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1367
Amphiphilic Carbohydrate-based
Mesogens, 3 [1]
D-MannitoI-l-O-n-Alkyl Ethers with
Hydroxy and l-O—D-Mannityl End-Groups:
Novel Double-Headed Thermotropic
Liquid Crystals
polar or functional g r o u p at the t e r m i n u s of the hyd r o p h o b i c n-alkyl chain linked to the c a r b o h y d r a t e
h e a d - g r o u p inhibits t h e r m o t r o p i c liquid crystal formation [2], It has h o w e v e r been shown that some
synthetic d o u b l e - h e a d e d amphiphiles ["bolaamphiphiles"] are capable of forming m o n o l a y e r lipid
m e m b r a n e s [3], Of particular interest are u n s y m m e t ric b o l a a m p h i p h i l e s , i.e. those having d i f f e r e n t sized
h e a d - g r o u p s thus inducing m e m b r a n e c u r v a t u r e [4],
In o r d e r to ascertain w h e t h e r or not such c o m p o u n d s
can be t h e r m o t r o p i c m e s o g e n s , new symmetric and
u n s y m m e t r i c alditol e t h e r b o l a a m p h i p h i l e s were prep a r e d as r e p o r t e d below.
Wilhelm V o l k e r Dahlhoff*
Max-Planck-Institut für Kohlenforschung,
Kaiser-Wilhelm-Platz 1, D-4330 Mülheim a. d. Ruhr
Z. Naturforsch. 43b, 1367-1369 (1988);
received May 9, 1988
Liquid Crystals, Double-headed l-0-/;-AlkylD-mannitol Amphiphiles
T h e syntheses giving b o t h types of d o u b l e - h e a d e d
amphiphiles can readily be achieved by glycosylation
of sufficiently long, a,o>-diols followed by endocyclic
acetal reductions. T h e two key steps in the synthetic
a p p r o a c h involve
Mesogenic 1,16-di-( 1 -O — D-mannityl)-hexadecane (8), l,22-di-(l-0-D-mannityl)-docosane (9),
l - ( l - 0 — D-mannityl)-hexadecane-16-ol (10) and
l - ( l - 0 — D-mannityl)-docosane-22-ol (11) are prepared from the respective a,ai-diols by glycosylation
followed by glycoside reduction and deprotection.
a) stoichiometric reactions of 2 , 3 : 5 , 6 - d i - O - e t h y l b o r a n e d i y l - a - D - m a n n o f u r a n o s y l b r o m i d e (1) [5] with
of h e x a d e c a n e - l , 1 6 - d i o l (2) or d o c o s a n e - l , 2 2 - d i o l
(3) a f t e r conversions to their reactive sodium trie t h y l b o r a t e s 4 and 5 [6, 7] and then
In a recent compilation of mesogenic carboh y d r a t e s , it was concluded that the presence of a
?2H5
H C BN
5 2 0—
1^35
N
—
v
H
,0—
5C2BJ
B0-(CH ) —0
2n
M(H 5 C 2 ) 3 BO-(CH 2 )-OB(C 2 H 5 ) 3 ] 2NA*
Br
nzl6 4
n = 22 5
NaBr
- 2
? N
oBr
-2(H5W
C H
2 5
= 16
i =22
>C,H
2 5
6
7
< H 5 C 2 ) 2 BH
H-C-S-O-BCJ)
J
0
(catalyst)
H3COH
h U
AcO
H3COH/NaOCH3
AcO
* Reprint requests to Dr. W. V. Dahlhoff.
Verlag der Zeitschrift für Naturforschung, D-7400 Tübingen
0932-0776/88/1000-1367/$ 01.00/0
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1368
Compound b
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[«]2D°
MSd
9.5°
(0.4, (H,C),SO)
10.6°
(0.4, (H,C),SO)
-6.7°
(0.9, CsHsN)
-6.1°
(0.9, C,H S N)
586
670
(c, solvent)
8
9
10
11
422
506
AH
c.p.
(KJmoP ') (°C)
AH
(KJmol ')
148.7
127
196
6
130
142
208
7
m.p.
(°C)
1)
2)
1)
2)
116
129
120
133
20.5
60.0
51.6
80.5
122.5
-
128
-
Table. Optical rotations, phase
transition temperatures and their
enthalpies for 8—ll a .
5C
-
6
-
a
Determined with a DuPont 1090-910 calorimeter; heating rate 10 °C min ';
satisfactory C,H-analyses were obtained for 8—11; c value found by cooling the
isotropic liquid; d all compounds gave M + N H 4 parent ions by D.C.I./MS using
ammonia as the reactant gas [12],
b
b) regioselective reductions of the i n t e r m e d i a t e dim a n n o s i d e s 6 and 7 by the new glycoside reducing
m e t h o d with e t h y l d i b o r a n e in the presence of
9-methanesulfonyloxy-9-borabicyclo[3.3.1]nonane
( M S B B N ) [8]. Following d e p r o t e c t i o n the doubleh e a d e d 8 and 9 are o b t a i n e d t o g e t h e r with the m o n o e t h e r s 10 and 11, respectively.
Pure 8—11 are easily o b t a i n e d by per-O-acetylation of the p r o d u c t mixtures to give 12—15 and
separating these by column c h r o m a t o g r a p h y . T h e
acetates are c o n v e r t e d to 8—11 by Z e m p l e n saponification.
H a v i n g isolated the b o l a a m p h i p h i l e s 8, 9, and the
u n s y m m e t r i c 1 0 a n d 1 1 it is readily established by
both D . S . C . and by polarizing microscopy [9], that
all f o u r c o m p o u n d s are indeed t h e r m o t r o p i c mesogens (see T a b l e ) .
S o m e w h a t surprisingly, the symmetric 8 and 9
both have higher melting points and larger LCranges than the respective " h a l v e s " of these amphiphiles: i. e. 8 a n d 9 f o r m stable m e s o p h a s e s having
ranges over 47 °C and 78 °C, respectively, w h e r e a s 1O-rc-octyl-D-mannitol and 1 - O - u n d e c y l - D - m a n n i t o l
have LC-ranges of 43 °C and 52 °C [10]. T h e unsymmetric 10 and 11 are d i m o r p h i c and only the lower
melting modification is mesogenic in each case. T h e
clearing points are best d e t e r m i n e d by D . S . C . on
cooling the isotropic liquids.
H e n c e the p r e s e n c e of polar g r o u p s at the term i n u s of the lipophilic «-alkyl chain of amphiphilic
c a r b o h y d r a t e s d o e s not necessarily p r e v e n t liquid
crystal f o r m a t i o n . A discogenic d o u b l e - h e a d e d scyllitol e t h e r has also b e e n r e p o r t e d [13], but in contrast
to 8—11, it is a n o n - h y d r o g e n b o n d i n g m o n o t r o p i c
mesogen.
Experimental Section
All e x p e r i m e n t s were carried out u n d e r an a t m o s p h e r e of dry argon. H e x a d e c a n e - l , 1 6 - d i o l was
p u r c h a s e d f r o m Aldrich and docosane-l,22-diol was
kindly d o n a t e d by D r . R o l a n d R i e n ä c k e r of this Institute.
I,16-Di-(l-0—D-mannityl)-hexadecane
l-(l-0—D-mannityl)-hexadecane-16-ol
(8) and
(10)
A solution of sodium triethylborate (1.58 g,
12.5 m m o l ) in diethyl e t h e r (5 ml) is a d d e d d r o p w i s e
at r o o m t e m p e r a t u r e to a stirred mixture of 2 (1.6 g,
6.2 m m o l ) and diethyl e t h e r (10 ml), liberating
285 N m l ( 1 0 3 % ) hydrogen. T h e slightly cloudy mixt u r e is then cooled to 0 °C a n d a solution of 1 (3.8 g,
I I . 9 m m o l ) in diethyl e t h e r (10 ml) is a d d e d d r o p wise in the course of 2 h. A f t e r 18 h at —20 °C the
sodium b r o m i d e is filtered off and the filtrate conc e n t r a t e d ( 1 0 - 3 torr. 40 °C) to give a colourless viscous sirup (3.8 g) with [a]D - 2 8 . 1 ° (c 1.4, CHC1 3 ).
T o s o m e of the product mixture (2.44 g), ethyld i b o r a n e (4 ml with 12.55%c H " ~ 40 m m o l ) a n d
M S B B N (0.18 g, 6.8 m m o l ) is added and the stirred
mixture is h e a t e d to 120 °C (bath t e m p e r a t u r e ) for
5 h. T h e clear solution is c o n c e n t r a t e d (60 °C,
10~3 torr) and the residue d e b o r o n a t e d with p o r t i o n s
of m e t h a n o l (5 ml) and e t h a n e - l , 2 - d i o l (5 ml). T h e
c r u d e mixture of 8 and 10 (1.71 g) is t r e a t e d with
e t h a n o l (10 ml) and the solid filtered off and dried
giving 1.02 g which is acetylated with acetic anhydride (8 ml) in pyridine (8 ml) for 30 h at 60 °C. T h e
mixture of 12 and 14 o b t a i n e d (1.7 g containing
4 4 . 5 % 12 and 40.5% 14) is separated by column
c h r o m a t o g r a p h y [silica gel 6 0 / 7 0 - 2 3 0 mesh M e r c k ,
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column 0 30 c m , length 18 cm; eluents ethyl acetate/
p e n t a n e mixtures 1:3 (500 ml) and 1:2 (500 ml);
5 ml f r a c t i o n s are collected], Fr. 25 — 75 contained 14
(0.7 g) of 9 9 . 7 % purity ( G C ) ; Fr. 1 2 0 - 1 8 0 eluted
with 1:2 solvent mixture gives 12 (0.51 g) of 98.1%
purity ( G C ) . T h e Rf values of 12 and 14 are 0.23 and
0.61, respectively (solvent, ethyl a c e t a t e / p e n t a n e ,
1:2).
D e a c e t y l a t i o n s are then carried out by standard
Z e m p l e n saponifications [11] to give 8 and 10 f r o m
12 and 14 resp.
[1] Part 2: See W. V. Dahlhoff, Z. Naturforsch. 42b, 661
(1987). A preliminary report of this work was given at
the XIII Int. Carbohydrate Symposium, p. 27, Ithaca.
N.Y. (1986).
[2] G. A. Jeffrey, Acc. Chem. Res. 19, 168 (1986).
[3] J.-H. Fuhrhop, H.-H. David, J. Mathieu, U. Liman,
H.-J. Winter, and E. Boekema, J. Am. Chem. Soc.
108, 1785 (1986).
[4] J.-H. Fuhrhop and J. Mathieu, Angew. Chem. 96, 124
(1984); Angew. Chem., Int. Ed. Engl. 23, 100 (1984).
[5] W. V. Dahlhoff, A. Geisheimer, and R. Köster, Synthesis 1980, 935.
[6] W. V. Dahlhoff, A. Geisheimer. G. Schroth, and
R. Mynott, Z. Naturforsch. 39b, 1004 (1984)..
[7] W. V. Dahlhoff and A. Geisheimer, Z. Naturforsch.
40b, 141 (1985).
1369
9 and 11 are prepared from
by the same reaction sequence
obtaining 8 and 10
docosane-1,22-diol
as described above
for
Step 1. Yield 8 6 % ; [a]2D° - 2 9 . 3 ° (c 0.9. CHC1 3 ).
Steps 2 and 3. Overall yield 7 7 % .
Step 4. Per-O-acetylation gives a mixture containing 5 1 % 13 and 3 7 % 15 by H P L C . 13 and 15 are then
s e p a r a t e d by column c h r o m a t o g r a p h y . Rf values for
13 and 15 are 0.22 and 0.36 resp., ethyl acetate/pentane 3:1.
Deacetylations then give 9 and 11.
[8] R. Köster, S. Penades-Ullate. and W. V. Dahlhoff.
Angew. Chem. 97, 508 (1985); Angew. Chem., Int.
Ed. Engl. 24, 519 (1985).
[9] G. W. Gray and J. W. Goodby, Smectic Liquid Crystals, Leonard Hill, Glasgow and London (1984).
[10] W. V. Dahlhoff, Abstr. III. Europ. Symposium on
Carbohydrates, p. 96. Grenoble. 16.-20. 9. 1985.
[11] Methods in Carbohydrate Chem. Vol. II. 215, Ed.
R. L. Whistler, M. L. Wolfrom. Academic Press, New
York (1963).
[12] D. Henneberg. H. Damen. W. Joppek. and
W. Schmöller, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr.
[13] B. Kohne, P. Marquardt, K. Praefcke, P. Psaras.
W. Stephan, and K. Turgay, Chimia 40, 360 (1986).
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