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O
BnO
BnO
Grubbs II
BnO
O
OBn
O
O
BnO
OBn
O
O
O
O
O
BnO
O
O
+
OBn
O
6
6'
O
OBn
BnO
Fruc
3xOBn
O
Gluc
3xOBn
22
OBn
OBn
O
45
4
O
O
+
BnO
BnO
OBn
OBn
O
O
O
O
O
O
BnO
OBn
O
E/Z
O
O
+
O
O
O
BnO
O
BnO
OBn
O
O
O
OBn
OBn
BnO
BnO
47
OBn
OBn
OBn
OBn
BnO
46
Scheme 10 Preparation of macrocycles via the RCM reaction.
3.1 Crown and aza-crown ethers
Chiral crown ethers and their analogs play an important role in
molecular recognition; they are able to differentiate chiral guests and
may be used in enantioselective reactions.
32
Especially interesting case
represents enantioselective recognition of chiral ammonium cations
derived from amines or aminoacids, which has found wide applications
in analytical chemistry (chiral modifiers for HPLC columns, capillary
electrophoresis, MS study of molecular recognition in gaseous phase)
etc. Many chiral, optically pure platforms were used to build such
receptors. From all of the chiral scaffolds applied, sugars are probably
the most promising, due to their availability and biocompatibility.
Up to date only mono-sugars found a wide application in the synthesis
of crown ether analogs.
12
The disaccharide scaffold is much less
pronounced.
Since we already demonstrated that the terminal positions in both sub-
units of sucrose can be connected via a bridge (see Scheme 9) we decided
to apply our platform for construction of crown and aza-crown ether
analogs. Reaction of sucrose diols (with the BOM or benzyl protection at
the 1
0
OH: 11b or 22 respectively) with polyethylene glycol di-tosylates
provided the corresponding macrocycles 48 (R
=
BOM) and 49 (R
=
Bn)
with the bridge of various length. It was possible to remove all blocks
from the target molecule by simple hydrogenolysis.
16
More sophisticated
macrocycles such as 50 are also available (Scheme 11).
20
Our methodology is also useful for the preparation of aza-crown ana-
logs, which should have better complexing properties. Diol 22 was con-
verted into di-ester 51 and further in so-called 'homologated' diol 52.
Activation of both hydroxyl groups (as iodides) and reaction with benzyl
amine provided macrocyclic derivative 53 in good yield (Scheme 12).
Diol 22 was also converted into diamine 54 which - after alkylation
with tert-butyl bromoacetate (to 55) and subsequent reduction of the
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