Stereoselective synthesis of (6S) and (6R)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one and their cytotoxic activity against cancer cell lines

Article abstract of DOI:10.1016/j.tet.2009.01.101

Stereoselective total synthesis of α,β-unsaturated lactone (1a), isolated from Ravensara crassifolia, has been achieved efficiently starting from chiral 2,3-O-isopropylidene-d-glyceraldehyde (3) followed by asymmetric allylation and ring-closing metathesi

Full text of DOI:10.1016/j.tet.2009.01.101

Tetrahedron 65 (2009) 2989–2994
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Stereoselective synthesis of (6S) and (6R)-5,6-dihydro-6-[(2R)-2-hydroxy-
6-phenylhexyl]-2H-pyran-2-one and their cytotoxic activity against
cancer cell lines
Manchala Narasimhulu a, Arepalli Sai Krishna b, Janapala Venkateswara Rao b,
,
Yenamandra Venkateswarlu a
*
a Natural Products Laboratory, Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500007, India
b Biology Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Stereoselective total synthesis of
been achieved efficiently starting from chiral 2,3-O-isopropylidene-
asymmetric allylation and ring-closing metathesis. The antiproliferative activities of compounds 1a, 1b
and the unusual bicyclic compound 2 were evaluated against three-cancer cell lines, THP-1 and U-937
(leukemia) and A-375 (melanoma).
a
,
b
-unsaturated lactone (1a), isolated from Ravensara crassifolia, has
-glyceraldehyde (3) followed by
Received 12 September 2008
Received in revised form 11 December 2008
Accepted 29 January 2009
D
Available online 4 February 2009
Ó 2009 Published by Elsevier Ltd.
Keywords:
5,6-Dihydro-a-pyrone
Ravensara crassifolia
Asymmetric allylation
Ring-closing metathesis
Cancer cell lines THP-1 and U-937
(leukemia) and A-375 (melanoma)
1. Introduction
Compound (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]
-2H-pyran-2-one (1a) is an example of this class of natural product,
The family of 5,6-dihydro-
a
-pyrone derivatives having an alkyl
which was isolated from plant Ravensara crassifolia by Hostettman
and co-workers.13 This natural pyrone was shown to possess anti-
fungal activity against the phytopathogenic fungus Cladosporium
side chain at the C6 position are important biologically active nat-
ural products, which have been isolated from plants. Some of these
compounds, such as fostriecin1–4 and goniothalamin,5–7 have been
found to be anti-cancer agents. Further, (ꢀ)-pyronetin8–10 exhibits
immunosuppressive activity, and passifloricin A11 and strictifo-
lione12 exhibit antifungal activity.
cucumarinum. Some of the compounds containing 5,6-dihydro-a-
pyrone moiety exhibits cytotoxic activity, such as callystatin A,14,15
spicigerolide16 and leptomycin B.17,18 Inspired by this type of lac-
tones showing anti-cancer activity, we decided to extend the
O
O
O
O
2
1
3
OH
2'
O
OH
O
O
6"
3"
4
1"
6
5"
4"
6'
4'
5
5'
1'
3'
2"
1b
1a
2
evaluation of the cytotoxic activity of compounds 1a, 1b and 2 to
the cancer cell lines THP-1 and U-937 (leukemia) and A-375
(melanoma). Several syntheses have been reported for natural
compound 1a.19–21 No synthesis has been reported for its 6-epimer
* Corresponding author. Tel.: þ91 40 27193167; fax: þ91 40 27160512.
E-mail address: luchem@iict.res.in (Y. Venkateswarlu).
0040-4020/$ – see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tet.2009.01.101

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M. Narasimhulu et al. / Tetrahedron 65 (2009) 2989–2994
OH
CN
O
O
O
O
OH
O
O
a
b
c
O
H
d
3
4
5
6
OH
OH
OH
OH
OTs
e
f
7
8
9
TBSO
OTBS
CN
O
g
h
H
10
11
Scheme 1. Conditions: (a) [Ph(CH2)3Ph3P]Br (1 equiv), n-BuLi (1 equiv), THF, 0 ꢁC, 2 h, 90%; (b) H2, 10% Pd/C, MeOH, rt, 6 h, 96%; (c) 2 M HCl, MeOH, 1 h, rt, 97%; (d) (i) PPh3 (2 equiv),
DIAD (2 equiv), p-NO2C6H4COOH (2 equiv), THF, rt, 2 h, 90%; (ii) catalytic Na, MeOH, rt, 1 h, 94%; (e) TsCl (1.1 equiv), (n-Bu)2SnO (0.1 equiv), Et3N (2.5 equiv), 0 ꢁC to rt, 4 h, 79%; (f)
KCN (1.5 equiv), rt, 12 h, 91%; (g) TBDMS-Cl (1 equiv), imidazole (2.5 equiv), dry CH2Cl2, 98%; (h) DIBAL-H (1 equiv), dry CH2Cl2, ꢀ78 ꢁC, 0.5 h, 70%.
TBSO
OH
OH
TBSO
b
a
11
12a
12b
Scheme 2. Conditions: (a) (ꢀ)-Ipc2BCl, allyl MgBr, ꢀ100 ꢁC, 2 h, 76%; (b) (þ)-Ipc2BCl, allyl MgBr, ꢀ100 ꢁC, 2 h, 76%.
O
O
TBSO
O
TBSO
O
c
b
a
1a + 2
12a
13a
14a
Scheme 3. Conditions: (a) CH2]CHCOCl, i-Pr2NEt, 0 ꢁC to rt, 88%; (b) Grubbs’ I generation catalyst [(PCy3)2Cl2Ru]CHPh] (5 mol %), dry CH2Cl2, 55 ꢁC, 12 h, 92%; (c) p-TSA
(0.1 equiv), MeOH, rt, 90%.
(1b). First time we are reporting the synthesis of natural, unnatural
isomers and its bicyclic compound 2.
in the natural product (1a) at C-20. The primary hydroxyl group in
(7) was protected with tosyl chloride using triethyl amine and
catalytic amount of Bu2SnO to produce tosylated compound (8) in
79% yield with the minor tosylation at the secondary hydroxyl
group of (7). The tosylate (8) was converted to corresponding nitrile
(9) in 91% yield by the reaction of KCN in ethanol and H2O (3:2) at
room temperature. The secondary hydroxyl group in the nitrile (9)
was protected with TBDMS-Cl/imidazole to give tertiary-butyl
dimethylsilyl ether (10) in 98% yield. The nitrile function was re-
duced with DIBAL-H in dry dichloromethane at ꢀ78 ꢁC to afford the
aldehyde (11) in 70% yield (Scheme 1).
2. Results and discussion
2.1. Chemistry
Our synthesis began with the chiral aldehyde (3), obtained
easily from D
-mannitol,22 which was subjected to a Wittig reaction
to give compound 4, in 90% yield. Hydrogenation of compound 4
over 10% Pd/C in methanol gave acetonide (5) followed on treating
with concd HCl in methanol afforded diol (6) in 97% yield. At this
stage the asymmetric center of the secondary hydroxyl group in the
diol (6) was inverted by the Mitsunobu reaction23,24 to give inver-
ted diol (7) in order to match with stereochemistry of the hydroxyl
The introduction of chirality at C-6 carbon is furnished by Brown’s
asymmetric allylboration.25,26 The resulting aldehyde (11) was sub-
jected to allylboration with (ꢀ)-Ipc2BCl/allyl magnesiumbromide
(Ipc¼diisopinocampheyl) and (þ)-Ipc2BCl/allyl magnesiumbromide,
O
O
TBSO
O
TBSO
O
c
a
b
1b
12b
13b
14b
Scheme 4. Conditions: same conditions as in Scheme 3.

M. Narasimhulu et al. / Tetrahedron 65 (2009) 2989–2994
2991
Table 1
involves asymmetric allylboration and RCM as key steps. We
achieved the biologically active natural product (6S)-5,6-dihydro-
6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one (1a) and its 6-
epimer (1b) in twelve steps with an 88.5% overall yield.
IC50 values for antiproliferative activities of compound 1a, 1b and 2 against cancer
cell linesa
Compound
THP-1 (
m
g/mL)
U-937 (
m
g/mL)
A-375 (mg/mL)
1a
1b
2
13.04ꢃ1.35
50.93ꢃ0.98
10.41ꢃ0.62
1.27ꢃ0.09
33.63ꢃ6.71
41.47ꢃ0.84
32.45ꢃ13.12
10.56ꢃ0.70
21.35ꢃ4.32
38.96ꢃ0.49
32.13ꢃ0.75
2.31ꢃ0.08
4. Experimental
4.1. Chemistry
Etoposideb
a
Concentration that elicit inhibition by 50% of the cell growth (IC50), given in mg/
mL, were determined from nonlinear regression analysis using the GraphPad Prism
4.1.1. General methods
software (r2>0.9).
b
Solvents were dried over standard drying agents and freshly
distilled prior to use.31 The reagents were purchased from Aldrich
and Acros, and were used without further purification unless other-
wise stated. All moisture-sensitive reactions were carried out under
nitrogen. Organic solutions were dried over anhydrous Na2SO4 and
concentrated below 40 ꢁC in vacuo. All column chromatographic
separations were performed using silica gel (Acme’s 60–120 mesh).
1H NMR (200 MHz and 300 MHz) and 13C NMR (50 MHz and
75 MHz) spectra were measured with a Varian Gemini FT-200 MHz
and Bruker Avence 300 MHz with tetramethylsilane as internal
standard for solutions in deuteriochloroform. J values are given in
hertz. IR spectra were recorded on a Perkin–Elmer IR-683 spectro-
photometer with NaCl optics. Optical rotations were measured with
Horiba high sensitive polarimeter SEPA-300 at 25 ꢁC. Mass spectra
were recorded on Agilent Technologies 1100 Series (Agilent Chem-
stations Software).
Etoposide was employed as positive control.
respectively, to furnish the required syn-1,3-diol (12a) and anti-1,3-
diol (12b) in 76% yield (Scheme 2), as a single diastereomer (the minor
stereoisomers were lost during chromatographic separation). The
relative stereochemistry of 1,3-diol in 13a and 13b was established by
their conversion to the corresponding acetonide. The syn and anti
relative configuration of the hydroxy groups was confirmed by the
analysis of 13C NMR spectrum,27 which showed signals at
19.8 ppmforthetwomethylgroupsand 98.4 ppmforthequaternary
carbon of the acetonide in syn-1,3-diol, while in the anti-1,3-diol
acetonide having signals at 24.52 and 24.54 ppm for the two methyl
groups and 100.4 ppm for the quaternary carbon. The homoallyl
d 30.1 and
d
d
d
alcohols 12a and 12b were transformed independently to lactones 1a
(Scheme 3) and 1b (Scheme 4), respectively.
The TBDMS protected homoallyl alcohol (12a) was reacted with
acryloyl chloride and diisopropyl ethylamine at 0 ꢁC in dichloro-
methane to afford ester (13a) in 88% yield for ring-closing me-
tathesis. The ring-closing metathesis was achieved with Grubbs’ I
generation catalyst28–30 to afford lactone (14a) in 92% yield, which
was subjected to deprotection of TBDMS with TBAF in THF to pro-
duce the natural product lactone (1a) in unsatisfactory yields (30%).
The low yield was circumvented by using p-toluene sulfonic acid in
methanol for the deprotection of TBDMS group to yield compound
(1a) in 90% yield. It has been observed that if the reaction was run
for more than 10 min, it gave the mixture of compounds 1a and 2 in
70:30 ratio, with an overall yield of 95%. The other diastereomer
12b was also subjected to the same sequence of reactions to realize
the 6-epimer of 1b; here the side product was not observed.
4.1.2. (S)-2,2-Dimethyl-4-[(E)-4-phenylbut-1-enyl]-1,3-
dioxolane (4)
To a suspension of [Ph3P(CH2)3Ph]Br (9.2 g, 20 mmol) in THF
(50 mL) was added n-BuLi (1.6 M in hexane, 12.5 mL, 20 mmol) at
0 ꢁC and stirred for 15 min. Then a solution of ketal (3) (2.6 g,
20 mmol) in THF (10 mL) was added dropwise and the mixture was
allowed to stir for an additional 0.5 h at room temperature. After
completion of the reaction, the reaction was quenched with satu-
rated NH4Cl solution (40 mL) and extracted into diethyl ether
(3ꢂ50 mL). The ether solution was washed with brine and dried
with anhydrous Na2SO4. After removal of solvent, the crude product
was purified on a flash column of silica gel (eluent PE/EtOAc, 98:2)
to afford the pure compound 4 (4.17 g, 90%) as a mixture of geo-
metric isomers (both are separated). Liquid, IR (KBr):
2860, 1635, 1457, 1374, 1217, 1063, 980 cmꢀ1 1H NMR (300 MHz,
CDCl3): 7.30–7.14 (m, 5H), 5.70–5.61 (m, 1H), 5.40 (t, 1H,
n
¼2956, 2926,
.
2.2. Biological activities
d
J¼8.49 Hz), 4.73–4.66 (m, 1H), 3.76 (dd, 1H, J¼6.04 and 8.1 Hz), 3.34
Antiproliferative activities of 5,6-dihydro-2H-pyran-2-ones 1a,
1b and a bicyclic compound 2 were evaluated in the following
human cancer cell lines: leukemia (THP-1 and U-937) and mela-
noma (A-375). Leukemia cell lines (THP-1 and U-937) were cul-
tured in RPMI-1640 and melanoma cell line (A-375) was cultured in
DMEM. Chemotherapeutic etoposide was used as positive control.
All the three compounds evaluated displayed antiproliferative
activity against the cancer cell lines tested in a concentration-de-
(t, 1H, J¼7.9 Hz), 2.81–2.70 (m, 1H), 2.68–2.56 (m, 1H), 2.53–2.30
(m, 2H), 1.39 (s, 3H), 1.36 (s, 3H). 13C NMR (75 MHz, CDCl3):
d 141.6,
134.5, 128.3, 128.2, 127.4, 125.8, 109.4, 75.0, 66.8, 35.5, 29.6, 26.9,
25
25.2. LCMS: m/z 255 [MþNa]þ. [
a
]
þ40.8 (c 1, CHCl3).
D
4.1.3. (S)-2,2-Dimethyl-4-(4-phenylbutyl)-1,3-dioxolane (5)
To a solution of compound 4 (3.9 g, 16.8 mmol) in methanol
(15 mL) was added 10% Pd/C (300 mg) and stirred under hydrogen
for 6 h at room temperature. After completion of the reaction, the
catalyst was removed by filtration, solvent evaporated and crude
product was purified on a flash column of silica gel (eluent PE/
EtOAc, 50:1) to afford compound 5 (3.78 g, 96%) as colourless oil.
pendent way. The IC50 values (mg/ml) for 1a, 1b, 2 and etoposide (a
positive drug control) are summarized in Table 1. Compound 1a is
more potent on A-375 (melanoma) cancer cell line than 1b and 2.
While the bicyclic compound 2 was more potent for leukemia cell
lines THP-1 and U-937 than 1a and 1b. The 6-epimer 1b is less
active than 1a and 2 on both the cell lines. Overall, these results
indicate that natural isomer 1a is having higher antiproliferative
activity on tumour cells than its structure like compound 1b.
Liquid, IR (KBr):
1061 cmꢀ1 1H NMR (300 MHz, CDCl3):
3.92 (m, 2H), 3.42 (t, 1H, J¼6.7 Hz), 2.60 (t, 2H, J¼6.7 Hz), 1.72–1.44
(m, 6H), 1.36 (s, 3H), 1.30 (s, 3H). 13C NMR (75 MHz, CDCl3):
142.2,
n
¼3061, 3026, 2985, 2934, 2860, 1603, 1496, 1216,
.
d
7.24–7.08 (m, 5H), 4.04–
d
128.2, 128.1, 125.6, 108.4, 75.8, 69.3, 35.6, 33.3, 31.3, 26.8, 25.6, 25.3.
25
3. Conclusion
LCMS: m/z 257 [MþNa]þ. [
a
]
þ5.8 (c 1.2, CHCl3).
D
In conclusion the Chiron approach synthesis of 1a and its 6-
epimer 1b was developed and its cytotoxic activity against cancer
cell lines was evaluated. The versatility of our synthetic route
4.1.4. (S)-6-Phenylhexane-1,2-diol (6)
To a solution of compound 5 (3.6 g, 15.4 mmol) in methanol
(20 mL) was added HCl (2 M, 10 mL) and the mixture was stirred for

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M. Narasimhulu et al. / Tetrahedron 65 (2009) 2989–2994
1 h at room temperature. After completion of the reaction, the
contents were neutralized with solid K2CO3 and removed the
methanol, diluted with water (30 mL) and extracted into ethyl ac-
etate three times (3ꢂ50 mL). The combined organic layers was
dried over anhydrous sodiumsulphate and the solvent was re-
moved under vacuum to obtain the crude product (6), which was
purified on a flash column of silica gel (eluent PE/EtOAc, 1:1) to
afford a colourless oil (2.89 g, 97%).
4.1.7. (R)-3-Hydroxy-7-phenylheptane nitrile (9)
The compound tosylate (8) (2.7 g, 7.76 mmol) was dissolved in
30 mL of 60% aq ethanol, cooled to 0 ꢁC, and then added KCN
(0.756 g, 11.63 mmol). The reaction mixture was stirred at room
temperature for 12 h. After completion of the reaction, ethanol was
removed under vacuum and diluted with water (20 mL), extracted
into EtOAc and the organic phase was washed with brine and dried
over anhydrous Na2SO4. After removal of solvent, the crude residue
was purified on a flash column of silica gel, eluting with PE/EtOAc
(7:3), to afford compound 9 (1.43 g, 91%) as colourless oil.
IR (KBr):
n
¼3395, 3016, 2983, 2929, 1637, 1608, 1486, 1453 cmꢀ1
.
1H NMR (300 MHz, CDCl3):
d 7.24–7.08 (m, 5H), 3.66–3.56 (m, 2H),
3.7 (t, 1H, J¼7.55 Hz), 3.30 (br s, 2H), 2.59 (t, 2H, J¼7.55 Hz), 1.64–
1.56 (m, 2H), 1.50–1.32 (m, 4H). 13C NMR (75 MHz, CDCl3):
142.4,
128.4, 128.3, 125.7, 72.2, 66.7, 35.8, 33.0, 31.4, 25.2. LCMS: m/z 194.2
IR (KBr):
n
¼3446, 3061, 3026, 2934, 2252, 1634, 1495 cmꢀ1. 1H
d
NMR (300 MHz, CDCl3): d 7.25–7.08 (m, 5H), 3.88–3.81 (m,1H), 2.81
(br s, 1H), 2.60 (t, 2H, J¼7.5 Hz), 2.41 (dd, 2H, J¼4.5 and 8.3 Hz),
25
[Mþ]. [
a
]
ꢀ28.2 (c 1.02, CHCl3).
1.69–1.29 (m, 6H). 13C NMR (75 MHz, CDCl3):
d 142.1, 128.2, 128.1,
D
125.6, 117.0, 69.3, 36.1, 35.5, 30.9, 25.8, 24.7. LCMS: m/z 203.2 [Mþ].
25
4.1.5. (R)-6-Phenyl hexane-1,2-diol (7)
[a
]
þ18.3 (c 1.8, CHCl3).
D
To a stirred solution of PPh3 (7.29 g, 27 mmol), diol (6) (2.7 g,
13.91 mmol) and p-nitrobenzoic acid (4.67 g, 27 mmol) in THF
(30 mL) was added DIAD (95%, 2.02 mL, 27 mmol) dropwise at 0 ꢁC.
The reaction mixture was stirred for 2 h at room temperature. After
the completion of reaction, the mixture was diluted with water
(20 mL) and extracted with ethyl acetate (3ꢂ30 mL). The combined
organic layer was washed with NaHCO3 and brine solutions, and
dried with anhydrous Na2SO4. Evaporation of the solvent gave
a crude product, which was purified by flash chromatography on
a column of silica gel (eluent PE/EtOAc, 9:1), to afford (R)-diester as
4.1.8. (R)-3-(tert-Butyl dimethyl silanyloxy)-7-phenyl-heptane
nitrile (10)
To a stirred solution of cyano compound (9) (1.4 g, 6.89 mmol)
and imidazole (1.172 g, 17.2 mmol) in dichloromethane (20 mL) at
0 ꢁC was added tertiary-butyl dimethylsilyl chloride (0.955 g,
6.89 mmol) dropwise. After the completion of reaction, the mixture
was diluted with water (15 mL) and extracted with dichloro-
methane (3ꢂ25 mL). The organic layer was washed with brine
solution (10 mL) and dried over anhydrous Na2SO4. The solvent
removed under vacuum to furnish the crude residue, which was
purified by flash chromatography on silica gel eluting with PE/
EtOAc (9:1) to afford compound 10 (2.04 g, 98%) as a colourless oil.
a light yellow viscous liquid (6.16 g, 90%). IR (KBr):
1734, 1715, 1528, 1336, 1278 cmꢀ1 1H NMR (300 MHz, CDCl3):
8.31–8.24 (m, 4H), 8.20–8.12 (m, 4H), 7.28–7.15 (m, 5H), 5.55 (m,
n
¼3028, 2978,
.
d
1H), 4.65 (dd, 1H, J¼3.2 and 12.0 Hz), 4.52 (dd, 1H, J¼6.9 and
IR (KBr):
n
¼3062, 3027, 2933, 2858, 2250, 1635, 1496, 1464,
12.08 Hz), 2.63 (t, 2H, J¼7.5 Hz), 1.92–1.80 (m, 2H), 1.78–1.67 (m,
1255 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d
7.08–7.25 (m, 5H), 3.92–
2H), 1.58–1.49 (m, 2H). 13C NMR (75 MHz, CDCl3):
d
164.2, 164.1,
3.83 (m, 1H), 2.60 (t, 2H, J¼7.5 Hz), 2.38 (d, 2H, J¼5.2 Hz), 1.72–1.50
150.5, 141.8, 135.1, 134.8, 130.6, 128.2, 125.7, 123.5, 73.0, 66.2, 35.4,
(m, 4H),1.45–122 (m, 2H), 0.881 (s, 9H), 0.09 (s, 3H), 0.04 (s, 3H). 13C
30.8, 30.5, 24.5. LCMS: m/z 492.3 [Mþ].
NMR (75 MHz, CDCl3):
d 142.1, 128.27, 128.24, 128.21, 125.6, 117.6,
Further, the diester (5.9 g, 12 mmol) was taken in methanol
(50 mL) and added sodium (60 mg, 2.4 mmol) and the reaction
mixture stirred for 1 h. After completion of the reaction, solid NH4Cl
(0.5 g) was added to the reaction mixture. After removal of meth-
anol under vacuum, the residue was dissolved in EtOAc (25 mL),
washed with brine and dried over anhydrous Na2SO4. The crude
product was purified by flash column chromatography on a silica
gel (eluent PE/EtOAc, 1:1), to afford the desired diol (7) (2.18 g, 94%)
68.1, 36.7, 35.6, 31.1, 26.0, 25.63, 25.60, 25.5, 24.4,17.8, ꢀ4.76, ꢀ4.79.
25
LCMS: m/z 340 [MþNa]þ. [
a
]
þ6.2 (c 1.4, CHCl3).
D
4.1.9. (R)-3-(tert-Butyl dimethyl silanyloxy)-7-phenyl-
heptanal (11)
To a stirred solution of compound 10 (2 g, 6.6 mmol) in dry
dichloromethane (25 mL) was added DIBAL-H (5.154 mL, 20 wt % in
solution) slowly for 15 min at ꢀ78 ꢁC and the reaction mixture was
stirred for half an hour at ꢀ78 ꢁC. After completion of reaction, the
reaction mixture was quenched with saturated sodium potassium
tartrate solution (15 mL) and was stirred vigorously at room tem-
perature for additional 1 h and the contents were extracted into
dichloromethane (3ꢂ25 mL). The combined organic layer was
washed with brine solution (30 mL), dried over anhydrous Na2SO4
and the solvent removed under vacuum to give a crude product,
which was purified by flash chromatography on a silica gel column
eluting with PE/EtOAc (50:2) to afford the aldehyde (11) (1.478 g,
as a colourless oil. Its spectroscopic data were identical to those of
25
compound 5, except that the optical rotation value is opposite: [
a]
D
þ27.8 (c 1.3, CHCl3).
4.1.6. (R)-2-Hydroxy-6-phenylhexyl-4-methyl benzene
sulfonate (8)
To an ice-cold solution of diol (7) (2 g, 10.3 mmol), catalytic
amount of dibutyl tin oxide (5 mg) and triethyl amine (3.16 mL,
22.68 mmol) in dichloromethane (30 mL) was added. Then a solu-
tion of tosyl chloride (1.96 g, 10.3 mmol) in dichloromethane
(10 mL) was added dropwise and stirred the reaction for 4 h at
room temperature. After completion of reaction, the mixture was
diluted with water and extracted into dichloromethane (3ꢂ50 mL).
The organic layer was washed with brine solution, dried over an-
hydrous Na2SO4 and concentrated under reduced pressure to get
the crude residue, which was purified on a silica gel column, eluting
with PE/EtOAc (7:3) to afford compound 8 as a viscous liquid
70%) as a colourless oil. IR (KBr):
1452 cmꢀ1. 1H NMR (300 MHz, CDCl3):
5H), 4.12 (m, 1H), 2.58 (t, 2H, J¼7.5 Hz), 2.51–2.42 (m, 2H), 1.65–1.21
(m, 6H), 0.86 (s, 9H), .008 (s, 6H). 13C NMR (75 MHz, CDCl3):
202.5,
n
¼3027, 2926, 2858, 1725, 1634,
d
9.75 (s, 1H), 7.24–7.10 (m,
d
142.5, 128.6, 128.5, 125.9, 68.3, 51.1, 37.6, 35.8, 31.3, 26.1, 25.9, 25.5,
24.7, 17.9, ꢀ4.7, ꢀ4.4. LCMS: m/z 320 [Mþ].
4.1.10. (4S,6R)-6-(tert-Butyl dimethyl silanyloxy)-10-phenyldec-1-
en-4-ol (12a)
(2.83 g, 79%). IR (KBr):
n
¼3442, 3062, 2933, 2858, 1636, 1454, 1357,
1212, 1176, 699 cmꢀ1
.
1H NMR (300 MHz, CDCl3):
d
7.77 (d, 2H,
To a stirred solution of (ꢀ)-Ipc2BCl (900 mg, 2.81 mmol) in dry
ether (15 mL), allyl magnesium bromide (1 M solution in Et2O,
2 mL, 2 mmol) was added dropwise under nitrogen atmosphere at
ꢀ78 ꢁC. After finishing the addition, the RB flask replaced from dry
ice–acetone bath to ice bath and the mixture was stirred for 1 h.
The solution was allowed to stand, whereby precipitation of
J¼8.3 Hz), 7.33 (d, 2H, J¼8.3 Hz), 7.24–7.06 (m, 5H), 4.03–3.98 (m,
1H), 3.86–3.78 (m, 2H), 2.57 (t, 2H, J¼7.5 Hz), 2.45 (s, 3H), 2.1 (br s,
1H),1.65–1.55 (m, 2H),1.50–1.36 (m, 4H). 13C NMR (75 MHz, CDCl3):
d
145.0, 142.2, 142.0, 132.6, 129.9, 129.8, 128.3, 128.2, 127.9, 127.8,
125.6, 73.9, 69.3, 35.6, 32.4, 31.2, 24.8, 21.6. LCMS: m/z 371.2 [Mþ].

M. Narasimhulu et al. / Tetrahedron 65 (2009) 2989–2994
2993
magnesium chloride took place. The supernatant solution was
carefully transferred to another flask through a cannula. After
cooling this flask at ꢀ100 ꢁC, a solution of the aldehyde (11) in dry
Et2O (5 mL) was added dropwise through a syringe. The resulting
solution was further stirred at ꢀ100 ꢁC for 2 h. The reaction mixture
was quenched by the addition of phosphate pH 7 buffer solution
(10 mL), MeOH (10 mL) and 30% H2O2 (5 mL). After stirring for
30 min, the mixture was poured into saturated aq NaHCO3 and
extracted into Et2O (3ꢂ25 mL), the combined organic layers were
dried over anhydrous magnesium sulfate and concentrated. The
crude residue was purified by silica gel column chromatography
eluted with normal hexane to 1:9 EA/PE to afford the corre-
sponding homoallyl alcohol (12a) (515 mg, 76%) as colourless oil. IR
1.29 (m, 6H), 0.85 (s, 9H), 0.03 (s, 6H). 13C NMR (75 MHz, CDCl3):
d
164.2,144.9,142.3,128.2,128.1,125.3,121.3, 75.1, 68.4,41.8, 36.3, 35.7,
25
31.4, 29.7, 25.7, 24.6, 17.8, ꢀ4.4, ꢀ4.6. LCMS: m/z 411 [MþNa]þ. [
a]
D
ꢀ9.6 (c, .45, CHCl3). The same above procedure was followed except
for the use of (4R,6R)-6-(tert-butyl dimethyl silanyloxy)-10-phenyl
dec-1-en-4-yl acrylate (13b), to afford the (6R)-5,6-dihydro-6-[(2R)-
2-(tert-butyl dimethyl silanyloxy)-6-phenylhexyl]-2H-pyran-2-one
25
(14b). For (6R,2R)-14b: [
a
]
ꢀ4.2 (c 1.2, CHCl3).
D
4.1.13. (6S)-5,6-Dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-
pyran-2-one (1a)
To a stirred solution of compound 13 (50 mg) in methanol cat-
alytic amount of p-toluene sulfonic acid (5 mol %) was added and
stirred for 10 min. Then the reaction mixture was treated with solid
NaHCO3. The methanol was removed and extracted into ethyl ac-
etate (3ꢂ10 mL). The combined organic layer was dried over an-
hydrous Na2SO4 and solvent was removed under reduced pressure
to yield crude product, which was purified on silica gel column
eluting with PE/EtOAc (6:4) to afford the pure product 14 (31 mg,
(KBr):
n
¼3437, 2936, 2853, 2363, 1636, 1454, 1052 cmꢀ1
.
1H NMR
(300 MHz, CDCl3):
d 7.33–7.12 (m, 5H), 5.95–5.73 (m, 1H), 5.13 (d,
2H, J¼15.42 Hz), 4.01–3.88 (m, 1H), 3.85–3.70 (m, 1H), 2.90 (br s,
1H), 2.65 (t, 2H, J¼7.3 Hz), 2.23 (t, 2H, J¼6.6 Hz), 1.75–1.28 (m, 8H),
0.94 (s, 9H), 0.15 (s, 3H), 0.124 (s, 3H). 13C NMR (75 MHz, CDCl3):
d
142.6, 135.2, 128.5, 128.4, 125.9, 117.6, 73.1, 70.4, 42.4, 42.3, 38.0,
25
36.1, 31.8, 26.1, 24.5, 18.1, ꢀ3.8, ꢀ4.4. LCMS: m/z 363 [Mþ1]þ. [
ꢀ6.9 (c 0.65, CHCl3).
a
]
90%) as a pale yellow solid. Mp¼34–36 ꢁC. IR (KBr):
¼3445, 2928,
n
D
2848, 1694, 1487, 1396, 1262 cmꢀ1 1H NMR (300 MHz, CDCl3):
.
The same above procedure was used except for the use of
d
7.30–7.13 (m, 5H), 6.93–6.84 (m, 1H), 6.01 (dd, 1H, J¼1.45 and
(þ)-Ipc2BCl instead of (ꢀ)-Ipc2BCl to afford (4R,6R)-6-(tert-butyl
9.46 Hz), 4.81–4.66 (m, 1H), 4.06–3.92 (m, 1H), 2.62 (t, 2H,
dimethyl silanyloxy)-10-phenyldec-1-en-4-ol 12b. For (4R,6R)-12b:
J¼7.5 Hz), 2.39–2.30 (m, 2H), 1.95–1.81 (m, 1H), 1.71–1.58 (m, 3H),
[
a]
ꢀ5.2 (c 0.8, CHCl3).
1.51–1.41 (m, 4H). 13C NMR (75 MHz, CDCl3):
d 164.4, 145.3, 142.3,
25
D
128.3, 128.2, 125.6, 121.3, 74.9, 67.1, 42.25, 37.8, 35.8, 31.3, 29.9, 25.1.
LCMS: m/z 275 [Mþ1]þ. [
a]
ꢀ63.8 (c 0.5, CHCl3). The same
25
4.1.11. (4S,6R)-6-(tert-Butyl dimethyl silanyloxy)-10-phenyl dec-1-
en-4-yl acrylate (13a)
D
above procedure was followed except for the use of (6R)-5,6-
dihydro-6-[(2R)-2-(tert-butyl dimethyl silanyloxy)-6-phenylhexyl]-
To a stirred solution of compound 12a (150 mg, 0.414 mmol) in
dichloromethane (10 mL) were added acryloyl chloride (67
m
L,
2H-pyran-2-one (14b), to afford the (4R,6R)-1b as gummy syrup.
25
.828 mmol) and i-Pr2NEt (138
m
L, 1.656 mmol) at 0 ꢁC. The mixture
For (6R,2R)-1b: [
a
]
ꢀ18.4 (c 0.5, CHCl3).
D
was allowed to warm to room temperature and stirred for 3 h. The
reaction mixture was diluted with water (5 mL) and extracted into
dichloromethane (3ꢂ10 mL). The combined organic layer was dried
over anhydrous Na2SO4 and the solvent was removed under vac-
uum to get the crude residue, which was purified by silica gel
column chromatography (PE/EtOAc, 1:9) to afford the pure product
4.1.14. Spectroscopic data for compound (2) [(1R,7R)-7-(4-
phenylbutyl)-2,6-dioxa-bicyclo[3.3.1]nonan-3-one]
It was obtained as a colourless solid, mp 36–38 ꢁC. IR (KBr):
n
¼2928, 2856, 2102, 1734, 1494, 1454, 1073 cmꢀ1
.
1H NMR
(300 MHz, CDCl3): d 7.30–7.15 (m, 5H), 4.92–4.88 (m, 1H), 4.38–4.32
(13a) (152 mg, 88%) as colourless oil. IR (KBr):
n
¼3075, 2927, 2858,
(m, 1H), 3.78–3.64 (m, 1H), 2.86–2.78 (m, 2H), 2.58 (t, 2H, J¼7.5 Hz),
1725, 1635, 1408, 1257, 1190, 1052 cmꢀ1. 1H NMR (300 MHz, CDCl3):
2.04–188 (m, 3H), 1.75–1.28 (m, 7H). 13C NMR (75 MHz, CDCl3):
d
7.25–7.11 (m, 5H), 6.39 (dd, 1H, J¼1.5 and 17.3 Hz), 6.09 (dd, 1H,
d 169.7, 142.3, 128.27, 128.2, 125.6, 73.0, 65.7, 65.5, 36.8, 36.4, 35.7,
25
J¼9.8 and 16.6 Hz), 5.85 (m, 1H), 5.78–5.66 (m, 1H), 5.09 (d, 2H,
J¼13.5 Hz), 5.08–5.02 (m, 1H), 3.77–3.64 (m, 1H), 2.65–2.59 (t, 2H,
J¼7.5 Hz), 2.42–2.32 (m, 2H), 1.71–1.28 (m, 8H), 0.89 (s, 9H), 0.05 (s,
35.6, 31.2, 29.7, 24.7. LCMS: m/z 297.4 [MþNa]þ. [
a
]
D
ꢀ16.8 (c 0.5,
CHCl3).
3H), 0.021 (s, 3H). 13C NMR (75 MHz, CDCl3):
d
165.6, 142.5, 133.3,
4.2. Biological activities
130.4, 130.3, 128.8, 128.7, 128.3, 128.2, 125.6, 117.8, 71.2, 68.7, 41.1,
40.7, 37.6, 35.9, 31.6, 25.8, 24.2,17.9, ꢀ4.5, ꢀ4.7. LCMS: m/z 416 [Mþ].
4.2.1. Biological assay
25
[
a]
þ4.3 (c 1, CHCl3). The same above procedure was used except
Since it is known that different cell lines display different sen-
sitivities towards a cytotoxic compound, the use of more than one
cell line is therefore considered necessary in the detection of cy-
totoxic compounds. Bearing this in mind different cell lines leu-
kemia (THP-1 and U-937) and melanoma (A-375) were used in the
present study. Human tumour cell lines were kindly provided by
National Center for Cellular Sciences (NCCS), Pune, India. Leukemia
cell lines were cultured in RPMI-1640 and melanoma cell line was
cultured in DMEM. Both the media were supplemented with 10%
D
for the use of (4R,6R)-6-(tert-butyl dimethyl silanyloxy)-10-phe-
nyldec-1-en-4-ol (12b), to afford the (4R,6R)-6-(tert-butyl dimethyl
silanyloxy)-10-phenyl dec-1-en-4-yl acrylate 13b. For (4R,6R)-13b:
25
[
a]
þ5.2 (c .85, CHCl3).
D
4.1.12. (6S)-5,6-Dihydro-6-[(2R)-2-(tert-butyl dimethyl silanyloxy)-
6-phenylhexyl]-2H-pyran-2-one (14a)
To a stirred solution of bis(tricyclohexyl phosphine)benzylidine
ruthenium(IV) dichloride (Grubbs catalyst, 13 mg, 5 mol %) in
dichloromethane (50 mL) at 55 ꢁC was added compound 13a
(125 mg, 0.3 mmol) dissolved in dichloromethane (25 mL). The
resulting mixture was heated for 12 h. After completion of the re-
action, the contents were cooled and solvent was removed under
reduced pressure to yield crude product, which was purified on
silica gel column eluting with (PE/EtOAc, 7:3) to afford the pure
heat-inactivated FCS, 1 mmol NaHCO3, 2 mmol L-glutamine and
penicillin–streptomycin in a humidified atmosphere of 95%, 5% CO2
at 37 ꢁC. In all experiments, THP-1, U-937 and A-375 cells were
seeded at a final density of 2ꢂ104 cells/well in 96 well microtiter
plates. The cells were treated with different test concentrations (10,
20, 40, 60, 80 and 100 mg/mL) of compounds 1a, 1b and 2 and their
cytotoxicities were compared with the activity of a positive control,
etoposide at identical conditions with five replicates each. Cyto-
toxicity was measured using the MTT [3-(4,5-dimethylthiazol-
2-yl)-2,5-diphenyl tetrazolium bromide] assay, according to the
Mosmann method32 (1983). Briefly, the cells (2ꢂ104) were seeded
compound (14a) (102 mg, 92%). IR (KBr):
n
¼2935, 1722, 1634, 1392,
772 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d
7.29–7.13 (m, 5H), 6.90–6.82
(m,1H), 6.02 (d,1H, J¼9.8 Hz), 4.59–4.50 (m,1H), 3.93–3.85 (m,1H),
2.60 (t, 2H, J¼7.5 Hz), 2.38–2.31 (m, 2H), 2.01–1.96 (m, 1H), 1.65–

2994
M. Narasimhulu et al. / Tetrahedron 65 (2009) 2989–2994
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2003, 17, 433–439.
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The authors would like to thank CSIR, New Delhi for their fi-
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Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.01.101.
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