First total synthesis of 3-Epi-calystegin B2

Article abstract of DOI:10.1515/znb-2011-0315

A straightforward chiral pool synthesis for a non-natural calystegin, 3-epi-B₂, is described. Key steps of this synthesis include an ultrasound-assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst-mediated ring closu

Full text of DOI:10.1515/znb-2011-0315

First Total Synthesis of 3-Epi-calystegin B2
Rene´ Csuk, Stefan Reißmann, Ralph Kluge, Dieter Stro¨hl, and Claudia Korb
Martin-Luther-Universita¨t Halle-Wittenberg, Bereich Organische Chemie, Kurt-Mothes-Straße 2,
06120 Halle (Saale), Germany
Reprint requests to Prof. Dr. Rene´ Csuk. Fax: 0049 345 5527030.
E-mail: rene.csuk@chemie.uni-halle.de
Z. Naturforsch. 2011, 66b, 317 – 323; received November 29, 2010
A straightforward chiral pool synthesis for a non-natural calystegin, 3-epi-B2, is described. Key
steps of this synthesis include an ultrasound-assisted Zn-mediated tandem ring opening reaction fol-
lowed by a Grubbs’ catalyst-mediated ring closure metathesis reaction. Compared to calystegin B2,
the target compound is no longer an inhibitor for a β-glycosidase hence proving that an equatorial
hydroxyl group at position C-3 is necessary for a tight binding of calystegins into the active site of
β-glycosidases.
Key words: Calystegin, Glucosidase Inhibitor, Ring Closure Metathesis
Introduction
been suggested [11] as pharmacoperones to treat pro-
tein folding disorders.
Diabetes mellitus type-2 is characterized [1] by high
blood glucose levels because of an impaired insulin
action. This impaired insulin action (“insulin resis-
tance”) is a contributing factor [2 – 4] to hypertension,
atherosclerosis and a risk factor for coronary heart dis-
Only a few non-natural calystegins have been syn-
thesized [12, 13] and screened for biological activity
so far. Recently, we were able to show that a fluorine
substitution at position C-3 in calystegine B2 (Fig. 1)
lowers its affinity to several glucosidases [14]. Based
on these findings we became interested in the role of
the hydroxyl group at position C-3 and therefore in the
synthesis of a 3-epi-calystegin B2 and the comparison
of its activity as an inhibitor of a β-glucosidase.
R
eases. Acarbose (Glucobayꢀ, Fig. 1) is an antidia-
betic drug [5] to treat type-2 diabetes mellitus and pre-
diabetes. It is a glucosidase inhibitor, and it acts by re-
ducing the rate of digestion of complex carbohydrates
into monosaccharides.
Calystegins [6] are polyhydroxylated bicyclic
nortropane alkaloids which were first isolated from
the roots of Calystegia sepium in 1988. They are lead
substances [7 – 10] for chemotherapeutic drugs for the
treatment of diabetes mellitus but also for viral infec-
tions, cancer and other metabolic disorders; they have
Results and Discussion
Olefin metathesis is one of the most powerful tools
in current organic synthesis. Routes to calystegins us-
ing ring closure metatheses [12, 13, 15] as key steps
appear most promising and straightforward. Formally,
calystegin B2 is derived from D-glucose; to obtain
an analog of inverted configuration at position C-3,
a suitable allose derivative can serve as a starting
material. Therefore, 1,2 : 5,6-di-O-isopropylidene-α-
D-allofuranose 1 [16] was selected as a starting point
for our synthesis of 3-epi-calystegin B2 (11).
Hydrolysis of 1 with aqueous sulfuric acid
(Scheme 1) resulted in the formation of a complex
mixture of anomeric pyranoses and furanoses. Treat-
ment of this mixture with methanol in the presence of
dry HCl gave a mixture of the corresponding methyl
glycosides whose in situ tritylation, benzylation, de-
tritylation and chromatography gave the methyl α-D-
Fig. 1. Structure of glycosidase inhibitors acarbose and ca-
lystegin B2.
c
0932–0776 / 11 / 0300–0317 $ 06.00 ꢀ 2011 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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R. Csuk et al. · First Total Synthesis of 3-Epi-calystegin B2
◦
Scheme 1. a) H2SO4; trityl chloride/pyridine/DMAP; DMF; BnBr/DMF; p-TsOH; b) PPh3, imidazole, I2, toluene, 95 C,
2 h; c) Zn, THF, 40 ◦C, ultrasound; BnNH2, 3 h, allyl bromide 4 h; d) PPh3, imidazole, I2, toluene, 95 ◦C, 2 h; e) Zn, THF,
40 ◦C, ultrasound; BnNH2, 3 h, allyl bromide 4 h.
◦
◦
◦
Scheme 2. a) Benzyl chloroformate, NaHCO3, 25 C, 2 h; b) Grubbs catalyst, 25 C, 30 h; c) BH3THF, H2O2, 25 C, 5 h;
d) PCC, CH2Cl2, 25 ◦C, 24 h; e) Pd/C, H2, EtOAc/HOAc, 25 ◦C, 5 d.
allopyranoside 2 [17] and the benzylated methyl β-D- of 8 using the borane-THF complex followed by oxida-
allopyranoside 3. Compound 2 is characterized in its tive work-up [23] and PCC oxidation of 9 gave the cy-
1H NMR spectra by the presence of a doublet at δ = cloheptanone 10. Compound 10 is characterized in its
4.71 ppm showing a 3J1-H,2-H = 4.2 Hz whereas for β- IR spectrum by a strong adsorption at ν = 1694 cm−1
configurated 3 [18] at δ = 4.81 ppm a doublet with for the carbonyl group of the ketone; this carbonyl
3J1-H,2-H = 7.9 Hz is found, the latter being typical for group is also detected by a 13C NMR signal at δ =
a β-anomeric configuration.
208.0 ppm. Hydrogenation of 10 with Pd/C (10 %) in
ethyl acetate/acetic acid finally gave the target com-
pound 11.
Iodination of 2 using triphenylphosphane, iodine
and imidazol [19] gave 6-deoxy-6-iodo-alloside 4 in
78 % yield; iodination of 3 under similar conditions
Compared with naturally occurring calystegin B2,
yielded 6 [20]. Ring opening [21, 22] of 4 gave 56 % of the signal of C-3 in 3-epi-B2 is shifted to δ = 66.9 ppm
the (R)-6-amino-diene 5. The same product could also (|∆δ| = 8.3 ppm, cf. C-3 in calystegin B2 δ =
be obtained from the ring opening of 6 although in a 75.2 ppm), and that of 3-H is shifted to δ = 3.67 ppm
lower yield.
(|∆δ| = 0.43; cf. 3-H in calystegin B2 δ = 3.24 ppm). A
proof for the D-allo-configuration is found in the cou-
Compound 5 was N-protected by carbobenzoxyla-
tion (Scheme 2) to afford 7, which was subjected to a
RCM reaction using Grubbs’ catalyst (2nd generation,
Cl2Ru(Imes)[P(cyclohexyl)3]=CHPh) [21, 22], and the
3
pling constants J2-H,3-H = 3.9 Hz (for calystegin B2
J = 8.5 Hz was detected) and 3J3-H,4-H = 4.2 Hz.
Calystegin B2 is a competitive inhibitor for the β-
cycloheptene 8 was obtained. Regioselective oxidation glucosidase from almonds. In a 4-nitro-phenolate as-
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R. Csuk et al. · First Total Synthesis of 3-Epi-calystegin B2
319
◦
say [24] a Ki = 5.9 µM was determined. A previously in dry DMF (100 mL), and at 0 C NaH (55 % in mineral
◦
oil, 2.79 g, 64 mmol) was added, stirring at 25 C contin-
ued for 15 min, and benzyl bromide (9.84 g, 57.6 mmol)
was added. After stirring for 5 h at 25 ◦C, methanol (30 mL)
was slowly added to quench the reaction, and the solvents
were removed under reduced pressure. The residue was re-
dissolved in diethyl ether (150 mL), the solution washed with
water (3×25 mL) and brine (2×25 mL) and dried (Na2SO4),
and the solvents were removed. The residue was dissolved in
a mixture of dichloromethane/methanol (100 mL, 2 : 1) con-
taining catalytic amounts of p-toluenesulfonic acid and the
solution stirred for 12 h at 25 ◦C. After neutralization with N-
methylmorpholine and a usual aqueous work-up, the residue
was purified by chromatography (silica gel, hexane/ethyl ac-
etate 5 : 3) to afford 2 (2.04 g, 19.0 %) and 3 (5.32 g, 49.6 %).
prepared 3-fluoro analog [14] gave a Ki = 82 µM. For
compound 11, however, no inhibition of the enzyme
could be measured even at an inhibitor concentration
of 10 mM. This might be explained by the axial posi-
tion of the hydroxyl group at position C-3, therefore
proving that an equatorial hydroxyl group at this posi-
tion is necessary for a tight binding of the inhibitor into
the active site of β-glycosidases.
Experimental Section
General methods
Melting points are uncorrected (Leica hot stage micro-
scope). Optical rotations were obtained using a Perkin-Elmer
341 polarimeter (1 cm micro cell, 20 ◦C). NMR spectra were
recorded using the Varian spectrometers Gemini 200, Gem-
ini 2000 or Unity 500 (δ given in ppm, J in Hz, internal
SiMe4 or internal CCl3F), IR spectra (film or KBr pellet)
on a Perkin-Elmer FT-IR spectrometer Spectrum 1000. Mass
spectra were taken on a Thermo Electron Finnigan LCQ in-
strument (electrospray, voltage 4.5 kV, sheath gas nitrogen).
For elemental analysis, a Foss-Heraeus Vario EL instrument
was used. TLC was performed on silica gel (Merck 5554,
detection by UV absorption or by treatment with a solution
of 10 % sulfuric acid, ammonium molybdate and cerium(IV)
sulfate, followed by gentle heating). The solvents were dried
according to usual procedures.
Data for 2: colorless oil. – [α]D = 77.6◦ (c = 0.7,
CHCl3). – Rf = 0.12 (hexane/ethyl acetate 5 : 3). – IR (film):
ν = 3261m, 3088m, 3064m, 3030s, 2929s, 1952w, 1879w,
1808w, 1737w, 1669w, 1606w, 1497s, 1454m, 1396m,
1359m, 1322m, 1244m, 1210m, 1103m, 973m, 912w, 844w,
736s, 697s cm−1. – 1H NMR (400 MHz, CDCl3): δ = 7.43 –
7.20 (m, 15 H, aryl), 4.95 (d, 1 H, J = 12.5 Hz, H-Bn), 4.85
3
(d, 1 H, J = 12.5 Hz, H-Bn), 4.71 (d, 1 H J1,2 = 4.2 Hz,
1-H), 4.59 (d, 1 H, J = 12.5 Hz, H-Bn), 4.54 (d, 1 H, J =
12.5 Hz, H-Bn), 4.50 (d, 1 H, J = 11.7 Hz, H-Bn), 4.35 (d,
1 H, J = 117 Hz, H-Bn), 4.16 (m, 2 H, 4-H and 5-H), 3.82
2
3
ꢀ
(dd, 1 H, J6,6 = 11.7 Hz J6,5 = 3.1 Hz, 6-H), 3.77 (dd,
1 H, 2J6 6 = 11.7 3J6 ,5 = 3.7 Hz, 6-Hꢀ), 3.42 (s, 3 H, CH3),
3.35 (m, 2 H, 2-H and 3-H). – 13C NMR (100 MHz, CDCl3):
δ = 139.1, 137.7 137.65, 128.4, 128.3, 128.2, 128.1, 128.0,
127.9, 127.83, 127.78, 127.74, 127.66, 127.6, 127.5, 127.0
(all Car), 98.3 (C-1), 76.2 (C3), 75.0 (C2), 73.5 (CH2-Ph),
71.9 (C4), 71.3 (CH2Ph), 70.9 (CH2-Ph), 66.5 (C5), 62.2
(C-6), 56.0 (CH3). – MS (ESI, MeOH+LiClO4): m/z (%) =
471.2 (100) [M+Li]+, 503.2 (10) [M+MeOH+Li]+, 935.3
(17) [M2+Li]+, 1041.3 (25) [M2Li2ClO4]+. – C28H32O6
(464.55): calcd. C 72.39, H 6.94; found C 72.11, H 7.03.
ꢀ
ꢀ
Methyl 2,3,4-tri-O-benzyl-α-D-allopyranoside (2) and
methyl 2,3,4-tri-O-benzyl-β-D-allopyranoside (3)
A suspension of 1 (6.0 g, 23.1 mmol) in water (50 m◦L)
and conc. sulfuric acid (98 %, 1 mL) was stirred at 25 C
for 24 h. The mixture was neutralized by the addition of
NaHCO3 (3.0 g), the solvents were removed and the residue
was suspended in dry methanol (50 mL), the mixture was
filtered and the filtrate was evaporated. The◦residue was dis-
solved in dry methanol (50 mL), and a 0 C cold solution
of methanol (5 mL) containing acetyl chloride (0.5 mL) was
added. The mixture was heated under reflux for 8 h, neu-
tralized (NaHCO3), filtered and the solvents were removed
from the filtrate. The residue was dissolved in dry pyridine
(50 mL), trityl chloride (9.63 g, 34.6 mmol) and DMAP
(0.4 g, 3.3 mmol) were added and stirring at 25 ◦C was con-
tinued for another 16 h. The solvent was removed, the residue
re-dissolved in ether (100 mL), the solution was extracted
with water (100 mL), the organic phase was dried (Na2SO4)
and the solvents were removed. Purification by chromatogra-
Data for 3: colorless oil. – [α]D = +11.2◦ (c = 0.9,
CHCl3) (lit. [18]: +17◦). – Rf = 0.28 (hexane/ethyl acetate
5 : 3). – IR (film): ν = 3482w, 3088w, 3063w, 3030m, 2888
5, 1954w, 1734w, 1605w, 1497m, 1454s, 1387m, 1349w,
1307w, 1248w, 1206s, 1126s, 1091s, 1046s, 1028s, 914w,
819w, 736s, 698s cm−1. – 1H NMR (500 MHz, CDC13): δ =
7.40 – 7.24 (m, 15 H, H-ar), 4.88 (d, 1 H, J = 12.0 Hz, H-Bn),
4.84 (d, 1 H 3J1,2 = 7.9 Hz, 1-H), 4.83 (d, 1 H, J = 12.2 Hz,
H-Bn), 4.80 (d, 1 H, J = 12.0 Hz, H-Bn), 4.62 (d, 1 H, J =
12.2 Hz, H-Bn), 4.52 (d, 1 H, J = 11.6 Hz, H-Bn), 4.41 (d,
3
3
1 H, J = 11.6 Hz, H-Bn), 4.11 (dd, 1 H J3,4 = 2.4, J3,2
=
=
2.6 Hz, 3-H), 3.97 (ddd, 1 H 3J5,6 = 3.1, 3J5ꢀ,6 = 4.1 J5,4
3
2
3
ꢀ
phy (silica gel, methanol/ethyl acetate 5 : 95) gave a mixture 9.7 Hz, 5-H), 3.87 (dd, 1 H, J6,6 = 11.7 J6,5 = 3.1 Hz,
of the corresponding pyranosides [(56 g, 12.8 mmol; α: Rf = 6-H), 3.73 (dd, 1 H, 2J6 ,6 = 11.7 3J6 ,5 = 4.1 Hz, 6-Hꢀ), 3.54
0.35 (in ethyl acetate), β: Rf = 0.49 (in ethyl acetate)]. The (s, 3 H, CH3), 3.41 (dd, 1 H 3J4,3 = 2.4, 3J4,5 = 9.7 Hz, 4-H),
ꢀ
ꢀ
mixture of the pyranosides (5.6 g, 12.8 mmol) was dissolved 3.17 (dd, 1 H J2,3 = 2.6 J2,1 = 7.9 Hz, 2-H). – 13C NMR
3
3
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R. Csuk et al. · First Total Synthesis of 3-Epi-calystegin B2
(100 MHz, CDCl3): δ = 138.9, 138.6, 137.6, 128.4, 128.3, pound 5 (56.5 %) was obtained from 4 as a colorless oil.
128.1, 128.0, 127.9, 127.81, 127.78, 127.7, 127.5 127.5, [α]D = −21.2◦ (c = 0.7, CHCl3). – Rf = 0.52 (hexane/ethyl
127.3 (all Car), 102.1 (Cl), 79.1 (C3), 75.7 (C2), 74.7 (C4), acetate 85 : 15). – IR (film): ν = 3064m, 3030m, 2865m,
74.4 (CH2-Ph), 72.9 (CH2Ph), 72.5 (C5), 71.6 (CH2Ph), 62.3 1699m, 1496s, 1454s, 1331w, 1208m, 1100s, 1070s, 1028s,
(C-6), 57.0 (CH3). – MS (ESI, MeOH+LiClO4): m/z (%) = 997m, 735s, 697s cm−1. – 1H NMR (400 MHz, CDCl3):
3
471.6 (100) [M+Li]+. – C28H32O6 (464.55): calcd. C 72.39, δ = 7.35 – 7.19 (m, 20 H, H-ar), 5.99 (ddd, 1 H J2,3 = 8.0
3
3
3
ꢀ
J2,1 = 10.4 J2,1 = 17.4 Hz, 2-H), 5.70 (dddd, 1 H J8,7 =
H 6.94; found C 72.18, H 7.07.
3
3
3
ꢀ
ꢀ
6.4 J8,7 = 8.0 J8,9 = 11.6, J8,9 = 15.6 Hz, 8-H), 5.34
2
3
ꢀ
(dd, 1 H, J1,1 = 1.5 J1,2 = 10.4 Hz, 1-H), 5.21 (dd, 1 H,
Methyl 2,3,4-tri-O-benzyl-6-deoxy-6-iodo-α-D-allopyranos-
ide (4)
2
3
3
J1 ,1 = 1.5 J1 ,2 = 17.4 Hz, 1ꢀ-H), 5.022 (d, 1 H J9,8
=
ꢀ
ꢀ
15.6 Hz, 9-H), 5.017 (d, 1 H J9 ,8 = 11.6 Hz, 9-Hꢀ), 4.87
(d, 1 H, J = 11.5 Hz, H-Bn), 4.80 (d, 1 H, J = 11.5 Hz,
H-Bn), 4.66 (d, 1 H, J = 11.5 Hz, H-Bn), 4.62 (d, 1 H,
J = 11.9 Hz, H-Bn), 4.60 (d, 1 H, J = 11.5 Hz, H-Bn),
4.37 (d, 1 H, J = 11.9 Hz, H-Bn), 4.24 (dd, 1 H J3,4
3
ꢀ
As described below for 6, from 2 (1.02 g, 2.2 mmol),
triphenylphosphane (1.26 g, 4.84 mmol), imidazole (0.67 g,
9.9 mmol), and iodine (1.11 g, 4.4 mmol), compound 4
3
(0.98 g, 78.0 %) was obtained as a colorless oil. [α]D
=
=
=
+41.2◦ (c = 0.6, CHCl3). – Rf = 0.30 (hexane/ethyl acetate
85 : 15). – IR (film): ν = 3650w, 3510w, 3088w, 3063m,
3030s, 3004w, 2890s, 2244w, 1953w, 1878w, 1813 1723w,
1703w, 1605w, 1586w, 1496s, 1455s, 1360m, 1312m,
1243m, 1199s, 1170s, 1143s, 1097s, 981s, 911s, 735s,
697s cm−1. – 1H NMR (500 MHz, CDC13): δ = 7.41 – 7.17
(m, 15 H, H-ar), 4.93 (d, 1 H, 2J = 12.5 Hz, H-Bn), 4.82 (d,
3
3
3
3.4 J3,2 = 8.0 Hz, 3-H), 3.92 (dd, 1 H J4,3 = 3.4 J4,5
6.9 Hz, 4-H), 3.78 (d, 1 H, J = 13.2 Hz, H-Bn-NHR), 3.69
(d, 1 H, J = 13.2 Hz, H-Bn-NHR), 3.63 (dd, 1 H 3J5,6 = 3.5
3J5,4 = 6.9 Hz, 5-H), 3.04 (ddd, 1 H J6,5 = 3.5 J6,7 = 4.1
3
3
3
J6,7 = 7.6 Hz, 6-H), 2.37 (ddd, 1 H, 2J7,7 = 14.7 3J7,6 = 4.1
ꢀ
ꢀ
3
3
J7,8 = 6.4 Hz, 7-H), 2.24 (ddd, 1 H, 2J7 ,7 = 14.7 3J7 ,6 = 7.6
ꢀ
ꢀ
J7 ,8 = 8.0 Hz, 7-Hꢀ). – 13C NMR (100 MHz, CDCl3): δ =
ꢀ
3
1 H, J = 12.5 Hz, H-Bn), 4.75 (d, 1 H J1,2 = 4.0 Hz, 1-H),
140.9, 138.9, 138.8, 136.5 (C-8), 135.5 (C2), 128.21, 128.19,
128.15, 128.12, 128.08, 128.0, 127.6, 127.33, 127.29, 127.2,
126.6 (all Car), 119.1 (C-1), 117.0 (C-9), 82.0 (C-3), 81.2
(C-4), 79.6 (C-5), 73.6 (CH2-Ph), 73.4 (CH2-Ph), 70.4 (CH2-
Ph), 57.5 (C-6), 52.0 (CH2-Ph), 34.7 (C-7). – MS (ESI,
MeOH): m/z (%) = 548.5 (100) [M+H]+. – C37H41NO3
(574.73): calcd. C 81.13, H 7.54; found C 81.00, H 5.68.
4.60 (d, 1 H, J = 12.5 Hz, H-Bn), 4.56 (d, 1 H, J = 12.5 Hz,
H-Bn), 4.50 (d, 1 H, J = 11.3 Hz, H-Bn), 4.35 (d, 1 H, 2J =
113 Hz, H-Bn), 4.16 (dd, 1 H 3J3,4 = 2.7 3J3,2 = 2.7 Hz, 3-H),
3.89 (ddd, 1 H 3J5,6 = 2.6 3J5,6 = 6.0 3J5,4 = 9.0 Hz, 5-H),
ꢀ
3.52 (dd, 1 H, 2J6,6 = 10.6 3J65 = 2.6 Hz, 6-H), 3.47 (s, 3 H,
ꢀ
CH3), 3.43 (dd, 1 H 3J2,3 = 2.7 3J2,1 = 4.0 Hz, 2-H), 3.38 (dd,
1 H, 2J6 ,6 = 10.6 3J6 ,5 = 6.0 Hz, 6-Hꢀ), 3.18 (dd, 1 H 3J4,3
=
ꢀ
ꢀ
2.7 J45 = 9.0 Hz, 4-H). – 13C NMR (100 MHz, CDCl3):
δ = 138.9, 137.7, 137.5, 134.3, 129.6, 128.9, 128.5, 128.4,
128.3, 128.0, 127.9, 127.84, 127.76, 127.65, 127.5, 127.2,
126.9 (all Car) 98.4 (C-1), 78.8 (C4), 76.5 (C2), 73.6 (CH2-
Ph), 71.5 (C3), 71.3 (CH2-Ph), 71.1 (CH2-Ph), 65.1 (C5),
56.3 (-CH3), 9.2 (C6). – MS (ESI, MeOH+LiClO4): m/z
(%) = 581.7 (100) [M+Li]+, 1260.9 (10) [M2Li2ClO4]+. –
C28H31IO5 (574.12): calcd. C 58.54, H 5.44; found C 58.31,
H 5.57.
3
Methyl 2,3,4-tri-O-benzyl-6-deoxy-6-iodo-β-D-allopyranos-
ide (6)
To a solution of 3 (2.66 g, 5.7 mmol), triphenylphosphane
(3.3 g, 12.54 mmol) and imidazole (1.75 g, 25.65 mmol) in
dry toluene (50 mL), iodine (2.91 g, 11.46 mmol) was added
◦
in several portions at 95 C. Stirring was continued for 2 h,
the hot solvent was decanted and the viscous residue rinsed
with diethyl ether (3 × 25 mL). Purification of the residue
by chromatography (silica gel, hexane/ethyl acetate 85 : 15)
yielded 6 (2.3 g, 70 %) as a colorless oil. [α]D = +29.9◦ (c =
0.6, CHCl3) (lit. [20]: +15.0◦). – Rf = 0.48 (hexane/ethyl
acetate 85 : 15). – IR (film): ν = 3063w, 3030m, 2895m,
(3 R, 4 R, 5 S, 6 R)-6-[(N-Benzyl)amino]-3,4,5-tris-
(benzyloxy)-l,8-nonadiene (5)
A suspension of 6 (1.52 g, 2.65 mmol) and activated zinc 1606s, 1496m, 1454s, 1346w, 1304w, 1210s, 1091s, 912w,
powder (1.73 g, 26.5 mmol) i◦n abs. THF (50 mL) was heated 753s, 697s cm−1. – 1H NMR (500 MHz, CDCl3): δ = 7.38 –
in an ultrasound bath at 40 C, and within 30 min benzyl- 7.23 (m, 15 H, H-ar), 4.86 (d, 1 H, J = 11.8 Hz, H-Bn), 4.85
3
amine (0.71 g, 6.62 mmol) was added. Sonification at 40 ◦C (d, 1 H, J = 12.1 Hz, H-Bn), 4.83 (d, 1 H, J1,2 = 7.9 Hz,
was continued for another 3 h. Allyl bromide (0.75 g, 6.62 g) 1-H), 4.76 (d, 1 H, J = 11.8 Hz, H-Bn), 4.61 (d, 1 H, J =
was added and sonification continued for 4 h. The mixture 12.1 Hz, H-Bn), 4.51 (d, 1 H, J = 11.5 Hz, H-Bn), 4.38 (d,
3
was filtered through a small layer of silica gel, the silica gel 1 H, J = 11.5 Hz, H-Bn), 4.08 (dd, 1 H, J3,4 = 2.4, 3J3,2
=
=
was washed with ethyl acetate (500 mL), the solvents were 2.6 Hz, 3-H), 3.71 (ddd, 1 H, 3J5,6 = 2.5, 3J5,6 = 7.1, 3J5,4
ꢀ
removed, and the residue was subjected to chromatography 9.3 Hz, 5-H), 3.56 (s, 3 H, CH3), 3.53 (dd, l H, 2J6,6 = 10.6,
ꢀ
3
3
2
ꢀ ꢀ
J6,5 = 2.5 Hz, 6-H), 3.26 (dd, 1 H, J6 ,6 = 10.6, J6 ,5 =
(silica gel, hexane/ethyl acetate 85 : 15) to afford 5 (350 mg,
49.2 %) as a colorless oil. In an analogous manner, com- 7.1 Hz, 6-Hꢀ), 3.22 (dd, 1 H, 3J2,3 = 2.6, 3J2,1 = 7.9 Hz, 2-H),
Unauthenticated
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R. Csuk et al. · First Total Synthesis of 3-Epi-calystegin B2
321
3.18 (dd, 1 H, J4,3 = 2.4, J4,5= 9.3 Hz, 4-H). – 13C NMR (3 R, 4 R, 5 Sꢀ, 6 R) 6-[(N-Benzyl-N-(benzyloxycarbonyl))-
(100 MHz, CDCl3): δ = 138.7 138.6 137.4 133.8 133.6 132.0 amino]-3,4,5-tris(benzyloxy)-cycloheptene (8)
128.7 128.51 128.47 128.43 128.37, 128.3, 128.2, 128.0,
3
3
A
solution of 7 (890 mg, 1.31 mmol) in dry
127.9, 127.6, 127.51, 127.47 (all Car), 101.9 (C-l), 79.4
(C-4), 79.1 (C-2), 74.5 (CH2-Ph), 74.2 (C-3), 73.0 (CH2-Ph),
71.5 (CH2-Ph), 71.1 (C-5), 56.9 (CH3), 8.0 (C6). – MS (ESI,
MeOH+LiClO4): m/z (%) = 581.7 (100) [M+Li]+, 1260.7
(25, M2Li2ClO4]+. – C28H31IO4 (574.12): calcd. C 58.54,
H 5.44; found C 58.39, H 5.51.
dichloromethane (50 mL)◦ containing Grubbs’ catalyst
(20 mg) was stirred at 25 C for 30 h. The mixture was
filtered, the filtrate evaporated and the residue purified by
chromatography (silica gel, hexane/ethyl acetate 80 : 20) to
yield 8 (735 mg, 86.1 %) as a colorless oil. [α]D = −77.5◦
(c = 0.5, CHCl3). – Rf = 0.35 (hexane/ethyl acetate 85 : 15). –
IR (film): ν = 3030m, 2925s, 2854m, 1698s, 1496m, 1454s,
1412m, 1346m, 1259s, 1206s, 1095s, 1069s, 1028s, 735s,
697s cm−1. – 1H NMR (400 MHz, CDCl3): δ = 7.35 – 7.06
(m, 25 H, H-ar), 5.78 – 5.61 (m, 2 H, 1-H, 2-H), 5.08 (d, 1 H,
J = 12.5 Hz, H-Bn-Cbz), 5.02 (d, 1 H, J = 12.5 Hz, H-Bn-
Cbz), 4.78 (d, 1 H, J = 11.6 Hz, H-Bn), 4.72 (d, 1 H, J =
13.1 Hz, H-Bn), 4.63 (d, 1 H, J = 11.8 Hz, H-Bn), 4.60
(d, 1 H, J = 11.6 Hz, H-Bn), 4.54 (d, 1 H, J = 11.8 Hz,
H-Bn), 4.55 – 4.38 (m, 3 H, Bn), 4.31 (m, 1 H, 3-H), 4.17
(3 R, 4 R, 5 S, 6 R) 6-[(N-BenzyI-N-(benzyloxycarbonyl))-
amino]-3,4,5-tris(benzyloxy)-l,8-nonadiene (7)
To a solution of 5 (819 mg, 1.50 mmol) in dichloro-
methane/water (5 : 1, 50 mL), NaHCO3 (1.26 g, 15.0 mmol)
and benzyl chloroformate (766 mg, 4.5 mmol) in ethyl ac-
etate (10 mL) were added. After stirring for 2 h at r. t., the
phases were separated, the aqueous phase extracted with
dichloromethane (3×25 mL). The organic phases were com-
bined and the solvents removed. The residue was subjected
to chromatography (silica gel, hexane/ethyl acetate 85 : 15)
to yield 7 (890 mg, 87.0 %) as a colorless oil. [α]D = +9.2◦
(c = 0.6, CHCl3). – Rf = 0.55 (hexane/ethyl acetate 85 : 15). –
IR (film): ν = 3453w, 3064w, 3031m, 2894w, 1748w, 1696s,
1642w, 1606w, 1496m, 1454s, 1233s, 1106s, 1028s, 993w,
914w, 735s, 698s, 599w cm−1. – 1H NMR (400 MHz,
(dd, 1 H, J = 3.5, J = 3.5 Hz, 4-H), 4.06 (d, 1 H, J =
3.5 Hz, 5-H), 3.93 (m, 1 H, 6-H), 2.95 (dd, 1 H, J7,7
2
ꢀ
=
2
ꢀ
15.6, J = 7.2 Hz, 7-H), 1.95 (dd, 1 H, J7,7 = 15.6, J =
7.3 Hz, 7-Hꢀ). – 13C NMR (100 MHz, CDCl3): δ = 156.4
(C = O, Cbz), 140.3, 138.8, 138.5, 136.5 (all Car), 130.2
(C-1), 129.1 (C-2), 128.1, 128.1, 128.0, 127.8, 127.5, 127.5,
127.35, 127.28, 127.1, 126.0, 125.8 (all Car), 78.9 (C-4),
78.8 (C-5), 77.8 (C-3), 72.6 (CH2-Ph), 72.4 (CH2-Ph), 71.8
(CH2-Ph), 67.1 (CH2-Cbz), 56.6 (C6), 48.6 (CH2-Ph), 28.1
(C-7). – MS (ESI, MeOH+LiClO4): m/z (%) = 660.9 (100)
[M+Li]+. – C43H43NO5 (653.81): calcd. C 78.99, H 6.63;
found C 78.74, H 6.84.
◦
CDCl3, 27.0 C): δ = 7.41 – 6.87 (m, 25 H, H-ar), 5.82 (m,
1 H, 2-H), 5.39 – 5.26 (m, 3 H, 8-H, 1-H, 1ꢀ-H), 5.10 (m, 2 H,
3
CH2-Bn-Cbz), 4.79 (d, 1 H J9,8 = 17.0 Hz, 9-H), 4.70 –
3.96 (m, 12 H, 3-H, 4-H, 5-H, 9-Hꢀ, 8× CH2-Bn), 3.60 (d,
1 H, J = 7.2 Hz, 6-H), 2.68 – 2.32 (m, 2 H, 7-H, 7-Hꢀ). –
1H NMR (500 MHz, [D6]DMSO, 120.0 ◦C): δ = 7.37 – 7.08
3
3
ꢀ
(m, 25 H, H-ar), 5.94 (ddd, 1 H J2,3 = 7.2 J2,1 = 10.4
(1 RS, 2 R, 3 S, 4 S, 5R) 5-[(N-Benzyl-N-(benzyloxy-
carbonyl))amino]-2,3,4-tris(benzyloxy)-cycloheptanol (9)
3
3
3
ꢀ
J2,1 = 17.5 Hz, 2-H), 5.43 (ddd, 1 H J83,7 = 7.4 J8,9
=
3
10.2 J8,9 = 17.0 Hz, 8-H), 5.27 (d, 1 H J1,2 = 17.5 Hz,
1-H), 5.25 (d, 1 H J1 ,2 = 10.4 Hz, 1ꢀ-H), 5.07 (s, 2 H,
To a solution of 8 (735 mg, 1.12 mmol) in abs. THF
3
ꢀ
CH2-Bn-Cbz), 4.74 (d, 1 H J9,8 = 17.0 Hz, 9-H), 4.71 (d, (60 mL) kept at −78 ◦C a solution of BH3· THF (1 M, 3 mL)
3
1 H J9 ,8 = 10.2 Hz, 9-Hꢀ), 4.61 (d, 1 H, 2J = 11.5 Hz, was added within 20 min. Stirring was continued at 25 C
H-Bn), 4.48 (d, 1 H, 2J = 15.9 Hz, H-Bn), 4.49 (d, 1H, for 12 h, aq. NaOH (2 N, 4.5 mL) and H2O2 (30 %, 0.9 mL)
2J = 11.1, H-Bn), 4.45 (d, 1 H, J = 11.7 Hz, H-Bn), 4.35 were added, and stirring was continued for another 5 h. The
3
◦
ꢀ
3
(d, 1 H, J = 11.5 Hz, H-Bn), 4.33 (d J3,2 = 7.2 Hz, 3-H), phases were separated, the aq. layer was extracted with di-
4.31 (d, 1 H, J = 11.7 Hz, H-Bn), 4.29 (d, 1 H, J = 11.1 Hz, ethyl ether (3×30 mL), the organic phases were combined,
H-Bn), 4.26 (d, 1 H, J = 15.9 Hz, H-Bn), 4.10 (d, 1 H 3J4,5
=
dried (Na2SO4), and the solvent was removed. The residue
7.1 Hz, 4-H), 4.08 (d, 1 H 3J5,4 = 7.1 Hz, 5-H), 3.69 (dd, 1 H was subjected to chromatography (silica gel, hexane/ethyl
3
3
ꢀ
J6,7 = l.9 J6,7 = 6.1 Hz, 6-H), 2.54 – 2.40 (m, 2◦H, 7-H, acetate 8 : 2) to afford 9 (660 mg, 87.7 %) as a colorless oil.
7-Hꢀ). – 13C NMR (125 MHz, [D6]DMSO, 120.0 C): δ = [α]D = −10.0◦ (c = 0.5, CHCl3). – Rf = 0.33 (hexane/ethyl
157.0 (C = 0, Cbz), 138.1, 137.9, 136.1 (all Car), 135.7 (C-8), acetate 5 : 3). – IR (film): ν = 3441w, 3088w, 3063w, 3031m,
135.5 (C-2), 127.7, 127.5, 127.4, 127.3, 127.1 127.0, 126.9, 2935m, 2872w, 1952w, 1809w, 1694s, 1606w, 1594w, 1496s,
126.81, 126.80, 126.6, 126.0 (all Car), 117.2 (C-1), 115.0 1454s, 1417m, 1362m, 1324m, 1261s, 1212s, 1177w, 1112s,
(C-9), 81.2 (C-3), 80.9 (C-4), 79.9 (C-5), 72.2 (CH2-Ph), 1052s, 1028s, 911w, 813w, 734s, 697s, 598w cm−1. –
71.0 (CH2-Ph), 69.8 (CH2-Ph), 66.0 (CH2-Ph), 58.2 (C-6), 1H NMR (400 MHz, CDCl3): δ = 7.39 – 6.80 (m, 25 H,
49.0 (CH2-Ph), 32.8 (C-7). – MS (ESI, MeOH+LiClO4): m/z H-ar), 5.1 (d, 1 H, J = 12.4 Hz, H-Bn-Cbz), 5.0 (d, 1 H,
(%) = 688.8 (100) [M+Li]+. – C45H47NO5 (681.86): calcd. J = 12.4 Hz, H-Bn-Cbz), 4.77 – 4.42 (m, 8 H, Bn), 4.05 –
C 79.27, H 6.95; found C 79.02, H 7.13.
3.90 (m, 4 H, 1-H, 2-H, 3-H, 4-H), 3.37 (dd, 1 H, J =
Unauthenticated
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322
R. Csuk et al. · First Total Synthesis of 3-Epi-calystegin B2
2.8, J = 8.0 Hz, 5-H), 2.32 (m, 1H, 7-H), 1.96 – 1.55 (m, 1.61 (m, 2 H, 6-H, 6-Hꢀ). – 13C NMR (100 MHz, CDCl3):
3 H, 6-H, 6-Hꢀ, 7-Hꢀ). – 13C NMR (100 MHz, CDCl3): δ = δ = 208.0 (C=O), 157.3 (C=O, Cbz), 139.8, 138.4, 137.8,
157.3 (C = O, Cbz), 140.3, 138.6, 138.2, 138.1, 136.5, 129.5, 137.6, 128.3, 128.14, 128.10, 128.07, 127.9, 127.8, 127.6,
128.4, 128.3, 128.2, 128.11, 128.08, 128.0, 127.90, 127.86, 127.5, 127.2, 126.3, 125.8 (all Car), 83.6 (C-2), 82.0 (C-3),
127.7, 127.6, 127.4, 127.3, 127.2, 126.3, 126.0, 125.9 (all 81.1 (C-4), 74.0 (CH2-Ph), 73.6 (CH2-Ph), 72.1 (CH2-Ph),
Car), 86.3 (C-2), 80.6 (C-3), 80.5 (C-4), 74.0 (C-1), 73.9 67.3 (CH2-Cbz), 58.0 (C-5), 47.8 (CH2-Ph), 38.6 (C-7), 24.3
(CH2-Ph), 73.7 (CH2-Ph), 73.1 (CH2-Ph), 67.2 (CH2-Cbz), (C-6). – MS (ESI, MeOH+LiClO4): m/z (%) = 676.6 (100)
58.1 (C-5), 47.8 (CH2-Ph), 29.5 (C-7), 25.9 (C-6). – MS [M+Li]+. – C43H43NO6 (669.80): calcd. C 77.11, H 6.47;
(ESI, MeOH+LiClO4): m/z (%) = 678.6 (100) [M+Li]+. – found C 76.86, H 6.95.
C43H45NO6 (671.82): calcd. C 76.87, H 6.75; found C 76.59,
H 6.89.
(1 R, 2 S, 3 S, 4 S, 5 R)-8-Azabicyclo[3.2.1]octane-1,2,3,4-
tetraol [(+)-calystegin 3-epi-B ] (11)
2
(2 S, 3 S, 4 S, 5 R)-5-[(N-Benzyl-N-(benzyloxycarbonyl))-
amino]-2,3,4-tris(benzyloxy)-cycloheptanone (10)
A solution of 10 (450 mg, 0.67 mmol) in ethyl ac-
etate (20 mL) and acetic acid (66 %, 80 mL) was hydro-
genated (35 psi) in the presence of Pd/C (10 %, 200 mg)
for 5 d. The catalyst was filtered off, the solvent re-
moved and the product purified by chromatography (sil-
To a solution of 9 (660 mg, 0.98 mmol) in dry
dichloromethane (100 mL), PCC (254 mg, 1.18 mmol) was
◦
added, and the mixture was stirred for 12 h at 25 C. Ad-
ditional PCC (254 mg, 1.18 mmol) was added and stirring ica gel, methanol/water/ammonia 95 : 5 : 1) to yield 11
continued for another 12 h. The solvent was partially re- (100 mg, 85.0 %) as a colorless semi-amorphous solid.
moved (50 mL), ethyl acetate (100 mL) added, and the mix- [α]D = +36.4◦ (c = 0.2, MeOH). – Rf = 0.05 (methanol/ethyl
ture was filtered through a layer (5 cm) of silica gel. The acetate/ammonia 95 : 5 : 1). – IR (film): ν = 3453w, 3064w,
filtrate was evaporated and the residue subjected to chro- 3031m, 2894w, 1748w, 1696s, 1642w, 1606w, 1496m,
matography (silica gel, hexane/ethyl acetate 8 : 2) to yield 10 1454s, 1233s, 1106s, 1028s, 993w, 914w, 735s, 698s,
(490 mg, 74.5 %) as a colorless oil. [α]D = −42.0◦ (c = 0.5, 599w cm−1. – 1H NMR (400 MHz, CD3OD): δ = 5 3.71
3
3
CHCl3). – Rf = 0.40 (hexane/ethyl acetate 5 : 3). – IR (film): (d, 1 H J2,3 = 3.9 Hz, 2-H), 3.67 (dd, 1 H J3,2 = 3.9
ν = 3088w, 3063w, 3031w, 2943w, 1954w, 1694s, 1604w, 3J3,4 = 4.2 Hz, 3-H), 3.54 (dd, 1 H J4,5 = 2.8 J4,3
=
3
3
3
3
1585w, 1497m, 1454s, 1416m, 1349m, 1254s, 1208s, 1102s, 4.2 Hz, 4-H), 3.35 (dd, 1 H J5,4 = 2.8 J5,6 = 7.7 Hz,
1028s, 916w, 827w, 772w, 736s, 698s, 650w, 595w cm−1. – 5-H), 2.05 (ddd, 1 H, J6,6 = 14.0 J6,5 = 7.7 J6,7
=
2
3
3
ꢀ
1H NMR (400 MHz, CDCl3): δ = 7.31 – 6.96 (m, 25 H, 10.7 Hz, 6-H), 1.74 – 1.67 (m, 2 H, 7-H, 7-Hꢀ), 1.45 (ddd,
H-ar), 5.09 (d, 1 H, J = 12.5 Hz, H-Bn-Cbz), 5.06 (d, 1 H, 1 H, J6,6 = 14.0 J6 ,7 = 5.7, J6 ,7 = 8.6 Hz, 6-Hꢀ). –
J = 12.5 Hz, H-Bn-Cbz), 4.98 (d, 1 H, J = 11.4 Hz, H-Bn), 13C NMR (100 MHz, CD3OD): δ = 91.1 (C-1), 76.9 (C-2),
4.89 (d, 1 H, J = 11.4 Hz, H-Bn), 4.63 (d, 1 H, J = 11.6 Hz, 72.0 (C-4), 66.9 (C-3), 58.5 (C-5), 31.7 (C-7), 23.3 (C-6). –
H-Bn), 4.56 (d, 1 H, J = 11.6 Hz, H-Bn), 4.54 (d, 1 H, MS (ESI, MeOH): m/z (%) = 176.1 (100) [M+H]+. –
J = 11.3 Hz, H-Bn), 4.49 – 4.13 (m, 6 H, 2-H, 3-H, 4-H, C7H13NO4 (175.18): calcd. C 47.99, H 7.48; found C 47.80,
3× H-Bn), 2.53 (m, 1 H, 5-H), 2.35 (m, 2 H, 7-H, 7-Hꢀ), H 7.63.
2
3
3
ꢀ
ꢀ
ꢀ
ꢀ
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Unauthenticated
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