4th EucheMs chemistry congress

Poster Session 2
s1354
chem. Listy 106, s257–s1425 (2012)
Poster session 2 - organic chemistry
P - 0 9 8 4
CAtALytiC hydroGenoLySiS of CALixArene
derivAtiveS
f. SteJSKAL 1 , P. LhotAK 1
1 Institute of Chemical Technology, Organic Chemistry, Prague 6,
Czech Republic
Tobisu et al. recently published work about selective
hydrogenolysis of alkyl(aryl)ethers and arylpivalates using silane
and nickel(0) as a catalyst. [1] Using this method on calix[4]arenes
can lead to dehydroxylated derivatives in high yield.
First step in the synthetic pathway is creation of derivatives
suitable for hydrogenolysis. Due to the presence of silane, all free
hydroxy groups have to be modified. Pivalate can be used as a
reactive group and rest of the substituents should be unreactive
propoxy group. This can lead to several derivatives differing in
conformational isomerism, number of reactive pivalates and
substituents on upper rim.
These derivatives can undergo hydrogenolysis using the
Ni(cod) /PCy catalytic system and dimethoxymethylsilane as a
2 3
hydrogenolytic agent. Preliminary results show creation of
didehydroxydipropoxycalix[4]arene in low yield.
Another method was recently published by Sergeev and
Hartwig. [2] They used N-heterocyclic carbene ligands instead of
relatively unstable PCy . Best results were achieved with
3
1,3-bis(2,6-diisopropylphenyl)imidazolidinium chloride activated
by sodium terc-butoxide. Hydrogen was used as the
hydrogenolytic agent although silanes can be used as well. Using
this system on tetramethoxycalix[4]arene afforded partially
hydrogenated products. Reaction optimization should lead to
higher yields and afford selectively hydrogenolysed derivatives.
references:
1. Tobisu M., Yamakawa K., Shimasaki T., Chatani N.;
Nickel-catalyzed reductive cleavage of aryl–oxygen bonds
in alkoxy- and pivaloxyarenes using hydrosilanes as a
mild reducing agent, Chem. Commun., 2011, 47,
2946–2948
2. Sergeev A. G., Hartwig J. F.; Selective, nickel-catalyzed
hydrogenolysis of aryl ethers, Science, 2011, 332, 439-443
Keywords: Calixarenes; Nickel; Carbene ligands; Silanes;
Hydrogen;
4 th EucheMs chemistry congress
P - 0 9 8 5
SyntheSiS And StruCturAL Study of SuGAr
derivAtiveS of oLiGoPyrroLeS uSinG
CirCuLAr diChroiSM
P. StePAneK 1 ,J. KAMinSKý 2 , o. šiMáK 2 , P. drAšAr 1
1 Institute of Chemical Technology Prague, Deaprtment of
Chemistry of Natural Compounds, Praha 6, Czech Republic
2 IOCB AS CR, Flemngovo nam. 2, Praha 6, Czech Republic
Email: jakub.kaminsky@uochb.cas.cz
Ultraviolet circular dichroism (CD) is a standard mean for
determining average secondary structure of many systems.
Empirical interpretations of the CD spectra are very often not
reliable. Unfortunately, CD is quite a complex phenomenon, and
its simulations are currently still restricted by limited computer
power and methodology problems [1] . This is unfortunate as CD
provides enhanced information not only about molecular
structure, but also about molecular interactions comprising solvent
or other molecules.
Therefore, combined computational techniques were utilized
to provide more reliable representation of the experimental data.
The theory was applied for carbohydrate-oligopyrrole
condensates. The cyclic oligopyrroles (e.g. calix[4]pyrroles),
similarly as porphyrin–carbohydrate conjugates, were found
important as sensitizers in the photodynamic therapy. They can
also incorporate into cell membranes, and interact with DNA and
nucleotides, and exhibit electrochemical properties suitable for
catalysis or usage in analytical chemistry. Calix[4]pyrrols were
described as anion and neutral binders, chromatic, fluorescent or
optical sensors.(e.g. Schell, 1999 or Zhang, 2001).
A single calix[4]pyrrole cycle has zero CD signal. But chiral
molecules (even not absorbing in UV-VIS, such as saccharides)
can induce measurable CD. The CD signatures were studied with
mono- or disubstituted tetrapyrroles. Effect of their aggregation
into bigger units were also tried to be studied by concentration
dependence.
We aimed our attention to the direct carbohydrate
functionalisation of oligopyrrole core via stable C-glycosidic
bound which mimics well normal O-glycosides. This area is very
challenging because even when we elarge the scope, cyclic
oligopyrroles with carbohydrate substitution the meso-like and
β-pyrrolic are rather rare [3] .
references:
1. Kaminský J. et al. J. Phys. Chem. A, 2011, 115,
1734–1742.
2. Štepánek P.; Šimák O.; Nováková Z.; Wimmer Z.; Drašar P.:
Org. Biomol. Chem., 2011, 9(3), 682-683.
3. a) Rusin, O., Král,V., Escobedo J. O., Strogin R. M., Org.
Lett., 2004, 6, 1373;
b) Zelenka K., Trnka T., Tislerová I., Král V., Dukh M.,
Drašar P., Collect. Czech. Chemm. Commun., 2004, 69,
1149.
Keywords: Circular dichroism; C-Glycosides; Supramolecular
chemistry;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc