The first convergent total synthesis of penarolide sulfate A2, a novel α-glucosidase inhibitor

Article abstract of DOI:10.1039/c3ob42364f

Penarolide sulfate A₂, a 31-membered macrolide encompassing a proline residue and three sulfate groups, was firstly synthesized in 16 linear steps with 4.8% overall yield. Three consecutive stereogenic centers in penarolide sulfate A₂ were efficiently derived from natural chiral template l-arabinose. The crucial assembly reactions included Brown asymmetric allylation, olefin cross-metathesis, alkyne-epoxide coupling, and macrolactamization. The anti-yeast α-glucosidase activities of penarolide sulfate A₂ and its fully desulfated derivative were examined showing IC₅₀ values of 4.87 and 10.74 μg mL^-1, respectively.

Full text of DOI:10.1039/c3ob42364f

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The first convergent total synthesis of penarolide
sulfate A2, a novel α-glucosidase inhibitor†
Cite this: Org. Biomol. Chem., 2014,
12, 2071
Yangguang Gao,a,b Qiuli Shan,a,b Jun Liu,a Linlin Wanga,b and Yuguo Du*a,b
Penarolide sulfate A2, a 31-membered macrolide encompassing a proline residue and three sulfate
groups, was firstly synthesized in 16 linear steps with 4.8% overall yield. Three consecutive stereogenic
centers in penarolide sulfate A2 were efficiently derived from natural chiral template L-arabinose. The
crucial assembly reactions included Brown asymmetric allylation, olefin cross-metathesis, alkyne-epoxide
coupling, and macrolactamization. The anti-yeast α-glucosidase activities of penarolide sulfate A2 and its
fully desulfated derivative were examined showing IC50 values of 4.87 and 10.74 µg mL−1, respectively.
Received 26th November 2013,
Accepted 19th January 2014
DOI: 10.1039/c3ob42364f
www.rsc.org/obc
compounds attracted our attention. A literature search revealed
that only one total synthesis of penarolide sulfate A1 has been
Introduction
α-Glucosidases play important roles in glycogenolysis and presented, in which the asymmetric centers were generated
glycoprotein processing in the endoplasmic reticulum (ER).1 It through regioselective Sharpless asymmetric dihydroxylation,
is well recognized that α-glucosidase inhibitors are promising Sharpless asymmetric epoxidation, and Jacobsen hydrolytic
therapeutic drug candidates to treat diabetes and obesity.2,3 kinetic resolution.10 Herein, we would like to report our
The known drugs acarbose and miglitol, which exhibit potent work toward the first total synthesis of penarolide sulfate A2
α-glucosidase inhibitory activities, have been applied to the taking advantage of the existing chiral centers from natural
clinical treatment of non-insulin-dependent type II diabetes.4 L-arabinose.
α-Glucosidase inhibitors, which cause misfolding of viral glyco-
proteins and interfere with viral life cycle, are expected to be
antiviral drugs. In addition, they also showed potential against
Results and discussion
tumors,5 HIV or HBV infection6 and Gaucher’s disease.7
Penarolide sulfates A1 (1) and A2 (2) were firstly isolated
from marine sponge Penares sp. by Fusetani and co-workers in
2000.8 Compounds 1 and 2 (Fig. 1), with unique 30- and 31-
membered macrolides encompassing a proline residue, exhibi-
ted good inhibitory activities against α-glucosidase with IC50
values of 1.2 µg mL−1 and 1.5 µg mL−1, respectively. More par-
ticularly, penarolide sulfate A1 contains three contiguous
sulfated stereogenic centers at C14, C15, and C16, while penar-
olide A2 shows sulfated stereochemistry as 15S, 16R, and 17S
based on spectral analyses. Further studies on the same
sponge by the same group disclosed penasulfate A (3), a
methyl pipecolate acylated with di-sulfated fatty acid, also
showing excellent inhibition activity against α-glucosidase.9
The structural novelty and promising bioactivity of these
Retrosynthetic analysis of penarolide sulfate A2 is summarized
in Scheme 1. Penarolide sulfate A2 (2) could be accomplished
from sulfation of its precursor 4, which could be assembled
from segments N-Cbz-L-proline 5, terminal alkyne 6, benzyl
ester 7, and alkene 8 via olefin cross-metathesis (CM), alkyne-
epoxide coupling, esterification and macrolactonization,
respectively. We envisaged that the stereogenic centre of C-27
could be installed via a stereoselective Brown allylation, while
the construction of three contiguous stereogenic hydroxyl
groups in compound 8 could be achieved from commercially
available L-arabinose.
We started from the synthesis of building block 6 as shown
in Scheme 2. The dianion of propargyl alcohol (9) was gener-
ated with n-BuLi in THF and treated with 1-bromohexane in
DMPU to yield 3-nonyn-1-ol (12) in 51.2% yield (Scheme 2).11
Zipper isomerization to the terminal alkyne 13 was accom-
plished by treatment of compound 12 with 1,3-diamino-
propane in the presence of n-BuLi and t-BuOK in THF with
86.7% yield.11a Swern oxidation12 of the primary alcohol in 13
and Brown asymmetric allylation13 to the resulting aldehyde
obtained 14 in 86% yield over 2 steps. The absolute configur-
ation for the newly formed hydroxyl group in 14 was
aState Key Laboratory of Environmental Chemistry and Eco-Toxicology, Research
Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing
100085, China. E-mail: duyuguo@rcees.ac.cn; Fax: +86-010-62923563
bSchool of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China
†Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
for compounds 2, 4, 6–8 and 13–23. See DOI: 10.1039/c3ob42364f
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Fig. 1 Structures of penarolide sulfates A1 (1), A2 (2), and penasulfate A (3).
Scheme 1 Retrosynthetic analysis of penarolide sulfate A2 (2).
Scheme 2 Synthesis of building block 6. Reagents and conditions: a. n-BuLi, THF, −78 to −30 °C, then 1-bromohexane, DMPU-THF, −30 °C to r.t.
51.2%; b. 1,3-diaminopropane, n-BuLi, t-BuOK, THF, 86.7%; c. DMSO, (COCl)2, DCM, −60 to −50 °C, then Et3N; d. allyl-Ipc2B from (−)-Ipc2BCl and
AllMgBr, Et2O, −100 °C, 86% for 2 steps; e. TBSCl, imidazole, DCM, 95%.
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determined using Mosher’s method,14 and the desired R using TsCl, Et3N and a catalytic amount of n-Bu2SnO in
1
product was the major (R/S = 6/1 based on H NMR spectrum CH2Cl2 at 0 °C afforded mono-tosyl fragment 8 in 85% yield.
of (+)-MTPA ester of 14). Silylation of 14 with TBSCl and imid-
With all the required building blocks 5–8 in hand, we then
azole in CH2Cl2 gave the key fragment 6 as an inseparable R,S- turned our attention to the construction of the target molecule
mixture in 95% yield (R/S = 6/1). The R,S enantiomers were 2 following our retrosynthetic analysis shown in Scheme 1.
expected to be separated by introducing more chiral centers Accordingly (Scheme 5), olefin cross-metathesis18 between
during target molecule assembly.
fragments 7 and 8 was promoted by the second-generation
The synthesis of C1–C14 fragment 7 was done from com- Grubbs catalyst in CH2Cl2 under reflux, and the residue was
mercially available 11-bromo-undecan-1-ol (10) in six steps directly subjected to TBAF-mediated epoxidation to give
(Scheme 3). Silylation of 10 with TBSCl and imidazole in epoxide 19 in a yield of 72.2% over two steps. Ring-opening of
CH2Cl2, condensation of the corresponding bromide with 19 with terminal alkyne 6 was carried out smoothly using
AllMgBr under CuI catalyst in dry THF at −78 °C, followed by t-BuLi, instead of n-BuLi, as a base under Yamaguchi–Hirao
removal of the TBS group with TBAF afforded primary alcohol conditions,19 and the resulting secondary hydroxyl group was
15 in 79% yield (3 steps). Through a sequence reaction of protected as its acetate with acetic anhydride in pyridine in the
Swern oxidation, Pinnick oxidation,15 and esterification with presence of DMAP to generate 20 in 84.9% yield. Removal of
benzyl alcohol, compound 15 was readily converted into the TBS group from 20 with TBAF in THF gave compound 21
benzyl ester 7 over 3 steps in a yield of 86%.
in good yield. At this stage, the contaminant from S-enantio-
The key building block 8 was derived from L-arabinose (11) mer of 6 could be removed on a normal silica gel column, and
in six steps (Scheme 4). L-Arabinose was treated with EtSH in compound 21 was obtained in an optically pure form.
conc. HCl at 0 °C, followed by acetal formation with acetone
Esterification of 21 with commercially available N-Cbz-L-
and conc. H2SO4 presenting compound 16 in 63% yield (2 proline (5) was performed under standard EDCI/DMAP con-
steps).16 Removal of thioacetal with HgO and HgCl2 in ditions15 affording compound 22 in high yield (96.4%). Hydro-
acetone–water (10 : 1) released the free aldehyde, which was genation of 22 under a 3 atm H2 atmosphere in ethyl acetate
subjected to in situ-generated methyl Wittig reagent affording using 10% Pd/C as a catalyst reduced the unsaturated bonds
61% yield of compound 17 (2 steps). Selective unblocking of and benzyl esters, and the resulting imine and carboxylic acid
the terminal isopropylidene group in 75% aq. HOAc (→18) and were directly subjected to macrolactamization under EDCI/
a subsequent regioselective tosylation17 on the primary alcohol HOBt conditions20 to furnish the macrocyclic skeleton 4 in
Scheme 3 Synthesis of building block 7. Reagents and conditions: a. TBSCl, imidazole, CH2Cl2; b. AllMgBr, CuI, THF, −78 °C to rt; c. TBAF, THF, 79%
for 3 steps; d. DMSO, (COCl)2, CH2Cl2, −60 to −50 °C, then Et3N; e. NaClO2, NaH2PO4·2H2O, 2-methyl-2-butene, t-BuOH, H2O; f. PTSA, benzyl
alcohol, toluene, reflux, 86% for 3 steps.
Scheme 4 Synthesis of block 8. Reagents and conditions: a. EtSH, conc. HCl, 0 °C to rt; b. acetone, conc. H2SO4, rt, 63% for 2 steps; c. HgO
(yellow), HgCl2, acetone-H2O (10 : 1), 60 °C; d. Ph3PCH3Br, t-BuOK, THF, 0 °C to rt, 61% for 2 steps; e. AcOH–H2O (3 : 1), rt, 81%; f. TsCl, n-Bu2SnO,
Et3N, CH2Cl2, 85%.
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Scheme 5 Synthesis of penarolide sulfate A2 (2). Reagents and conditions: a. (i) Grubbs II catalyst, CH2Cl2, reflux; (ii) TBAF, THF, 72.2% for 2 steps;
b. 6, t-BuLi, THF, −78 to −20 °C, 2.5 h later, BF3·E2O, −78 °C, then 19, THF, −78 °C; c. Ac2O, pyridine, DMAP, rt, 84.9% for 2 steps; d. TBAF, THF, 82%;
e. N-Cbz-L-proline (5), EDCI, DMAP, CH2Cl2, 0 °C to rt, 96.4%; f. H2, 10% Pd/C, EtOAc; g. EDCI, HOBt, DCM, 0 °C to rt, 62.2% for 2 steps; h. AcCl,
MeOH, rt, 81%; i. (i) SO3·py, dry pyridine, 60 °C; (ii) sat. NaHCO3, 0 °C, 75%.
62.2% yield over 2 steps. It is worth noting that the α-proton
signal of L-proline (δ 4.37 ppm in CDCl3) of 4 presented an
unexpected splitting pattern, which was ascribed to a rota-
meric effect on the trisubstituted amine. This phenomenon
could be confirmed by high-temperature H NMR at 100 °C in
DMSO-d6 (δ 4.56 ppm, corresponding to δ 4.37 ppm in CDCl3),
and has also been reported previously.10,21
Global deprotection of the acetyl and acetonide of 4 in one
pot was successfully achieved using 1% AcCl in methanol to
generate penarolide sulfate A2 precursor triol 23 in 81% yield.
Persulfation on compound 23 was initially tried with Py·SO3 in
dry DMF,22 but failed to afford the desired product. To our
delight, treatment of triol 23 with Py·SO3 in pyridine,23 fol-
lowed by a saturated NaHCO3 washing, yielded the target com-
pound 2 (75%) in sodium salt form. The spectral and
analytical data (1H, 13C NMR, HRMS and optical rotation
values) of synthetic compound 2 completely matched that of
the natural product reported by Fusetani et al.8
Table 1 α-Glucosidase inhibitory activities of penarolide sulfates A2 (2),
desulfated derivative compound (23) and known α-glucosidase inhibi-
tors (IC50, μg mL−1
)
Compound (μg mL−1
)
IC50
1
2
23
4.87
10.74
48
Deoxynojirimycin
Castanospermine
N/Aa
a N/A: not active at 100 μg mL−1
.
desulfated triol 23 also showed good inhibition activity under
the same testing conditions with an IC50 value of 10.74 µg
mL−1 (Table 1).
Conclusions
The bioactivity of the synthetic penarolide sulfate A2 (2) and
its precursor 23 was tested as α-glucosidase inhibitors. Com-
pound 2 exhibited good inhibition toward α-glucosidase
G7256 with an IC50 value of 4.87 µg mL−1, slightly different
from its reported data (IC50 = 1.5 µg mL−1).8 Interestingly,
In summary, we have achieved the first total synthesis of
penarolide sulfate A2 (2) in 16 linear steps and in 4.8% overall
yield. The highlight of our synthetic venture was that natural
chiral template L-arabinose was employed to construct three
contiguous stereogenic centers on the macrocyclic skeleton
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using Brown asymmetric allylation, olefin cross-metathesis, 3.62 (t, J = 6.8 Hz, 2H), 2.19–2.15 (m, 2H), 1.92 (t, J = 2.4 Hz,
Yamaguchi–Hirao alkyne-epoxide coupling, and macrolactami- 1H), 1.57–1.48 (m, 5H), 1.42–1.31 (m, 5H). 13C NMR (100 MHz,
zation as pivotal steps. Penarolide sulfate A2 (2) and its desul- CDCl3) δ 84.78, 68.25, 63.06, 32.80, 28.98, 28.77, 28.49, 25.71,
fated derivative compound 23 showed good inhibitory 18.47. ESI-HRMS (m/z): calcd for C9H19ONa: ([M + Na]+),
activities against α-glucosidase with IC50 values of 4.87 and 163.1099; found, 163.1078.
10.74 µg mL−1, respectively. Our strategy is convergent and
(R)-Dodec-1-en-11-yn-4-ol (14). DMSO (5.2 mL, 67.29 mmol)
provides an alternative for the synthesis of other related in 10 mL of DCM was added dropwise to a solution of oxalyl
analogs using a carbohydrate chiral pool.
chloride (2.75 mL, 30.25 mmol) in 15 mL of DCM at −60 °C.
5 min later, 13 (2 g, 14.27 mmol) in 10 mL of DCM was added
over 3 min, and a white slurry was obtained gradually. The
mixture was kept at the same temperature for 1.5 h, then
quenched with Et3N (10 mL, 71.35 mmol), and poured into
30 mL of water. The aqueous layer was extracted with DCM
Experimental section
General experimental methods
All moisture sensitive reactions were carried out in a flame (3 × 50 mL), washed with brine, dried over Na2SO4 and evapor-
dried flask under a nitrogen atmosphere. Unless otherwise ated in vacuo. The yellow residue was directly subjected to the
stated, materials were obtained from commercial suppliers next step without further purification. Allylmagnesium
and used without further purification. Anhydrous solvents bromide (1 M in Et2O, 12 mL, 12 mmol) was added dropwise
were obtained as follows: THF and diethyl ether by distillation under N2 via a syringe to a solution of (−)-DIPCl (1.7 M in
from sodium and benzophenone; DCM, DMF, pyridine and heptane, 10.6 mL, 18.02 mmol) in dried Et2O at −78 °C. After
toluene from CaH2. Column chromatography was carried out replacing the former cooling well by an ice bath, the mixture
using silica gel (100–200 mesh) unless otherwise stated. Reac- was stirred at 0 °C for 1 h. The solution was then allowed to
1
tions were monitored by silica gel 60 F254 TLC plates. H and stand, which caused precipitation of magnesium chloride. The
13C NMR spectra were measured using a Bruker AVANCE-III supernatant solution was then carefully transferred to another
(400 MHz) spectrometer. High resolution mass spectra flask via a syringe. The above aldehyde (1.1 g, 7.96 mmol) in
(HRMS) were measured using a Bruker microTOF Q II mass 10 mL of THF was added to the flask via a dropping funnel at
spectrometer. Optical rotations were measured using
WZZ-2SS automatic digital polarimeter.
a
−100 °C and further stirred at the same temperature for 2 h.
The mixture was quenched by adding 10 mL of methanol, then
Non-2-yn-1-ol (12). To a cooled solution of propargyl alcohol warmed to room temperature, treated with NaOH (2 M, 10 mL)
9 (2.65 mL, 45.84 mmol) in THF (50 mL) was added n-BuLi and H2O2 (10 mL), and stirred for further 2 h under reflux con-
(2.2 M in hexane, 43 mL, 94.6 mmol) at −78 °C and the ditions. The mixture was extracted with Et2O (3 × 20 mL),
mixture was stirred for 1 h at the same temperature. The reac- washed with brine, dried over Na2SO4 and concentrated. Purifi-
tion mixture was warmed to −30 °C, and then 1-bromohexane cation on silica gel chromatography (petroleum ether–EtOAc,
(6 mL, 42.18 mmol) and DMPU (16 mL) in 16 mL of THF were 6 : 1) furnished 14 (1.23 g, 86% for 2 steps) as a colorless oil.
added dropwise. The mixture was warmed to room tempera- [α]2D5 +20.6 (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3)
ture gradually and stirred for 48 h and quenched with satu- δ 5.80–5.74 (m, 1H), 5.12 (dd, J = 3.2, 1.2 Hz, 1H), 5.08 (d, J =
rated aqueous NH4Cl (20 mL). The organic layer was separated 0.8 Hz, 1H), 3.63–3.59 (m, 1H), 2.28–2.23 (m, 1H), 2.17–2.09
and the aqueous layer was extracted with EtOAc (3 × 100 mL). (m, 3H), 1.91 (t, J = 2.8 Hz, 1H), 1.70 (br d, 1H), 1.52–1.43 (m,
The combined organic layer was dried over Na2SO4 and con- 2H), 1.41–1.35 (m, 4H), 1.32–1.27 (m, 3H). 13C NMR (100 MHz,
centrated under reduced pressure. The residue was purified by CDCl3) δ 135.01, 118.17, 84.79, 70.74, 68.27, 42.08, 36.84,
silica gel column chromatography (petroleum ether–EtOAc, 29.21, 28.78, 28.51, 25.63, 18.48. ESI-HRMS (m/z): calcd for
6 : 1) to give 12 (3.29 g, 51.2%) as a yellow oil. The spectra were C12H20ONa: ([M + Na]+), 203.1349; found, 203.1358.
consistent with the reported literature.24
(R)-tert-Butyl(dodec-1-en-11-yn-4-yloxy)dimethylsilane (6). To
Non-8-yn-1-ol (13). To a solution of 1,3-diaminopropane a solution of compound 14 (1 g, 5.55 mmol) in DCM were
(9 mL, 107.67 mmol) in 30 mL of THF at 0 °C was added n- added imidazole (1.133 g, 16.65 mmol) and TBSCl (0.92 g,
BuLi (2.2 M in hexane, 49.1 mL, 108 mmol) dropwise. The 6.1 mmol) at room temperature. The reaction mixture was
reaction mixture was stirred for 20 min, and t-BuOK (1.0 M in quenched with saturated NaHCO3 solution (10 mL) after 2 h,
THF, 84 mL, 84 mmol) was added slowly. Then, 12 (2.82 g, extracted with DCM (3 × 20 mL), washed with brine, dried over
20 mmol) in 20 mL of THF was added dropwise, the resulting Na2SO4 and evaporated in vacuo. Column chromatography of
solution was warmed to room temperature and stirred for an the residue on a silica gel column (eluent: from petroleum
additional 2 h, poured into 20 mL of saturated aqueous ether to petroleum ether–EtOAc, 6 : 1) afforded 6 (1.55 g, 95%)
NH4Cl, and extracted with EtOAc (3 × 50 mL). The combined as a colorless oil. [α]2D5 +12.6 (c 3.15, CHCl3); 1H NMR
organic layer was washed with 5% HCl (20 mL), saturated (400 MHz, CDCl3) δ 5.85–5.78 (m, 1H), 5.04 (d, J = 6.4 Hz, 1H),
aqueous NaHCO3, brine, then dried over Na2SO4 and evapor- 5.01 (s, 1H), 3.68 (t, J = 5.6 Hz, 1H), 2.22–2.16 (m, 4H), 1.93 (t,
ated in vacuo. The residue was purified by silica gel column J = 2.8 Hz, 1H), 1.56–1.49 (m, 2H), 1.44–1.39 (m, 4H), 1.38–1.27
chromatography (petroleum ether–EtOAc, 3 : 1) to give 13 (m, 4H), 0.89 (s, 9H), 0.05 (s, 3H), 0.04 (s, 3H). 13C NMR
(2.44 g, 86.7%) as a yellow oil. 1H NMR (400 MHz, CDCl3) δ (100 MHz, CDCl3) δ 135.45, 116.54, 84.70, 71.97, 68.06, 41.93,
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36.73, 29.23, 28.73, 28.44, 25.18, 18.38, 18.14, −4.38, −4.52. (s, 2H), 5.00 (ddd, J = 15.6, 3.6, 1.6 Hz, 1H), 4.94 (dt, J = 10.0,
ESI-HRMS (m/z): calcd for C18H34OSiNa: ([M + Na]+), 317.2277; 0.8 Hz, 1H), 2.36 (t, J = 7.6 Hz, 2H), 2.08–2.02 (m, 2H),
found, 317.2271.
1.67–1.61 (m, 3H), 1.40–1.26 (m, 15H). 13C NMR (100 MHz,
Tetradec-13-en-1-ol (15). To a solution of 11-bromoundecan- CDCl3) δ 173.68, 139.47, 139.25, 136.18, 128.75, 128.53, 128.37,
1-ol (10, 2.51 g, 10 mmol) in 20 mL of DCM were added imid- 128.15, 114.29, 114.08, 66.26, 66.05, 34.57, 34.35, 34.03, 33.81,
azole (2.042 g, 30 mmol) and TBSCl (1.65 g, 11 mmol). After 29.55, 29.47, 29.35, 29.23, 29.13, 28.95, 25.18, 24.96. ESI-HRMS
2 h, the reaction mixture was quenched with saturated (m/z): calcd for C21H32O2Na: ([M + Na]+), 339.2300; found,
NaHCO3 solution (10 mL), extracted with DCM (3 × 20 mL), 339.2284.
washed with brine, dried and evaporated in vacuo. To the
above crude product in 50 mL of THF was added CuI (0.75 g, oxolan-4-yl)-2,2-dimethyl-1,3-dioxolane
(4R,5S)-4-(Bis(ethylthio)methyl)-5-((S)-2,2-dimethyl-1,3-di-
(16). L-Arabinose
3.94 mmol), and the resulting solution was then cooled to (80 g, 0.533 mol) was dissolved in 80 mL of conc. HCl (37%),
−78 °C. Allylmagnesium bromide (1 M in Et2O, 14 mL, and to the solution was added EtSH (90 mL, 1.24 mol) on an
14 mmol) was added dropwise under a nitrogen atmosphere. ice bath. The reaction mixture was stirred for 3 h, filtered, and
The mixture was allowed to warm to room temperature, and the solid was washed with absolute ethanol to give a white
quenched with saturated aqueous NH4Cl (10 mL) until TLC solid, which was re-crystallized from water. To this solid (30 g,
indicated a complete consumption of the starting material. 0.117 mol) in acetone (100 mL) was added conc. H2SO4 (3 mL),
The organic layer was removed and the water phase was and then the reaction mixture became deep brown slowly.
extracted with EtOAc (3 × 20 mL), and the combined organic After stirring at room temperature for 24 h (monitoring by
layer was concentrated. The residue was directly dissolved in TLC), the brown solution was neutralized (pH 7) by the
15 mL of THF, and treated with TBAF (2.8 g, 10.71 mmol) for addition of aqueous ammonia, the formed white ammonium
3 h. The solvent was evaporated under reduced pressure, and salt was filtered and the filtrate was concentrated under
column chromatography of the residue on silica gel (pet- reduced pressure. Column chromatography of the residue on
roleum ether–EtOAc, 3 : 1) yielded 15 (1.67 g, 79% for 3 steps) silica gel column (petroleum ether–EtOAc, 6 : 1) gave 16
1
as a colorless oil. H NMR (400 MHz, CDCl3) δ 5.85–5.77 (m, (24.77 g, 63% for 2 steps) as a syrup. [α]2D5 −67.3 (c 1.2, CHCl3);
1H), 4.99 (ddd, J = 15.6, 3.6, 1.6 Hz, 1H), 4.96 (dt, J = 10.4, 1H NMR (400 MHz, CDCl3) δ 4.31–4.29 (m, 1H), 4.14–4.12 (m,
0.8 Hz, 1H), 3.64 (t, J = 6.8 Hz, 2H), 2.07–2.02 (m, 2H), 1H), 4.08–3.98 (m, 3H), 3.97–3.95 (m, 1H), 2.77–2.69 (m, 4H),
1.59–1.51 (m, 3H), 1.41–1.27 (m, 17H). 13C NMR (100 MHz, 1.45 (s, 3H), 1.41 (s, 3H), 1.37 (s, 3H), 1.34 (s, 3H), 1.30–1.24
CDCl3) δ 139.43, 114.25, 63.24, 33.99, 32.99, 29.80, 29.78, (q, J = 7.6 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ 110.16,
29.68, 29.62, 29.33, 29.13, 25.93. ESI-HRMS (m/z): calculated 109.67, 84.52, 79.13, 67.78, 52.39, 27.33, 27.09, 26.66, 25.26,
for C14H28ONa: ([M + Na]+), 235.2038; found, 235.2010.
Benzyl tetradec-13-enoate (7). DMSO (2 mL, 25.88 mmol) in C15H28O4S2Na: ([M + Na]+), 359.1327; Found, 359.1321.
10 mL of DCM was added dropwise to a solution of oxalyl (4R,5S)-4-((S)-2,2-Dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyl-5-
25.19, 24.90, 14.45, 14.38. ESI-HRMS (m/z): calculated for
chloride (1.2 mL, 13.2 mmol) in 15 mL of DCM at −60 °C. vinyl-1,3-dioxolane (17). To a solution of 16 (15 g, 44.6 mmol)
5 min later, 15 (1.3 g, 6.13 mmol) in 10 mL of DCM was added in acetone–water (110 mL, v/v 10 : 1) was added HgO (22.5 g,
over 3 min, and the mixture was then stirred at the same temp- 102.72 mmol) and HgCl2 (22.5 g, 81.2 mmol). The mixture was
erature for 1 h. Et3N (5.5 mL, 39.24 mmol) was added to heated at 60 °C under a nitrogen atmosphere for 2 h. At the
quench the reaction, and 20 mL water was poured into the end of this time, the mixture was filtered and the filtrate was
solution. The organic layer was removed and the aqueous layer washed with 1 M NaI solution (50 mL), extracted with DCM
was extracted with DCM (3 × 20 mL), washed with brine, and (3 × 100 mL), and the combined organic fraction was evapor-
the combined organic solvents were evaporated in vacuo to ated in vacuo to afford a yellow oil. The yellow oil was directly
give a yellowish residue. The residue was dissolved in 25 mL of subjected to the coming Wittig reaction without further purifi-
t-BuOH; to the solution was added NaClO2 (1.49 g, 16.6 mmol) cation. In another flask, methyl triphenyl phosphonium
in 25 mL of water after addition of 2-methyl-2-butene (3.6 mL) bromide (15 g, 42.13 mmol) was suspended in 100 mL of dried
and NaH2PO4·2H2O (2.575 g, 16.51 mmol). The reaction was THF, and t-BuOK (5.2 g, 46.42 mmol) was added on an ice
monitored by TLC until all starting materials disappeared. At bath. After stirring for 1 h at 0 °C, to this yellow Wittig reagent
the end of this time, the organic layer was removed, extracted was added the above yellow oil (7.2 g) in 15 mL of dried THF
with EtOAc (3 × 30 mL), the combined organic layer was dropwise. The resulting solution was allowed to warm to room
washed with brine, dried over Na2SO4, and then concentrated temperature and stirred overnight. Finally, the solution was
to give a colorless oil. To the colorless oil in dry toluene quenched by the addition of saturated aqueous NH4Cl
(20 mL) were added benzyl alcohol (2.4 mL, 23.12 mmol) and (20 mL), extracted with EtOAc (3 × 40 mL), and concentrated
a catalytic amount of PTSA (22.8 mg, 0.12 mmol), and stirred under reduced pressure. The residue was purified by silica gel
under reflux for 3 h. The resulting yellow solution was evapor- column chromatography (petroleum ether–EtOAc, 6 : 1) to
ated in vacuo, and the residue was purified by silica gel provide 17 (4.35 g, 61% for 2 steps) as a syrup. [α]2D5 +4 (c 2.9,
1
column chromatography (petroleum ether–EtOAc, 25 : 1) to CHCl3); H NMR (400 MHz, CDCl3) δ 5.90 (ddd, J = 16.8, 10.4,
1
generate 7 (1.67 g, 86% for 3 steps) as a colorless oil. H NMR 6.0 Hz, 1H), 5.40 (dt, J = 17.2, 1.6 Hz, 1H), 5.20 (dt, J = 10.4,
(400 MHz, CDCl3) δ 7.38–7.33 (m, 5H), 5.86–5.79 (m, 1H), 5.13 1.6 Hz, 1H), 4.35 (t, J = 6.8 Hz, 1H), 4.12–4.06 (m, 2H),
2076 | Org. Biomol. Chem., 2014, 12, 2071–2079
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3.95–3.92 (m, 1H), 3.69 (t, J = 3.2 Hz, 1H), 1.40 (s, 6H), 1.39 (s, 2.35 (t, J = 7.6 Hz, 2H), 2.08–2.04 (m, 2H), 1.66–1.51 (m, 4H),
3H), 1.33 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 136.12, 117.34, 1.45–1.25 (m, 20H). 13C NMR (100 MHz, CDCl3) δ 173.64,
109.82, 109.60, 81.35, 80.63, 67.20, 27.14, 27.11, 26.85, 25.44. 137.03, 136.19, 128.52, 128.13, 126.39, 109.33, 79.97, 79.89,
ESI-HRMS (m/z): calcd for C12H20O4Na: ([M + Na]+), 251.1260; 66.03, 51.19, 44.42, 34.33, 32.31, 29.53, 29.51, 29.42, 29.22,
found, 251.1268.
29.15, 29.12, 28.86, 27.08, 27.01, 26.72, 26.66, 24.95. ESI-HRMS
(S)-1-((4S,5S)-2,2-Dimethyl-5-vinyl-1,3-dioxolan-4-yl)ethane- (m/z): calcd for C28H42O5Na: ([M + Na]+), 481.2930; Found,
1,2-diol (18). Compound 17 (2 g, 8.77 mmol) in HOAc–water 481.2882.
(12 mL, v/v 3 : 1) was stirred at room temperature until com-
Compound 20. To a solution of alkyne 6 (360 mg,
plete consumption of the starting material. The reaction solu- 1.222 mmol) in dried THF (2 mL) was added t-BuLi (1.3 M in
tion was basified (pH 9) at 0 °C with saturated NaHCO3 hexane, 1 mL, 1.404 mmol) dropwise at −78 °C. The reaction
solution, then extracted with EtOAc (3 × 50 mL), and concen- was allowed to warm gradually from −78 °C to −20 °C and
trated in vacuo. Column chromatography of the residue on stirred for 3 h, and then the solution was cooled to −78 °C and
silica gel (petroleum ether–EtOAc, 1 : 2) afforded 18 (1.336 g, added BF3·Et2O (1.38 mL, 1.42 mmol). The above reaction
81%) as a syrup. [α]2D5 −9.8 (c 0.32, CHCl3); 1H NMR (400 MHz, mixture was stirred at −78 °C for 30 min, and then a solution
CDCl3) δ 5.87 (ddd, J = 17.2, 10.4, 6.8 Hz, 1H), 5.41 (d, J = of epoxide 19 (140 mg, 0.306 mmol) in THF (1 mL) was added
17.2 Hz, 1H), 5.25 (d, J = 10.4 Hz, 1H), 4.40 (t, J = 7.6 Hz, 1H), via a syringe. The mixture was quenched with saturated
3.87–3.83 (m, 1H), 3.78–3.75 (m, 1H), 3.71–3.68 (m, 2H), 2.60 aqueous NaHCO3 (2 mL) based on TLC analysis, and extracted
(br d, 2H), 1.41 (s, 3H), 1.40 (s, 3H). 13C NMR (100 MHz, with EtOAc (3 × 5 mL). The combined organic layer was dried
CDCl3) δ 136.04, 118.82, 109.55, 81.31, 79.45, 72.15, 63.61, over Na2SO4 and concentrated. The residue was stirred in pyri-
27.13, 27.06. ESI-HRMS (m/z): calcd for C9H16O4Na: dine (3 mL) and acetic anhydride (0.5 mL) with a catalytic
([M + Na]+), 211.0947; found, 211.0941.
(S)-2-((4S,5S)-2,2-Dimethyl-5-vinyl-1,3-dioxolan-4-yl)-2-hydroxy- erature, then concentrated in vacuo to dryness, which was puri-
ethyl-4-methylbenzenesulfonate (8). To solution of 18 fied on silica gel column chromatography (petroleum ether–
amount of DMAP (5 mg, 0.04 mmol) overnight at room temp-
a
(720 mg, 3.83 mmol) in 10 mL of DCM were added Et3N EtOAc, 16 : 1) to give 20 (206 mg, 84.9% for 2 steps) as a color-
(0.6 mL, 4.28 mmol), TsCl (830 mg, 4.37 mmol), and n-Bu2SnO less oil. [α]2D5 +8 (c 0.5, CHCl3); 1H NMR (400 MHz, CDCl3)
(12 mg, 0.048 mmol) successively at 0 °C. The reaction was δ 7.35 (s, 5H), 5.84–5.75 (m, 2H), 5.45 (dd, J = 15.6, 8.0 Hz, 1H),
stirred overnight at room temperature, quenched with satu- 5.13–5.09 (m, 3H), 5.03 (d, J = 6.4 Hz, 1H), 5.00 (s, 1H), 4.36 (t,
rated NaHCO3 (TLC monitoring), extracted with DCM (3 × J = 8.0 Hz, 1H), 3.86 (dd, J = 8.0, 5.6 Hz, 1H), 3.68 (t, J = 6.0 Hz,
10 mL), and then concentrated. Purification of the residue by 1H), 2.52 (t, J = 6.4 Hz, 2H), 2.35 (t, J = 7.2 Hz, 2H), 2.19 (t, J =
silica gel column chromatography (petroleum ether–EtOAc, 3.2 Hz, 2H), 2.12 (t, J = 7.2 Hz, 2H), 2.10–2.04 (m, 5H),
3 : 1) yielded 8 (1.113 g, 85%) as a syrup. [α]2D5 −12 (c 1.6, 1.65–1.58 (m, 3H), 1.47–1.24 (m, 34H), 0.877 (s, 9H), 0.04 (s,
1
CHCl3); H NMR (400 MHz, CDCl3): δ 7.80 (d, J = 8.4 Hz, 2H), 3H), 0.03 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 173.71, 169.98,
7.35 (d, J = 8.0 Hz, 2H), 5.85 (ddd, J = 16.8, 10.0, 6.4 Hz, 1H), 137.11, 136.14, 135.46, 128.55, 128.17, 126.87, 116.59, 109.03,
5.38 (d, J = 16.8 Hz, 1H), 5.21 (d, J = 10.4 Hz, 1H), 4.39 (t, J = 82.58, 80.10, 79.51, 74.70, 71.97, 71.31, 66.07, 41.94, 36.80,
7.2 Hz, 1H), 4.21 (dd, J = 10.4, 3.2 Hz, 1H), 4.07–4.03 (m, 1H), 34.35, 32.42, 29.59, 29.57, 29.50, 29.46, 29.35, 29.30, 29.27,
3.96 (s, 1H), 3.67 (t, J = 7.2 Hz, 1H), 2.45 (s, 3H), 1.37 (s, 3H), 29.15, 28.96, 28.88, 27.15, 26.76, 25.92, 25.27, 24.97, 21.45,
1.36 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 145.17, 135.69, 21.01, 18.71, 18.16, −4.37, −4.49. ESI-HRMS (m/z): calculated
132.65, 129.96, 128.03, 118.43, 109.70, 79.88, 79.67, 71.22, for C48H78O7SiNa: ([M + Na]+), 817.5415; found, 817.5375.
70.71, 26.90, 26.87, 21.66. ESI-HRMS (m/z): calcd for
Compound 21. To the solution of 20 (150 mg, 0.189 mmol)
in 20 mL of THF was added TBAF (400 mg, 1.531 mmol), the
C16H22O6SNa: ([M + Na]+), 365.1035; found, 365.1029.
(E)-Benzyl-14-((4S,5R)-2,2-dimethyl-5-((R)-oxiran-2-yl)-1,3- mixture was stirred at room temperature for 10 h, and then the
dioxolan-4-yl)tetradec-13-enoate (19). To solution of solvent was removed; column chromatography of the residue
a
8
(200 mg, 0.585 mmol) and 7 (250 mg, 0.791 mmol) in 10 mL on silica gel (petroleum ether–EtOAc, 3 : 1) afforded 21
of dry DCM was added Grubbs II catalyst (14.9 mg, (105 mg, yield 82%) as a colorless oil. [α]2D5 +4.55 (c 1.45,
0.017 mmol), and then refluxed for 10 h. The resulting orange CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.36 (s, 5H), 5.86–5.79
solution was concentrated and subjected to the next step (m, 2H), 5.45 (dd, J = 15.6, 8.0 Hz, 1H), 5.16 (s, 2H), 5.12 (s,
without further purification. The crude product was dissolved 3H), 4.38 (t, J = 8.4 Hz, 1H), 3.87 (dd, J = 8.4, 5.6 Hz, 1H), 3.65
in 10 mL of THF, treated with TBAF (0.6 g, 2.295 mmol) for 4 h (m, 1H), 2.54–2.51 (m, 2H), 2.38–2.29 (m, 3H), 2.16–2.10 (m,
at room temperature, and then the solvent was removed. 3H), 2.08–2.03 (m, 5H), 1.66–1.61 (m, 4H), 1.47–1.25 (m, 30H).
Column chromatography of the residue on silica gel 13C NMR (100 MHz, CDCl3) δ 173.74, 170.03, 137.17, 136.13,
(300–400 mesh, petroleum ether–EtOAc, 16 : 1) gave 19 134.91, 128.55, 128.18, 126.85, 118.12, 109.05, 82.53, 80.12,
(193 mg, 72.2% for 2 steps) as a colorless oil. [α]2D5 +10.8 (c 0.7, 79.47, 74.79, 71.31, 70.59, 66.08, 41.97, 36.78, 34.35, 32.42,
CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.36–7.32 (m, 5H), 29.59, 29.57, 29.50, 29.46, 29.30, 29.27, 29.15, 28.95, 28.78,
5.87–5.83 (m, 1H), 5.47 (dd, J = 15.6, 8.0 Hz, 1H), 5.12 (s, 2H), 28.76, 27.15, 26.76, 25.57, 24.97, 21.44, 21.02, 18.68. ESI-HRMS
4.32 (t, J = 8.0 Hz, 1H), 3.67–3.62 (m, 1H), 3.08 (dd, J = 6.8, 4.0 (m/z): calcd for C42H64O7Na: ([M + Na]+), 703.4550; found,
Hz, 1H), 2.81 (t, J = 4.8 Hz, 1H), 2.72 (dd, J = 4.8, 2.4 Hz, 1H), 703.4521.
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Compound 22. To a solution of 21 (75 mg, 0.11 mmol) in quenched by addition of Et3N (0.2 mL), and concentrated
DCM (8 mL) were added N-Cbz-L-proline (5) (38 mg, in vacuo. The residue was purified by silica gel chromatography
0.154 mmol), EDCI (34 mg, 0.176 mmol), and DMAP (2.4 mg, (petroleum ether–EtOAc, 2 : 3) to give 23 (42.6 mg, 81%) as a
0.022 mmol) at 0 °C. The mixture was stirred for 2 h and colorless oil. [α]2D5 +38 (c 0.3, CHCl3); 1H NMR (400 MHz,
quenched with water (5 mL), the organic layer was separated, CDCl3) δ 4.93–4.86 (m, 1H), 4.50 (dd, J = 8.8, 3.6 Hz, 1H), 4.38
and the water phase was extracted with DCM (3 × 10 mL). The (rotamers), 3.91–3.86 (m, 1H), 3.82–3.79 (m, 1H), 3.63–3.49 (m,
combined organic layer was dried over Na2SO4 and concen- 2H), 3.47–3.40 (m, 1H), 2.82 (bd, 3H), 2.35–2.10 (m, 4H),
trated in vacuo to dryness, which was purified on silica gel 2.05–1.91 (m, 4H), 1.64–1.48 (m, 12H), 1.44–1.26 (m, 32H),
column (petroleum ether–EtOAc, 16 : 1) to give 22 (96.8 mg, 0.92–0.87 (m, 3H). 13C NMR (100 MHz, CDCl3) δ 172.33, 172.20
96.4%) as a colorless oil. [α]2D5 −13.6 (c 0.5, CHCl3); 1H NMR (rotamers), 172.08, 75.99, 75.03 (rotamers), 74.90, 74.58 (rota-
(400 MHz, CDCl3) δ 7.36–7.31 (m, 10H), 5.84–5.77 (m, 2H), mers), 73.97, 73.76 (rotamers), 70.49, 70.35 (rotamers), 60.25,
5.44 (dd, J = 15.2, 8.4 Hz, 1H), 5.18–4.85 (m, 8H), 4.38–4.32 (m, 59.32 (rotamers), 47.15, 46.39 (rotamers), 36.36, 36.19 (rota-
2H), 3.85 (dd, J = 8.0, 5.6 Hz, 1H), 3.62–3.48 (m, 2H), 2.57–2.45 mers), 34.65, 34.03, 33.98, 33.09, 33.05, 32.75, 31.71, 29.57,
(m, 2H), 2.34 (t, J = 7.6 Hz, 2H), 2.28–2.14 (m, 2H), 2.11–2.01 29.47, 29.40, 29.38, 29.28, 29.12, 29.11, 29.08, 28.94, 28.92,
(m, 7H), 2.00–1.83 (m, 3H), 1.65–1.62 (m, 2H), 1.46–1.34 (m, 28.85, 28.74, 28.40, 25.67, 25.60, 25.36, 25.07, 24.99, 24.90,
12H), 1.27–1.24 (m, 20H). 13C NMR (100 MHz, CDCl3) 24.86, 22.71, 18.91, 18.64 (rotamers), 14.12, 14.01 (rotamers).
δ 173.77, 172.46, 172.37 (rotamers), 170.04, 154.86, 154.46 ESI-HRMS (m/z): calcd for C35H65NO6Na: ([M + Na]+), 618.4710;
(rotamers), 137.10, 136.98 (rotamers), 136.69, 136.30 (rota- found, 618.4673.
mers), 133.70, 133.57 (rotamers), 128.65, 128.56 (rotamers),
Penarolide sulfate A2 (2). To a solution of compound 23
128.52, 128.27 (rotamers), 128.02, 127.89 (rotamers), 127.84, (20 mg, 0.034 mmol) in dry pyridine (2 mL) was added SO3·py
127.06 (rotamers), 117.87, 117.81 (rotamers), 109.15, 82.52, (50 mg, 0.314 mmol). The mixture was stirred at 60 °C for 1 h,
80.28, 79.65, 77.40, 74.95, 74.19, 71.49, 67.06, 66.99 (rotamers), then cooled to 0 °C on an ice bath, and basified to pH 9 by
66.16, 59.66, 59.23 (rotamers), 47.40, 46.51 (rotamers), 38.64, adding saturated NaHCO3 solution. The mixture was filtered
38.49 (rotamers), 34.45, 33.49, 32.51, 31.17, 30.14, 29.68, 29.67, and the filtrate was evaporated in vacuo to give a yellowish
29.59, 29.56, 29.37, 29.25, 29.07, 28.92, 28.80, 27.27, 26.88, solid, which was purified by HPLC to afford compound 2
25.19, 25.15, 25.08, 24.37, 23.50, 21.60, 21.09, 18.79. ESI-HRMS (22.7 mg, 75%) as a white powder. [α]2D5 −40.1 (c 0.31,
(m/z): calcd for C55H77NO10Na: ([M + Na]+), 934.5445; found, MeOH); 1H NMR (400 MHz, CD3OD) δ 4.96 (d, J = 5.6 Hz,
934.5441.
1H), 4.71–4.66 (m, 2H), 4.39 (dd, J = 8.8, 4.0 Hz, 1H),
Compound 4. A suspension of 22 (150 mg, 0.164 mmol) 3.65–3.51 (m, 2H), 2.42 (dt, J = 15.2, 7.6 Hz, 1H), 2.31–2.24
and 10% Pd/C (80 mg) in EtOAc (10 mL) was stirred under a (m, 2H), 2.19–2.14 (m, 1H), 2.06–1.82 (m, 6H), 1.59–1.49 (m,
3 atm hydrogen atmosphere at room temperature. After 2 h, 12H), 1.30 (m, 30H), 0.92 (t, J = 7.6 Hz, 3H). 13C NMR
the reaction mixture was filtered through a Bush funnel and (100 MHz, CDCl3) δ 174.45, 173.89, 80.76, 79.61, 78.74,
the filtrate was concentrated. The crude product was dissolved 77.22, 76.19, 61.13, 37.50, 35.31, 35.25, 32.08, 31.64, 30.49,
in dried DCM (50 mL), and EDCI (80 mg, 0.416 mmol) and 30.26, 30.06, 26.62, 26.05, 25.94, 19.73, 14.37. ESI-HRMS
HOBt (80 mg, 0.6 mmol) were added to the solution at 0 °C. (m/z): calcd for C35H62O15NS3Na2: ([M − Na]−), 878.3077;
The mixture was stirred overnight and concentrated, the Found, 878.3074.
residue was purified by silica gel chromatography (petroleum
α-Glucosidase inhibition evaluation. The enzyme inhibition
ether–EtOAc, 3 : 1) to give 4 (69.2 mg, 62.2% for 2 steps) as a experiment was performed according to the literature pro-
colorless oil. [α]2D5 −30.8 (c 0.23, CHCl3); 1H NMR (400 MHz, cedure.8,25 α-Glucosidase (Type III from Yeast, G7256, pur-
CDCl3) δ 5.08–5.02 (m, 1H), 4.93–4.85 (m, 1H), 4.49 (dd, J = chased from Sigma Chemical Co. at St. Louis) was dissolved
8.8, 3.6 Hz, 1H), 4.37 (rotamers), 3.93–3.86 (m, 1H), 3.80–3.76 in a buffer (0.1 M potassium phosphate, 3.2 mM MgCl2, pH
(m, 1H), 3.63–3.49 (m, 2H), 2.31–2.10 (m, 3H), 2.08 (s, 3H), 6.8), and the substrate p-nitrophenyl α-D-glucopyranoside
2.06–1.87 (m, 3H), 1.63–1.58 (m, 8H), 1.56–1.43 (m, 7H), (PNPG) was also dissolved in buffer (0.1 M potassium phos-
1.38–1.25 (m, 37H), 0.90 (t, J = 7.2 Hz, 3H). 13C NMR phate, 3.2 mM MgCl2, pH 6.8) independently. To a set of
(100 MHz, CDCl3) δ 172.27, 171.96 (rotamers), 170.82, 108.95, parallel wells of microtiter plates were added 20 μL of
108.91 (rotamers), 81.84, 81.69 (rotamers), 76.06, 74.84, 72.99, testing solution, 80 μL of H2O, 25 μL of buffer solution
72.70 (rotamers), 60.30, 59.43, 47.20, 46.45 (rotamers), 36.36, (0.5 M potassium phosphate, 16 mM MgCl2, pH 6.8), and
36.18 (rotamers), 34.73, 34.19, 34.15 (rotamers), 33.76, 33.46 50 μL of the above enzyme solution (0.5 U mL−1). The
(rotamers), 31.88, 29.70, 29.67, 29.62, 29.59, 29.55, 29.47, plates were incubated at 37 °C for 30 min, and then
29.39, 29.35, 29.30, 29.14, 29.04, 28.91, 28.73, 27.60, 27.10, the substrate PNPG (5 μmol mL−1) was added to each well.
25.51, 25.39, 25.19, 25.14, 25.04, 24.95, 22.83, 21.35, 18.73. The absorbance of the mixture was measured at time 0 and
ESI-HRMS (m/z): calculated for C40H71NO7Na: ([M + Na]+), after incubation at 37 °C using a Biotek Synergy 2 microplate
700.5129; found, 700.5097.
reader at 410 nm. The IC50 value was defined by GraphPad
Compound 23. To a solution of compound 4 (60 mg, Prism 5 as the concentration of α-glucosidase inhibitor
0.088 mmol) in methanol (2 mL) was added AcCl (20 μL). The to inhibit 50% of its activity under the experimental
solution was allowed to stir at room temperature for 9 h, then conditions.
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12 (a) A. K. Ghosh, K. A. Shurrush and Z. L. Dawson, Org.
Biomol. Chem., 2013, 11, 7768–7777; (b) S. L. Huang and
D. Swern, J. Org. Chem., 1978, 43, 4537–4538; (c) P. Davoli,
A. Spaggiari, L. Castagnetti and F. Prati, Org. Biomol.
Chem., 2004, 2, 38–47.
Acknowledgements
This work was supported in part by the National Basic
Research Program of China (grant 2012CB822101), National
Innovative Drug Foundation (project 2012ZX09502001), and
NNSF of China (projects 21072217 and 21372254). The 13 (a) U. S. Racherla and H. C. Brown, J. Org. Chem., 1991, 56,
authors would like to thank Prof. Yoichi Nakao of Waseda
University for sending NMR copies of penarolide sulfate A2.
401–404; (b) J. Murga, J. Garcia-Fortanet, M. Carda and
J. A. Marco, J. Org. Chem., 2004, 69, 7277–7283.
14 I. Ohtani, T. Kusumi, Y. Kashman and H. Kakisawa, J. Org.
Chem., 1991, 56, 1296–1298.
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T. R. Pradhana and J. S. Yadav, Org. Biomol. Chem., 2011, 9,
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