An alternative stereoselective total synthesis of Verbalactone

Article abstract of DOI:10.24820/ark.5550190.p010.527

A simple and efficient synthesis of Verbalactone has been accomplished from inexpensive and commercially available starting material, hexanal. This concise synthesis utilizes stereoselective reduction of β-hydroxyketone using catecholborane, regioselective opening of epoxide and Yamaguchi reaction for the construction of the macrolactone.

Full text of DOI:10.24820/ark.5550190.p010.527

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Arkivoc 2018, part vii, 50-57
An alternative stereoselective total synthesis of Verbalactone
Sreelatha Vanjivaka,a Kakarla Ramanakumar,b M. Rajeswari,c Jyothi Vantikommu,a Gattu Sridhar, d
and Sadanandam Pallea*
a Centre for Chemical Sciences & Technology, Institute of Science & Technology, Jawaharlal Nehru
Technological University, Hyderabad – 500 085, India
b Department of Chemistry, CMR Institute of Technology, Medchal, Secunderabad – 01, India
c Organic Chemistry Department, Telangana university, Dichpally, Nizamabad, Telangana, India
d Organic and Biomolecular Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad,
500107, India
E-mail: rk1org@yahoo.com
Received 02-11-2018
Accepted 05-31-2018
Published on line 08-28-2018
Abstract
A simple and efficient synthesis of Verbalactone has been accomplished from inexpensive and commercially
available starting material, hexanal. This concise synthesis utilizes stereoselective reduction of β–hydroxy-
ketone using catecholborane, regioselective opening of epoxide and Yamaguchi reaction for the construction
of the macrolactone.
Keywords: Hexanal, regioselective epoxide opening, Yamaguchi macrolactonisation, stereoselective synthesis,
Verbalactone
DOI: https://doi.org/10.24820/ark.5550190.p010.527
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Introduction
Macrolides are large lactone ring molecules and these molecules are derived by the internal esterification of
the corresponding hydoxy acids. Macrodiolides and macrocyclic monolactones are two types of macrolides.
Researchers across the world concentrated towards the synthesis of both homo and hetero dimers (macro
dilactones)1-3 and macrocyclic monolactones4-6. Macrodiolides are interesting natural products which can be
isolated from marine sponges and different fungi. These macrodiolides exhibited potent biological activities
including antihelmintic,7,8 antifungal9,10 and phytotoxic activities11.
Verbalactone 1 is a 12 membered C2 symmetric dilactone and it was isolated from the roots of Verbascum
undulatum Lam., a biennial plant of the genus Verbascum that belongs to the family Scrophulariacea by
Mitaku et al.12 It showed antibacterial activity against Gram-positive (MIC=62.5 mg/cm3) and Gram-negative
bacteria (MIC=125 mg/cm3). Verbalactone (1) is thus a dimeric lactone with C2-symmetry and has a NMR
profile similar to the monomer lactone of (3R,5R)-dihydroxydecanoic acid.13-16 The structure and absolute
stereochemistry of verbalactone was detemined as 4R,6R,10R,12R by the 1D and 2D NMR spectroscopic
methods and chemical correlations. The NMR profile of 1 is similar to the NMR data of (3R,5R)-
dihydroxydecanoic acid.13-16 The structure of verbalactone was shown in Figure 1.
Figure 1
Meanwhile, several scientists reported the total synthesis of Verbalactone due to its interesting
biologically active nature and stereochemical complexicity.17-27 The reported methods involve long reaction
sequences, low yields and dependence of chiral pool resources were disadvantages. In continuation of
our research work on the synthesis of biologically active natural products, herein we report an efficient
straightforward and an alternative concise synthetic route for stereoselective total synthesis of Verbalactone
starting from commercially available material hexanal with overall high yield.
Results and Discussion
Our retrosynthetic analysis of 1 is outlined in Scheme 1. Retrosynthetically (Scheme 1), the target molecule 1
could be obtained from dihydroxy acid 2 by Yamaguchi’s macrolactonization. While compound 2 could be
obtained from opening of epoxide 4 with 2-pentyl-1,3-dithiane 3, the 1,3-dithiane 3 could be prepared from
the aldehyde 5.
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Vanjivaka, S. et al.
OH OH
O
COOH
H
O
HO
H
H
O
O
H
OH
2
1
O
S
S
+
CHO
OMPM
H
5
4
3
Scheme 1. Retrosynthetic route of Verbalactone.
OH
S
S
S
S
b
a
CHO
OMPM
H
3
5
6
OH OH
O
OH
e
d
c
OMPM
OMPM
8
7
OTBS OTBS
COOH
OTBS OTBS
OTBS OTBS
g
f
OH
OMPM
11
10
9
O
O
OH OH
H
i
HO
H
H
OH
O
h
COOH
H
O
2
1
O
OMPM
4
Reagents and conditions: (a) 1,3-propanedithiol, BF3•OEt2, CH2Cl2, 0 °C-rt, 12h.(b) 4, n-BuLi, dry THF, -78 °C to
–20 °C, 3h. (c) CaCO3, I2, THF/H2O (4:1), 0 °C, 30 min (d) catecholborane, dry THF, -10 °C, 4h, (e) TBSCl,
Imidazole, CH2Cl2, rt, 4h; (f) DDQ, CH2Cl2:H2O (19:1), rt, 3 h. (g) TEMPO, BIAB, H2O:CH2Cl2, (1:1), 0 °C, 1 h. (h)
TBAF, THF, 0 oC to rt, 3 h. (i) ) 2,4,6-trichlorobenzoyl chloride, Et3N, THF, rt, 2 h then DMAP, toluene, reflux, 6 h
Scheme 2. Stereoselective total synthesis of Verbalactone.
The synthesis (Scheme 2) was started from the commercially available hexanal 5, which was converted as
corresponding 1,3- dithiane using 1,3-propanedithiol and BF3•OEt2 in CH2Cl2 for 12 h. Later, 1,3- dithiane 3 on
treatment with n-BuLi followed by the regioselective opening of known epoxide 428 with resulting carbanion
gave alcohol 6 in 77% yield. Later, the 1,3-dithioacetal group was removed from 6 to furnish the β-hydroxy
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ketone 7. For this tranformation, we first tried with DDQ in aqueous MeCN. But in this reaction conditions the
yield of the required compound is low (< 40%) and some of the Starting material remains unchanged. To
overcome this, we next tried with CaCO3, I2, in THF/H2O (4:1), in this method the reaction took place with
good yield (74%). The stereoselective reduction of β–hydroxyl ketone 7 to the corresponding syn 1, 3-diol 8
o
was achieved using catecholborane (3.0 eq.) in THF at -10 C in 84% yield with high diastereoselectivity (syn:
anti, 99:1). The resulting diol 8 was masked as silylethers with TBSCl and imidazole in CH2Cl2 to give 9 (81%),
which on selective cleavage of PMB ether in the presence of DDQ in aq. CH2Cl2 gave alcohol 10 in 78% yield.
The alcohol 10 was oxidized to acid by treating with TEMPO and BIAB in aq. CH2Cl2 to afford acid 11 in 71%
yield, which on desilylation with TBAF in dry THF afforded the dihydroxy acid 2.
Finally, The resulting dihydroxy acid 2 was immediately subjected to macrolactonisation under Yamaguchi
reaction conditions (2,4,6-trichlorobenzoyl chloride, Et3N and DMAP) to afford the target molecule
1
13
Verbalactone 1 in in 57% yield. The H NMR, C NMR and optical rotation value of synthetic 1 were in good
agreement with those of the previously reported natural product.21
Conclusions
In conclusion, a stereoselective total synthesis of Verbalactone 1 was accomplished by a versatile strategy. A
combination of stereoselective reduction of β–hydroxyl ketone using catecholborane, regioselective ring
opening of epoxide and Yamaguchi macrolactonisation were effectively utilized in accomplishing the synthesis.
Experimental Section
General. All chemicals and solvents were purchased from Sigma–Aldrich and Merck and used without further
purification. All reactions were monitored by thin-layer chromatography (TLC) on silica Merck 60 F254
1
13
precoated aluminum plates. H and C NMR spectra were recorded with 500, 300, 150, and 75 MHz Bruker
spectrometer. Chemical shifts are reported in d units (ppm) with tetramethylsilane (TMS) as a reference. All
coupling constants (J) are reported in Hertz. Multiplicity is indicated as s (singlet), d (doublet), dd (double
doublet), t (triplet), q (quartet), m (multiplet). FT-IR spectra were taken on IR spectrophotometer using NaCl
optics. Mass spectra were performed on direct inlet system or LC by MSD trap SL, the HRMS data were
obtained using Q-TOF mass spectrometry. Optical rotation values are recorded on digital polarimeter at 25 oC.
2-Pentyl-1,3-dithiane (3).29 To a stirred solution of hexanal (5.0 mL, 49.07 mmol) in CH2Cl2 (20 mL) was added
1,3-propanedithiol (6.4 mL, 58.89 mmol). The mixture was cooled to 0 °C and BF3•OEt2 (3.0 mL, 24.53 mmol)
was added dropwise. The mixture was allowed to warm to room temperature stirred for 12 h. After
completion of reaction the reaction was quenched by the addition of saturated aqueous NaHCO3. The mixture
was diluted with CH2Cl2 and washed twice with 0.1 M NaOH then three times with brine. The combined
aqueous phases were extracted twice with CH2Cl2 and the combined organic layers were dried over NaSO4
then concentrated and purified by Flash chromatography (silica gel, 60–120 mesh, 4% EtOAc in pet. ether)
1
afforded 3 (8.0 g 86%) as a colorless oil. H NMR (300 MHz, CDCl3): δ 4.05 (t, J 6.9 Hz, 1H), 2.91-2.80 (m, 4H),
2.15-2.09 (m, 1H), 1.90-1.82 (m, 1H), 1.76-1.72 (m, 2H), 1.51 (quintet, J 7.6 Hz, 2H), 1.33-1.25 (m, 4H), 0.89 (t, J
13
7.0 Hz, 3H); C NMR (100 MHz, CDCl3): δ 47.9, 35.6, 31.6, 30.7, 26.5, 26.3, 22.6, 14.2; IR (neat) 2930, 1422,
1275, 1182, 908 cm-1; HRMS (ESI): m/z calcd for C9H18NaS2: 213.0748; found: 213.0751 [M+Na]+.
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(S)-4-(4-Methoxybenzyloxy)-1-(2-pentyl-1,3-dithian-2-yl)butan-2-ol (6). To a solution of 3 (5.0 g, 26.31 mmol)
in dry THF (20 mL) was added n-BuLi (15.7 mL, 39.47 mmol, 2.5 N hexane solution) dropwise under N2
o
atmosphere at -78 C and stirred for 30 min. then the reaction mixture was sequentially treated with a
solution of epoxide 4 (6.0 mL, 28.94 mmol) in dry THF (15 mL) at 10 min interval and stirred for an additional 3
o
h at –20 C. After completion of reaction, Saturated NaHCO3 solution (20 mL) followed by saturated NH4Cl
solution (20 mL) were added to the reaction mixture at –20 oC and allowed to warm to room temperature. The
reaction mixture was extracted with EtOAc (2 x 50 mL). The organic layers were washed with water (50 mL),
dried (Na2SO4), evaporated and the residue obtained was purified by column chromatography (60-120 Silica
gel, 8% EtOAc in pet. ether) to give 6 (8.06 g, 77%) as a yellow syrup. []D –18.7 (c 1.6, CHCl3); 1H NMR (CDCl3,
300 MHz):  7.19 (d, 2H, J 8.6 Hz, Ar-H), 6.83 (d, 2H, J 8.6 Hz, Ar-H), 4.51 (d, 1H, J 11.7 Hz, -OCH2Ph), 4.41 (d,
1H, J 11.7 Hz, -OCH2Ph), 3.81 (s, 3H, -OCH3), 3.75-3.79 (m, 1H, H-3), 3.48 (t, 2H, J 5.7 Hz, H-1, 1’), 3.05 (br s, 1H,
-OH), 2.88–3.01 (m, 2H), 2.66–2.75 (m, 2H),1.86–1.99 (m, 2H), 1.55-1.79 (m, 8H, 4 x CH2), 1.26-1.34 (m, 4H, 2 x
CH2), 0.92 (t, 3H, J 5.7 Hz, -CH3); 13C NMR (75 MHz, CDCl3):  158.6, 129.8, 129.4, 114.3, 76.3, 69.1, 66.9, 62.3,
56.7, 44.8, 40.1, 38.3, 33.7, 27.3, 25.2, 23.3, 22.8, 14.6; IR (neat) 3373, 2984, 1372, 1175, 1082, 928 cm-1;
HRMS (ESI): m/z calcd for C21H34O3NaS2: 421.1847; found: 421.1852 [M+Na]+.
(S)-3-Hydroxy-1-(4-methoxybenzyloxy)decan-5-one (7). To a solution of compound 6 (4.1 g, 10.30 mmol) and CaCO3
o
(8.24 g, 82.41 mmol) in THF/H2O (v/v, 4:1, 100 mL) was added iodide (5.21 g, 20.6 mmol) at 0 C. The resulting mixture
was stirred at 0 oC for 30 min. The reaction was quenched by adding saturated aqueous Na2S2O3, filtered through a pad
of Celite, and then extracted with EtOAc (3 × 100 mL), water, brine, dried over Na2SO4 and concentrated in vacuo.
Purification by flash chromatography (silica gel, 60–120 mesh, 15% EtOAc in pet. ether) to gave compound 7 (2.34 g,
74% yield) as colorless oil: []D –98.7 (c 1.6, CHCl3); 1H NMR (CDCl3, 300 MHz):  7.22 (d, 2H, J 8.8 Hz, Ar-H), 6.79 (d, 2H, J
8.8 Hz, Ar-H), 4.47 (d, 1H, J 11.6 Hz, -OCH2Ph), 4.39 (d, 1H, J 11.6 Hz, -OCH2Ph), 3.79 (s, 3H, -OCH3), 3.66-3.58 (m, 1H),
3.51 (t, 2H, J 6.1 Hz, 2.91 (br s, 1H, -OH), 2.68–2.54 (m, 2H), 2.06 (t, 2H, J 6.7 Hz, -CH2), 1.52–1.39 (m, 4H, 2 x CH2), 1.29-
1.18 (m, 4H, 2 x CH2), 0.89 (t, 3H, J 5.8 Hz, -CH3); 13C NMR (75 MHz, CDCl3):  206.7, 159.0, 129.7, 129.4, 114.1, 76.6, 68.3,
67.9, 56.6, 50.1, 40.9, 36.6, 32.9, 26.7, 14.1; HRMS (ESI): m/z calcd for C18H28O4Na: 331.1885; found: 331.1890 [M+Na]+.
(3S,5R)-1-(4-Methoxybenzyloxy)decane-3,5-diol (8). To a stirred solution of compound 7 (2.25 g, 7.30 mmol)
o
in dry tetrahydrofuran, freshly distilled catecholborane (2.3 mL, 21.9 mmol) was added at -10 C (reaction
mixture was kept in MeOH–ice bath). After 4 h, the reaction mixture was quenched by the addition of 1mL of
anhydrous MeOH and 2mL of a saturated aqueous solution of sodium potassium tartarate. This mixture was
allowed to stir at room temperature for 2 h. The layers were separated, and aqueous layer was extracted with
ethyl acetate (3 x 30 ml). The organic extracts were washed with brine (30 ml) and dried over anhydrous
Na2SO4, and purified by column chromatography (silica gel, 60–120 mesh, 25% EtOAc in pet. ether) to afford
1
the diol 8 (1.9 g, 84%) as a liquid. []D –38.1 (c 1.6, CHCl3); H NMR (CDCl3, 300 MHz):  7.22 (d, 2H, J 8.8 Hz,
Ar-H), 6.79 (d, 2H, J 8.8 Hz, Ar-H), 4.47 (d, 1H, J 11.6 Hz, -OCH2Ph), 4.39 (d, 1H, J 11.6 Hz, -OCH2Ph), 3.83 (s, 3H,
-OCH3), 3.76-3.64 (m, 2H), 3.43 (t, 2H, J 5.8 Hz), 3.03-2.88 (br s, 2H, 2 x -OH), 1.78–1.64 (m, 4H, 2 x -CH2), 1.52–
13
1.28 (m, 8H, 4 x CH2), 0.83 (t, 3H, J 5.8 Hz, -CH3); C NMR (75 MHz, CDCl3):  158.7, 129.7, 129.5, 114.3, 76.7,
67.9, 67.5, 67.3, 56.1, 45.6, 36.3, 33.8, 32.7, 25.6, 14.2; HRMS (ESI): m/z calcd for C18H30O4Na: 333.2042;
found: 333.2047 [M+Na]+.
(5S,7R)-5-(2-(4-Methoxybenzyloxy)ethyl)-2,2,3,3,9,9,10,10-octamethyl-7-pentyl-4,8-dioxa-3,9-disilaun-
decane (9). A mixture of the above alcohol 8 (1.74 g, 5.61 mmol) and imidazole (1.52 g, 22.45 mmol) in dry
CH2Cl2 (40 mL) was treated with TBSCl (2.10 g, 14.02 mmol) at 0 °C under nitrogen atmosphere and stirred at
room temperature for 4 h. The reaction mixture was quenched with aq. NH4Cl solution (10 mL) and extracted
with CH2Cl2 (2 x 50 mL). The combined extracts were washed with water (30 mL), brine (30 mL), dried (Na2SO4)
and concentrated. The residue was purified by column chromatography (60-120 Silica gel, 5% EtOAc in pet.
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1
ether) to furnish 9 (2.44 g, 81%) as a colorless liquid. [α]D -57.4 (c 0.76, CHCl3); H NMR (CDCl3, 300 MHz): 
7.22 (d, 2H, J 8.8 Hz, Ar-H), 6.79 (d, 2H, J 8.8 Hz, Ar-H), 4.47 (d, 1H, J 11.6 Hz, -OCH2Ph), 4.39 (d, 1H, J 11.6 Hz, -
OCH2Ph), 3.83 (s, 3H, -OCH3), 3.52-3.41 (m, 2H), 3.41 (t, 2H, J 6.0 Hz), 1.74-1.56 (m, 6H, 3 x CH2), 1.42–1.25 (m,
6H, 3 x -CH2), 0.88 (t, 3H, J 5.8 Hz, -CH3), 0.83 (s, 9H, t-butyl), 0.79 (s, 9H, t-butyl), 0.08 (s, 6H, 2 x –CH3), 0.03 (s,
13
6H, 2 x –CH3); C NMR (75 MHz, CDCl3):  158.6, 129.7, 129.4, 114.2, 113.2, 75.9, 70.3, 67.9, 67.6, 56.0, 46.1,
36.2, 33.7, 31.9, 26.6, 26.3, 25.7, 22.8, 17.9, 13.9, -4.3, -4.6; HRMS (ESI): m/z calcd for C30H58O4NaSi2:
561.3771; found: 561.3774 [M+Na]+.
(3S,5R)-3,5-Bis(tert-butyldimethylsilyloxy)decan-1-ol (10). To a solution of 9 (2.3 g, 4.27 mmol) in aq. CH2Cl2
(20 mL, 19:1), DDQ (1.16 g, 5.13 mmol) was added and stirred at room temperature for 3 h. The reaction
mixture was quenched with sat. NaHCO3 solution (30 mL), filtered and washed with CH2Cl2 (50 mL). The filtrate
was washed with water (30 mL), brine (30 mL), dried (Na2SO4) and evaporated under reduced pressure. The
residue was purified by column chromatography (60-120 Silica gel, 15% EtOAc in pet. ether) to furnish 10 (1.39
1
g, 78%). [α]D -57.4 (c 0.76, CHCl3); H NMR (CDCl3, 300 MHz):  3.72-3.61 (m, 2H), 3.57 (br s, 1H, –OH), 3.47
(m, 1H), 3.41 (m, 1H), 1.82-1.66 (m, 8H, 4 x CH2), 1.39-1.21 (m, 2H, -CH2), 1.19-1.11 (m, 2H, -CH2), 0.87 (t, 3H, J
5.8 Hz, -CH3), 0.81 (s, 9H, t-butyl), 0.79 (s, 9H, t-butyl), 0.07 (s, 6H, 2 x -CH3), 0.01 (s, 6H, 2 x -CH3); 13C NMR (75
MHz, CDCl3):  70.3, 69.0, 61.3, 46.3, 38.3, 35.2, 32.3, 26.3, 26.1, 25.3, 23.1, 19.1, 14.0, -4.4, -4.7; HRMS (ESI):
m/z calcd for C22H50O3NaSi2: 441.3196; found: 441.3199 [M+Na]+.
(3R,5R)-3,5-Bis(tert-butyldimethylsilyloxy)decanoic acid (11). To a stirred solution of 10 (1.20 g, 2.87 mmol)
o
in CH2Cl2:H2O (1:1, 10 mL), TEMPO (0.15 g, 0.97 mmol) and BIAB (2.77 g, 8.61 mmol) were added at 0 C and
stirred for 1 h. The reaction mixture was diluted with water (5 mL) and extracted with CH2Cl2 (2 x 20 mL). The
organic layers were washed with brine (10 mL), dried (Na2SO4), evaporated and the residue purified by column
chromatography (silica gel, 60–120 mesh, 20% EtOAc in pet. ether) to give acid 11 (0.88 g, 71%) as a colorless
1
gummy oil. [α]D –7.4 (c 0.9, CHCl3). H NMR (CDCl3, 300 MHz):  4.26- 4.22 (m, 1 H); 3.73-3.67 (m, 1 H); 2.59
(dd, J 15.0, 5.0 Hz, 1 H); 2.45 (dd, J 15.0, 6.8 Hz, 1 H); 1.78-1.55 (m, 2 H); 1.45-1.12 (m, 8 H); 0.91 (t, 3H, J 7.1
Hz, -CH3), 0.81 (s, 9H, t-butyl), 0.79 (s, 9H, t-butyl); 0.07 (s, 6 H); 0.04 (s, 6H). 13C NMR (75 MHz, CDCl3):  176.9,
69.3, 66.8, 44.4, 42.1, 37.3, 32.1, 29.8, 25.8, 25.7, 24.6, 22.6, 17.9, 17.8, 14.0, -4.2, -4.5, -4.8 ; HRMS (ESI): m/z
calcd for C22H48O4NaSi2: 455.2989; found: 455.2994 [M+Na]+.
(3R,5R)-3,5-Dihydroxydecanoic acid (2). To a cooled (0 oC) solution of 11 (0.72 g, 1.66 mmol) in dry THF (5 mL)
under nitrogen atmosphere, TBAF (4.2 mL, 4.2 mmol) was added and stirred for 3 h. After completion of
reaction, reaction mixture was diluted with water (5 mL) and extracted with ethyl acetate (2 x 20 mL). Organic
layers were washed with water (2 x 10 mL), brine (10 mL), dried (Na2SO4), evaporated and purified the residue
by colomn chromatography to give 2 (0.26 g, 78%) as semisolid which was directly used for next reaction
without any purification.
Verbalactone (1). To a stirred solution of 2 (0.26 g, 1.27 mmol) and Et3N (0.53 mL, 3.81 mmol) in dry THF (2
mL), a solution of 2, 4, 6-trichlorobenzoyl chloride (0.30 mL, 1.91 mmol) in dry THF (1 mL) was added. The
resulting mixture was stirred for 2 h at room temperature under nitrogen atmosphere and evaporated to
afford the mixed anhydride. It was diluted with toluene (10 mL) and filtered quickly through celite. The filtrate
was added drop wise to a stirred solution of DMAP (1.54 g, 12.7 mmol) in toluene (35 mL) at 90 °C over a
period of 6 h. After the complete addition, the reaction mixture was stirred at 100 °C for 2 h. It was cooled,
washed with 7% aq NaHCO3 (40 mL), 2M aqueous HCl (40 mL), brine (40 mL) and dried (Na2SO4). The organic
layer was evaporated and the obtained residue purified by column chromatography (60-120 Silica gel, 15%
1
EtOAc in pet. ether) to give 1 (0.13 g, 57%) as a syrup. []D +10.1 (c 1.1, CHCl3). H-NMR (CDCl3, 300 MHz): 
4.97-4.90 (m, 2 H, 2 x -CH); 4.11-4.04 (m, 2 H, 2 x -CH); 3.73 (br s, 2 x OH); 2.71 (d, 4 H, J 3.1 Hz, 2 x –CH2); 2.04
(ddd, 2 H, J 15.3, 10.2, 3.1 Hz, 2 x -CH); 1.98 (td, 2 H, J 4.0, 15.0 Hz, 2 x -CH); 1.69-1.39 (m, 4 H, 2 x –CH2); 1.37-
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1.20 (m, 12 H, 6 x CH2); 0.85 (t, 6H, J 6.3 Hz, 2 x –CH3). CNMR (CDCl3, 75 MHz):  173.1, 72.7, 64.9, 39.3,
38.1, 31.6, 31.5, 25.4, 22.5, 14.3; HRMS (ESI): m/z calcd for C20H36O6Na: 395.2410; found: 395.2414 [M+Na]+.
Acknowledgements
The autohrs are thankful to Jawaharlal Nehru Technological University Hyderabad, CMR Institute of
Technology Secunderabad, QIS College of Engineering & Technology (Autonomous), Vengamukkapalem,
Ongole for constant encouragement in providing laboratory facilities and analytical data.
Supplementary Material
Copies of 1H and 13C NMR spectra associated with this paper can be found in the online version.
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