5e127.0, (C6H5), 110.9
[OC(CH3)2], 81.5 (C-3), 80.4 (C-4), 74.8 (C-2), 64.2 (C-5), 55.6
(CH2Ph), 31.5 (C ), 26.2 (CH3), 24.8 (CH3), 16.4 (CH2D), 14.0
3.86 mmol) in THF (25 mL) gave after flash chromatography
(EtOAc/cyclohexane, 7/3) compound 20 (0.39 g, 37%) as a syrup;
D
½
a 1D6
ꢂ
þ21 (c 1.03, CHCl3); 1H NMR (CDCl3, 300 MHz)
d
7.37e7.27 (m,
(CHCH3), 9.6 (CH2D); HRMS C18H27N2O2: calcd 303.2073, found
303.2075.
10H, C6H5), 5.46 (br s, 2H, NH2), 4.80 (d, J¼12.0 Hz, 2H, CH2Ph),
4.49e4.40 (m, 5H, CH2Ph), 4.32 (d, J¼12.0 Hz, 2H, CH2Ph),
3.87e3.85 (m, 1H, H-5), 3.82e3.80 (m, 1H, H-4), 3.65 (t, J¼3.0 Hz,
1H, H-3), 3.02 (d, J¼13.2 Hz, 1H, CH2Ph), 2.86 (dd, J5,6a¼4.4 Hz,
J6a,6b¼10.7 Hz, 1H, H-6a), 2.42 (t, 1H, H-6b), 1.96 (d, J2,3¼3.0 Hz, 1H,
H-2), 1.31e1.26 (m, 1H, CH2D), 1.03e0.97 (m, 1H, CH2D), 0.74e0.69
(m, 1H, CH2D), 0.29e0.24 (m, 1H, CH2D); 13C NMR (CDCl3, 75 MHz)
5.3.11. (2S,3S,4R,5S)-2-(1-Aminocyclopropyl)-1-N-benzyl-3,4-O-iso-
propylidene-5-methylpyrrolidine-3,4-diol (26). Following the gen-
eral method A, 24 (50 mg, 0.18 mmol), Ti(OiPr)3Me (66
mL,
0.27 mmol), EtMgBr (140
mL, 0.271 mmol, 2.2 M) and BF3$OEt2
(46 mL, 0.36 mmol) in THF (2.5 mL) gave after flash chromatography
d
138.6e136.6, 129.2e127.4 (C6H5), 78.9 (C-3), 73.7 (C-5), 73.3
(OCH2Ph), 72.5 (OCH2Ph), 71.8 (C4), 71.4 (NCH2Ph), 63.6 (C-2), 59.2
(OCH2Ph), 49.4 (C-6), 34.8 (C ), 15.7 (CH2D), 7.8 (CH2D); HRMS
(EtOAc) compound 26 (20 mg, 38%) as a syrup; ½a D20
þ12 (c 0.64,
ꢂ
CHCl3); 1H NMR (CDCl3, 300 MHz)
d 7.41e7.25 (m, 5H, C6H5), 4.76
D
(dd, J2,3¼3.0 Hz, J3,4¼6.3 Hz, 1H, H-3), 4.65 (t, J3,4¼6.3 Hz, 1H, H-4),
4.12 (d, JA,B¼14.0 Hz, 1H, H-A CH2Ph), 3.71 (d, 1H, H-B CH2Ph), 3.52
(m, 1H, H-5), 2.30 (d, 1H, H-2), 1.96 (br s, 2H, NH2), 1.54 (s, 3H, CH3),
1.40 (s, 3H, CH3), 1.00 (d, JH,CH3¼6.6 Hz, 3H, CHCH3), 0.76e0.69 (m,
C36H41N2O3: calcd 549.3117, found 549.3116.
5.3.8. (2R,3S,4S,5R)-2-(1-Aminocyclopropyl)-1-N-benzyl-3,4-di-O-
benzyl-5-benzyloxymethylpyrrolidine (21). Following the general
method A, 18 (2.0 g, 3.86 mmol), Ti(OiPr)3Me (1.37 mL, 5.79 mmol),
1H, CH2D), 0.60e0.50 (m, 2H, CH2D), 0.49e0.42 (m, 1H, CH2D); 13
C
NMR (CDCl3, 75 MHz) d 139.1, 128.5e127.0 (C6H5), 112.9 [OC(CH3)2],

1808
D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
82.7 (C-3), 79.7 (C-4), 72.4 (C-2), 58.0 (C-5), 51.1 (CH2Ph), 33.2 (C
26.0 (CH3), 25.1 (CH3), 17.2 (CH2D), 9.8 (CHCH3), 9.4 (CH2D); HRMS
C18H27N2O2: calcd 303.2073, found 303.2072.
D
),
vacuum, MgBr2$OEt2 was obtained as a white solid and was used in
the next step without further purification. To a solution of compound
29 (100 mg, 0.32 mmol) in anhydrous THF (3.5 mL) was added a so-
lution of MgBr2$OEt2 (36.5 mg, 0.32 mmol) in CH2Cl2 (1 mL) followed
by a solution of PPh3 (84 mg, 0.32 mmol) in anhydrous THF (1 mL).
After stirring at room temperature for 5 h 30 and evaporation of the
solvent, the crude was flash chromatographed (EtOAc/MeOH, 7/3) to
5.3.12. (2S,3S,4R,5S)-5-Aminomethyl-1-N-benzyl-2-cyano-3,4-O-iso-
propylidenepyrrolidine-3,4-diol (28). Following the general method
A, 27 (50 mg, 0.16 mmol), Ti(OiPr)3Me (57
mL, 0.24 mmol), EtMgBr
(120
mL, 0.24 mmol, 2 M) and BF3$OEt2 (40
m
L, 0.32 mmol) in THF
afford compound 32 (154 mg, 88%) as a syrup; ½a D16
þ8 (c 1.0, CHCl3);
ꢂ
(2.5 mL) gave after flash chromatography (EtOAc) compound 28
1H NMR (CDCl3, 300 MHz)
d 8.10e7.82 (m, 3H, C6H5), 7.86e7.76 (m,
(21 mg, 46%) as a syrup; ½a D16
ꢂ
þ78 (c 0.58, CHCl3); 1H NMR (CDCl3,
12H, C6H5), 7.28e7.25 (m, 3H, C6H5), 7.20e7.18 (m, 2H, C6H5), 4.99(dd,
J4,5¼4.0 Hz, J3,4¼6.2 Hz, 1H, H-4), 4.85 (dd, J2,3¼5.2 Hz, 1H, H-3), 3.89
(d, JA,B¼14.7 Hz,1H, H-ACH2Ph), 3.74 (d, J2,3¼5.2 Hz,1H, H-2), 3.65 (d,
1H, H-B CH2Ph), 3.08e2.95 (m, 3H, H-5, H-6a, H-6b),1.41 (s, 3H, CH3),
300 MHz)
d
7.40e7.12 (m, 5H, C6H5), 4.75 (dd, J4,5¼6.3 Hz,
J3,4¼4.6 Hz, 1H, H-4), 4.62 (m, 1H, H-3), 4.05 (d, JA,B¼14.8 Hz, 1H, H-
A CH2Ph), 3.95 (d, 1H, H-B CH2Ph), 3.34 (d, J2,3¼5.0 Hz, 1H, H-2),
3.12 (m, 2H, H-6a, H-6b), 2.53 (m, 1H, H-5), 1.67 (s, 3H, CH3), 1.46 (s,
1.31 (s, 3H, CH3); 13C NMR (CDCl3, 75 MHz)
d 136.9, 135.2e127.5
3H, CH3); 13C NMR (CDCl3, 75 MHz)
d
133.5, 129.7e128.1 (C6H5),
(C6H5), 121.3e119.3 (C6H5), 116.2 (CN), 112.6 [OC(CH3)2], 79.7 (C-4),
77.7 (C-3), 67.0 (C-2), 59.7 (C-5), 55.5 (CH2Ph), 40.3 (C-6), 25.3 (CH3),
24.7 (CH3); HRMS C34H35N3O2P: calcd 548.2467, found 548.2443.
115.8 (CN), 113.5 [OC(CH3)2], 80.2 (C-4), 77.4 (C-3), 64.4 (C-5), 57.9
(C-2), 53.2 (CH2Ph), 38.9 (C-6), 26.1 (CH3), 25.4 (CH3); HRMS
C16H21N3O2: calcd 288.1712, found 288.1701.
5.3.16. (2R,3S,4R,5S)-1-N-Benzyl-5-bromomethyl-2-cyano-3,4-O-
isopropylidenepyrrolidine-3,4-diol (33). Magnesium bromide was
first obtained from reaction of magnesium (31.5 mg, 1.30 mmol) and
5.3.13. (2R,3S,4R,5S)-5-Aminomethyl-1-N-benzyl-2-cyano-3,4-O-
isopropylidenepyrrolidine-3,4-diol (30). To a solution of compound
29 (500 mg, 1.60 mmol) in THF (25 mL) was added EtMgBr (905
mL,
1,2-dibromoethane (110 mL, 1.27 mmol) in Et2O (2 mL). After elimi-
2.4 mmol, 2 M) dropwise. After 1 h at room temperature, water and
EtOAc were added followed by addition of HCl (1 M) until appari-
tion of two distinct phases. Then NaOH (3 M) was added until pH
became strongly basic. After separation of the organic phase, the
aqueous layer was extracted with EtOAc (ꢃ2). The organic layers
were gathered, dried over Na2SO4, filtered and evaporated to dry-
ness. After flash chromatography (EtOAc/MeOH, 7/3), compound 30
nation of the solvent under vacuum, MgBr2$OEt2 was obtained as
a white solid and was used in the next step without further purifi-
cation. To a solution of 29 (201 mg, 0.64 mmol) in distilled THF (9 mL)
was slowly added a solution of MgBr2$OEt2 (73 mg, 0.64 mmol) in
CH2Cl2 (2 mL), BF3$Et2O (165 mL, 1.28 mmol), and a solution of PPh3
(168 mg, 0.64 mmol) in THF (2 mL). After stirring at room tempera-
ture overnight and elimination of the solvent, the residue was puri-
fied by flash chromatography (EtOAc/cyclohexane, 5/95) to afford 33
(340 mg, 74%) was isolated as a white solid; mp¼107e108 ꢁC; ½a D21
ꢂ
ꢀ49 (c 0.1, CH2Cl2); 1H NMR (CDCl3, 300 MHz)
d
7.46e7.29 (m, 5H,
(70 mg, 31%) as a white solid; mp¼131e133 ꢁC; ½a D20
ꢀ11 (c 0.50,
ꢂ
C6H5), 4.94 (dd, J3,4¼4.6 Hz, J2,3¼6.3 Hz, 1H, H-3), 4.83 (d, 1H, H-2),
4.30 (br s, 2H, NH2), 4.07 (d, JA,B¼13.1 Hz, 1H, H-A CH2Ph),
3.98e3.96 (m, 1H, H-6a), 3.57 (d, 1H, H-B CH2Ph), 3.44 (m, 2H, H-5,
H-6b), 3.02 (t, J4,5¼4.6 Hz, 1H, H-4), 1.55 (s, 3H, CH3), 1.35 (s, 3H,
CH2Cl2); 1H NMR (CDCl3, 300 MHz)
d 7.33e7.20 (m, 5H, C6H5), 4.69
(dd, J4,5¼3.9 Hz, J3,4¼5.6 Hz, 1H, H-4), 4.58 (t, J2,3¼5.6 Hz, 1H, H-3),
3.97 (d, JA,B¼14.9 Hz,1H, H-A CH2Ph), 3.81 (d,1H, H-B CH2Ph), 3.41 (q,
J5,6a¼J6a,6b¼9.9 Hz, 1H, H-6a), 3.36 (dd, J5,6b¼3.9 Hz, 1H, H-6b), 3.31
(d, J2,3¼5.6 Hz,1H, H-2), 2.71 (dt,1H, H-5),1.56 (s, 3H, CH3),1.33 (s, 3H,
CH3); 13C NMR (CDCl3, 75 MHz)
d 134.9, 129.3e128.6 (C6H5), 114.1
(CN), 113.3 [OC(CH3)2], 81.4 (C-3), 80.0 (C-2), 61.2 (C-4), 58.6 (C-5),
52.7 (CH2Ph), 37.7 (C-6), 25.6 (CH3), 23.9 (CH3); HRMS C16H22N3O2:
calcd 288.1712, found 288.1711.
CH3); 13C NMR (CDCl3, 75 MHz)
d 133.9, 129.4e128.3 (C6H5), 115.6
(CN), 113.6 [OC(CH3)2], 79.5 (C-4), 76.9 (C-3), 66.6 (C-5), 58.9 (C-2),
53.9 (CH2Ph), 27.3 (C-6), 26.3 (CH3), 25.9 (CH3); HRMS C16H19N2O2
-
NaBr: calcd 373.0528, found 373.0543.
5.3.14. (1R,5S,6R,7S)-2-Amino-8-benzyl-3,8-diaza-6,7-
isopropylidenebicyclo[3.2.1]oct-2-ene-6,7-diol (31). To a solution of
compound 29 (100 mg, 0.32 mmol) in THF (5 mL) was added EtMgBr
5.3.17. (2S,3R,4R,5S)-1-N-Benzyl-5-chloromethyl-2-cyano-3,4-O-iso-
propylidenepyrrolidine-3,4-diol (34). To a solution of 29 (200 mg,
0.64 mmol) in distilled THF (9 mL) was slowly added MgCl2 (60 mg,
(242
mL, 0.48 mmol, 2 M) dropwise. After 1 h at room temperature,
BF3$OEt2 (80
mL, 0.64 mmol) was added and the reaction mixture
0.64 mmol) in CH2Cl2 (2 mL), BF3$Et2O (165 mL, 1.28 mmol), and
was stirred for 1 h. Water and EtOAc were added followed by addi-
tion of HCl (1 M) until apparition of two distinct phases. Then NaOH
(3 M) was added until pH became strongly basic. After separation of
the organic phase, the aqueous layer was extracted with EtOAc (ꢃ2).
The organic layers were gathered, dried over Na2SO4, filtered and
evaporated to dryness. After flash chromatography (EtOAc/MeOH, 9/
a solution of PPh3 (168 mg, 0.64 mmol) in THF (2 mL). After stirring
at room temperature overnight and elimination of the solvent, the
residue was purified by flash chromatography (EtOAc/cyclohexane,
5/95) to afford 34 (74 mg, 38%) as a white solid; mp¼124e127 ꢁC;
½
a 2D0
ꢂ
ꢀ21 (c 0.85, CH2Cl2); 1H NMR (CDCl3, 300 MHz)
d 7.42e7.30
(m, 5H, C6H5), 4.78 (dd, J4,5¼4.4 Hz, J3,4¼6.1 Hz, 1H, H-4), 4.70 (dd,
J2,3¼5.2 Hz, 1H, H-3), 4.08 (d, JA,B¼14.9 Hz, 1H, H-A CH2Ph), 3.91 (d,
1H, H-B CH2Ph), 3.76e3.60 (m, 2H, H-6a, H-6b), 3.40 (d, 1H, H-2),
2.80e2.74 (m, 1H, H-5), 1.65 (s, 3H, CH3), 1.42 (s, 3H, CH3); 13C NMR
1), compound 31 (33 mg, 36%) was isolated as a syrup; ½a D16
þ6 (c
ꢂ
1.01, CHCl3); 1H NMR (CDCl3, 300 MHz)
d 7.37e7.29 (m, 5H, C6H5),
4.90 (dd, J¼6.2e7.6 Hz, 1H, H-6), 4.77 (dd, J¼5.7e7.6 Hz, 1H, H-7),
4.08 (d, J¼6.2 Hz,1H, H-5), 3.92 (d, JA,B¼13.1 Hz,1H, H-A CH2Ph), 3.83
(d, 1H, H-B CH2Ph), 3.56e3.42 (m, 3H, H1þH2), 1.49 (s, 3H, CH3), 1.36
(CDCl3, 75 MHz)
d 133.9, 129.5e128.3 (C6H5), 115.6 (CN), 113.7
[OC(CH3)2], 79.3 (C-4), 77.1 (C-3), 66.6 (C-5), 58.7 (C-2), 54.0
(CH2Ph), 39.9 (C-6), 26.3 (CH3), 25.8 (CH3); HRMS C16H19N2O2NaCl:
calcd 329.1033, found 329.1027.
(s, 3H, CH3); 13C NMR (CDCl3, 75 MHz)
d 164.3 (CeNH2), 136.3,
129.8e127.9 (C6H5), 117.1 [OC(CH3)2], 80.6 (C-6), 78.1 (C-7), 61.2 (C-
5), 55.4 (C-1), 52.4 (CH2Ph), 34.8 (C-2), 25.8 (CH3), 24.9 (CH3); HRMS
C16H22N3O2: calcd 288.1712, found 288.1711.
5.3.18. (2R,3S,4R,5S)-2-(1-Aminocyclopropyl)-5-hydroxymethyl pyr-
rolidine-3,4-diol bis-hydrochloride (35). Following the general
method B, 14 (200 mg, 0.49 mmol), Pd/C (156 mg) in MeOH (12 mL)
5.3.15. (2R,3S,4R,5S)-1-N-Benzyl-2-cyano-3,4-O-isopropylidene-5-
triphenylphosphanilydeniminomethylpyrrolidine-3,4-diol
(32). Magnesium bromide was first obtained from reaction of mag-
followed by addition of HCl 3 M (500 mL) gave 35 (48 mg, 38%) as an
amorphous solid; ½a D20
ꢂ
ꢀ12 (c 0.27, MeOH); 1H NMR (CD3OD,
nesium (31.5 mg, 1.30 mmol) and 1,2-dibromoethane (110
mL,
300 MHz)
d
5.10 (br s, 6H, NH, NH2, 3ꢃ OH), 4.82e4.80 (m, 1H),
1.27 mmol) in Et2O (2 mL). After elimination of the solvent under
4.42e4.40 (m, 1H), 4.07e4.04 (m, 2H), 3.78e3.75 (m, 2H), 1.37e1.30

D. Declerck et al. / Tetrahedron 68 (2012) 1802e1809
1809
(m, 4H, CH2D); 13C NMR (CD3OD, 75 MHz)
2, C-3, C-4, C-5), 58.7 (C-6), 33.5 (C ), 12.9 (CH2D), 10.6 (CH2D);
HRMS C8H17N2O3: calcd 189.1239, found 189.1241.
d
72.4, 71.4, 65.3, 63.4 (C-
References and notes
D
1. Stutz, A. E. Iminosugars as Glycosidase Inhibitors: Nojirimycin and Beyond; Wiley-
VCH GmbH: Weinheim (Federal Republic of Germany), 1999.
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3. Moreno-Clavijo, E.; Carmona, A. T.; Moreno-Vargas, A. J.; Molina, L.; Robina, I.
Chimia 2011, 65, 40e44.
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C.; Goti, A. Eur. J. Org. Chem. 2008, 2929e2947.
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5.3.19. (2S,3R,4R,5S)-2-(1-Aminocyclopropyl)-5-hydroxymethyl pyr-
rolidine-3,4-diol bis-hydrochloride (36). A solution of compound 20
(249 mg, 0.45 mmol) with Pd/C (145 mg) in MeOH (15 mL) with
a few drop of HCl 1 M was stirred overnight. After evaporation of
the solvent, compound 36 (79 mg, 68%) was obtained as an amor-
phous chlorhydrate salt; ½a D20
ꢂ
þ26 (c 0.75, MeOH); 1H NMR (CD3OD,
6. Fleet, G. W. J.; Namgoong, S. K.; Barker, C.; Baines, S.; Jacob, G. S.; Winchester, B.
Tetrahedron Lett. 1989, 30, 4439e4442.
300 MHz)
d 5.24 (br s, 6H, NH, NH2, 3OH), 4.38e4.31 (m, 2H),
7. Dubernet, M.; Defoin, A.; Tarnus, C. Bioorg. Med. Chem. Lett. 2006, 16, 1172e1174.
8. Li, H.; Schuetz, C.; Favre, S.; Zhang, Y.; Vogel, P.; Sinay, P.; Bleriot, Y. Org. Biomol.
Chem. 2006, 4, 1653e1662.
9. Li, H.; Liu, T.; Zhang, Y.; Favre, S.; Bello, C.; Vogel, P.; Butters, T. D.; Oikonomakos,
N. G.; Marrot, J.; Bleriot, Y. ChemBioChem 2008, 9, 253e260.
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4.07e4.06 (m, 1H), 3.45 (d, J¼19.1 Hz, 2H), 3.38e3.23 (m, 1H),
1.56e1.53 (m, 1H, CH2D), 1.35e1.27 (m, 3H, CH2D); 13C NMR
(CD3OD, 75 MHz)
d 70.8, 69.9, 63.1, 57.9 (C-2, C-3, C-4, C-5), 44.9 (C-
6), 35.8 (C ), 12.3 (CH2D), 11.6 (CH2D); HRMS C8H17N2O3: calcd
D
189.1239, found 189.1238.
11. Liang, P.-H.; Cheng, W.-C.; Lee, Y.-L.; Yu, H.-P.; Wu, Y.-T.; Lin, Y.-L.; Wong, C.-H.
ChemBioChem 2006, 7, 165e173.
5.3.20. (2R,3S,4S,5R)-2-(1-Aminocyclopropyl)-5-hydroxymethyl pyr-
rolidine-3,4-diol bis-hydrochloride (37). A solution of compound 21
(475 mg, 0.87 mmol) with Pd/C (276 mg) in MeOH (15 mL) with
a few drops of HCl 1 M was stirred overnight. After evaporation of
the solvent, compound 37 (224 mg, 99%) was obtained as an
12. Fiaux, H.; Kuntz, D. A.; Hoffman, D.; Janzer, R. C.; Gerber-Lemaire, S.; Rose, D. R.;
Juillerat-Jeanneret, L. Bioorg. Med. Chem. 2008, 16, 7337e7346.
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Juillerat-Jeanneret, L. J. Med. Chem. 2005, 48, 4237e4246.
14. Popowycz, F.; Gerber-Lemaire, S.; Demange, R.; Rodriguez-Garcıa, E.; Asenjo, A.
T. C.; Robina, I.; Vogel, P. Bioorg. Med. Chem. Lett. 2001, 11, 2489e2493.
15. Kim, D.-K.; Gam, J.; Kim, H.-T.; Kim, K. H. Bioorg. Med. Chem. Lett. 1996, 6,
771e774.
16. Bogdanovich, T.; Esel, D.; Kelly, L. M.; Bozdogan, B.; Credito, K.; Lin, G.; Smith,
K.; Ednie, L. M.; Hoellman, D. B.; Appelbaum, P. C. Antimicrob. Agents Chemother.
2005, 49, 3325e3333.
17. Pearson, M. S. M.; Floquet, N.; Bello, C.; Vogel, P.; Plantier-Royon, R.; Szymoniak,
J.; Bertus, P.; Behr, J.-B. Bioorg. Med. Chem. 2009, 17, 8020e8026.
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Asymmetry 2008, 19, 1829e1832.
amorphous chlorhydrate salt; ½a D20
ꢂ
ꢀ19 (c 0.71, MeOH); 1H NMR
(CD3OD, 300 MHz)
d
5.08 (br s, 6H, NH, NH2, 3ꢃ OH), 4.41e4.33 (m,
2H), 4.11e4.09 (m, 1H), 3.54 (s, 1H), 3.48e3.47 (m, 2H), 1.59e1.53
(m, 1H, CH2D), 1.44e1.29 (m, 3H, CH2D); 13C NMR (CD3OD,
300 MHz)
d 71.0, 70.0, 63.2, 58.0 (C-2, C-3, C-4, C-5), 45.1 (C-6), 35.8
(C ), 12.3 (CH2D), 11.7 (CH2D); HRMS C8H17N2O3: calcd 189.1239,
D
found 189.1238.
19. Pearson, M. S. M.; Plantier-Royon, R.; Szymoniak, J.; Bertus, P.; Behr, J.-B. Syn-
thesis 2007, 3589e3594.
20. Laroche, C.; Plantier-Royon, R.; Szymoniak, J.; Bertus, P.; Behr, J.-B. Synlett 2006,
223e226.
21. Laroche, C.; Behr, J.-B.; Szymoniak, J.; Bertus, P.; Schuetz, C.; Vogel, P.; Plantier-
Royon, R. Bioorg. Med. Chem. 2006, 14, 4047e4054.
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Szymoniak, J.; Lequin, O.; Karoyan, P. ChemBioChem 2011, 12, 1039e1042.
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26. Declerck, D.; Josse, S.; Nhien, A. N. V.; Postel, D. Tetrahedron Lett. 2009, 50,
2171e2173.
27. Moura, M.; Delacroix, S.; Postel, D.; Van, N. A. N. Tetrahedron2009, 65, 2766e2772.
5.3.21. (2S,3S,4R,5S)-2-(1-Aminocyclopropyl)-5-methylpyrrolidine-
3,4-diol bis-hydrochloride (38). Following the general method B, 25
(45 mg, 0.15 mmol), Pd/C (48 mg) in MeOH (3 mL) followed by
addition of HCl 3 M (120 mL) gave 38 (18 mg, 50%) as an amorphous
solid; ½a 2D0
ꢂ
ꢀ3 (c 0.27, MeOH); 1H NMR (CD3OD, 300 MHz)
d 5.00 (br
s, 5H, NH, NH2, 2ꢃ OH), 4.75 (dd J¼3.4e9.2 Hz, 1H), 4.19e4.18 (m,
1H), 3.66e3.63 (m, 2H), 1.49 (d, JH,CH¼6.5 Hz, 3H, CH3), 1.38e1.13
(m, 4H, CH2D); 13C NMR (CD3OD, 75 MHz)
d 73.3, 72.5, 65.6, 57.7 (C-
2, C-3, C-4, C-5), 35.5 (CD), 12.9 (CH2D), 11.6 (CH3), 10.4 (CH2D);
HRMS C8H17N2O2: calcd 173.1290, found 173.1290.
́
~
28. Elhalem, E.; Comin, M. J.; Leitofuter, J.; García-Linares, G.; Rodriguez, J. B. Tet-
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rahedron: Asymmetry 2005, 16, 425e431.
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The experiments were performed essentially as described pre-
viously.40,41 Briefly, 0.01e0.5 unit/mL of enzyme (1unit¼1 mol of
glycoside hydrolyzed/min), preincubated for 5 min at 20 ꢁC with
the inhibitor, and increasing concentration of aqueous solution of
the appropriate p-nitrophenyl glycoside substrates (buffered to the
optimum pH of the enzyme) were incubated for 20 min at 37 ꢁC.
35. Calveras, J.; Egido-Gabas, M.; Gomez, L.; Casas, J.; Parella, T.; Joglar, J.; Bujons, J.;
The reaction was stopped by the addition of 100 mL of 0.3 M solu-
Clapes, P. Chem.dEur. J. 2009, 15, 7310e7328.
tion borate buffer pH 9.8. The p-nitrophenolate formed was quan-
tified at 405 nm, and IC50 values were calculated. Double-reciprocal
(LineweavereBurk) plots were used to determine the inhibition
characteristics of compounds 35, 36, 37 and 38.
36. Moreno-Clavijo, E.; Carmona, A. T.; Vera-Ayoso, Y.; Moreno-Vargas, A. J.; Bello,
C.; Vogel, P.; Robina, I. Org. Biomol. Chem. 2009, 7, 1192e1202.
37. Ho, C.-W.; Lin, Y.-N.; Chang, C.-F.; Li, S.-T.; Wu, Y.-T.; Wu, C.-Y.; Chang, C.-F.; Liu,
S.-W.; Li, Y.-K.; Lin, C.-H. Biochemistry 2006, 45, 5695e5702.
38. Chang, C.-F.; Ho, C.-W.; Wu, C.-Y.; Chao, T.-A.; Wong, C.-H.; Lin, C.-H. Chem. Biol.
2004, 11, 1301e1306.
Acknowledgements
39. Wu, C.-Y.; Chang, C.-F.; Chen, JS.-Y.; Wong, C.-H.; Lin, C.-H. Angew. Chem., Int. Ed.
2003, 42, 4661e4664.
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