The first total synthesis of neohelmanticins A-D, amino derivatives of the 1,2-dihydroxypropane core and biological evaluation

Article abstract of DOI:10.1016/j.tetasy.2009.02.022

A concise total synthesis of neohelmanticins A-D has been accomplished in 15 steps starting from commercially available gallic acid. Swern oxidation conditions, a Grignard reaction, Sharpless kinetic resolution, and regioselective ring opening of an epoxide with lithium aluminum hydride (LAH) are the key features to install the basic core, dihydroxy phenyl propane 2. One hydroxyl group of this core was esterified with tiglic acid followed by the oxidation and esterification with corresponding acids to yield neohelmanticins A-D.

Full text of DOI:10.1016/j.tetasy.2009.02.022

Tetrahedron: Asymmetry 20 (2009) 440–448
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
The first total synthesis of neohelmanticins A–D, amino derivatives
of the 1,2-dihydroxypropane core and biological evaluation
Eppakayala Sreedhar, R. Sateesh Chandra Kumar, G. Venkateswar Reddy, A. Robinson,
*
K. Suresh Babu, J. Madhusudana Rao, P. V. Srinivas
Natural Products Laboratory, Division of Organic Chemistry-1, Indian Institute of Chemical Technology, Hyderabad 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A concise total synthesis of neohelmanticins A–D has been accomplished in 15 steps starting from com-
mercially available gallic acid. Swern oxidation conditions, a Grignard reaction, Sharpless kinetic resolu-
tion, and regioselective ring opening of an epoxide with lithium aluminum hydride (LAH) are the key
features to install the basic core, dihydroxy phenyl propane 2. One hydroxyl group of this core was ester-
ified with tiglic acid followed by the oxidation and esterification with corresponding acids to yield neo-
helmanticins A–D.
Received 17 December 2008
Accepted 10 February 2009
Available online 25 March 2009
Ó 2009 Published by Elsevier Ltd.
1. Introduction
toxic activity. To the best of our knowledge this is the first report
on the synthesis of neohelmanticins.
Bioactive natural products continue to be a source of inspiration
for chemical biology and medicinal chemistry research.1 Neohel-
manticins A–D (Fig. 1) are an architecturally novel group of highly
oxygenated phenyl propanoid class of compounds isolated from
the European medicinal plant Tapsia garganica (umbelliferaceae)
by Liu et al. in 2006 (Fig. 1).2 The structure and absolute configura-
tion of the neohelmanticins were established on the basis of spec-
troscopic data as well as on degradation experiments. These
compounds have shown significant cytotoxic activity against leu-
kemia (EL4), carcinoma (S180), and MCF7 cell lines, respectively.
Neohelmanticins share a common phenyl propanoid core attached
to different esters; the common phenyl propanoid core contains
two stereogenic centers, a phenyl ring, and an angelate moiety.
Due to their remarkable anticancer activity and scarce availability
from the natural sources, the neohelmanticins have become attrac-
tive synthetic targets. As a part of our synthetic studies on biolog-
ically important natural products,3 we were attracted to the
neohelmanticins on the basis of their cytotoxic activity and as
potential small molecule leads for the development of new thera-
peutics. Herein, we report efficient total synthesis of neohelman-
ticins A–D by utilizing the Swern oxidation, a Grignard reaction,
and Sharpless kinetic resolution as key steps. In addition, we also
prepared a series of dihydroxy phenyl propanoid analogues by
introducing the various amines and assessed them for their cyto-
2. Results and discussion
2.1. Chemistry
2.1.1. Retrosynthetic analysis of neohelmanticins A–D
As outlined in Scheme 1, we envisioned retrosynthetically that
all the neohelmanticins can be obtained via esterification of the
corresponding acids (angelic acid for 1a, octanoic acid for 1b, hex-
anoic acid for 1c, and butanoic acid for 1d) with alcohol 3. Com-
pound 3 could in turn be obtained from the epoxide 4 via the
regioselective ring opening of an epoxide, esterification with tiglic
acid followed by asymmetric dihydroxylation. Further disconnec-
tion of epoxide 4 led to secondary alcohol 5, which itself could
be constructed via the addition of vinyl Grignard to the aldehyde
11. The aldehyde 11 (Scheme 2) may be accessible from commer-
cially available gallic acid 6 in a five-step sequence.
2.1.2. Synthesis of basic core of the neohelmanticins A–D
According to this retrosynthetic analysis, the preliminary exper-
iments for the synthesis of the phenyl propanoid core are depicted
in Scheme 2. The synthesis began with gallic acid 6, which was
converted to its methyl ester 7 in 90% yield through reaction with
thionyl chloride (SOCl2) refluxing in MeOH. Methylenation4 of 7 in
the presence of CuO furnished 8, which was further converted into
methyl ether 9 in the presence of dimethyl sulfate.5 Reduction of 9
with lithium aluminum hydride, followed by Swern oxidation6
afforded aldehyde 11. The Grignard reaction of 11 by the addition
of vinyl magnesium bromide in THF afforded secondary alcohol 5
as a racemic mixture in excellent yield (98%). The Sharpless kinetic
* Corresponding author at present address: Process Research Laboratory, Biocon
Limited, 20th Km Hosur Road, Bangalore 560 100, India. Tel.: +91 40 27193166; fax:
+91 40 27160512.
E-mail address: srinivaspv@yahoo.com (P.V. Srinivas).
0957-4166/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tetasy.2009.02.022

E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
441
O
OR
OH
O
O
O
O
O
O
O
O
O
O
OH
(neohelmanticin A)
1a. R =
1b. R =
O
(neohelmanticin B)
O
OH
dihydroxy phenyl propane 2
1a-1d
1c. R =
1d. R =
(neohelmanticin C)
O
(neohelmanticin D)
Figure 1. Chemical structures of neohelmanticins A–D and dihydroxyphenyl propane.
resolution7 of this racemic mixture of secondary alcohol 5 with cu-
mene hydroperoxide in the presence of titanium isopropoxide and
(ꢀ)-DIPT in DCM at ꢀ20 °C furnished 12 (48%) and epoxide 4 (47%)
with 99% ee. The stereochemistry of the compounds 12 and 4 was
established by 2D NMR spectroscopy. Finally, ring opening of epox-
ide 4 with LAH8 in THF afforded the basic phenylpropanoid core 2
(dihydroxyphenyl propane) of the neohelmanticins.
biogenetic precursor, 1,2-dihydroxy propane derivative 2. How-
ever, except for neohelmanticin A, other compounds are equal or
less potent than 22 (di hydroxyl phenyl propane). Further, in order
to improve the activity of 1,2-dihydroxy propane, we planned for
the synthesis of 1,2-dihydroxy propane derivatives and for an
investigation of their structure activity relationships (SARs). There-
fore, we initially focused our attention to introduce the amine
functionality and synthesis of the derivatives as illustrated in
Scheme 4. It is well known that introduction of NH functionality
into organic molecules can often dramatically change their physi-
cal and chemical properties.13 In addition, extension and branching
of the hydrocarbon chain may affect their bioactivity. Thus, we
synthesized a series of (1R,2S)-3-(substituted amino)-1-(4-meth-
oxybenzo[a][1,3]dioxol-6-yl) propan-1,2-diol14 derivatives 19–27
by introducing the aliphatic amines, aromatic amines, and hetero-
aromatic amines, respectively.
2.1.3. Synthesis of neohelmanticins A–D
The synthesis of neohelmanticins A–D commenced from epox-
ide 4, in which the hydroxyl group was protected as a THP ether,9
and the resultant epoxy THP ether 13 was subjected to ring open-
ing with LAH8 to furnish 14, in an overall yield of 91% (Scheme 3).
Compound 14 was converted to tiglate ester 15 through reaction
with tiglic acid in the presence of EDCI and DMAP in pyridine10
in 90% yield. Upon treatment of 15 with AD-mix-a in (1:1) aqueous
t-BuOH at 2–5 °C, highly stereoselective dihydroxylation2 occurred
to give the threo isomer diol 16 in 97% yield, which was further
esterified with the corresponding acid derivatives in the presence
of EDCI and DMAP in pyridine10 to afford 17a–17d in quantitative
yield. Finally, deprotection of the THP group,11 followed by the
esterification with angelic acid afforded the neohelmanticins
A–D, 1a–1d.12
3. Biological activity
All of the synthesized derivatives were tested in vitro against a
panel of cancer cell lines. The cell lines used for this study are the
colon cancer (colo-205), skin cancer (A-431), breast cancer (MCF-
7), and lung cancer (A-549).15 To our disappointment, introduction
of the amine moiety at C-9 was not a good site to modify since
none of the derivatives showed any activity. The lack of activity
of synthetic derivatives cannot be explained simply by reaction
mechanism. The binding affinity or selectivity of the structures of
2.1.4. Synthesis of 1,2-dihydroxyphenyl propanoid derivatives
In prior studies, it has been reported that the neohelmanticins
could increase their cytotoxic activity in comparison with their
O
O
OR
OH
OH
OH
O
O
O
O
O
O
O
O
O
O
OH
O
O
O
OH
OH
2
3
1a-1d
O
O
OH
O
O
HO
HO
O
OH
O
O
OH
OH
O
5
4
6
Scheme 1. Retrosynthetic analysis of neohelmanticins A–D.

442
E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
OH
OH
O
O
HO
HO
HO
HO
a
c
b
OH
O
O
HO
O
O
O
6
7
8
O
O
O
O
O
O
O
O
O
d
f
e
O
O
OH
O
11
10
9
O
O
O
O
O
O
O
h
O
O
OH
O
O
g
+
O
O
OH
OH
OH
OH
2
4
5
12
Scheme 2. Reagents and conditions: (a) SOCl2, CH3OH, reflux, 2–4 h, 90%; (b) K2CO3, CuO, CH2I2, DMF, 130 °C, 5 h, 60%; (c) (CH3)2SO4, NaOH, EtOH, reflux, 5 h, 87%; (d) LAH,
THF, 0 °C to 30 °C, 30 min, 96%; (e) (CO)2Cl2, DMSO, TEA, DCM, ꢀ78 °C, 1 h, 96%; (f) CH2CHMgBr, THF, 0 °C to rt, 15 min, 98%; (g) (ꢀ)-DIPT 0.6 equiv, Ti(OiPr)4 0.5 equiv,
cumene hydroperoxide, 0.6 equiv, DCM, ꢀ20 °C, 12 h, 4 (47%), 12 (48%); (h) LAH, THF, 0 °C to rt, 3 h, 92%.
the compounds to the reactive site of the target (enzyme) must
play a key role. At this point, it may be that the esterification of
the hydroxyl groups remains the optimum functional group to ex-
hibit activity. These early conclusions point the way for further
more focused studies aiming at the design and synthesis of the
more potent and selective analogues as biological tools and poten-
tial drug candidates.
recorded on Bruker 300 MHz spectrometers, with tetramethylsil-
ane as an internal standard, using CDCl3. The chemical shifts are
expressed as d values in parts per million (ppm) and the coupling
constants (J) are given in hertz (Hz). Yields were of purified com-
pounds and were not optimized. Optical rotations were measured
with JASCO DIP 300 digital polarimeter at 25 °C.
5.1.1. Methyl 3,4,5-trihydroxybenzoate 7
To a solution of the gallic acid 6 (4.000 g, 23.53 mmol) in MeOH
(30 mL) at room temperature was slowly added thionyl chloride
(2 mL) dropwise at 0 °C. The mixture was refluxed at 65 °C for
4 h. The mixture was cooled to room temperature and solvent
was evaporated to dryness. The resulting residue was dissolved
in DCM, washed with saturated NaHCO3 solution, and dried
(Na2SO4). Removal of the solvent afforded the crude product,
which was purified by silica gel column chromatography eluting
with CHCl3–acetone (80:20) to give 7 (90%) as a colorless syrupy
oil. 1H NMR (300 MHz, acetone-d6): d 3.88 (s, 3H), 7.15 (d, 1H,
J = 1.5 Hz), 7.32 (d, 1H, J = 1.5 Hz); HREIMS: m/z [M]+ found
184.0351; calcd 184.0372 for C8H8O5.
4. Conclusion
In conclusion, we have described first total synthesis of neohel-
manticins A–D comprising the construction of the dihydroxy-
phenyl propane core 2 and esterification with the appropriate
acids of the core skeleton of the neohelmanticins. In addition, we
also demonstrated the synthesis and biological evaluation of dihy-
droxy phenyl propane derivatives 19–27. Although compounds
with improved cytotoxic activity have not yet been found, this laid
a solid foundation for the further lead optimization of the deriva-
tives by the systematic modifications. Efforts aimed to prepare
the potent analogues are underway in our group.
5. Experimental
5.1. General
5.1.2. Methyl 3,4-methylenedioxy,5-hydroxy benzoate 8
To a solution of 7 (3.000 g, 16.30 mmol) in dry DMF (25 mL)
were added sequentially CH2I2 (5.460 g, 20.40 mmol), CuO
(0.340 g, 4.27 mmol), and K2CO3 (4.750 g, 34.36 mmol). The reac-
tion mixture was stirred at 130 °C for 5 h. After completion of
the reaction, the mixture was cooled to room temperature, K2CO3
was removed by filtration, and DMF was removed by vacuum dis-
tillation. Then, water (30 mL) was added to the residue and ex-
tracted with EtOAc (2 ꢁ 100 mL). The combined organic layers
All commercially available reagents were used without further
purification unless otherwise stated. The solvents used were all
of AR grade and were distilled under a positive pressure of dry
nitrogen atmosphere where necessary. All reactions were per-
formed in pre-dried apparatus under an atmosphere of nitrogen
unless otherwise stated. The progress of the reactions was moni-
tored by analytical thin-layer chromatography (TLC) performed
on Merck Silica Gel 60 F254 plates. Visualization was performed
with 5% methanolic H2SO4 solution followed by heating. Column
chromatography was carried out using silica gel 60–120 mesh
(Qingdao Marine Chemical, China). High-resolution spectra were
obtained on LC-MSD-Trap-SL instrument. NMR spectra were
were washed with aqueous HCl, saturated NaHCO3
solution, brine,
dried over Na2SO4, and evaporated under vacuum. The crude prod-
uct was purified by silica gel column chromatography using hex-
ane–EtOAc (85:15) as eluent to give 8 (60%) as a pale yellow
colored liquid. 1H NMR (300 MHz, CDCl3): d 3.88 (s, 3H), 6.06 (s,
2H), 7.15 (d, 1H, J = 1.5 Hz), 7.32 (d, 1H, J = 1.5 Hz); 13C NMR
(75 MHz, CDCl3): d 170.2, 150.4, 143.4, 136.7, 134.6, 102.8, 101.6,

E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
443
O
O
O
O
O
O
O
O
O
O
O
O
OH
O
a
c
O
O
O
b
O
O
O
OH
O
O
O
13
4
14
15
O
O
OR
OH
O
O
O
OR
O
O
O
OH
OH
O
O
O
O
O
O
O
OH
f
d
e
O
O
OH
O
O
17a-17d
18a-18d
16
18a. R = angeloyl
18b
18c. R = hexanoyl
18d. R = butanoyl
17a. R = angeloyl
17b
17c. R = hexanoyl
17d. R = butanoyl
. R = octanoyl
. R = octanoyl
O
(neohelmanticin A)
(neohelmanticin B)
O
O
OR
OH
1a. R =
1b. R =
O
O
g
O
O
O
O
1c. R =
1d. R =
O
O
(neohelmanticin C)
(neohelmanticin D)
1a-1d
Scheme 3. Reagents and conditions: (a) CSA, DHP, DCM, rt, 5 h, 96%; (b) LAH, THF, 0 °C to rt, 3 h, 91%; (c) tiglic acid, EDCI, DMAP, Py, rt, 16 h, 90%; (d) AD-mix-a, CH3SO2NH2,
(CH3)3COH–H2O; 1:1, 2–5 °C, 24 h, 97%; (e) angelic acid for a, octanoic acid for b, hexanoic acid for c, n-butyric acid for d, EDCI, DMAP, Py, rt, 16 h, 90% for 17a, 95% for 17b,
92% for 17c, 92% for 17d, 16 h;(f) CSA, CH3OH, rt, 12 h, 90% for 18a, 92% for 18b, 90% for 18c, 90% for 18d; (g) angelic acid, EDCI, DMAP, Py, rt, 16 h, 90% for 1a, 92% for 1b, 85%
for 1c, 80% for 1d.
101.6, 52.1; HREIMS m/z [M]+ found 196.0384; calcd 196.0372 for
C9H8O5.
15 min at room temperature, dimethyl sulfate (1.175 g,
9.33 mmol) was added dropwise and reaction mixture was allowed
to reflux for 5 h. After completion of the reaction, ethanol was con-
centrated to dryness. Then water (30 mL) was added and extracted
with EtOAc (2 ꢁ 30 mL). The combined organic layers were dried
and evaporated. The product was purified by column chromatogra-
phy using 10% ethyl acetate in hexane as eluent to give 9 (87%) as
5.1.3. Methyl 3,4-methylenedioxy,5-methoxy benzoate 9
To a solution of 8 (0.913 g, 4.66 mmol) in ethanol (15 mL) at
0 °C temperature under nitrogen was slowly added a solution of
NaOH (0.373 g, 9.33 mmol) in EtOH. After being stirred for
O
O
O
R1
R2
O
NH
OH R1
O
MeOH, Reflux,
12 h, 80-90%
N
R2
O
O
OH
OH
19-27
4
1
2
19
. R = R = Ethyl
20. R1 = H, R2 = n-Propyl
1
2
21
. R = H, R = Isobutyl
22. R1 = H, R2 = p-Methoxy benzyl
23. R1 = H, R2 = m-Triflouromethyl benzyl
1
2
24
. R = H, R = p-Triflouromethyl benzyl
25. R1 = H, R2 = Mercaptobenzamidazolyl
1
2
26
. R = H, R = 3-Amino-5-mercapto-1,2,4,-triazolyl
27. R1 = H, R2 = 2-Amino-5-mercapto1,3,4-thia-diazolyl
Scheme 4. Synthesis of dihydroxy phenyl propane derivatives.

444
E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
an oil. 1H NMR (300 MHz, CDCl3): d 3.89 (s, 3H), 3.94 (s, 3H), 6.06
(s, 2H), 7.21 (d, 1H, J = 1.5 Hz), 7.33 (d, 1H, J = 1.5 Hz); 13C NMR
(75 MHz, CDCl3): d 172.0, 149.8, 143.2, 135.8, 134.6, 105.6, 102.6,
101.6, 58.8, 52.1; HREIMS m/z [M]+ found 210.0562; calcd
210.0528 for C10H10O5.
dropwise. The reaction mixture was allowed to stir for 12 h. The
reaction was quenched by a solution containing 1.7 g of NaOH dis-
solved in 17 mL of saturated NaCl at 0 °C and continued to stir for 3
hours at rt. Then, 17 g of Na2SO4 and 2 g of Celite were added and
stirring was continued for 15 min, and this mixture was filtered
through Celite. The filtrate was concentrated. The product was
purified by silica gel column chromatography using hexane–EtOAc
(90:10) as eluent to give 12 (48%) and using hexane–EtOAc (75:25)
5.1.4. 3,4-Methylenedioxy,5-methoxy benzyl alcohol 10
To a solution of lithium aluminum hydride (0.070 g, 1.90 mmol)
in dry THF (5 mL) was slowly added a solution of 9 (0.200 g,
0.95 mmol) in dry THF at 0 °C. The reaction mixture was allowed
to stir at room temperature for 30 min. After completion of the
reaction (TLC), aqueous saturated NH4Cl solution (5 mL) was added
at 0 °C and stirred for additional 15 min. The reaction mixture was
filtered through Celite and extracted with EtOAc (2 ꢁ 10 mL). The
combined organic layers were dried (Na2SO4) and evaporated to af-
ford crude product, which was purified by silica gel column chro-
matography using hexane–EtOAc (80:20) as eluent to give 10
(96%) as an oil. 1H NMR (300 MHz, CDCl3): d 3.91 (s, 3H), 4.59 (d,
2H, J = 5.4 Hz), 5.97 (s, 2H), 6.56 (s, 1H), 6.57 (s, 1H); HREIMS m/z
[M]+ found 182.0621; calcd 182.0579 for C9H10O4.
as eluent to give 4 (47%) as a syrupy liquid. ½a D25
¼ ꢀ25:6 (c 3.75,
ꢂ
CHCl3); 1H NMR (300 MHz, CDCl3) d 2.76–2.79 (m, 1H), 2.95 (q,
1H, J = 2.7 Hz), 3.18–3.21 (m, 1H), 3.92 (s, 3H), 4.83 (d, 1H,
J = 2.7 Hz), 5.98 (s, 2H), 6.59 (s, 2H); 13C NMR (75 MHz, CDCl3):
149.0, 143.4, 134.8, 132.6, 107.6, 102.1, 101.6, 77.6, 66.2, 63.4,
58.0; HREIMS m/z [M]+ found 224.0664; calcd 224.0685 for
C11H12O5.
5.1.8. (1R,2S)-1-(3,4-Methylenedioxy,5-methoxy phenyl)propane
1,2-diol 2
To a solution of lithium aluminum hydride (0.969 g, 0.002
mmol) in dry THF (5 mL) under nitrogen atmosphere at 0 °C was
slowly added a solution of 4 (0.05 g, 0.22 mmol) in dry THF. The
reaction mixture was allowed to stir for 3 h at room temperature.
After completion, the reaction was quenched with saturated NH4Cl
solution and allowed to stir for an additional 15 min. The reaction
mixture was filtered through Celite and the filtrate was extracted
with EtOAc (2x20 mL). The combined organic layer was dried and
evaporated to get crude product, which was purified by silica gel
column chromatography using hexane–EtOAc (80:20) as eluent
5.1.5. Preparation of myristicinaldehyde 11
To a solution of oxalyl chloride (2.013 g, 15.85 mmol) in dry
DCM (15 mL) at ꢀ78 °C under inert atmosphere was added
dimethylsulfoxide (2.474 g, 31.71 mmol) dropwise. After being
stirred at ꢀ78 °C for 15 min, a solution of 10 (1.924 g, 10.57 mmol)
in dry DCM (5 mL) was added dropwise and allowed to stir for
30 min. Then, triethylamine (7.474 g, 74.00 mmol) was added
and allowed to stir for 15 min, the reaction mixture was brought
to room temperature and the reaction was quenched with water
(40 mL). The organic layer was washed with brine, dried over so-
dium sulfate, and solvent was evaporated to dryness. The crude
product was purified by silica gel column chromatography using
hexane–EtOAc (90:10) as eluent to give 11 (96%) as an amorphous
to give 2 (92%) as an oil. ½a D25
¼ ꢀ16:6 (c 0.16, CHCl3), (reported
ꢂ
½
a 2D5
ꢂ
¼ ꢀ23 (c 0.62, CHCl3), 1H NMR (300 MHz, CDCl3): d 1.11 (d,
3H, J = 6.6 Hz), 3.90 (s, 3H), 3.95 (dq, 1H, J = 6.6, 4.5 Hz), 4.55 (d,
1H, J = 4.5 Hz), 5.97 (s, 2H), 6.56 (s, 2H); 13C NMR (75 MHz, CDCl3):
d 149.1, 143.7, 135.3, 134.9, 106.0, 101.5, 101.0, 77.5, 72.2, 56.8,
17.6; HREIMS m/z [M]+ found 226.0824; calcd 226.0841 for
C11H14O5.
solid. IR (KBr), 3430, 2922, 1694, 1627, 1508 cmꢀ1 1H NMR
;
(300 MHz, CDCl3): d 3.97 (s, 3H), 6.11 (s, 2H), 7.05 (d, 1H,
J = 1.5 Hz), 7.14 (d, 1H, J = 1.5 Hz), 9.79 (s, 1H); HREIMS m/z [M]+
found 180.0460; calcd 180.0423 for C9H8O4.
5.1.9. 4-Methoxy-6-((R)-((S)-oxiran-2-yl)(tetrahydro-2H-pyran-
2-yloxy)methyl) benzo[d][1,3]dioxole 13
To a solution of 4 (0.050 g, 0.22 mmol) in dry DCM (2 mL) at 0 °C
was added camphorsulfonic acid (0.005 g, 0.002 mmol). After
being stirred for 5 min, dihydropyran (DHP) (0.022 g, 0.27 mmol)
was added and the reaction mixture was allowed to stir for 5 h
at room temperature. The reaction was quenched with aqueous
saturated NaHCO3 solution (20 mL) and stirred for an additional
10 min. and the aqueous layer was extracted with DCM (2 ꢁ
10 mL). The combined organic layers were dried over sodium
sulfate and evaporated to give 13 (96%) as a colorless liquid.
5.1.6. 1-(3,4-Methylenedioxy,5-methoxy phenyl) prop-2-en-1-
ol 5
To a solution of myristicinaldehyde 11 (2.736 g, 15.20 mmol) in
dry THF (30 mL) under nitrogen atmosphere at 0 °C was added vi-
nyl magnesium bromide (6.72 mL of 1 M solution in THF) drop-
wise. The reaction mixture was allowed to stir for 15 min at
room temperature. After completion (TLC), the reaction was
quenched with saturated NH4Cl solution at 0 °C and extracted with
EtOAc (2 ꢁ 50 mL). The combined organic layers were washed with
brine, dried over Na2SO4, and solvent was evaporated to dryness.
The crude product was purified by column chromatography using
hexane–EtOAc (90:10) as eluent to give 5 (98%) as a gummy liquid.
IR (KBr), 3417, 2978, 1892, 2780, 1634, 1507, 1130, 1195 cmꢀ1; 1H
NMR (300 MHz, CDCl3) d 3.90 (s, 3H), 5.10 (d, 1H, J = 6.0 Hz), 5.18–
5.20 (m, 1H), 5.34 (dd, 1H, J = 12 Hz, J = 8 Hz), 5.94–6.10 (m, 1H,),
5.96 (s, 2H), 6.56 (d, 1H, J = 1.2 Hz), 6.57 (d, 1H, J = 1.2 Hz).
½
a 2D5
ꢂ
¼ ꢀ26:2 (c 0.70, CHCl3) 1H NMR (300 MHz, CDCl3) d 1.6–
1.80 (m, 6H), 2.70–2.81 (m, 2H), 3.06–3.12 (m,1H), 3.6–3.7 (m,
1H), 3.90 (s, 1H), 3.92 (s, 3H), 4.50–4.53 (m, 1H), 4.73–4.76 (m,
1H), 5.96 (s, 2H), 6.52–6.54 (m, 2H). 13C NMR (75 MHz, CDCl3):
d150.0, 142.6, 134.6, 131.9, 106.9, 104.0,102.0, 101.6, 78.4, 76.2,
74.4, 58.0, 58.0, 31.0, 25.8, 21.5; HRESIMS m/z [M]+ found
308.1256; calcd 308.1260 for C16H20O6.
5.1.10. (1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-yl)-1-
(tetrahydro-2H-pyran-2-yloxy)propan-2-ol 14
5.1.7. (R)-(3,4-Methylenedioxy,5-methoxy phenyl)((S)-oxiran-
2-yl) methanol 4 and (R)-1-(4-methoxybenzo[d][1,3]dioxol-6-
yl)prop-2-en-1-ol 12
To a stirred solution of evacuated flame dried powdered 4 Å
molecular sieves (5 g) and (ꢀ)-DIPT (1.091 g, 4.66 mmol) in DCM
(25 mL) was added slowly Ti(iOPr)4 (1.103 g, 3.88 mmol) at
ꢀ20 °C. Subsequently, the mixture was allowed to stir for 20 min
then cumene hydroperoxide (0.717 g, 4.65 mmol) was added at
the same temperature. After being stirred for 20 min, a solution
of compound 5 (1.615 g, 7.76 mmol) in DCM (5 mL) was added
To a solution of lithium aluminum hydride (0.034 g, 0.92 mmol)
in dry THF (3 mL) at 0 °C was slowly added a solution of 13
(0.950 g, 0.30 mmol) in THF (0.5 mL) dropwise. After being stirred
for 3 h at room temperature, reaction was quenched with aqueous
saturated NH4Cl solution at 0 °C and allowed to stir for an addi-
tional 15 min. The reaction mixture was filtered through Celite
and extracted with EtOAc (2 ꢁ 20 mL). The combined organic lay-
ers were dried and evaporated to dryness. The product was puri-
fied by column chromatography using hexane–EtOAc (75:25) as

E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
445
eluent to give 14 (91%) as a colorless oil. ½a D25
ꢂ
¼ ꢀ32:6 (c 0.9, CHCl3)
was concentrated to remove pyridine. The reaction was quenched
with aqueous 1 N HCl and was extracted with DCM (2 ꢁ 20 mL).
The combined organic layers were washed with brine, dried
(Na2SO4), and evaporated to dryness. The product was purified
by column chromatography using hexane–EtOAc (85:15) as eluent
to give 17a–17d.
1H NMR (300 MHz, CDCl3) d 1.16 (d, 3H, J = 6.7 Hz), 1.58–1.60 (m,
6H), 3.49–3.58 (m, 1H), 3.92 (s, 3H), 3.93–3.96 (m, 2H), 4.48–
4.51 (m, 2H), 5.98 (s, 2H), 6.48 (d, 1H, J = 1.5 Hz), 6.52 (d, 1H,
J = 1.5 Hz). 13C NMR (75 MHz, CDCl3): d 149.8, 142.0, 133.9,
132.0, 107.0, 104.6, 102.0, 101.6, 78.1, 77.6, 57.9, 57.8, 30.9, 25.9,
21.6, 16.9; HRESIMS m/z [M]+ found 310.1424; calcd 310.1416
for C16H22O6.
5.2.1. (Z)-(2S,3R)-3-(((1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-
6-yl)-1-(tetrahydro-2H-pyran-2-yloxy)propan-2-yloxy)carbonyl)-
3-hydroxybutan-2-yl2-methylbut-2-enoate 17a
5.1.11. (E)-(1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-yl)-1-
(tetrahydro-2H-pyran-2-yloxy)propan-2-yl 2-methylbut-2-
enoate 15
Syrupy liquid, yield 90%; IR (KBr): 3450, 2941, 1733, 1644, 1526,
1258, 1025 cmꢀ1; ½a D25
ꢂ
¼ ꢀ12:0 (c 0.3, CHCl3); 1H NMR (300 MHz,
To a solution of tiglic acid (0.050 g, 0.50 mmol) in pyridine
(5 mL) were added EDCI (0.099 g, 0.33 mmol) and DMAP (0.004 g,
0.03 mmol) at 0 °C. The resultant white cloudy suspension was
brought to room temperature and stirred until EDCI completely
dissolved. Then, a solution of 14 (0.052 g, 0.17 mmol) in pyridine
was added dropwise. After being stirred for 16 h, the reaction mix-
ture was concentrated to remove pyridine, aqueous 1 N HCl was
added and extracted with DCM (2 ꢁ 10 mL). The combined organic
layers were washed with brine, dried, and evaporated. The product
was purified by column chromatography using hexane–EtOAc
CDCl3): d 1.12 (d, 3H, J = 6.4 Hz), 1.40–1.30 (m, 8H), 1.60–1.50
(m, 4H), 1.88 (q, 3H, J = 4 Hz), 3.27–3.37 (m, 1H), 3.45–3.56 (m,
1H), 3.88 (s,1H), 3.90 (s, 3H), 4.45, 4.53 (t, 1H, J = 2.8 Hz), 4.58
(dd, 1H, J = 4.7 Hz, 2.8 Hz), 4.99–5.10 (m, 2H), 5.94 (s, 2H), 6.45
(d, 1H, J = 1.1 Hz), 6.47 (d, 1H, J = 1.1 Hz), 6.51 (d, 1H, J = 1.1 Hz),
6.55 (d, 1H, J = 1.13 Hz), 6.82–6.93 (m, 1H). 13C NMR (75 MHz,
CDCl3): d 174.2, 168.4, 147.6, 144.3, 137.4, 134.6, 134.6, 126. 8,
107.6, 102.9, 101.6, 101.4, 82.6, 74.6, 74.8, 72.8, 64.4, 56.8, 32.8,
25.4, 21.6, 21.0, 18.4, 16.1, 16.4, 15.9; HRESIMS m/z [M]+ found
508.2342; calcd 508.2308 for C26H36O10
.
(85:15) as eluent to give 15 (90%) as a colorless oil. ½a D25
¼ ꢀ8:8
ꢂ
(c 1.1, CHCl3) 1H NMR (300 MHz, CDCl3):
d
1.16 (d, 3H,
5.2.2. (2S,3R)-3-(((1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-
yl)-1-(tetrahydro-2H-pyran-2-yloxy)propan-2-yloxy)carbonyl)-
3-hydroxybutan-2-yl octanoate 17b
J = 6.4 Hz), 1.31 (d, 3H, J = 6.4 Hz), 1.42–1.69 (m, 6 H), 1.82 (d,
3H, J = 6.4 Hz), 3.31–3.40, 3.44–3.53 (m, 1H), 3.88 (s, 1H) 3.90 (s,
3H), 4.51, 4.92 (t, 1H, J = 3.02 Hz), 4.65 (dd, 1H, J = 5.2 Hz), 5.16–
5.00 (m,1H), 5.95 (s, 2H), 6.49 (d, 1H, J = 1.3 Hz), 6.52 (d, 1H, J
=1.3 Hz), 6.57–6.62 (m, 1H); 13C NMR (75 MHz, CDCl3): d 168.8,
148.3, 143.8, 138.4, 136.2, 133.0, 125.6, 105.0, 103.8, 102.6,
101.0, 78.5, 72.1, 62.8, 57.6, 30.9, 25.80, 21.7, 21.0, 16.8, 15.8; HRE-
SIMS m/z [M]+ found 392.1827; calcd 392.1835 for C21H8O7.
Liquid, yield 95%; IR (KBr), 3464, 2926, 1734, 1642, 1546, 1250,
1124 cmꢀ1; ½a 2D5
ꢂ
¼ ꢀ10:15 (c 0.5, CHCl3); 1H NMR (300 MHz,
CDCl3): d 0.93 (t, 3H, J = 7.4 Hz), 1.11 (s, 3H), 1.17 (d, 3H,
J = 6.4 Hz), 1.20 (d, 3H, J = 6.8 Hz), 1.28–1.40 (m, 6H), 1.60–1.80
(m, 8H), 1.8–2.0 (m, 2H), 2.0–2.3 (m, 2H), 3.20 (br s, 1H), 3.30–
3.38, 3.48–3.57 (m, 1H), 3.94 (s, 3H), 4.48 (t, 1H, J = 2.8 Hz), 4.60
(dd, 1H, J = 6 Hz, 4 Hz), 5.10–5.18 (m, 2H), 5.94 (s, 2H), 6.54 (d,
1H, J = 1.8 Hz), 6.48 (d, 1H, J = 1.5 Hz); 13C NMR (75 MHz, CDCl3):
d 174.2, 172.3, 148.7, 143.3, 135.2, 132.4, 107.6, 103.6, 102.0,
101.3, 81.6, 74.8, 73.9, 73.6, 62.9, 56.2, 35.6, 32.0, 25.6, 21.5,
18.5, 19.0, 16.5, 16.2, 16.1, 15.9, 14.3; HRESIMS m/z [M]+ found
5.1.12. (2R,3S)-(1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-yl)-
1-(tetrahydro-2H-pyran-2-yloxy)propan-2-yl 2,3-dihydroxy-2-
methylbutanoate 16
To a solution of compound 15 (0.038 g, 0.09 mmol) in 2 mL of
tert-butyl alcohol–water (1:1) were added AD-mix-
a
(0.136 g)
552.2890; calcd 552.2934 for C29H44O10.
and CH3SO2NH2 (0.09 mmol) at room temperature. The mixture
was allowed to stir for 24 h at 2–5 °C. The reaction was quenched
with sodium sulfite (0.14 g) and the mixture was continued to stir
for additional 30 min. The mixture was extracted with ethyl ace-
tate (3 ꢁ 20 mL) and the combined organic layers were dried and
concentrated to afford the crude product. The product was purified
by column chromatography over silica gel using hexane–EtOAc
(65:35) as an eluent to give 16 (97%) as an oil. IR (KBr), 3455,
5.2.3. (2S,3R)-3-(((1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-
yl)-1-(tetrahydro-2H-pyran-2-yloxy)propan-2-yloxy)carbonyl)-
3-hydroxybutan-2-yl hexanoate 17c
Liquid, yield 92%; IR (KBr), 3456, 2921, 1730, 1642, 1528, 1236,
1026 cmꢀ1; ½a 2D5
ꢂ
¼ ꢀ13:3 (c 0.6, CHCl3); 1H NMR (300 MHz, CDCl3):
d 0.93 (t, 3H, J = 7.4 Hz), 1.14 (s, 3H), 1.18 (d, 3H, J = 6.6 Hz), 1.20 (d,
3H, J = 6.8 Hz), 1.30–1.48 (m, 4H), 1.74–1.86 (m, 4H), 2.10–2.20 (m,
2H), 3.20 (br s,1H), 3.28–3.30, 3.48–3.60 (m, 1H), 3.94 (s, 3H), 4.48
(t, 1H, J = 2.8 Hz), 4.58 (dd, 1H, J = 6.4 Hz, 4 Hz), 5.08–5.23 (m, 2H),
5.90 (s, 2H), 6.56 (d, 1H, J = 1.8 Hz), 6.48 (d, 1H, J = 1.5 Hz); 13C NMR
(75 MHz, CDCl3): d 175.0, 167.9, 147.7, 144.5, 138.0, 134.8, 134.7,
126.9, 108.0, 102.8, 101.6, 101.8, 82.6, 74.7, 74.9, 72.9, 64.6, 56.9,
32.8, 25.4, 21.8, 21.2, 18.6, 16.2,16.6, 16.0,16.1, 15.8, 14.2. HRESIMS
2941, 1731, 1635, 1508, 1258, 1025 cmꢀ1; ½a D25
¼ ꢀ28:5 (c 7.5,
ꢂ
CHCl3); 1H NMR (300 MHz, CDCl3) d 1.17 (d, 3H, J = 5.2 Hz), 1.20
(d, 3H, J = 5.2 Hz), 1.22 (s, 3H), 1.57–1.62 (m, 6H), 3.49–3.51 (m,
1H), 3.89 (s, 2H), 3.91 (s, 3H), 4.67–4.72 (m, 1H), 4.91–4.93 (m,
1H), 5.15–5.18 (m, 1H), 5.95 (s, 2H), 6.49 (d, 1H, J = 3.7 Hz), 6.57
(d, 1H, J = 3.7 Hz). 13C NMR (75 MHz, CDCl3): d 175.8, 149.3,
143.8, 135.4, 132.9, 107.8, 104.0, 102.0, 101.9, 78.5, 76.9, 75.3,
72.0, 62.8, 57.0, 30.9, 25.8, 21.7, 16.9, 16.0, 14.5; ESIMS: m/z 427
(M++1); HRESIMS m/z [M]+ found 426.1862; calcd 426.189 for
C21H30O9.
m/z [M]+ found 524.2610; calcd 524.2621 for C27H40O10
.
5.2.4. (2S,3R)-3-(((1R,2S)-1-(4-Methoxybenzo[d][1,3]dioxol-6-
yl)-1-(tetrahydro-2H-pyran-2-yloxy)propan-2-yloxy)carbonyl)-
3-hydroxybutan-2-yl-butanoate 17d
5.2. General procedure for the preparation of compounds 17a–
17d
Syrupy liquid, yield 92%; IR (KBr), 3500, 3041, 1736, 1638, 1524,
1268, 1084 cmꢀ1; ½a D25
ꢂ
¼ ꢀ11:1 (c 0.4, CHCl3) 1H NMR (300 MHz,
CDCl3): d 0.93 (t, 3H, J = 7.6 Hz), 1.11 (s, 3H), 1.22 (d, 3H,
J = 6.7 Hz), 1.26 (d, 3H, J = 6.7 Hz), 1.20–1.38 (m, 2H), 1.50–1.70
(m, 8H), 2.18–2.30 (m, 2H), 3.22 (br s, 1H), 3.30–3.40, 3.36–3.50
(m,1H), 3.90 (s, 1H), 4.60 (dd, 1H, J = 6.4 Hz), 4.90 (t, 1H,
To a solution of the acid (0.21 mmol) in pyridine were added
EDCI (0.068 g, 0.35 mmol) and DMAP (0.003 g, 0.03 mmol) at
0 °C. The reaction mixture was allowed to stir at room temperature
until EDCI had completely dissolved in the reaction mixture. Then
immediately a solution of compound 16 (0.06 g, 0.14 mmol) in pyr-
idine was added. After being stirred for 16 h, the reaction mixture
J = 2.4 Hz), 5.24–5.00 (m, 2H), 5.98 (s, 2H), 6.56 (d, 1H,
J
=1.91 Hz), 6.48 (d, 1H, J = 1.9 Hz); 13C NMR (75 MHz, CDCl3): d
174.2, 172.3, 148.9, 143.3, 135.0, 132.6, 107.6, 103.5, 101.6,

446
E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
101.4, 81.9, 74.8, 73.8, 73.6, 62.3, 56.6, 36.1, 31.9, 25.4, 21.4, 18.4,
5.08 (m, 1H), 5.10 (q, 1H, J = 6.4 Hz), 5.95 (s, 2H), 6.52 (s, 2H);
13C NMR (75 MHz, CDCl3): d 174.2, 172.3, 148.9, 143.3, 135.0,
132.6, 107.6, 101.6, 101.5, 103.5, 74.8, 73.7, 74.8, 57.0, 21.5, 18.3,
16.4, 15.5, 14.0; HRESIMS m/z [M]+ found 412.1704; calcd
412.1733 for C20H28O9.
18.3, 16.1, 15.7, 14.0; HRESIMS m/z [M]+ found 496.2362; calcd
496.2308 for C25H36O10
.
5.3. General procedure for the preparation of compounds 18a–
18d
5.4. General procedure for the preparation of neohelmanthacins
A–D, 1a–1d
To a solution of compounds 17a–17d (0.10 mmol) in MeOH
(2 mL) at 0 °C was added slowly CSA (0.005 g, 0.002 mmol). After
addition, the ice bath was removed and the reaction mixture was
allowed to stir for 12 h at room temperature. The reaction mixture
was concentrated to remove MeOH; aqueous saturated NaHCO3
solution (20 mL) was added and stirred for an additional 10 min.
The aqueous layer was extracted with DCM (2 ꢁ 20 mL). The com-
bined organic layers were washed with water, dried, and concen-
trated to afford compounds 18a–18d.
To a solution of angelic acid (0.029 g, 0.29 mmol) in pyridine at
0 °C was added a mixture of EDCI (0.028 g, 0.15 mmol) and DMAP
(0.002 g, 0.01 mmol). After addition, the ice bath was removed and
the reaction mixture was allowed to stir at room temperature until
EDCI completely dissolved. Then, a solution of compounds 18a–
18d (0.06 mmol) in pyridine was added. After being stirred for
16 h, the reaction mixture was concentrated to remove pyridine.
The reaction was quenched with aqueous 1 N HCl and aqueous
layer was extracted with DCM (2 ꢁ 20 mL). The combined organic
layers were washed with brine, dried, and evaporated to dryness.
The product was purified by column chromatography using hex-
ane–EtOAc as eluent to give 1a–1d (80–92%). All the data matched
exactly with the literature.2
5.3.1. (Z)-(2S,3R)-3-(((1R,2S)-1-Hydroxy-1-(4-methoxybenzo[d]-
[1,3]dioxol-6-yl)propan-2-yloxy)carbonyl)-3-hydroxybutan-2-yl
2-methylbut-2-enoate 18a
Oil, yield 90%; [
a]
D = ꢀ23.1 (c 1.5, CHCl3), IR (KBr), 3450, 2940,
1736, 1635, 1508, 1256, 1025 cmꢀ1
;
1H NMR (300 MHz, CDCl3): d
1.09 (d, 3H, J = 6.2 Hz), 1.22 (s, 3H), 1.27 (d, 3H, J = 6.4 Hz), 3.20
(br s, 1H), 3.90 (s, 3H), 4.64 (d, 1H, J = 5.0 Hz), 4.92–5.02 (m, 1H),
5.13 (q, 1H, J = 6.4 Hz), 5.95 (s, 2H), 6.51 (s, 2H), 6.84–6.74 (m,
1H); 13C NMR (75 MHz, CDCl3): d 176.4, 168.4, 164.5, 150.0,
144.0, 135.6, 133.1, 124.8, 108.0, 103.0, 101.9, 76.2, 75.6, 73.8,
72.4, 71.1, 57.1, 20.2,18.4, 16.2, 15.8, 14.5; HRESIMS m/z [M]+
found 424.1730; calcd 424.1733 for C21H28O9.
5.4.1. Neohelmanticin A 1a
Oil, yield 90%; [
a
]
D = ꢀ25.5 (c 1.65, CHCl3), (reported [ D = ꢀ25
a]
(c 0.37, CHCl3)); 1H NMR (300 MHz, CDCl3): d 1.19 (d, 3H, J = 6.2 Hz),
1.22 (s, 3H), 1.27 (d, 3H, J = 6.4 Hz), 1.82 (q, 3H, J = 1.8 Hz), 1.85
(s, 3H), 3.20 (br s, OH), 3.90 (s, 3H), 4.64 (d, 1H, J = 5.0 Hz), 5.08
(q, 1H, J = 6.4 Hz), 5.12–5.20 (m, 1H), 5.86 (d, 1H, J = 4.8 Hz), 5.98
(q, 1H, J = 7.0, 1.5 Hz), 5.95 (s, 2H), 6.21 (q, 1H, J = 7.6 Hz), 6.51 (s,
2H), 6.1–6.3 (m, 1H); HRESIMS m/z [M]+ found 506.2146; calcd
5.3.2. (2S,3R)-3-(((1R,2S)-1-Hydroxy-1-(4-methoxybenzo[d][1,3]-
dioxol-6-yl)propan-2-yloxy)carbonyl)-3-hydroxybutan-2-yl
octanoate 18b
506.2152 for C26H34O10
.
Syrupy liquid, yield 92%; [
a
]
D = ꢀ22.1 (c 1.2, CHCl3), IR (KBr),
5.4.2. Neohelmanticin B 1b
Oil, yield 92%; [
D = ꢀ22.0 (c 0.1, CHCl3), (reported [
(c 0.096, CHCl3); 1H NMR (300 MHz, CDCl3):
3H, J = 7.5 Hz), 1.18 (d, 3H, J = 6.4 Hz), 1.24 (s, 3H), 1.22 (d, 3H,
J = 6.4 Hz), 1.33–1.38 (m, 2H), 1.48–1.60 (m, 4H), 1.92 (q, 3H,
J = 1.5 Hz), 1.76–2.24 (m, 6H), 2.36 (br s, 1H), 3.17 (br s, 1H),
3.94 (s, 3H), 4.60 (d, 1H, J = 4.8 Hz), 4.98–5.02 (m, 1H), 5.16 (q,
1H, J = 6.4 Hz), 5.88 (d, 1H, J = 4.6 Hz), 5.98 (s, 2H), 6.12 (q, 1H,
J = 7.4 Hz), 6.52 (s, 2H); HRESIMS m/z [M]+ found 550.2764; calcd
3436, 2656, 1738, 1642, 1564, 1265, 1084 cmꢀ1
;
1H NMR
a]
a
]
D = ꢀ21
(300 MHz, CDCl3): d 0.93 (t, 3H, J = 7.5 Hz), 1.15 (d, 3H, J = 6.4 Hz),
1.20 (s, 3H), 1.26 (d, 3H, J = 6.4 Hz), 1.33–1.40 (m, 2H), 1.48–1.60
(m, 4H), 1.70–2.21 (m, 4H), 2.36 (br s, 1H), 3.17 (br s, 1H), 3.94 (s,
3H), 4.60 (d, 1H, J = 4.8 Hz), 4.80–4.99 (m, 1H), 5.16 (q, 1H,
J = 6.4 Hz), 5.98 (s, 2H), 6.52 (s, 2H); 13C NMR (75 MHz, CDCl3): d
174.1, 171.9, 148.9, 143.4, 136.0, 132.6, 107.5, 101.4, 102.8, 74.7,
74.8, 73.8, 57.0, 36.1, 18.6, 18.1, 16.2, 16.1, 16.0, 14.1; HRESIMS m/
z [M]+ found 468.2341; calcd 468.2359 for C24H36O9.
d
0.92 (t,
550.2778 for C29H42O10
.
5.3.3. (2S,3R)-3-(((1R,2S)-1-Hydroxy-1-(4-methoxybenzo[d][1,3]-
dioxol-6-yl)propan-2-yloxy)carbonyl)-3-hydroxybutan-2-yl
hexanoate 18c
5.4.3. Neohelmanticin C 1c
Liquid, yield 85%;
[
a
]
D = ꢀ31.1 (c 0.2, CHCl3), (reported
[a]
D = ꢀ32 (c 0.23, CHCl3)); 1H NMR (300 MHz, CDCl3): d 0.93 (t,
Liquid, yield 90%; [
a
]
D = ꢀ28.2 (c 1.5, CHCl3), IR (KBr), 3506,
2984, 1738, 1626, 1584, 1286, 1102 cmꢀ1
;
1H NMR (300 MHz,
3H, J = 7.5 Hz), 1.17 (d, 3H, J = 6.4 Hz), 1.26 (s, 3H), 1.20 (d, 3H,
J = 6.4 Hz), 1.33–1.38 (m, 2H), 1.56–1.58 (m, 4H), 1.91 (q, 3H,
J = 1.5 Hz), 1.76–2.24 (m, 2H), 2.36 (br s, 1H), 3.17 (br s, 1H), 3.94
(s, 3H), 4.60 (d, 1H, J = 4.8 Hz), 5.08–5.12 (m, 1H), 5.16 (q, 1H,
J = 6.42 Hz, 1H), 5.88 (d, 1H, J = 4.6 Hz), 5.98 (s, 2H), 6.16 (q, 1H,
J = 7.4 Hz), 6.53 (s, 2H); HRESIMS m/z [M]+ found 522.2450; calcd
CDCl3): d 0.93 (t, 3H, J = 7.5 Hz), 1.13 (d, 3H, J = 6.4 Hz), 1.24 (s,
3H), 1.26 (d, 3H, J = 6.42 Hz), 1.36–1.38 (m, 2H), 1.40–1.50 (m,
2H), 1.78–2.18 (m, 2H), 2.33 (br s, 1H), 3.20 (br s, 1H), 3.94 (s,
3H), 4.68 (d, 1H, J = 4.6 Hz), 4.88–5.0 (m, 1H), 5.14 (q, 1H,
J = 6.42 Hz), 5.98 (s, 2H), 6.54 (s, 2H); 13C NMR (75 MHz, CDCl3):
d 174.1, 172.0, 148.7, 143.4, 136.1, 132.5, 107.4, 101.4, 103.0,
74.8, 74.7, 73.8, 57.1, 36.1, 18.5, 18.1, 16.1, 16.1, 16.1, 15.8, 14.1;
HRESIMS m/z [M]+ found 440.2024; calcd 440.2046 for C22H32O9.
522.2465 for C27H38O10
.
5.4.4. Neohelmanticin D 1d
Oil, yield 80%; [
D = ꢀ32.0 (c 0.2, CHCl3), (reported [
(c 0.5, CHCl3)); 1H NMR (300 MHz, CDCl3)
0.92 (t, 3H,
a]
a]D = ꢀ33
d
5.3.4. (2S,3R)-3-(((1R,2S)-1-Hydroxy-1-(4-methoxybenzo[d][1,3]-
dioxol-6-yl)propan-2-yloxy)carbonyl)-3-hydroxybutan-2-yl
butanoate 18d
J = 7.5 Hz), 1.17 (d, 3H, J = 6.4 Hz), 1.21 (s, 3H), 1.24 (d, 3H,
J = 6.4 Hz), 1.58–1.70 (m, 2H), 1.94(q, 3H, J = 1.5 Hz), 1.98 (q,
1H, J = 1.5 Hz), 2.08–2.10 (m, 1H), 2.18–2.20 (m, 2H), 2.36 (br
s, 1H), 3.17 (br s,1H), 3.90 (s, 3H), 5.05–5.10 (m, 1H), 5.10 (q,
1H, J = 6.4 Hz), 5.95 (s, 2H), 6.16 (q, 1H, J = 7.5 Hz), 6.52 (s,
2H); HRESIMS m/z [M]+ found 494.2100; calcd 494.2152 for
Oil, yield 90%; [
a
]
D = ꢀ29.1 (c 1.0, CHCl3), IR (KBr), 3484, 2946,
1736, 1636, 1526, 1284, 1032 cmꢀ1
;
1H NMR (300 MHz, CDCl3): d
0.93 (t, 3H, J = 7.5 Hz), 1.17 (d, 3H, J = 6.4 Hz), 1.21 (s, 3H), 1.24
(d, 3H, J = 6.4 Hz), 1.58–1.70 (m, 2H), 2.20–2.30 (m, 2H), 2.36 (br
s, 1H), 3.17 (br s, 1H), 3.90 (s, 3H), 4.66 (d, 1H, J = 4.8 Hz), 4.95–
C25H34O10
.

E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
447
5.5. General procedures for preparation of compounds 19–27
5.5.6. (1R,2S)-3-(4-(Trifluoromethyl)benzylamino)-1-(4-
methoxybenzo[a][1,3]dioxol-6-yl)propane-1,2-diol 24
To a solution of epoxide 4 (0.005 g, 0.22 mmol) in MeOH under
N2 atmosphere was added corresponding amine (0.24 mmol) at
room temperature. Subsequently, the reaction mixture was al-
lowed to reflux for 12 h. After completion of reaction (monitored
by TLC), reaction mixture was cooled to room temperature and sol-
vent was evaporated to dryness. The crude product was purified by
silica gel column chromatography using hexane–EtOAc as eluent to
give the compounds 19–27 in good yields (80–90%).
Yellow oil, yield 80%; [
a
]
D = ꢀ23.1 (c 1.0, CHCl3); 1H NMR
(300 MHz, CDCl3): d 2.63–2.57 (m, 1H), 2.84–2.91 (m, 1H), 3.85–
3.93 (m, 1H), 3.85 (s, 3H), 3.83–3.88 (m, 2H), 4.75 (br s, 1H), 5.93
(s, 2H), 6.50 (d, 2H, J = 3.6 Hz), 7.28 (d, 2H, J = 9.9 Hz), 7.51 (d,
2H, J = 7.8 Hz); 13C NMR (75 MHz, CDCl3): d 149.2, 143.8, 134.9,
134.6, 130.1, 125.5, 105.9, 101.5, 100.2, 75. 3, 71.2, 59.0, 56.7,
54.9; HRESIMS m/z [M]+ found 399.1263; calcd 399.1294 for
C19H20F3NO5.
5.5.7. 1-(2-Mercapto-1H-benzo[d]imidazol-1-yl)-2-(4-methoxy-
benzo[d]dioxol-6-yl)ethane-1,2-diol 25
5.5.1. (1R,2S)-3-(Diethylamino)-1-(4-methoxybenzo[a][1,3]dioxol-
6-yl)propane-1,2-diol 19
Oil, yield 70%; [
a
]
D = ꢀ7.1 (c 0.8, CHCl3), 1H NMR (300 MHz,
Pale yellow liquid, yield 85%; [
a
]
D = ꢀ9.0 (c 0.66, acetone); IR
(KBr), 3330, 2261, 1642, 1614, 1520, 1234, 1022 cmꢀ1
;
1H NMR
CDCl3): d 3.49–3.38 (m, 1H), 3.69–3.72 (m, 1H), 3.89 (s, 3H),
4.02–4.06 (m, 1H), 4.57 (d, 1H, J = 7.2 Hz), 5.94 (s, 2H), 6.68 (s,
2H), 7.12–7.16 (m, 2H), 7.41–7.48 (m, 2H); 13C NMR (75 MHz,
CDCl3): d 156.8, 153.1, 147.8, 142.7, 138.8, 134.7, 126.5, 125.5,
106.25, 106.0, 80.1, 79.3, 61.3, 41.0; HRESIMS m/z [M]+ found
374.0929; calcd 374.0936 for C18H18N2O5S.
(300 MHz, acetone-d6): d 1.07 (t, 6H, J = 7.2 Hz), 2.57–2.70 (m,
6H), 3.67 (q, 1H, J = 6.9 Hz), 3.86 (s, 3H), 4.49 (d, 1H, J = 6.9 Hz),
5.94 (s, 2H) 6.62 (d, 1H, J = 1.5 Hz), 6.68 (d, 1H, J =1.5 Hz); 13C
NMR (75 MHz, acetone-d6): d 149.4, 144.1, 138.6, 135.0, 107.7,
101.9, 101.7, 78.4, 71.1, 58.1, 56.8, 48.2, 11.8; HRESIMS m/z [M]+
found 297.1646; calcd 297.1600 for C15H23NO5.
5.5.8. 1-(5-Mercapto-1H-1,2,4-triazol-3-ylamino)-2-(4-methoxy-
benzo[d][1,3]dioxol-6-yl)ethane-1,2-diol 26
5.5.2. (1R,2S)-1-(4-Methoxybenzo[a][1,3]dioxol-6-yl)-3-(propyl-
amino)propane-1,2-diol 20
Oil, yield 83%; [
a
]
D = ꢀ15.3 (c 0.76, CHCl3); 1H NMR (300 MHz,
CD3OD): d 3.02–3.08 (m, 1H), 3.18–3.30 (m, 1H), 3.77 (s, 3H),
3.70–3.80 (m, 1H), 4.42 (d, 2H, J = 6.6 Hz), 5.81 (s, 2H), 6.49
(d,1H, J = 1.2 Hz), 6.54 (d, 1H, J = 1.2 Hz); 13C NMR (75 MHz,
CD3OD): d 150.1, 144.7, 137.6, 135.9, 108.9, 102.5, 102.3, 76.8,
75.8, 57.2, 36.6; HRESIMS m/z [M]+ found 340.0834; calcd
340.0841 for C13H16N4O5S.
Yellow oil, yield 82%; [
a]
D = ꢀ37.7 (c 0.2, CHCl3); IR (KBr), 3300,
2264, 1622, 1610, 1526, 1244, 1020 cmꢀ1
;
1H NMR (300 MHz,
CDCl3): d 0.93 (t, 3H, J = 7.2 Hz), 1.57–1.50 (sextet, 2H, J = 7.2 Hz),
2.64–2.58–2.60 (m, 2H), 2.78–2.81 (m, 2H), 3.76–3.78 (m,1H),
3.90 (s, 3H,OMe), 4.77 (d, 1H, J = 4.8 Hz), 5.97 (s, 2H), 6.57 (s,
1H), 6.59 (s, 1H); 13C NMR (75 MHz, CDCl3): d 149.1, 143.8,
135.7, 134.7, 105.8, 101.6, 100.4, 77.7, 71.9, 56.8, 51.2, 50.1, 21.8,
11.6; HRESIMS m/z [M]+ found 283.1366; calcd 283.1420 for
C14H21NO5.
5.5.9. 1-(2,5-Dihydro-5-mercapto-1,3,4-thiazol-2-ylamino)-2-
(4-ethoxybenzo [d][1,3]dioxol-6-yl)ethane-1,2-diol 27
Oil, yield 90%; [
a
]
D = ꢀ13.1 (c 1.0, CHCl3), 1H NMR (300 MHz,
acetone-d6): d 3.20–3.30 (m, 1H), 3.48–3.38 (m,1H), 3.86 (s, 3H),
3.90–3.98 (m, 1H), 4.59 (d, 1H, J = 6.0 Hz), 5.94 (s, 2H), 6.63 (d,
1H, J = 1.2 Hz), 6.69 (d, 1H, J = 1.2 Hz); 13C NMR (75 MHz, ace-
tone-d6): d 148.1, 142.8, 138.4, 136.4, 133.7, 113.2, 106.2, 100.5,
100.3, 75.0, 73.9, 55.4, 37.6; HRESIMS m/z [M]+ found 357.0402;
calcd 357.0453 for C13H15N3O5S2.
5.5.3. (1R,2S)-3-(Isobutylamino)-1-(4-methoxybenzo[a][1,3]-
dioxol-6-yl)propane-1,2-diol 21
Oil, yield 90%; [
a
]
D = ꢀ17.25 (c 0.16, CHCl3); 1H NMR (300 MHz,
CDCl3): d 0.95 (d, 6H, J = 6.6 Hz), 1.94–1.83 (m, 1H), 2.46–2.59 (m,
2H), 2.87 (d, 2H, J = 4.8 Hz), 3.90 (s, 3H), 3.93–4.0 (m,1H), 4.83 (d,
1H, J = 4.2 Hz), 5.96 (s, 2H), 6.62 (s, 1H), 6.58 (s, 1H); 13C NMR
(75 MHz, CDCl3): d 149.2, 143.8, 134.0, 134.6, 105.7, 101.6, 100.4,
76.8, 76.8, 71.6, 57.0, 56.7, 50.4, 27.6, 20.5; HRESIMS m/z [M]+
found 297.3446; calcd 297.3468 for C15H23NO5.
5.6. Cytotoxicity evaluation
All the derivatives were tested for in vitro cytotoxicity on differ-
ent cancer cell lines by MTT assay. The cell lines used in this study
were Colo-205 (Colon-cancer), A-431 (Skin cancer), and MCF-7
(breast cancer). All the cells were obtained from National Center
for cellular Sciences (NCCS)-Pune, India. DMEM (Dulbeccos Modi-
fied eagles medium), MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-di-
phenyl tetrazolium bromide], trypsin, and EDTA were purchased
from sigma chemicals Co (St. Louis, MO), and Fetal bovine serum
was purchased from Gibco.
5.5.4. (1R,2S)-3-(4-Methoxyphenylamino)-1-(4-methoxybenzo-
[a][1,3]dioxol-6-yl)propane-1,2-diol 22
Oil, yield 88%; [
a]
D = ꢀ22.9 (c 0.56, CHCl3); 1H NMR (300 MHz,
CDCl3): d 2.48 (d, 1H, J = 12.0 Hz), 2.66–2.73 (m, 1H), 3.57 (q, 1H,
J = 13.2 Hz), 3.79 (s, 3H), 3.70–3.79 (m, 2H), 3.87 (s, 3H), 4.68 (d,
1H, J = 4.4 Hz), 5.95 (s, 2H), 6.49 (s, 1H), 6.50 (s, 1H), 6.79 (d, 2H,
J = 8.1 Hz), 7.05 (d, 2H, J = 8.1 Hz); 13C NMR (75 MHz, CDCl3): d
159.2, 149.1, 143.7, 143.7,135.0, 134.7, 130.8, 114.0, 105.9, 101.6,
100.5, 75.0, 72.0, 59.6, 56.8, 55.3; HRESIMS m/z [M]+ found
361.1576; calcd 361. 1525 for C19H23NO6.
Cells in 96 well plates were incubated with compounds tested
for 48 h at 37 °C in DMEM with 10% FBS medium. Then, the above
media were replaced with 90
10 l of MTT reagent (5 mg/mL), and plates were incubated at
37 °C for 4 h, thereafter above media were replaced with 200
ll of fresh serum-free DMEM and
l
5.5.5. (1R,2S)-3-(3-(Trifluoromethyl)benzylamino)-1-(4-methoxy-
benzo[a][1,3]dioxol-6-yl)propane-1,2-diol 23
l
l
of DMSO and incubated at 37 °C for 15 min. The absorbance at
570 nm was measured on a spectrophotometer (Spectra max,
Molecular devices). The values for each point were calculated from
the triplicate wells.
Oil, yield 82%; [
a]
D = ꢀ21.1 (c 1.0, CHCl3); 1H NMR (300 MHz,
CDCl3): d 2.08 (d, 1H, J = 12 Hz, 1H), 2.80–2.89 (m,1H), 3.78–
3.84 (m, 3H), 3.87 (s, 3H), 4.71–4.72 (m, 1H), 5.95 (s, 2H), 6.50
(d, 1H, J = 3.0 Hz), 6.52 (s, 1H), 7.47–7.56 (m, 4H); 13C NMR
(75 MHz, CDCl3) d 55.0, 56.6, 59.6, 71.8, 75.5, 100.1, 101.5,
105.6, 124.8, 125.4, 125.7, 129.2, 132.1, 134.7, 135.0, 143.6,
149.0; HRESIMS m/z [M]+ found 399.1227; calcd 399.1294 for
C19H20F3NO5.
Acknowledgments
The Authors thank Dr. J. S. Yadav, Director, IICT, for his constant
encouragement. The Authors also thank Dr. S. Rama Krishna, Phar-

448
E. Sreedhar et al. / Tetrahedron: Asymmetry 20 (2009) 440–448
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