Liquid crystal dimers derived from naturally occurring chiral moieties: synthesis and characterization

Article abstract of DOI:10.1016/j.tet.2008.02.013

Naturally occurring cholesterol and α-chloroalkanoyl units derived from natural α-amino acids (l-valine, l-leucine, and l-isoleucine) have been utilized to prepare three different series of nonsymmetric liquid crystal dimers. Tolane (diphenylacetylene), w

Full text of DOI:10.1016/j.tet.2008.02.013

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 3760e3771
www.elsevier.com/locate/tet
Liquid crystal dimers derived from naturally occurring chiral
moieties: synthesis and characterization
*
Channabasaveshwar V. Yelamaggad , Govindaswamy Shanker
Centre for Liquid Crystal Research, Jalahalli, Bangalore 560013, India
Received 30 November 2007; received in revised form 5 February 2008; accepted 6 February 2008
Available online 8 February 2008
Abstract
Naturally occurring cholesterol and a-chloroalkanoyl units derived from natural a-amino acids (L-valine, L-leucine, and L-isoleucine) have
been utilized to prepare three different series of nonsymmetric liquid crystal dimers. Tolane (diphenylacetylene), which is known to possess
several promising structural features, has been chosen as the other mesogenic segment to covalently tether with cholesterol through a flexible
spacer. In each series, the terminal a-chloro ester group attached to the tolane unit is kept constant, while the length and parity of the spacer have
been varied; specifically, three dimers comprising even-parity spacer of varying length, and one compound with an odd-parity spacer constituted
a series. The phase behavior of these dimers has been ascertained mainly by polarizing microscopic and calorimetric studies. Except one, all the
11 dimers display enantiotropic mesomorphism. Within the series, clearing temperatures exhibit a dramatic oddeeven effect wherein the even-
parity dimers possess higher values. In general, the dimers comprising a-chloro ester group derived from L-valine and L-leucine stabilize chiral
nematic and/or smectic phase/s, while the compounds with terminal group resulting from L-isoleucine show twist grain boundary phase addi-
tionally; this implies that the nature of the a-chloro ester group influences the phase behavior. Notably, an odd-parity dimer with an a-chloro
ester group derived from L-valine exhibits a transition from an intercalated smectic A phase to a monolayer (unknown) smectic phase, as evi-
denced by optical, calorimetric, and X-ray diffraction studies. As representative case, a dimer has been screened for antimicrobial activity by disc
diffusion method; a notable activity has been found against some microbes.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
(N*) or chiral smectic C (SmC*) have been recognized for
their use in thermochromic4 and electro-optic devices, respec-
tively.5 Besides, electroclinic property of the orthogonal lay-
ered phase, the chiral smectic A (SmA) phase holds a great
promise in spatial light modulation applications.6 However,
the properties of these chiral mesophases fundamentally de-
pend on the chirality of the constituent molecules, which in
turn critically depends on the nature of the chiral segment/s
they possess.2,3 Likewise, the origin of a particular chiral LC
phase in preference to other or their occurrence in a phase se-
quence is also speculated to be evolving from the molecular
chirality of the constituent mesogens. In other words, by the
rational design of chiral LCs incorporating appropriate chiral
building block/s, the features of the chiral mesophases can
be modified; of course, not all the optically active LC mate-
rials prepared based on such directed molecular design exhibit
the speculated property.
Liquid crystal (LC) phases (mesophases) are fascinating
orientationally ordered fluids formed by the self-assembly of
shape-anisotropic molecules, so called mesogens.1 The chiral
LC phases generated by optically active mesogens or by dop-
ing the mesophase with a suitable chiral dopant are even more
fascinating as they possess a dizzying array of special proper-
ties and structures that are promising from both fundamental
science and application view points.2e6 For example, the frus-
trated fluid phases such as blue phases (BPs)2,3b and twist
grain boundary (TGB) phases2,3 are of fundamental scientific
curiosity, while the helical structures of the chiral nematic
* Corresponding author.
E-mail address: yelamaggad@yahoo.com (C.V. Yelamaggad).
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.013

C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3761
The chiral moieties employed in building mesogens are
generally chosen from the chiral pool, the readily available
natural products or their modified forms, and synthetic prod-
ucts.2,7,8 The former approach appear to be more appropriate
given the fact that the natural products, needless to say, are
structurally diverse and economically feasible. Besides, natu-
rally occurring moieties or their derivatives are well known
to induce interesting features in the systems where they are
used. For example, chiral polar terminal chains, the a-chloro-
alkanoyl units, derived from a-amino acids viz., L-valine,
L-leucine, and L-isoleucine have been evidenced to be suitable
for stabilizing wide thermal range ferroelectric LC (SmC*)
phase associated with high spontaneous polarization (Ps) and
low rotational viscosity.7e12 The cause for the high Ps in these
systems is attributed to the presence of a-chloro ester group
that induces a large lateral overall molecular dipole moment.12
In addition, the materials possessing such chiral moiety are
known to exhibit polymesomorphic sequences involving N*,
SmC*, SmA phases as well as highly ordered smectic phases;9
some of them have also shown the frustrated (BP and TGB)
phases.7e,9b,10,11 Likewise, a variety of steroids have been
used to generate chiral mesophases,13 but only cholesterol
cholesterol and 4-n-hexyloxytolane moieties interlinked
through an 6-oxyhexanoyl spacer displays a reentrant TGBA
(comprising blocks of SmA) phase besides TGBC* phase,
where the slabs of the mesogens have a local SmC* struc-
ture.23e,24 Moreover, the tolane as an anisometric segment, is
reasonably stable to heat and moisture and hence, all the cho-
lesterol-based dimers featuring this core show highly repro-
ducible mesomorphism. Another prominent aspect is that the
tolane moiety has been considered in designing bioactive mo-
lecular systems in recent times.29 Therefore, it seemed inter-
esting to us to continue to work on nonsymmetric dimers
composed of cholesteryl ester and tolane mesogenic segments;
besides, owing to the several remarkable features of the
a-chloroalkanoyl units derived from a-amino acids as discussed
above, we intend to incorporate them in the dimeric molecular
design. Precisely, in order to further our understanding of the
structureeproperty correlations of cholesterol-based dimers
composed of tolane entity, and to evaluate the influence of dif-
ferent a-chloroalkanoyl tails on the overall phase behavior, we
designed and prepared three series of dimers. In each series,
a particular type of chiral tail derived either from L-valine or
L-leucine or L-isoleucine and four different spacers, namely,
trimethylene (4-oxybutanoyl), tetramethylene (5-oxypenta-
noyl), pentamethylene (6-oxyhexanoyl), and heptamethylene
(8-oxyoctanoyl) have been used. The acronyms used to denote
these three series of dimers are TDV-n, TDL-n, and TDI-n,
where T, D, V, L, and I refer to Tolane, Dimer, Valine, Leu-
cine, and Isoleucine, respectively; n signifies the number of
methylene units in the flexible spacer.
has been incorporated extensively as an important building
13,14
block
owing to its rigid molecular structure possessing
eight chiral centers. In fact, the first example of a thermotropic
LC is derived from cholesterol, the cholesteryl benzoate.15
Hitherto, well over 3000 cholesterol-containing compounds
falling under the category of monomers,13e15 oligomers,16e26
and polymers27 have been reported; indeed, the vast majority
of them are the low molar mass systems, in particular the
monomers.13,14
2. Synthesis and molecular structural characterization
The accumulated experimental results clearly reveal the
ability of cholesterol in generating mesomorphism in its vari-
ous derivatives several of which possess remarkable phase se-
quences. This is especially notable in the case of optically
active nonsymmetric dimers formed by covalently interlinking
cholesteryl ester unit axially with different conventional aro-
matic mesogens containing Schiff’s base,18 salicylaldimine,19
stilbene,20 azo,21 or biphenyl,22 tolane,23,24 diphenylbuta-
diene,25 bent-core26 units through a flexible spacer. For exam-
ple, they exhibit several kinds of frustrated phases including
a rarely found incommensurate smectic A (SmAic) phase;18a
in fact, this SmAic phase exists in an unusual phase sequence
appearing at the temperatures above as well as below the reen-
trant SmC* phase. Besides, some of these molecular systems
stabilize technologically important SmA, SmC*, and N* phase
over a wide thermal range.18e26 In the context of stabilizing
the frustrated and/or other chiral mesophases, our group23
and Jin et al.24 have been able to recognize that the tolane (di-
phenylacetylene) core, being nearly rigid with a little confor-
mation deviation,28 is highly promising. For instance, upon
tethering achiral tolane entity to cholesterol unit through a pen-
tamethylene (6-oxyhexanoyl) spacer, the N* phase of the re-
sultant dimers is stabilized over a wide thermal range;23a,b
on the other hand, when chiral tolane segment is used instead
of the achiral one, the SmA phase (showing electroclinic
effect) is stabilized.23c,d Remarkably, a dimer made of
The proposed dimers were prepared by the synthetic routes
shown in Schemes 1 and 2. The requisite optically pure
2-chloroalkanoic acids 1a, 1b, and 1c were prepared starting
from the corresponding a-amino acids L-valine, L-leucine,
and L-isoleucine according to a reported procedure;30 given
the fact that this reaction involves a double inversion process
where the partial racemization occurs, only the fraction (color-
less oil) collected in the temperature range of 75e77 ꢀC (at
10 mm) was used. These acids were converted to the corre-
sponding acyl chlorides 2aec by treating with oxalyl chloride
Cl
NH2
Cl
(b)
(a)
OH
OH
Cl
R
R
R
O
O
O
1a : R = i-Pr
1b : R = i-Bu
1c : R = (S)-sec-Bu
2a : R = i-Pr
L-Valine
: R = i-Pr
2b : R = i-Bu
L-Leucine : R = i-Bu
L-Isoleucine : R = (S)-sec-Bu
2c : R = (S)-sec-Bu
(d)
(c)
THPO
I
R
HO
I
THPO
3
4 : R = C(CH3)2OH
5 : R = H
(e)
Scheme 1. Reagents and conditions: (a) NaNO2, 6 N HCl, ꢁ3 to 0 ꢀC (50e
55%); (b) (COCl)2, rt, 4 h (quantitative); (c) 3,4-dihydro-2H-pyran, PTSA,
CH2Cl2, 2 h (82%); (d) 2-methylbut-3-yn-2-ol, CuI, Ph3P, (Ph3P)2PdCl2,
THF, NEt3, 85 ꢀC, 12 h (88%); (e) KOH, toluene, reflux, 1 h (60%).

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C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
temperatures obtained in DSC thermograms due to phase tran-
sitions during the first heating and cooling cycles (at a rate of
5 ꢀC/min), respectively, were in agreement with those of the
optical experiments. Of course, when the thermal signatures
were not found in DSC traces, the transition temperatures
are taken from the microscopic observations; the results of
these investigations are shown in Table 1. In the following sec-
tion, the details of these studies with analysis of the results are
presented.
In general, with the exception of a dimer viz., TDL-4, all
the members are enantiotropic mesogens. As can be seen,
the dimers TDV-3 and TDV-5 belonging to TDV-n series,
where the a-chloroalkanoyl tail they possess is derived from
L-valine, display an identical enantiotropic dimesomorphic se-
quence. On cooling isotropic phase, they show a focal-conic
texture (Fig. 1a), which on slight mechanical shear give
a Grandjean planar (with oily streak, see Fig. 1b) texture typ-
ical of the N* phase.31 Upon cooling the unperturbed sample
further, multidomains begin to appear that rapidly coalesce to
give a pattern consisting of focal-conic fan and pseudoiso-
tropic textures, a diagnostic feature of the orthogonal SmA
phase.31 The occurrence of this phase was confirmed by the
observation of focal-conic texture in slides treated for planar
( )
O
n
I
O
O
6a : n = 3; 6b : n = 4; 6c : n = 5; 6d : n = 7
(a)
( )
O
n
RO
O
O
7a : n = 3; 7b : n = 4; 7c : n = 5; 7d : n = 7
R = THP
R = H
(b)
8a : n = 3; 8b : n = 4; 8c : n = 5; 8d : n = 7
(c)
( )
O
n
Cl
R
O
O
O
O
TDV-3 : n = 3; R = i-Pr
TDV-4 : n = 4; R = i-Pr
TDV-5 : n = 5; R = i-Pr
TDV-7 : n = 7; R = i-Pr
TDL-3 : n = 3; R = i-Bu
TDL-4 : n = 4; R = i-Bu
TDL-5 : n = 5; R = i-Bu
TDL-7 : n = 7; R = i-Bu
TDI-3 : n = 3; R = (S)-sec-Bu
TDI-4 : n = 4; R = (S)-sec-Bu
TDI-5 : n = 5; R =(S)-sec-Bu
TDI-7 : n = 7; R = (S)-sec-Bu
Scheme 2. Reagents and conditions: (a) 5, CuI, Ph3P, (Ph3P)2PdCl2, THF,
NEt3, 85 ꢀC, 12 h (68e72%); (b) PTSA, CH3OH, THF, rt, 30 min
(75e80%); (c) 2aec, pyridine, THF, 0 ꢀC to rt, 12 h, (75e80%).
just prior to use. Next, 2-(4-ethynylphenoxy)-tetrahydro-2H-
pyran (5) was prepared in three steps starting from 4-iodophe-
nol.17aec The phenol group was first protected as the THP
ether to get compound 3; palladium-catalyzed Sonogashira
cross-coupling of this intermediate with 2-methylbut-3-yn-
2-ol yielded protected acetylene 4, which was subjected to
a deprotection reaction to remove the acetylene protected
group selectively to generate the free acetylene 5 as shown
in Scheme 1.
The coupling of cholesteryl u-(4-iodophenoxy)-alkanoa-
tes23f (6aed) with acetylene 5 using Sonogashira conditions
gave dimeric THP ethers 7aed, which on deprotection using
PTSA in a mixture of solvents viz., CH3OHeTHF furnished
the functionalized dimers 8aed.17a Finally, the esterification
of phenols 8aed with appropriate acyl chlorides 2aec in the
presence of a mild base (pyridine) gave the target dimers in
reasonably good yields as shown in Scheme 2. The molecular
structure of all the intermediates and final products was ascer-
tained using a combination of spectral and elemental analyses
(see Supplementary data).
Table 1
Phase transition temperaturesa (ꢀC) and enthalpies [kJ molꢁ1] of the dimesogens
Dimers
Heating/cooling
TDV-3
Cr 117.5 [21.6] SmA 191b N* 194.2 [0.7] I
I 189.3 [0.4] N* 186b SmA 104.9 [1.6] Cr
Cr 116.3 [46.1] SmA 131.8 [3.3] I
TDV-4
TDV-5
TDV-7
TDL-3
TDL-4
TDL-5
TDL-7
TDI-3
TDI-4
TDI-5
TDI-7
I 131 [3.2] SmA 113.7 [2.2] SmX 68.7 [13.4] Cr
Cr 117.6 [18.6] SmA 167.7 [2.1] N* 172.2 [2.4] I
I 170.4 [2.4] N* 165.5 [2.1] SmA 85.7 [14] Cr
Cr 127.5 [25.7] SmA 153.1 [8.3] I
I 148.3 [5.6] SmA 58.6 [15.4] Cr
Cr 159.8 [15.3] SmA 198.6 [0.8] N* 208.5 [2.8] I
I 198.4 [2.4] N* 187.3 [0.8] SmA 136.2 [15.7] Cr
Cr1 123.2 [2.3] Cr2 143.1 [19.6] I
I 135.4 [0.9] N* 109.1 [19] Cr
Cr 142.5 [19.6] SmA 168.8b N* 169.4 [1.5] I
I 166.5 [1.5] N* 165.3b SmA 119.1 [16.3] Cr
Cr 132.0 [12.5] SmA 164.4 [3.9] N* 170.6 [3.3] I
I 169.7 [3.2] N* 163.1 [3.4] SmA 85.4 [5.5] Cr
Cr 160.0 [29.8] SmA 186.4beTGBceN* 196.4 [1.3] I
I 193.5 [1.3] N* 183beTGBceSmA 83.6 [3.9] Cr
Cr 119.6 [28.6] SmA 124.8beTGBceN* 138.6 [1.1] I
I 136.5 [1.1] N* 122.5beTGBceSmA 68.7 [2.7] Cr
Cr 119.7 [24.4] SmA 155.4 [4 ]deTGBceN* 163.3 [3.1] I
I 161.9 [3.1] N* 153.9. [3.4]deTGBceSmA 55.2 [3.9] Cr
Cr 127.5 [34.3] SmA 155.1 [1.6]deTGBceN* 178.6 [3.4] I
I 177.9 [3.4] N* 153.1. [1.2]deTGBceSmA 90.7 [13.9] Cr
3. Result and discussion
3.1. Evaluation of mesomorphism
The thermal behavior for each of these nonsymmetric di-
mers belonging to three different series was ascertained using
polarizing optical microscope (POM), differential scanning
calorimeter (DSC), and X-ray diffraction (XRD). The sample
placed between a clean untreated glass slide and a cover slip
was used for the POM study; for confirmation of assignments,
two differently surface-coated slides, one treated for homoge-
neous alignment, the other for homeotropic alignment of the
mesogens were used. The endothermic and exothermic peak
Phase identified are abbreviated as Cr: crystals; N*: chiral nematic; SmA:
smectic A phase; TGB: twist grain boundary phase with either SmA or
SmC blocks; SmX: unknown smectic phase; I: isotropic liquid state.
a
Peak temperatures in the DSC thermograms obtained during the first heat-
ing and cooling cycles at 5 ꢀC/min.
b
The phase transition was observed under POM; it was too weak to be
detected by DSC.
c
A transient phase observed under POM.
d
The enthalpy (DH) value represents the combined enthalpy for both
SmAeTGB and TGBeN* transition.

C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3763
Figure 1. Photomicrographs showing the focal-conic (a) and planar (b) textures of the N* phase observed for the dimer TDV-3. Note that the latter texture is
obtained on applying mechanical stress to the former.
Figure 2. Microphotographs of the textures obtained for the homogeneously aligned SmA (a) and SmX (b) phases of the dimer TDV-4.
orientation and a dark field of view in slides treated for home-
otropic orientation.
was filled into a Lindemann capillary tube in the isotropic phase
and then both the ends of tube were flame sealed. The XRD pat-
terns obtained in the SmA and SmX phases at 125 ꢀC and 90 ꢀC,
respectively (for graphs see Supplementary data) were collected
on an image plate separately and were found to be almost iden-
tical except for the notable changes in the spacing values. The
diffractograms of the SmA and SmX phases consisted of a dif-
Surprisingly, the N* phase gets extinguished in other two
members of the series viz., TDV-4 and TDV-7 as they were
ascertained to display an enantiotropic SmA behavior; how-
ever, the former dimer having an odd-parity (5-oxypentanoyl;
C5) spacer stabilizes an additional metastable mesophase,
hereafter referred to as SmX phase. On cooling the isotropic
liquid of the samples placed between a pair of ordinary glass
substrates, exhibit SmA phase with typical textures. On further
cooling, the dimer TDV-7 transforms into a crystal phase,
whereas TDV-4 shows a transition into SmX phase before it
crystallizes. When the SmX phase is obtained by cooling of
the preceding focal-conic texture (Fig. 2a) of the SmA phase,
it showed a sort of broken focal-conic like pattern as shown in
Figure 2b.
On the other hand, if it is allowed to grow from the homeo-
tropic regions of the SmA phase, a poorly defined texture was
obtained, see Figure 3a. The DSC thermograms obtained for
the two successive heating and cooling cycles at a rate of
5 ꢀC/min are shown in Figure 3b where a prominent signature
due to the SmAeSmX transition can be seen; it may also be
noted that the phase transitions are reproducible signifying
the thermal stability of the dimer.
˚
fuse peak in the wide angle region with d (spacing)-value of 5 A
˚
and 5.2 A, respectively, which is a characteristic of liquid-like
correlations within the smectic planes. Besides, two sharp re-
flections were observed in the low angle regions for both the
˚
phases with the spacing being 34.1 A and 19.9 A for the SmA
˚
˚
˚
phase and 42.2 A and 23.6 A for the SmX phase confirming
a layer structure for both the mesophases; the reflections at
˚
˚
19.9 A and 23.6 A are the second harmonic and are generally
seen in dimeric systems.23c,d As can be seen, the layer periodic-
ity in the SmA phase is less than the length (L) of the dimer
˚
TDV-4 (L¼43 A) in its all-trans conformation (measured using
Chem3D software); this suggests an intercalated (partially-
bilayered) arrangement of the molecules where the mesogenic
segments, spacers, and terminal tails are mixed, as schemati-
cally shown in Figure 4a. On the other hand, the small angle re-
˚
flection corresponding to periodicity of 42.2 A is nearly equal to
the length of the molecule, with a d/L ratio of 0.98, indicating the
monolayer molecular packing in the SmX phase (Fig. 4b)
wherein the mesogenic segments, spacers, and tails form three
different regions.
Powder XRD measurements using Cu Ka radiations
˚
(l¼1.5418 A) were carried out to know the precise molecular
organization in both SmA and SmX phases. The dimer TDV-4

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C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
trimesomorphic sequence was established by optical textural
(a)
observation. On cooling isotropic phase of any one of these
four dimers placed between a pair of clean glass sides and ob-
served under POM, a focal-conic texture of the N* phase ap-
pears that on shearing transforms to an oily streaks texture. On
lowering the temperature from planar texture of the N* phase,
the transition to a transient TGB phase occurs with a blurred
gray planar texture that rapidly transforms into a focal-conic
texture typical of the SmA phase. If the sample is cooled
from the natural focal-conic (unsheared) texture of the N*
phase, the transition to the SmA was clearly visible where fo-
cal-conic as well as pseudoisotropic textures persisted; how-
ever, the latter pattern existed predominately, which upon
heating (0.1 to 0.5 ꢀC/min) slowly gave a striking filament tex-
ture of the TGB phase,31 see Figure 5b. It may be note here
that the TGB phase may have either SmA or smectic C
(SmC) slabs.2
The important results obtained by analyzing the thermal be-
havior of these 12 new nonsymmetric dimers are the follow-
ing. Seemingly, the thermal behavior of dimers belonging to
TDV-n, TDL-n, and TDI-n series, as surmised in parts (aec)
of Figure 6, respectively, shows some dependence on the
length and parity of the spacer; the influence of the parity of
the spacer on the clearing temperature is especially remark-
able. For instance, the dimers TDV-4, TDL-4, and TDI-4
comprising an 5-oxypentanoyl (odd-parity; C5) spacer show
lower clearing temperatures; as is well known, such a behavior
can be explained in terms of the overall molecular shape of the
dimer governed by the geometry and flexibility of the spacer it
possesses. The entropy changes associated with isotropic liq-
uid-chiral nematic phase also exhibits oddeeven effect for
the TDI-n (see Supplementary data) and TDL-n (see,
Fig. 6d). The space-filling models of energy-minimized mo-
lecular structures, deduced from MM2 computations of CS
Chem Draw 3D (version 5) program, of dimers TDV-3 and
TDV-4 are shown in Figure 7a and b, respectively, as represen-
tative cases. Apparently, the tolane and cholesterol segments
in dimer TDV-4 are inclined giving a bent molecular shape
to the molecule, and thus, the shape anisotropy is reduced ac-
counting for the lower clearing temperatures. It is also percep-
tible that on increasing the length of the even-parity spacers,
except in a few cases, the clearing temperature decreases
(b)
Heating
Cooling
24
22
20
IInd
Ist
Cr
SmA
I
Ist
SmX
I
SmA
Cr
IInd
60
80
100
Temperature (°C)
120
Figure 3. (a) Texture microphotograph of the SmX phase emanated from the
pseudoisotropic pattern (homeotropic region) of the preceding SmA phase
of compound TDV-4. (b) DSC traces obtained during the two successive heat-
ing and cooling cycles for the dimer TDV-4; notice an exothermic peak due to
SmAeSmX phase transition.
It can be seen in Table 1 that all even-members viz., TDL-3,
TDL-5, and TDL-7 of the TDL-n series, where the terminal
tail is derived from L-leucine, exhibit an enantiotropic dimeso-
morphic sequence involving a transition from N* phase to
SmA phase; Figure 5a shows a texture microphotograph where
this phase transition obtained for the dimer TDL-3 can be
seen. Whereas, the dimer TDL-4 comprising an odd-parity
spacer exhibits a monotropic chiral nematic phase. The occur-
rence of both the mesophases, needless to say, was confirmed
by textural observation as described before. All the four com-
pounds of TDI-n series, which possess a chiral a-chloroalka-
noyl tail derived from L-isoleucine, exhibit enantiotropic N*,
and SmA phases in addition to a transient TGB phase; this
Figure 4. Schematic representation of molecular organizations in an intercalated SmA phase (a) and a fluid monolayer SmX phase (b) formed by the dimer TDV-4.

C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3765
Figure 5. (a) Microphotograph showing characteristic focal-conic texture (left portion) of the SmA phase as seen growing from the N* phase (right portion) of
dimer TDL-3. (b) Filamentary texture photomicrograph of the TGB phase obtained during the transition from a homeotropically aligned SmA phase to N* phase
for the dimer TDI-3.
that can be obviously attributed to the higher degree of confor-
mational freedom of the molecules.
Thus, the occurrence of positive pitch band indicates right-
handed screw sense of the chiral nematic structure, which is in
accordance with our earlier observation that the dimers pos-
sessing cholesteryl ester entity are right handed.34
Furthermore, the nature of a-chloroalkanoyl tail seems to
influence the phase behavior moderately; for example, the
compounds of TDI-n series possessing a terminal derived
L-isoleucine, unlike the dimers belonging to TDV-n and
TDL-n series, exhibit a frustrated phase. Most importantly,
contrary to general expectation, none of the dimers synthe-
sized exhibit the SmC* phase; this can be perhaps attributed
to the presence of short terminal tail length as well as the bulk-
iness/non-linearity of the cholesterol, which disfavor the
required staggering of the cores.32
As is well known, a large number of drugs and medicinal
agents are derived from natural substances; they have advan-
tages over synthetic compounds owing to their diverse struc-
tural features with remarkable biological activity.35 Besides,
they offer several ways of amending their molecular structure
such that the molecular material features such as self-organiz-
ing ability, fluidity, molecular recognition can be imbued. For
example, as discussed above, cholesterol and its derivatives
are not only familiar in the area of supramolecular chemistry,14
but also in health care.36 Likewise, the amino acid deriva-
tives are widely recognized for their biological significance.37
As discussed earlier, tolane core has now been considered as
an important building block to generate biologically active
compounds. Given the fact that such promising components are
incorporated in nonsymmetric dimers of the present investiga-
tion, we were motivated to examine their biological property.
As a first step in this direction, we intended to evaluate antimicro-
bial activity of a representative compound. Thus, an indiscri-
minately selected dimer TDI-5 was subjected for antibacterial
and antifungal screening by disc diffusion technique (DDT);
the results obtained are tabulated in Table 2. DDT was carried
out using molten Muller Hinton agar media. The inoculum size
was standardized under aseptic condition such that each mL
contains 108 cells. The inoculum was uniformly inoculated using
sterile cotton swab. Dimer TDI-5 (200 mL, 1 mg/mL) was placed
at regular intervals over inoculated medium using Whatmann
No. 2 filter paper disc of 6 mm in diameter. The plates were
then incubated at 37 ꢀC for 24 h. The zone of inhibition was
read using zone reader, Ciprofloxcin and Clotrimazole of
10 mg/disc potency was used as standard discs for bacteria and
fungi, respectively, as shown in zone plate photographs (see
Supplementary data).
It is well established that the chiral nematic phase exhibits
circular dichroism (CD) where the incident light is resolved
into its two circularly polarized components, left and right, at
a given wavelength.1a,33 At this wavelength, depending upon
the natural helical sense of the phase, circularly polarized light
of a particular handedness is completely reflected while its
counterpart is transmitted. Thus, the handedness (screw sense)
of the helical array of the phase can be ascertained. Recently,
we have reported the first elaborative study on the chiroptical
property of the N* phase formed by nonsymmetric chiral di-
mers; an oddeeven effect was evidenced for the selective re-
flection wavelengths.34a Importantly, our study indicated that
the N* pitch is right handed for all the studied dimers, which
is in agreement with the fact that most steroidal esters are right
handed; with a view to obtain a similar information formally,
CD measurement was carried out in the neat N* phase of dimer
TDL-4. The dimer sandwiched between two quartz plates was
heated to isotropic phase and cooled slowly with repeated me-
chanical shearing to attain Grandjean (planar) texture so that
the helix of the phase becomes normal to the quartz plates and
the structure reflects the incident light. Figure 8 shows
temperature dependence of the CD spectra recorded in the N*
phase during the cooling cycle. In the CD spectra obtained at
temperatures 133 ꢀC, 130 ꢀC, 125 ꢀC, 120 ꢀC, and 115 ꢀC strong
positive peaks at l¼364 cmꢁ1 (CD¼405 mdeg), 373 cmꢁ1
(CD¼364 mdeg), 377 cmꢁ1 (CD¼323 mdeg), 379 cmꢁ1
(CD¼301 mdeg), and 382 cmꢁ1 (CD¼281 mdeg), respectively,
were seen.
Apparently, the dimer shows some marked activity against
Candida albicans; for other microbes it showed little activity.
However, resistance (inhibition) was observed against Staphy-
lococcus albus and Staphylococcus faecalis. This preliminary

3766
C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
study indicates that nonsymmetric dimers having pro-bioac-
200
180
160
140
120
100
80
(a)
tive components could be of some pharmacological interest;
indeed, a systematic study involving design and synthesis of
such dimers with variations in their molecular fragment/s is
essential to prove their real credibility.
I-N*
I-SmA
N*-SmA
SmA-SmX
SmA-Cr
SmX-Cr
3.2. Summary
Twelve new optically active nonsymmetric dimers have
been synthesized and their liquid crystal behavior is investi-
gated. Specifically, in order to study structureeproperty rela-
tionships of cholesterol-based dimers comprising tolane
segment, and to evaluate the effect of different a-chloroalka-
noyl tails on the phase behavior, three different series of di-
mers have been studied. In each series, the length and parity
of the spacer is varied while the chiral a-chloroalkanoyl tail
is held constant. The experimental results show that both the
spacer parity and the nature of terminal tail influence the ther-
mal behavior. The former affects the clearing temperature sig-
nificantly; the dimers comprising even-parity spacer show
higher values. Whereas, the latter seems to play an important
role in deciding the phase sequence; the dimers possessing
a-chloro ester group derived from L-valine/L-leucine stabilize
chiral nematic and/or smectic phase/s, while the systems
with terminal group resulting from L-isoleucine show twist
grain boundary phase additionally. For an odd-parity dimer
with an a-chloro ester group derived from L-valine, the occur-
rence of a transition from intercalated smectic A phase to an
unknown smectic phase with monolayer molecular packing
has been established by XRD study. To explore the biological
activity, one of the randomly selected dimer has been screened
for antibacterial and antifungal activities by disc diffusion
method; the dimer seems to be active against some microbes.
60
40
3
4
5
6
m
7
8
9
200
180
160
140
120
100
80
(b)
(c)
(d)
I-N*
N*-SmA
N*-Cr
SmA-Cr
60
40
3
4
5
6
m
7
8
9
200
180
160
140
120
100
80
I-N*
N*-SmA
SmA-Cr
4. Experimental
4.1. General information
The requisite precursors were purchased either from Al-
drich or Lancaster Company and used as received. Solvents
were purified and dried by literature methods prior to the
use. Crude compounds were purified by column chromato-
graphic technique using either silica gel (400 mesh) or neutral
aluminum oxide as a stationary phase. Thin layer chromatog-
raphy (TLC) was performed on aluminum sheets pre-coated
with silica gel (Merck, Kieselgel 60, F254). Absorption spectra
were recorded on a PerkineElmer Lambda 20 UVeVis
60
40
3
4
5
6
m
7
8
9
0.8
0.6
0.4
0.2
0
Figure 6. The influence of the number of carbon atoms m (nþ1) in the u-oxy-
alkanoyl spacer on the transition temperatures for TDV-n (a), TDL-n (b), and
TDI-n (c). Note that in TDI-n series phase diagram (c), the TGB phase has not
been included owing to its transient nature (for details see Table 1). Also
shown is the dependence of isotropic liquid-chiral nematic phase transition en-
tropy on the number of carbon atoms (m) in the u-oxyalkanoyl spacer of
TDL-n series (d). In all the plots dashed lines joining points are suggestive
of the general trend; it may be noted that experimental data do not cover for
n¼7.
3
4
5
6
m
7
8
9

C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3767
Elemental analyses were done using Eurovector model EA
3000 CHNS analyzer. The specific rotation of the target mole-
cules was measured using a JASCO DIP-370 digital polari-
meter. CD measurements were carried out using Jasco J-810
spectropolarimeter. The identification of the mesophases and
the transition temperatures of the compounds were initially de-
termined using a polarizing microscope (Leitz DMRXP) in
conjunction with a programmable hot stage (Mettler FP90).
The phase transition temperatures and associated enthalpies
were determined from thermograms recorded at a scanning
rate of 5 ꢀC/min on a differential scanning calorimeter
(DSC; PerkineElmer DSC-7 with the PC system operating
on Pyris software) apriorically calibrated using pure indium
as a standard. The energy-minimized space-filling molecular
structures of dimers were obtained using MM2 computations
of the CS ChemDraw3D (version 5) program. The X-ray mea-
surements were performed using Cu Ka radiations
Figure 7. Space-filling models of energy-minimized molecular structures of
dimers TDV-3 (a) and TDV-4 (b); notice that in the later case the tolane
and cholesterol entities are leaning.
˚
(l¼1.5418 A) from a fine focus sealed-tube generator (Enraf
Nonius FR590), in conjunction with double mirror focusing
optics. The detector employed was an image plate detector
(MAC Science, Japan; Model DIP 1030).
133 °C
400
130 °C
125 °C
120 °C
300
115 °C
4.2. General procedure for the synthesis of TDV-n, TDL-n,
and TDI-n series of dimers
200
The a-chloro acid (1aec) (3.3 mmol, 1.0 equiv) was taken
in a two-necked round bottomed flask under nitrogen atmo-
sphere to which oxalyl chloride (10 mmol, 3 equiv) was
added. The reaction mixture was stirred at room temperature
for 4 h. The excess of oxalyl chloride was distilled off under
reduced pressure. The acid chloride obtained was thoroughly
dried under vacuo to which a mixture of cholesteryl u-[(4-hy-
droxyphenylethynyl)-4-phenoxy]alkanoates (8aed) (0.15 mmol,
1.0 equiv) and pyridine (0.5 mL) in dry THF (10 mL) was
added drop wise at 0 ꢀC. The reaction mixture was slowly al-
lowed to attain room temperature and continued to stir for
12 h. The reaction mixture was filtered on Celite bed; after
evaporating the solvent from the filtrate, a colorless mass
was obtained that was dissolved in CH2Cl2. The organic layer
was thoroughly washed with 3 N HCl(aq) (2ꢂ10 ml), 5% solu-
tion of NaOH(aq) (2ꢂ10 ml), water (2ꢂ10 ml), brine, and dried
over anhydrous Na2SO4. The crude mass obtained upon evap-
oration of the solvent was purified by column chromatography
on silica gel (100e200 mesh). Elution with a mixture of 5% of
EtOAcehexanes afforded the product. It was further purified
by repeated recrystallizations from a mixture of EtOHe
CH2Cl2 (9:1) to get a pure white solid.
100
0
250
300
350
400
450
(nm)
500
550
600
Figure 8. Temperature dependence of the CD spectra of the N* phase recorded
in the cooling cycle for dimer TDL-4.
Table 2
Results of antimicrobial (antibacterial and antifungal) activity measured by
DDT
Organism
Diameter of the inhibition zone (in mm)
TDI-5
Standard
Staphylococcus aureus
Staphylococcus albus
Staphylococcus faecalis
Escherichia coli
15
Ra
Ra
14
20
15
13
20
30
35
40
24
40
35
25
26
Pseudomonas aeruginosa
Klebsiella aerogenes
Proteus vulgaris
Candida albicans
a
Resistance.
4.2.1. Cholesteryl 4-[(4-(2-chloro-3-methylbutanoyloxy)-
phenylethynyl)-4-phenoxy]butanoate (TDV-3)
spectrometer. IR spectra were recorded using PerkineElmer
Spectrum 1000 FT-IR spectrometer. 1H NMR spectra were re-
corded using either a Bruker AMX-400 (400 MHz) or a Bruker
Aveance series DPX-200 (200 MHz) spectrometer and the
chemical shifts are reported in parts per million (ppm) relative
to tetramethylsilane (TMS) as an internal standard. Mass spec-
tra were recorded on a Jeol-JMS-600H spectrometer in FABþ
mode using 3-nitrobenzyl alcohol as a liquid matrix.
Rf¼0.40 in 10% EtOAcehexane; yield: 75%; IR (KBr
pellet) nmax in cmꢁ1: 2951, 2219, 1772, 1718, 1607, 1247,
1197, 1163, 770; UVevis: lmax¼311.6 nm, 3¼2.59ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ13.2 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.54 (d, J¼9.1 Hz, 2H, Ar), 7.45 (d,
J¼8.8 Hz, 2H, Ar), 7.11 (d, J¼8.2 Hz, 2H, Ar), 6.86 (d,
J¼8.8 Hz, 2H, Ar), 5.37 (br d, J¼3.7 Hz, 1H, 1ꢂolefinic),

3768
C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
4.64 (m, 1H, 1ꢂCHOCO), 4.33 (d, J¼6.6 Hz, 1H, CHCl), 4.04
(t, J¼6.1 Hz, 2H, 1ꢂOCH2), 2.49e1.05 (m, 33H, 7ꢂCH,
2ꢂallylic methylene, 11ꢂCH2), 1.04 (s, 3H, 1ꢂCH3), 1.01
(s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.5 Hz,
3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C NMR
(100 MHz, CDCl3): 172.49, 168.24, 159.05, 149.91, 139.63,
133.07, 132.65, 122.69, 121.89, 121.20, 115.16, 114.58,
89.79, 86.08, 74.13, 66.89, 63.85, 56.71, 56.17, 55.65,
50.05, 43.39, 42.33, 39.75, 39.52, 38.15, 26.98, 36.60,
36.19, 35.78, 35.78, 31.89, 31.08, 28.99, 28.22, 28.01,
27.82, 25.31, 24.65, 24.28, 23.83, 22.80, 22.55, 21.48,
21.04, 19.30, 18.72, 18.20, 11.71, 10.69; MS (FABþ): m/z
calcd for C50H67ClO5: 782.47. Found: 782.52; Anal. Calcd
for C50H67ClO5: C, 76.65; H, 8.62. Found: C, 76.88; H, 8.78.
121.20, 114.92, 114.54, 89.85, 87.00, 73.83, 67.71, 63.70,
56.69, 56.14, 50.03, 43.37, 42.31, 39.73, 39.51, 39.10, 38.16,
36.98, 36.59, 36.18, 35.78, 34.55, 32.70, 31.89, 28.86, 28.21,
28.01, 27.82, 25.57, 24.76, 24.27, 23.82, 22.80, 22.56, 21.47,
19.31, 18.71, 18.20, 11.70, 10.81; MS (FABþ): m/z calcd for
C52H71ClO5: 810.50. Found: 810.57; Anal. Calcd for
C52H71ClO5: C, 76.96; H, 8.82. Found: C, 77.03; H, 8.80.
4.2.4. Cholesteryl 8-[(4-(2-chloro-3-methylbutanoyloxy)-
phenylethynyl)-4-phenoxy]octanoate (TDV-7)
Rf¼0.40 in 10% EtOAcehexane; yield: 70%; IR (KBr
pellet) nmax in cmꢁ1: 2938, 2219, 1770, 1728, 1606, 1249,
1198, 1163, 749; UVevis: lmax¼312.1 nm, 3¼3.01ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ9.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.7 Hz, 2H, Ar), 7.10 (d, J¼8.6 Hz, 2H, Ar), 6.86 (d,
J¼8.7 Hz, 2H, Ar), 5.37 (br d, J¼3.9 Hz, 1H, 1ꢂolefinic),
4.60 (m, 1H, 1ꢂCHOCO), 4.3 (d, J¼6.6 Hz, 1H, CHCl),
3.99 (t, J¼6.3 Hz, 2H, 1ꢂOCH2), 2.45e1.05 (m, 41H,
7ꢂCH, 2ꢂallylic methylene, 15ꢂCH2), 1.03 (s, 3H,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92
(d, J¼6.4 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3),
0.85 (d, J¼1.6, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
NMR (100 MHz, CDCl3): 173.01, 167.45, 159.60, 149.23,
139.71, 133.20, 132.65, 127.81, 127.40, 122.69, 121.85,
121.26, 116.00, 109.39, 68.52, 62.80, 58.65, 51.50, 50.98,
44.87, 34.55, 32.96, 31.80, 30.98, 30.55, 29.42, 25.59,
23.73, 23.10, 22.61, 20.59, 19.71, 19.05, 17.30, 15.82,
14.36, 14.05, 12.97, 10.91; MS (FABþ): m/z calcd for
C54H75ClO5: 838.53. Found: 838.71; Anal. Calcd for
C54H75ClO5: C, 77.25; H, 9.0. Found: C, 77.60; H, 8.87.
4.2.2. Cholesteryl 5-[(4-(2-chloro-3-methylbutanoyloxy)-
phenylethynyl)-4-phenoxy]pentanoate (TDV-4)
Rf¼0.40 in 10% EtOAcehexane; yield: 71%; IR (KBr
pellet) nmax in cmꢁ1: 2938, 2220, 1771, 1733, 1607, 1250,
1197, 1174, 660; UVevis: lmax¼312.1 nm, 3¼3.22ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ10.1 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.8 Hz, 2H, Ar), 7.10 (d, J¼8.6 Hz, 2H, Ar), 6.8 (d,
J¼6.8 Hz, 2H, Ar), 5.37 (br d, J¼3.8 Hz, 1H, 1ꢂolefinic),
4.3 (d, J¼6.6 Hz, 1H, CHCl), 4.6 (m, 1H, 1ꢂCHOCO), 3.99
(t, J¼3.8 Hz, 2H, 1ꢂOCH2), 2.45e1.05 (m, 35H, 7ꢂCH,
2ꢂallylic methylene, 12ꢂCH2), 1.03 (s, 3H, 1ꢂCH3), 1.01
(s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.91 (d, J¼6.5 Hz,
3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C NMR
(100 MHz, CDCl3): 173.21, 168.30, 159.33, 149.85, 139.71,
133.05, 132.64, 122.61, 121.95, 121.25, 114.86, 114.57,
89.89, 86.98, 73.75, 67.99, 63.90, 56.70, 56.16, 50.04,
43.40, 42.32, 39.74, 39.52, 39.14, 38.17, 36.99, 36.60,
36.19, 35.79, 34.64, 32.79, 31.89, 28.98, 28.21, 28.01,
27.83, 25.83, 24.94, 24.28, 23.83, 22.80, 22.54, 21.03,
19.30, 18.72, 18.21, 11.68, 10.80; MS (FABþ): m/z calcd
for C51H69ClO5: 796.48. Found: 796.46; Anal. Calcd for
C51H69ClO5: C, 76.80; H, 8.72. Found: C, 77.07; H, 8.52.
4.2.5. Cholesteryl 4-[(4-(2-chloro-4-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]butanoate (TDL-3)
Rf¼0.74 in 10% EtOAcehexanes; yield: 70%; IR (KBr
pellet): nmax in cmꢁ1: 2950, 2218, 1765, 1724, 1606, 1247,
1196, 1164, 768; UVevis: lmax¼311.7 nm, 3¼2.53ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ11.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.5 Hz, 2H, Ar), 7.45 (d,
J¼8.6 Hz, 2H, Ar), 7.11 (d, J¼8.5 Hz, 2H, Ar), 6.87 (d,
J¼8.6 Hz, 2H, Ar), 5.38 (br d, J¼4.8 Hz, 1H, 1ꢂolefinic),
4.62 (m, 1H, 1ꢂCHOCO), 4.52 (t, J¼7.4 Hz, 1H, CHCl), 4.02
(t, J¼6.1, 2H, 1ꢂOCH2), 2.50e1.06 (m, 35H, 7ꢂCH,
2ꢂallylic methylene, 12ꢂCH2), 1.04 (s, 3H, 1ꢂCH3), 1.01
(s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.4 Hz,
3H, 1ꢂCH3), 0.86 (d, J¼1.4 Hz, 3H, 1ꢂCH3), 0.85 (d,
J¼1.4 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C NMR
(100 MHz, CDCl3): 172.49, 167.65, 159.06, 149.88, 139.63,
133.07, 132.65, 122.69, 121.89, 121.25, 115.16, 114.58,
89.78, 87.08, 74.12, 66.88, 63.88, 56.70, 56.16, 50.05,
42.32, 39.74, 39.52, 39.03, 38.15, 36.99, 36.60, 36.19,
35.78, 34.45, 32.78, 31.89, 28.20, 27.99, 27.81, 24.64,
24.27, 23.83, 22.78, 22.54, 21.03, 19.61, 19.29, 18.72,
18.21, 11.84, 10.80; MS (FABþ): m/z calcd for C51H69ClO5:
796.48. Found: 796.5; Anal. Calcd for C51H69ClO5: C,
76.80; H, 8.72. Found: C, 77.01; H, 8.45.
4.2.3. Cholesteryl 6-[(4-(2-chloro-3-methylbutanoyloxy)-
phenylethynyl)-4-phenoxy]hexanoate (TDV-5)
Rf¼0.40 in 10% EtOAcehexane; yield: 70%; IR (KBr pellet)
nmax in cmꢁ1: 2935, 2215, 1769, 1728, 1606, 1249, 1198, 1165,
649; UVevis: lmax¼312 nm, 3¼3.01ꢂ104 L molꢁ1 cmꢁ1; [a]2D2
1
ꢁ9.1 (c 1.0, CHCl3); H NMR (400 MHz, CDCl3): d 7.53
(d, J¼8.6 Hz, 2H, Ar), 7.45 (d, J¼8.7 Hz, 2H, Ar), 6.86 (d,
J¼8.7 Hz, 2H, Ar), 7.10 (d, J¼8.6 Hz, 2H, Ar), 5.37 (br d,
J¼3.7 Hz, 1H, 1ꢂolefinic), 4.62 (m, 1H, 1ꢂCHOCO), 4.33
(d, J¼6.6 Hz, 1H, CHCl), 3.97 (t, J¼6.4 Hz, 2H, 1ꢂOCH2),
2.45e1.05 (m, 37H, 7ꢂCH, 2ꢂallylic methylene, 13ꢂCH2),
1.03 (s, 3H, 1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H,
1ꢂCH3), 0.93 (d, J¼8.2 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz,
3H, 1ꢂCH3), 0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3): 173.00, 168.26,
159.23, 149.86, 139.66, 133.05, 132.63, 122.63, 121.91,

C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3769
4.2.6. Cholesteryl 5-[(4-(2-chloro-4-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]pentanoate (TDL-4)
(400 MHz, CDCl3): d 7.53 (d, J¼8.68 Hz, 2H, Ar), 7.45 (d,
J¼8.76 Hz, 2H, Ar), 7.11 (d, J¼8.7 Hz, 2H, Ar), 6.86 (d,
J¼8.8 Hz, 2H, Ar), 5.37 (br d, J¼3.8 Hz, 1H, 1ꢂolefinic),
4.60 (m, 1H, 1ꢂCHOCO), 4.53 (t, J¼7.3 Hz, 1H, CHCl),
3.97 (t, J¼6.3 Hz, 2H, 1ꢂOCH2), 2.33e1.05 (m, 43H,
7ꢂCH, 2ꢂallylic methylene, 16ꢂCH2), 1.03 (s, 3H,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.91
(d, J¼6.5 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3),
0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
NMR (100 MHz, CDCl3): 172.99, 167.66, 159.25, 149.85,
139.68, 133.06, 132.64, 122.64, 121.93, 121.25, 114.93,
114.56, 89.86, 87.01, 73.84, 67.72, 63.89, 56.70, 56.16,
50.04, 42.31, 39.74, 39.52, 39.07, 38.16, 36.99, 36.60,
36.18, 35.78, 34.55, 32.78, 31.88, 28.85, 28.21, 28.00,
27.82, 25.57, 24.76, 24.27, 23.82, 22.79, 22.54, 21.03,
19.62, 19.30, 18.71, 18.19, 11.83, 10.76; MS (FABþ): m/z
calcd for C55H77ClO5: 852.55. Found: 853; Anal. Calcd for
C55H77ClO5: C, 77.38; H, 9.09. Found: C, 77.24; H, 8.82.
Rf¼0.74 in 10% EtOAcehexanes; yield: 71%; IR (KBr
pellet) nmax in cmꢁ1: 2955, 2216, 1752, 1727, 1606, 1246,
1190, 1167, 772; UVevis: lmax¼312 nm, 3¼3.18ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ8.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.9 Hz, 2H, Ar), 7.11 (d, J¼8.7 Hz, 2H, Ar), 6.86 (d,
J¼8.8 Hz, 2H, Ar), 5.37 (br d, J¼3.9 Hz, 1H, 1ꢂolefinic),
4.6 (t, J¼7.4 Hz, 1H, CHCl), 4.2 (m, 1H, 1ꢂCHOCO), 3.99
(t, J¼5.2 Hz, 2H, 1ꢂOCH2), 2.38e1.05 (m, 37H, 7ꢂCH,
2ꢂallylic methylene, 13ꢂCH2), 1.04 (s, 3H, 1ꢂCH3), 1.01
(s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.4 Hz,
3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C NMR
(100 MHz, CDCl3): 172.82, 168.84, 159.13, 149.80, 139.65,
133.06, 132.64, 122.66, 121.92, 121.26, 115.47, 115.03,
114.57, 89.90, 87.04, 73.96, 67.48, 63.89, 56.70, 56.16,
50.05, 42.32, 39.74, 39.52, 39.16, 38.16, 36.99, 36.60,
36.19, 35.78, 34.27, 32.79, 31.89, 28.57, 28.19, 28.01,
27.82, 25.87, 24.93, 27.28, 23.84, 22.79, 22.55, 21.69,
21.04, 19.62, 19.30, 18.71, 18.20, 11.66, 10.75; MS
(FABþ): m/z calcd for C52H71ClO5: 810.50. Found: 810.45;
Anal. Calcd for C52H71ClO5: C, 76.96; H, 8.82. Found: C,
77.02; H, 8.79.
4.2.9. Cholesteryl 4-[(4-(2-chloro-3-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]butanoate (TDI-3)
Rf¼0.42 in 10% EtOAcehexanes; yield: 65%; IR (KBr
pellet) nmax in cmꢁ1: 2946, 2219, 1763, 1727, 1607, 1246,
1198, 1164, 770; UVevis: lmax¼312 nm, 3¼2.75ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ8.3 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.7 Hz, 2H, Ar), 7.11 (d, J¼8.6 Hz, 2H, Ar), 6.87 (d,
J¼8.7 Hz, 2H, Ar), 5.37 (br d, J¼3.7 Hz, 1H, 1ꢂolefinic),
4.64 (m, 1H, 1ꢂCHOCO), 4.37 (d, J¼7.0 Hz, 1H, CHCl),
4.04 (t, J¼6.0 Hz, 2H, 1ꢂOCH2), 2.50e1.05 (m, 35H,
7ꢂCH, 2ꢂallylic methylene, 12ꢂCH2), 1.02 (s, 3H,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92
(d, J¼8.5 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3),
0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
NMR (100 MHz, CDCl3): 172.77, 167.65, 159.14, 149.65,
139.65, 133.06, 132.63, 122.65, 121.90, 121.25, 115.03,
114.57, 89.83, 87.04, 73.94, 67.48, 62.55, 56.70, 56.16,
50.05, 42.32, 39.74, 39.04, 39.04, 38.16, 36.99, 36.60,
36.19, 35.78, 34.26, 31.89, 31.89, 28.56, 28.21, 28.01,
27.83, 25.15, 24.27, 23.83, 22.79, 22.54, 21.69, 21.04,
19.30, 18.71, 15.96, 11.84, 10.85; MS (FABþ): m/z calcd
for C51H69ClO5: 796.48. Found: 796.55; Anal. Calcd for
C51H69ClO5: C, 76.80; H, 8.72. Found: C, 77.01; H, 8.66.
4.2.7. Cholesteryl 6-[(4-(2-chloro-4-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]hexanoate (TDL-5)
Rf¼0.74 in 10% EtOAcehexanes; yield: 72%; IR (KBr
pellet) nmax in cmꢁ1: 2937, 2217, 1764, 1731, 1606, 1247,
1199, 1166, 772; UVevis: lmax¼312 nm, 3¼4.15ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ13.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.7 Hz, 2H, Ar), 6.86 (d, J¼8.7 Hz, 2H, Ar), 7.09 (d,
J¼8.6 Hz, 2H, Ar), 5.37 (br d, J¼4.0 Hz, 1H, 1ꢂolefinic),
4.62 (m, 1H, 1ꢂCHOCO), 4.53 (t, J¼7.3 Hz, 1H, CHCl),
3.96 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.31e1.05 (m, 39H,
7ꢂCH, 2ꢂallylic methylene, 14ꢂCH2) 1.04 (s, 3H, 1ꢂCH3),
1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.91 (d,
J¼6.4 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.5 Hz, 3H, 1ꢂCH3),
0.85 (d, J¼1.5 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
NMR (100 MHz, CDCl3): 172.99, 167.66, 159.25, 149.85,
139.68, 133.06, 132.64, 122.64, 121.93, 121.25, 114.93,
114.56, 89.86, 87.01, 73.84, 67.72, 63.89, 56.70, 56.16,
50.04, 42.31, 39.74, 39.52, 39.04, 38.16, 36.99, 36.60,
36.18, 35.78, 34.55, 32.78, 31.88, 28.85, 28.21, 28.00,
27.82, 25.57, 24.76, 24.27, 23.83, 22.79, 22.54, 21.0., 19.62,
19.30, 18.71, 18.20, 11.80, 10.75; MS (FABþ): m/z calcd
for C53H73ClO5: 824.15. Found: 824.68; Anal. Calcd for
C53H73ClO5: C, 77.10; H, 8.91. Found: C, 77.25; H, 8.45.
4.2.10. Cholesteryl 5-[(4-(2-chloro-3-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]pentanoate (TDI-4)
Rf¼0.42 in 10% EtOAcehexane; yield: 70%; IR (KBr
pellet) nmax in cmꢁ1: 2938, 2216, 1770, 1730, 1607, 1250,
1196, 1174, 740; UVevis: lmax¼312.1 nm, 3¼2.75ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ10.3 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.53 (d, J¼8.7 Hz, 2H, Ar), 7.45 (d,
J¼8.8 Hz, 2H, Ar), 7.10 (d, J¼1.8 Hz, 2H, Ar), 6.8 (d,
J¼8.8 Hz, 2H, Ar), 5.37 (br d, J¼3.8 Hz, 1H, 1ꢂolefinic),
4.6 (m, 1H, 1ꢂCHOCO), 4.3 (d, J¼7.0 Hz, 1H, CHCl), 3.99
(t, J¼5.3 Hz, 2H, 1ꢂOCH2), 2.38e1.05 (m, 37H, 7ꢂCH,
2ꢂallylic methylene, 13ꢂCH2), 1.03 (s, 3H, 1ꢂCH3), 1.01
(s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.48 Hz,
4.2.8. Cholesteryl 8-[(4-(2-chloro-4-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]octanoate (TDL-7)
Rf¼0.74 in 10% EtOAcehexane; yield: 69%; IR (KBr
pellet) nmax in cmꢁ1: 2949, 2217, 1762, 1732, 1606, 1248,
1199, 1163, 773; UVevis: lmax¼312.1 nm, 3¼2.37ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ10.5 (c 1.0, CHCl3); 1H NMR

3770
C.V. Yelamaggad, G. Shanker / Tetrahedron 64 (2008) 3760e3771
3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C NMR
(100 MHz, CDCl3): 172.78, 167.80, 159.21, 149.20, 139.71,
133.10, 132.67, 122.68, 121.95, 121.28, 115.24, 114.64,
89.80, 87.63, 73.99, 67.56, 62.58, 56.77, 56.24, 50.13, 42.38,
39.81, 39.57, 39.10, 38.21, 37.04, 36.66, 36.24, 35.82, 34.30,
31.94, 30.87, 28.61, 28.24, 28.03, 27.87, 25.21, 24.31, 23.88,
22.80, 22.56, 21.73, 21.09, 19.33, 18.75, 15.98, 11.88, 10.87;
MS (FABþ): m/z calcd for C52H71ClO5: 810.50. Found:
810.54; Anal. Calcd for C52H71ClO5: C, 76.96; H, 8.82. Found:
C, 77.02; H, 8.85.
25.82, 25.15, 24.93, 24.28, 23.83, 22.79, 22.54, 21.03,
19.62, 19.30, 18.71, 15.96, 11.85, 10.85; MS (FABþ): m/z
calcd for C55H77ClO5: 852.55. Found: 852.65; Anal. Calcd
for C55H77ClO5: C, 77.38; H, 9.09. Found: C, 77.45; H, 8.84.
Acknowledgements
We sincerely thank Dr. D.S. Shankar Rao and Dr. S.
Krishna Prasad (CLCR) for carrying out X-ray diffraction
measurement and helpful discussions.
Supplementary data
4.2.11. Cholesteryl 6-[(4-(2-chloro-3-methylpentanoyloxy)-
phenylethynyl)-4-phenoxy]hexanoate (TDI-5)
Supplementary data associated with this article can be
found in the online version, at doi:10.1016/j.tet.2008.02.013.
Rf¼0.42 in 10% EtOAcehexane; yield: 65%; IR (KBr
pellet) nmax in cmꢁ1: 2940, 2214, 1767, 1723, 1608, 1249,
1198, 1167, 760; UVevis: lmax¼312.1 nm, 3¼3.09ꢂ
104 L molꢁ1 cmꢁ1; [a]D22 ꢁ10.7 (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 7.54 (d, J¼8.6 Hz, 2H, Ar), 7.45 (d,
J¼8.7 Hz, 2H, Ar), 6.86 (d, J¼8.8 Hz, 2H, Ar), 7.10 (d,
J¼8.6 Hz, 2H, Ar), 5.37 (br d, J¼3.8 Hz, 1H, 1ꢂolefinic),
4.62 (m, 1H, 1ꢂCHOCO), 4.37 (d, J¼7.0 Hz, 1H, CHCl),
3.97 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.31e1.13 (m, 39H,
7ꢂCH, 2ꢂallylic methylene, 14ꢂCH2), 1.12 (s, 3H,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.91
(d, J¼6.5 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼1.6 Hz, 3H, 1ꢂCH3),
0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
NMR (100 MHz, CDCl3): 173.25, 167.73, 159.39, 149.90,
139.77, 133.10, 132.69, 122.65, 121.98, 121.30, 114.92,
114.62, 89.93, 87.03, 73.79, 68.04, 62.60, 56.75, 56.20,
50.09, 42.37, 39.79, 39.57, 39.09, 38.22, 37.05, 36.65,
36.23, 35.83, 34.69, 31.94, 29.02, 28.26, 28.05, 27.88,
25.87, 25.19, 24.99, 23.88, 22.84, 22.59, 21.08, 19.35,
18.76, 16.01, 11.89, 10.90; MS (FABþ): m/z calcd for
C53H73ClO5: 824.51. Found: 824.94; Anal. Calcd for
C53H73ClO5: C, 77.10; H, 8.91. Found: C, 76.88; H, 9.16.
References and notes
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1196, 1164, 780; UVevis: lmax¼311.9 nm, 3¼3.12ꢂ
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(400 MHz, CDCl3): d 7.53 (d, J¼8.7 Hz, 2H, Ar), 7.45 (d,
J¼8.7 Hz, 2H, Ar), 7.11 (d, J¼8.68 Hz, 2H, Ar), 6.86 (d,
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7ꢂCH, 2ꢂallylic methylene, 16ꢂCH2), 1.13 (s, 3H,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.98 (s, 3H, 1ꢂCH3), 0.92
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0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3), 0.67 (s, 3H, 1ꢂCH3); 13C
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139.70, 133.04, 132.62, 122.59, 121.93, 121.24, 114.86,
114.56, 89.88, 86.98, 73.74, 67.99, 62.55, 56.70, 56.16,
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36.19, 35.78, 34.64, 31.89, 28.97, 28.21, 28.00, 27.83,
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