4th EucheMs chemistry congress

Poster Session 2
s1333
chem. Listy 106, s257–s1425 (2012)
Poster session 2 - organic chemistry
P - 0 9 4 1
CAtALytiC CArBonyLAtion reACtionS:
verSAtiLe tooLS for the SyntheSiS of
SteroidAL CArBoxAMide diMerS And AMino
ACid derivAtiveS
M. S. M. Moreno 1 , r. M. B. CArriLho 2 ,
A. r. ALMeidA 2 , r. d. S. diAS 2 , L. KoLLár 2 ,
M. M. PereirA 2
1 University of Coimbra, Faculdade de Farmácia, Coimbra,
Portugal
2 University of Coimbra, Departamento de Química, Coimbra,
Portugal
Steroids are biologically active molecules widely found in
both plant and animal kingdoms, and play significant roles in
biological systems. Therefore, there is huge interest in promote
structural modifications on steroidal molecules, since the
introduction of different functionalities, such as formyl, amide or
amino acid groups, into the steroid skeleton, can render marked
changes in their biological activity. [1, 2] Particularly, dimeric
steroids represent a class of compounds that have recently
attracted attention for their rigid, predictable and inherently
asymmetric architecture. Steroid dimers, such as natural
cephalostatins, ritterazines and the respective analogues have
found remarkable pharmaceutical properties, namely, antimalarial,
antineoplastic and cholesterol lowering activities. [3]
Since the early discovery of carbonylation reactions in the
presence of O- and N-nucleophiles, iodoalkenes of various
structures have been transformed into α, β-unsaturated
carboxamides, through aminocarbonylations. [4] However, the use
of diamines as N-nucleophiles in such reactions is rather limited
and the preparation of dimeric molecules using this synthetic
strategy has never been described.
In this communication, we report the first Pd-catalyzed
aminocarbonylation reactions involving steroids with
iodo-functionality and several diamine nucleophiles, as an
efficient tool for the preparation of steroidal carboxamide dimers
with unprecedented structures. Herein, we also report the
synthesis of formyl-steroid derivatives through Rh-catalyzed
hydroformylation of unsaturated steroids, and the respective
sequential one-pot derivatization into amino acids, via Strecker
reaction, followed by acidic hydrolysis of the previous
aminonitriles.
Acknowledgments: The authors thank financial support
from Programa Compete and QREN/FEDER/FCT
(PTDC/QUI-QUI/112913/2009).
references:
1. R. Skoda-Foldes, L. Kollár, Chem. Rev. 2003, 103,
4095–4129.
2. A.F. Peixoto, M.M. Pereira, A.M.S. Silva, C.M. Foca,
J.C. Bayón, M.J.S.M. Moreno, A.M. Beja, J.A. Paixo,
M.R. Silva, J. Mol. Catal. A: Chem., 2007, 275, 121–129.
3. L. Nahar, S.D. Sarker, A.B. Turner, Current Med. Chem.,
2007, 14, 1349-1370.
4. R.M.B. Carrilho, M.M. Pereira, A. Takács, L. Kollár,
Tetrahedron, 2012, 68, 204-207.
Keywords: Aminocarbonylation; Steroids; Carboxamide
dimers; Hydroformylation/Strecker reaction; Amino acids;
4 th EucheMs chemistry congress
P - 0 9 4 2
BottoM-uP SyntheSiS of StruCturALLy
defined And hundred-nAnoMeter-LonG
GrAPhene nAnoriBBonS
A. nAritA 1 , x. fenG 1 , K. MüLLen 1
1 Max Planck Institute for Polymer Research, Synthetic
Chemistry Group, Mainz, Germany
Graphene nanoribbons (GNRs) are stripes of graphene and
possess band gaps in contrast to zero-band-gap graphene. The
electronic properties of GNRs depend on their width and edge
structures, which make it highly important to fabricate GNRs with
structural precision. Top-down approaches such as lithographic
cutting of graphene and longitudinal unzipping of carbon
nanotubes cannot produce GNRs of defined lateral structures. We
have employed a bottom-up approach utilizing the intramolecular
oxidative cyclodehydrogenation of highly twisted polyphenylene
precursors, and achieved syntheses of structurally defined GNRs.
However, it was hitherto impossible to synthesize GNRs with
average length of more than 30 nm with this method. In this study,
we aimed at the synthesis of structurally defined and
longitudinally extended GNRs, and employed Diels-Alder
polymerization, instead of previously used Suzuki and Yamamoto
polymerization, for the synthesis of polyphenylene precursors. An
AB-type monomer based on tetraphenylcyclopentadienone was
thus designed and synthesized. Interestingly, the molecular weight
of the polyphenylene polymers, resulting from the monomer,
could be controlled by changing the concentration and the reaction
time, and weight-average molecular weight of up to 600000 g/mol
was achieved, corresponding to the resulting GNRs of ca. 600 nm.
Subsequently, GNRs were synthesized from thus obtained
polyphenylene precursors by cyclodehydrogenation.
Characterization by IR and Raman spectroscopies as well as an
investigation of a model dimer proved the efficiency of the
cyclodehydrogenation in this system and the homogeneity of the
GNRs. Thanks to the long alkyl chains attached to the periphery,
the GNRs could be dispersed in standard organic solvents such as
THF and chlorobenzene, which allowed UV-Vis absorption
analysis, solution processing, and STM visualization of individual
GNRs. In summary, we achieved the synthesis of structurally
defined and hundred-nanometer-long GNRs via Diels-Alder
polymerization, which also indicated the suitability of this method
for the fabrication of highly homogeneous GNRs.
Keywords: Graphene; Polycycles; Cycloaddition; Raman
spectroscopy; UV/Vis spectroscopy;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc