Stereoselective synthesis of (+)-nephrosteranic acid by ring-closing metathesis and its biological evaluation

Article abstract of DOI:10.1080/00397910903011337

A simple and efficient approach to (+)-nephrosteranic acid from dodecanol as a starting material is described, employing Sharpless asymmetric epoxidation, ring-closing metathesis, and Gilman addition of a vinyl group as key steps. These key reactions allow fast access to trisubstituted-butyrolactone. The molecule synthesized exhibits potent antifungal, antibacterial, and cytotoxic activities against all the tested strains.

Full text of DOI:10.1080/00397910903011337

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Stereoselective Synthesis of (+)-
Nephrosteranic Acid by Ring-Closing
Metathesis and Its Biological Evaluation
a
b
b
Arun Kumar Perepogu , D. Raman , U. S. N. Murty & Vaidya
a c
Jayathirtha Rao
a
Organic Chemistry Division II, Indian Institute of Chemical
Technology , Tarnaka, Hyderabad, India
b
National Institute of Pharmaceutical Education and Research ,
Balanagar, Hyderabad, India
c
Biology Division, Indian Institute of Chemical Technology ,
Hyderabad, India
Published online: 04 Feb 2010.
To cite this article: Arun Kumar Perepogu , D. Raman , U. S. N. Murty & Vaidya Jayathirtha Rao (2010)
Stereoselective Synthesis of (+)-Nephrosteranic Acid by Ring-Closing Metathesis and Its Biological
Evaluation, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 40:5, 686-696, DOI: 10.1080/00397910903011337
To link to this article: http://dx.doi.org/10.1080/00397910903011337
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1
Synthetic Communications , 40: 686–696, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903011337
STEREOSELECTIVE SYNTHESIS OF
þ)-NEPHROSTERANIC ACID BY RING-CLOSING
METATHESIS AND ITS BIOLOGICAL EVALUATION
(
1
Arun Kumar Perepogu, D. Raman, U. S. N. Murty,
2
2
1
,3
and Vaidya Jayathirtha Rao
1
Organic Chemistry Division II, Indian Institute of Chemical Technology,
Tarnaka, Hyderabad, India
2
National Institute of Pharmaceutical Education and Research, Balanagar,
Hyderabad, India
3
Biology Division, Indian Institute of Chemical Technology, Hyderabad, India
A simple and efficient approach to (þ)-nephrosteranic acid from dodecanol as a starting
material is described, employing Sharpless asymmetric epoxidation, ring-closing metath-
esis, and Gilman addition of a vinyl group as key steps. These key reactions allow fast
access to trisubstituted c-butyrolactone. The molecule synthesized exhibits potent antifun-
gal, antibacterial, and cytotoxic activities against all the tested strains.
Keywords: Antimicrobial activity; chemoselective reduction; Gilman 1,4 addition; paraconic acids;
ring-closing metathesis; sharpless asymmetric epoxidation
INTRODUCTION
Lichens, the natural source of paraconic acids, are successful alliances between
fungi and algae. Each is doing what it does best and thriving as a result of natural
cooperation=symbiosis. They live as one organism, both inhabiting the same body,
and produce a variety of substances friendly to the environment and human health,
except for few poisonous examples. Screening and isolation of molecules from suit-
able lichen symbionts or medicinal plants has resulted in a great number of paraco-
[
1]
nic acids with antineoplastic, antibiotic, and antibacterial properties, which
prompted many researchers to devise new synthetic routes toward these natural
products. The diversity of their biogenetic origin suggests that the structure
[
2]
may be one of the key elements in their biosynthesis. Paraconic acids are naturally
occurring c-butyrolactones, having a carboxylic acid in the 3-position as
their characteristic functionality (Fig. 1). Consequently, a number of syntheses
[
3]
have been developed, leading to a variety of paraconic acids either in racemic or
Received January 17, 2009.
Address correspondence to Vaidya Jayathirtha Rao, Organic Chemistry Division II, Indian
Institute of Chemical Technology (IICT), Uppal Road, Tarnaka, Hyderabad 500607, Andhra Pradesh,
India. E-mail: jrao@iict.res.in
6
86

(
þ)-NEPHROSTERANIC ACID
687
Figure 1. Paraconic acids.
Scheme 1. Retrosynthesis of (þ)-nephrosteranic acid.
[
in enantiopure form and using starting materials from chiral pool, chiral auxill-
4]
[
5]
[6]
[7]
aries, or asymmetric methodology. Surprisingly, (þ)-nephrosteranic acid 1 with
1-carbon alkyl chain at the c-position has been the least often prepared of the
common members of this important group of natural products. As part of our
1
[
8]
ongoing program toward synthesis of biologically active compounds, we became
interested in developing a simple and flexible route to stereoselective synthesis of
(
þ)-nephrosteranic acid, employing Sharpless asymmetric epoxidation as the source
of chirality, ring-closing metathesis (RCM) to build the carbon framework, and
Gilman addition of vinyl group as key steps. The retrosynthetic analysis of
(
þ)-nephrosteranic acid (Scheme 1) indicates compound 9 is the key intermediate,
which is derived from bis-olefin 8 upon RCM. Olefin 8 could be envisaged as
deriving from asymmetric epoxide 6, which would be prepared from inexpensive
dodecanol 2.
RESULTS AND DISCUSSION
The formal synthesis of target molecule (þ)-nephrosteranic acid was initiated
from commercially available dodecanol 2, which was subjected to pyridinumchloro-
chromate (PCC) oxidation to give dodecanal 3 in 95% yield (Scheme 2). Compound
[
9]
3
was subjected to a two-carbon homologation by means of Wittig reaction using
ethoxycarbonylmethylenetriphenylphosphorane. The reaction was carried out in
refluxing benzene for 2 h, which gave a mixture of trans and cis conjugated ester
in 88:12 ratio. The trans compound 4 was purified and then subjected to chemose-
[10]
lective reduction using LAH=AlCl in anhydrous ether to afford allyl alcohol 5 in
3

688
A. K. PEREPOGU ET AL.
Scheme 2. (a) PCC, DCM, rt, 3 h, 95%; (b) Ph
3
P=CHCO
2
Et, anhyd. benzene, reflux, 2 h, 90%; (c) LAH=
ꢁ
ꢁ
i
AlCl
Ph P, pyridine, I
h, 75%; (g) (Pcy
3
, THF, 0 C, 1=2 h, 86%; (d) Ti(OPr )
4
, (ꢀ)DET, PhC(CH
3
)
2
O
2
H, dry DCM, ꢀ20 C, 3 h, 85%; (e)
ꢁ
, Et
Cl
2
O:CH CN (5:3), 0 C, H
3
2
O, reflux, 6 h, 95%; (f) CH
2
=CHCOCl, Et
, 40 C, 36 h, 79%; (h) CuI, MeLi, vinyl-
, NaIO , CCl
3
N, DMAP,
3
2
i
ꢁ
5
3
)
2
2
Ru ¼ CHPh (12 mol%), Ti(OPr )
4
, CH
ꢁ
2
Cl
2
ꢁ
magnesium bromide ꢀ78 C, 81%; (i) NaHMDS, MeI, ꢀ78 C, THF, 76%; and (j) RuCl
3
4
4
,
3 2
CH CN, H O, 80%.
[
11]
8
2
2
6% yield. Sharpless asymmetric epoxidation
,3-epoxy alcohol 6 in 85% yield. Accordingly, a one-pot transformation
,3-epoxy alcohol (6) into allyl alcohol (7) was achieved by the in situ formation
of 5 with D-(ꢀ)-DET produced
[
12]
of
of the epoxy iodide and its subsequent reduction with phosphine hydroxyiodide
13]
[
in 95% yield. Reaction of 7 with acryloyl chloride
a catalytic amount of dimethylaminopyridine (DMAP) in CH Cl provided the
and Et N in the presence of
3
2
2
acrylate ester 8 in 75% yield. Compound 8 was subjected to RCM under reflux con-
ditions for 24 h in CH Cl in the presence of Grubb’s first-generation (I) catalyst
2
2
[
14a,b]
(
12 mol%) (Fig. 2) following standard RCM procedure. The expected (5R)-5-
undecyl-2,5-dihydro-2-furanone 9 was obtained in 30% yield; however, the yield
[14c]
of the RCM
product was improved by working with same mol% catalyst but
in more dilutions of 8 as well as catalyst, which indeed minimized the formation
of dimeric alkene products arising from undesired cross-metathesis. Thus, com-
pound 9 was obtained in 79% yield. The conjugate addition of a vinyl group on
9
was first carried out by utilizing vinyllithium to generate the cuprate reagent.
Figure 2. Grubbs first-generation catalyst.

(
þ)-NEPHROSTERANIC ACID
689
Because the yields obtained by utilizing vinyl lithium were not satisfactory, a further
[
15]
experiment was carried out by utilizing a mixed cuprate method.
vinyl cuprate reagent was generated from the reaction of vinylmagnesium
bromide
In this case,
[
16]
and methyl copper (generated in situ from methyl lithium and purified
cuprous iodide). The vast majority of cyclic enones reacted with organocopper
reagents to form conjugate adducts in which the newly introduced vinyl group is
[
17]
axial
in position. This is typical of kinetically controlled 1,4-additions, which
are subject to the stereoelectronic requirement that the reagent approach the a,b-
[
18]
unsaturated substrate in a plane perpendicular to the a,b-double bond and main-
tain the orbital overlap throughout the transition state. Thus 1,4-addition product
1
ated
0 was obtained in 81% as a single diastereomer. The lactone 10 was a-methyl-
[
19]
with methyl iodide in excess and NaN(SiMe ) as the base, furnishing 11
3 2
in 76% yield. As anticipated, the alkylation is diastereoselective (dr 91: 9), and
the Me group in 11 is trans to the b substituent. The ratios between diastereoi-
somers were determined by GC-MS analysis of crude reaction mixture. The final
step was achieved by the oxidation of double bond by treatment with RuO , as
4
[20]
reported in the literature.
The physical and spectral data of 1 are identical to
[7]
those reported in the literature. The synthesized (þ)-nephrosteranic acid 1 was
evaluated in vitro for antibacterial and antifungal activity using agar well diffusion
antimicrobial assay. The antibacterial activity was evaluated against Gram-positive
bacterial strains Staphylococcus aureus (MTCC 737), Staphylococcus epidermidis
(MTCC 435), and Gram-negative strains Escherichia coli (MTCC 1687) and
Pseudomonas aeruginosa (MTCC 1688). The antifungal activity was evaluated
against pathogenic strains Sacharomyces sereviseae (MTCC 36), Candida albicans
(MTCC 227), Aspergillus niger (MTCC 1344), and Rhizopus oryzae (MTCC 262).
The MIC (minimum inhibitory concentration) values for antibacterial activity were
[
21]
determined using standard Broth microdilution technique described by NCCLS.
Nitrofurantoin was used as a reference antimicrobial drug. Clotrimazole was used
as a reference antifungal drug, and streptomycin was used as a reference antibacter-
ial drug. All the biological data are depicted in Tables 1 and 2 as zone of inhibition
of growth (ZI), MIC, and inhibitory concentration (IC ) values. From the activity
5
0
results, compound 1 has show potent antifungal and antibacterial activity against
all the tested fungal and bacterial strains. The analysis of ZI and MIC values for
antibacterial activity revealed compound 1 has more than 60% antibacterial activity
against Pseudomonas aeruginosa and moderate activity against other tested bacterial
strains in comparison with the tested reference drug’s antibacterial activity. Zone of
inhibition results for antifungal activity revealed compound 1 has more than 80%
activity against Aspergillus niger and more than 60% activity against other fungal
strains in comparison with tested reference drug’s antifungal activity. Cytotoxic
activity was evaluated against THP-1 and U-937 human cancer cell lines (human
acute monocytic leukemia cell line and human leukemic monocyte lymphoma cell
line). Cytotoxicity was measured using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-
[
22]
diphenyl tetrasolium bromide] assay, according to the method of Mosmann.
Etoposide was used as reference cytotoxic drug. IC50 values of the test compound
1) were calculated and presented in Table 2. It is evident from the results that the
(
test compound has shown significant decreases in cell viability in the test cell line in
a concentration-dependant manner.

690
A. K. PEREPOGU ET AL.
Table 1. In vitro antimicrobial activity of synthesized (þ)-nephrosteranic acid 1
a
Zone of inhibition (mm)
MIC (mg=mL)
Microorganism
Compd. 1 Streptomycin
Compd. 1
Nitrofurantoin
b
Bacterial strains
SA
SE
EC
PA
14
14
15
15
26
27
100
125
100
120
50
50
31
23
25
100
c
Fungal strains
SS
Clotrimazole
16
14
16
15
23
22
18
21
CA
AN
RA
a
MIC (minimum inhibitory concentration in mg=mL) was determined as 90% inhibition of growth with
respect to positive growth control. Negative control: DMSO, no inhibition.
b
SA, Staphylococcus aureus; SE, Staphylococcus epidermis; EC, Escherichia coli; PA, Psudomonas
aeruginosa.
c
SS, Saccharomyces serviseae; CA, Candida albicans; AN, Aspergillus niger; RA, Rhizopus orizae.
Table 2. Cytotoxicity of (þ)-nephrosteranic acid 1
a
IC50 (mg=mL)
Cell line
Compd. 1
Control (etoposide)
b
THP-1
c
U-937
27.66 ꢂ 5.92
24.45 ꢂ 4.32
1.4
1.2
a
IC50: Inhibitory concentration.
b
THP-1: Human acute monocytic leukemia cell line.
Human leukemic monocyte lymphoma cell line.
c
In conclusion, a simple, flexible, and highly efficient route to (þ)-
nephrosteranic acid has been developed employing Sharpless asymmetric epoxida-
tion, RCM, and Gilman addition of vinyl group as key steps. The merits of this
synthesis are high enantio- and diastereoselectivity with high-yielding reaction steps.
This strategy provides rapid access to a range of analogs of the chiral trisubstituted
c-butyrolactones. The synthesized (þ)-nephrosteranic acid 1 is tested for antimicro-
bial activity, and it was found that compound 1 exhibited potent antifungal, signifi-
cant antibacterial, and significant cytotoxic activities.
EXPERIMENTAL
NMR spectra were measured on a Gemini 200-MHz Varian instrument and
Avance 300-MHz Bruker UX NMR instrument in CDCl as reference solvent,
3
and chemical shifts were expressed as d. Coupling constants J are given in hertz.
Tetramethylsilane (TMS) was used as an internal standard for H NMR. Mass
spectra were recorded on VG Micromass 7070 H (EI and ESI) and Finnigan Mat 1020
1

(
þ)-NEPHROSTERANIC ACID
691
Mass (GC-MS) instruments. High-resolution (HR) mass spectra were recorded using a
VG Autospec magnetic sector mass spectrometer (Waters, Manchester, UK). Infra-
red (IR) spectra were recorded on Perkin-Elmer model 283B and Nicolet-740 Fourier
transform (FT)–IR instruments, and band positions were reported in wave numbers
ꢀ
1
(
cm ). Column chromatography was performed using silica gel H (60–120 mm).
[(2S, 3R)-3-Undecyloxiran-2-yl] Methanol (6)
ꢁ
˚
To a cooled (ꢀ30 C) suspension of activated, powdered 4 A MS (1 g) in
i
CH Cl (25 mL), (ꢀ)-DET (0.04 mL, 0.24 mmol), Ti(OPr ) (0.06 mL, 0.21 mmol),
2
2
4
and cumene hydroperoxide (0.3 mL, 1.01 mmol) were added. After 20 min, a solution
ꢁ
of allylic alcohol 5 (0.5 g, 2.35 mmol) in CH Cl (10 mL) was added at ꢀ30 C over
2
2
20 min. The resulting mixture was stirred at that temperature for 3 h, quenched with
a cooled solution of ferrous sulfate and tartaric acid (stoichiometric amount) in deio-
nized water, stirred vigorously for 30 min, and extracted with ether (50 mL ꢃ 3). The
ꢁ
combined organic layers were treated with a precooled (0 C) solution of 5 mL of 30%
NaOH (w=v) in brine and stirred for 1 h at rt. The two layers were separated, and the
aqueous layer was extracted with ether (40 mL ꢃ 3). The combined ether layers were
washed with brine, dried over Na SO , filtered, and concentrated. The residue was
2
4
chromatographed (SiO , ethylacetate=hexane ¼ 1.5:8.5) to give 6 (0.46 g, 85%) as a
2
white solid.
[
2
7
ꢀ1
a]D ¼ þ 14.9 (c ¼ 1.0, CHCl ); IR (KBR), n (cm ): 3445, 2619, 2849, 1598,
3
1
1
1
384, 1262, 725; H NMR (300 MHz, CDCl ): d 0.88 (t, J ¼ 6.80 Hz, 3H, CH CH ),
3
2
3
.26 (s, 18H, 9 ꢃ CH ), 1.41–1.60 (m, 2H, CH ), 2.80–2.88 (m, 1H, CH), 2.89–2.96
2
2
1
3
(m, 1H, CH), 3.52–3.62 (m, 1H, CH OH), 3.80–3.90 (m, 1H, CH OH); C NMR
2 2
(
75 MHz, CDCl ): d 14.0, 22.6, 25.9, 29.3, 29.5, 31.5, 31.8, 56.0, 58.5, 61.7; ESI-MS:
3
þ
m=z ¼ 251 [M þ Na] .
(3R)-1-Tetradecen-3-ol (7)
To a stirred solution of epoxy alcohol 6 (2.25 g, 9.8 mmol) in dry
Et OꢀCH CN (5:3), 15 mL were added sequentially of PPh (7.46 g, 28.6 mmol),
2
3
3
ꢁ
pyridine (3.1 mL, 38.1 mmol), and I (4.82 g, 19.06 mmol) at 0 C. After stirring for
2
ꢁ
2 h at 0 C, H O (0.35 mL, 19.06 mmol) was added into the system. The reaction mix-
ꢁ
ture was refluxed for 6 h at 40 C, then 20% Na S O (aq.) (15 mL) and saturated
2
2
2
3
NaHCO (aq.) (15 mL) were added to quench the reaction, and the organic layer
3
was extracted with ether (3 ꢃ 50 mL). The combined ether extracts were washed with
5
the residue, which was flash-chromatographed [eluting with hexane–ethylacetate
% HCl (4 ꢃ 10 mL), H O, and brine and then dried. Evaporation of the solvent gave
2
(
9:1)] to give 7 (2.0 g, 95%) as colorless oil.
2
7
ꢀ1
[
a]D ¼ ꢀ6.5 (c ¼ 1.0, CHCl ); IR (neat), n (cm ): 3350, 2925, 2854, 1640,
3
1
1
462, 990, 920, 721; H NMR (300 MHz, CDCl ): d 0.88 (t, J ¼ 6.80 Hz, 3H,
3
CH CH ), 1.25 (s, 18H, 9 ꢃ CH ), 1.49–1.59 (m, 2H, CH ), 4.02–4.08 (m, 1H,
2
3
2
2
CHOH), 5.05–5.22 (dd, J ¼ 15.8, 12.0 Hz, 2H, CHCH ), 5.78–5.90 (dq, J ¼ 16.6,
2
1
3
1
2
(
0.5, 6.0 Hz, 1H, CHCH ); C NMR (75 MHz, CDCl ): d 14.0, 22.6, 25.4, 29.2,
2 3
þ
9.6, 32.0, 37.0, 73.2, 114.4, 141.4; EI-MS: m=z (%) ¼ 212 (M , 6), 195 (6), 129
10), 45 (100).

692
A. K. PEREPOGU ET AL.
1
R-1-Undecyl-2-propenyl Acrylate (8)
To a cooled solution of 7 (2.15 g, 10.14 mmol) in dry DCM (20 mL), DMAP
cat. amt.) and triethyl amine (7.1 mL, 50.7 mmol) were added under an N atmos-
(
2
phere After 15 min, acryloyl chloride (0.9 mL, 12.16 mmol) was added, and resulting
.
solution was stirred at rt for 4 h. It was washed with 5% HCl (1 ꢃ 5 mL), saturated
NaHCO , H O (1 ꢃ 5 mL), and brine (1 ꢃ 5 mL). After the combined organic
3
2
extracts were dried over sodium sulfate, the solvent was evaporated and the residue
was purified by column chromatography (silica gel, 60–120 mesh, ethylacetate–
hexane 0.5:9.5) to give 8 (2.04 g, 75%) as a colorless syrup.
2
7
ꢀ1
[
a]D ¼ ꢀ10.5 (c ¼ 1.0, CHCl ); IR (neat), n (cm ): 2925, 2854, 1727, 1637,
3
1
1
1
5
1
6
404, 1191, 984; H NMR (300 MHz, CDCl ): d 0.88 (t, J ¼ 6.80 Hz, 3H, CH CH ),
3
2
3
.25 (s, 18H, 9 ꢃ CH ), 1.54–1.60 (m, 2H, CH ), 5.15–5.20 (m, 1H, CHCH ),
2
2
2
.25–5.28 (m, 1H, CHCH ), 5.68–5.85 (m, 1H, CHCH ), 5.76–5.82 (dd, J ¼ 2.1,
2
2
0.2 Hz, 1H, COCHCH ), 6.0–6.16 (dd, J ¼ 17.4, 10.1 Hz, 1H, COCHCH ),
2
2
1
3
.34–6.43 (dd, J ¼ 17.4, 2.1 Hz, 1H, COCHCH ); C NMR (75 MHz, CDCl ):
2
3
d 14.0, 22.6, 25.0, 29.3, 29.5, 31.8, 34.2, 74.9, 116.5, 128.8, 130.4, 136.5, 165.4;
þ
ESI-MS: m=z ¼ 289 [M þ Na] . ESI-HRMS calcd. for C H O Na [M þ Na]:
1
7
30
2
2
89.2157; found: 289.2143.
(5R)-5-Undecyl-2,5-dihydro-2-furanone (9)
i
Ti(OPr ) (3.2 mL, 10.82 mmol) was added to a stirred solution of 8 (0.96 g,
4
ꢁ
3
.6 mmol) in CH C1 (30 mL) under a nitrogen atmosphere at 23 C. The resulting
2
2
ꢁ
solution was refluxed at 40 C for 1 h, and then Grubb’s catalyst (0.355 g, 0.43 mmol)
in CH C1 (36 mL) was added. The reaction mixture was stirred at reflux for an
additional 35 h. The mixture was cooled to 23 C and filtered through a pad of silica
gel. Evaporation of the solvent gave a residue, which was flash chromatographed
over silica gel to provide the lactone 9 (0.68 g, 79.3%) as a colorless syrup.
2
2
ꢁ
2
7
ꢀ1
[
a]D ¼ ꢀ66.2 (c ¼ 1.0, CHCl ); IR (neat), n (cm ): 2920, 2852, 1741, 1657,
3
1
1
1
467, 1442, 1160, 1013; H NMR (300 MHz, CDCl ): d 0.88 (t, J ¼ 6.80 Hz, 3H),
3
.25 (s, 18H, 9 ꢃ CH ), 1.60–1.76 (m, 2H), 4.96–5.02 (m, 1H, HCO), 6.07–6.10
2
(
dd, J ¼ 6.0, 2.2 Hz, 1H, CHCHCO), 7.38–7.41 (dd, J ¼ 6.0, 1.5 Hz, 1H, CHCHCO);
1
3
C NMR (75 MHz, CDCl ): d 14.0, 22.6, 24.9, 29.2, 29.5, 31.8, 33.1, 83.3, 121.4,
3
þ
1
56.2, 173.0; ESI-MS: m=z ¼ 261 [M þ Na] . ESI-HRMS calcd. for C H O Na
1
5
26
2
[
M þ Na]: 261.1840; found: 261.1830.
(4R, 5R)-5-Undecyl-4-vinyltetrahydro-2-furanone (10)
Recrystallized CuI (1.42 g, 7.5 mmol) was taken in 20 mL THF (under dry and
ꢁ
nitrogen purged conditions) and was cooled to ꢀ78 C, and methyl lithium (7.5 mL,
7
1
ꢀ
.5 mmol of 1 M) in ether was added. The suspension warmed to rt and stirred for
5 min. The resultant bright-orange suspension of methyl copper was cooled to
78 C, and vinyl magnesium bromide (7.5 mL, 7.5 mmol of 1 M in THF) was added.
ꢁ
ꢁ
The mixture was stirred for 15 min at ꢀ78 C, and then 9 (0.18 g, 0.75 mmol)
was added.

(
þ)-NEPHROSTERANIC ACID
693
The pale yellow solution was allowed to warm at rt, whereupon the solution
became black. The mixture was stirred at rt for 2 h and then rapidly poured into
1
adjusted to 8–10 by addition of conc. NH OH. The hydrolysis mixture was stirred
00 mL of vigorously stirred, saturated NH Cl solution. The pH of solution was
4
4
at rt until all the copper salts had dissolved (1.5 h). The bright-blue solution was
extracted with ether, dried over Na SO , and concentrated under reduced pressure.
The residue was purified by column chromatography (silica gel, 60–120 mesh, ethy-
2
4
lacetate–hexane, 0.1:9.9) to give 10 (161 mg, 80.7%) as colorless syrup.
ꢀ1
2
D
7
½
aꢄ ¼ þ 36.4 (c ¼ 1.0, CHCl ); IR (neat), n (cm ): 3081, 2925, 2854, 1782,
3
1
1
3
643, 1462, 1423, 1208, 922, 760; H NMR (300 MHz, CDCl ): d 0.88 (t, J ¼ 6.80Hz,
3
H, CH CH ), 1.25 (s, 18H, 9 ꢃ CH ), 1.60–1.72 (m, 2H), 2.35–2.68 (dq, 2H,
2
3
2
CH CO), 2.71–2.81 (m, 1H, CHCHCH ), 4.02–4.12 (m, 1H, HCO), 5.13–5.21
2
2
1
3
(
(
1
m, 2H, CHCH ), 5.65–5.72 (ddd, J ¼ 17.3 Hz, 10.5, 7.5 1H, CHCH ); C NMR
2
2
75 MHz, CDCl ): d 14.0, 22.6, 25.6, 29.2, 29.5, 31.8, 33.6, 35.4, 46.2, 84.7,
3
þ
17.9, 135.7, 175.6; ESI-MS: m=z ¼ 289 [M þ Na] . ESI-HRMS calcd. for
C H O Na [M þ Na]: 289.2143; found: 289.2155.
1
7
30
2
(3S,4S,5R)-3-Methyl-5-undecyl-4-vinyltetrahydro-2-furanone (11)
Compound 10 (129 mg, 0.48 mmol) in anhydrous tetrahydrofuran (THF) was
added to a solution of NaHMDS (1.06 mL, 1.06 mmol) in 4 mL of anhydrous
ꢁ
THF and stirred for 0.5 h at ꢀ78 C. CH I (0.3 mL, 4.6 mmol) was added and stirred
3
ꢁ
for another 2 h. The reaction mixture was allowed to warm to ꢀ20 C, quenched with
8
mL of 2 N HCl, and extracted with ethyl acetate. The solvent was evaporated under
reduced pressure, and the residue was purified by column chromatography (silica gel,
1
7
00–200 mesh, ethylacetate–hexane, 0.2:9.8) to afford 11 as colorless syrup (102 mg,
6%, de ¼ 91:9 from GC MS).
2
D
7
ꢀ1
½
aꢄ ¼ þ 28.5 (c ¼ 1.0, CHCl ); IR (neat), n (cm ): 2925, 2854, 1776, 1646,
3
3
1
1
460, 1218, 1031, 771; H NMR (300 MHz, CDCl ): d 0.91 (t, J ¼ 6.80 Hz, 3H,
2 3 3 2
CH CH ), 1.2 (d, J ¼ 8.3 Hz, 3H, CHCH ), 1.28 (s, 9 ꢃ CH , 18H), 1.60–1.72 (m,
2
H), 2.21–2.49 (dq, J ¼ 11.3, 7.5, 4.5 Hz, 1H, CHCO), 2.70–2.84 (m, 1H,
2 2
CHCHCH ), 4.1 (m, J ¼ 8 Hz, 1H, HCO), 5.18–5.24 (m, 2H, CHCH ), 5.60–5.80
1
3
(
1
ddd, J ¼ 17.3, 9.8, 8.3 Hz, 1H, CHCH ); C NMR (75 MHz, CDCl ): d 12.9,
2
3
4.2, 22.7, 25.8, 29.4, 29.4, 29.6, 31.9, 33.5, 33.8, 49.6, 82.4, 118.9, 135.2, 177.4;
þ
ESI-MS: m=z ¼ 303 [M þ Na] . ESI-HRMS calcd. for C H O Na [M þ Na]:
1
8
32
2
3
03.2306; found: 303.2300.
(
þ)-Nephrosteranic Acid (1)
NaIO (98 mg, 0.45 mmol) and RuCl (3.0 mg, 0.011 mmol) were added to a
3
4
stirred solution of 11 (45 mg, 0.11 mmol) in a solvent mixture of CCl (0.2 mL),
4
CH CN (0.2 mL), and H O (0.3 mL) at rt. After 3 h at rt, CH Cl (2 mL) was added,
2
3
2
2
and the aq. phase was separated and extracted with CH Cl . The combined organic
2
2
layers were filtered through celite. After evaporation of the volatiles, the residue was
diluted with Et O (2 mL), and sat. NaHCO solution (2 mL) was added. The organic
2
3
phase was separated, and the aqueous one was acidified with 3 mL of 1 M HCl
solution. The product was extracted with CH Cl and dried (Na SO ). The solvent
2
2
2
4

694
A. K. PEREPOGU ET AL.
was evaporated and purified by column chromatography (ethylacetate=hexane
ꢁ
27
0:30) to afford 1 as white crystals (26 mg, 80%). Mp 105 C; ½aꢄ þ 27.6 (c 0.5,
7
D
[
7]
27
D
ꢀ1
CHCl ) [lit. ½aꢄ þ 27.2 (c 1.45, CHCl ]; IR (neat), n (cm ): 3448, 2924, 2854,
3
3
1
1
3
(
748, 1436, 1188, 1116, 721; H NMR (CDCl , 300 MHz): d 0.88 (t, J ¼ 6.3 Hz,
3
H, CH CH ), 1.26–1.78 (m, 23H), 1.35 (d, J ¼ 6.8 Hz, 3H, CHCH ), 2.65–2.85
2
3
3
m, J ¼ 11.3, 9.0 Hz, 1H, CHCO), 2.90–3.10 (m, 1H, CHCO H) 4.48–4.61 (ddd,
2
1
3
J ¼ 9.0, 4.0 Hz, 1H, HCO); C NMR (75 MHz, CDCl ): d 14.2, 14.8, 22.5, 25.3,
3
2
(
9.1, 29.3, 29.4, 29.6, 32.0, 36.1, 54.0, 79.1, 175.3, 176.7; EI-MS: m=z (%) 298
þ
[M] , 4), 283 (49), 253 (10), 143 (6), 129 (21), 45 (100).
ACKNOWLEDGMENTS
We thank the director of the Indian Institute of Chemical Technology, project
director of NIPER, and head of the Organic Chemistry Division II for their encour-
aging support. P.A.K. thanks the Council of Scientific and Industrial Research for
fellowship.
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