Synthesis and characterization of novel cyclohexane- based molecular triskelions
PhD thesis outline
Dr. Gábor Neumajer
Doctoral School of Pharmaceutical Sciences Semmelweis University
Supervisor:
Prof. Dr. Béla Noszál, DSc
Official reviewers:
Dr. Gábor Dibó, PhD Dr. Péter Tétényi, PhD
Head of the Final Examination Committee:
Prof. Dr. Huba Kalász, PhD
Members of the Final Examination Committee:
Dr. Krajsovszky Gábor, PhD Prof. Dr. Perjési Pál, PhD
Budapest
2015
1
Introduction
Small molecules with receptor-like ion-binding properties, especially symmetric polydentate complexing agents are of great interest in medicinal and coordination chemistry, as shown by the large number of C3 symmetric molecules (i.e. “molecular triskelions”) that have recently been synthesized.
N
NH O NH O
N H
O
COOEt S
H EtOOC
SH
EtOOC SH
Objectives
The aim of our work was to increase the variability, and characterize the newly synthesized entities. The main focus was on preparative organic synthesis of the compounds, while the characterization of their conformational behaviour and ion-binding properties was planned only by studying some specific aspects (e.g. NMR analysis, protonation, copper(I)-binding).
In 2006, Tajc and Miller created a new pH-switchable molecule by coupling tyrosine and cyclohexane 1,3,5-trimethanol which possesses a closed conformation only in the range of 9.2
< pH < 10.5 and can also serve as ion-receptor in aqueous solution at high pH either for various anions (e.g. Cl-, Br-) or cations (e.g. Zn2+, Cd2+). We have decided to synthesize this compound for thorough characterization, and aimed at designing other receptor molecules with various amino acid ‘arms’ to alter the structure’s pH-dependent behavior. For the better understanding of their protonation properties all derivatives’ mono- and disubstituted analogues were also created.
Further C3 symmetric compounds were also planned to be synthesized by reversing the esterification procedure, and coupling cyclohexane 1,3,5-tricarboxylic acid with various alcohols (and amines). Designing the structures we focused on ion-binding functions, especially on 1,2,3-triazoles as building blocks by utilizing Cu(I) and Ru(II) catalysis. In the case of C3 triazole derivatives we also decided to investigate their Cu(I)-binding capabilities.
2
Methods
Cyclohexane 1,3,5-cis-trimethanol was coupled with a tert-butyloxycarbonyl protected amino acid (tyrosine, tryptophan, histidine) in the presence of N,N'-dicyclohexylcarbodiimide and 4-dimethylaminopyridine. After purification with column chromatography deprotection was accomplished with trifluoroacetic acid, yielding the final products as trifluoroacetate salts.
O O
O
O NH O
O NH
O O
NH
O BOC
BOC BOC
BOC
BOC
BOC TFA Et3SiH CH2Cl2
DCC, DMAP DMF
88%
O O
O
O N H2 O H
O NH2
OH O
NH2
O H
95%
*3TFA OH
O H
OH
Boc-Tyr(Boc)-OH (6,0 eq.)
*3TFA N
H
O O
O
NH2 O
N H2
O
NH N H2
O N H
O O
O
O N H2
O NH2 O
NH2
N NH
N N H N
N H
*6TFA
The derivative of the tyrosine analogue non-classical amino acid, p-amino phenylalanine was synthesized as well. The esterification step was carried out with carboxybenzyl-protected p-nitro phenylalanine; the deprotection was made with catalytic hydrogenation which reduced the nitro group simultaneously. Preventing the product from decomposition trifluoroacetate salt was formed with trifluoroacetic acid.
3
COOH NH
O2N CBZ
O O
O
O N H2 N H2
O NH2
NH2 O
NH2
N H2
*6TFA O
O
O
O NH O2N
O NH
NO2 O
NH
O2N
CBZ CBZ
CBZ
95% 70%
(6 ekv.) DCC DMAP
DMF
1. H2, Pd/C EtOAc 2. TFA CH2Cl2 OH
O H
OH
The mono- and disubstituted derivatives were also prepared for all above mentioned amino acid. Two equivalents of protected amino acid was used for the esterification step which produced the mixture of the protected mono- and disubstituted derivatives. After separation with column chromatography the protecting groups were removed, and trifluoroacetate salt products were formed.
O O
H
O N H2 O H
O H
*TFA
O O
H
O
O N H2 O H
O NH2
OH
*2TFA
OH
O H
O N H2
O N H
*TFA
*2TFA O
O H
O
NH2 O
NH N H2
O N H
O O
H
O H
O N
H2 N
NH
*2TFA
O O
H
O
O N H2
O NH2
N NH
N N H
*4TFA
4
O O
H
O N H2
N H2
O H
*2TFA
O O
H
O
O N H2
N H2
O NH2
NH2
*4TFA
For further esters several saturated and unsaturated alcohols was prepared in Sonogashira reaction and in a subsequent catalytic hydrogenation step from 4-iodoanisole or 5-iodo-2- methylpyridazin-3(2H)one. The effect of the solvent on the Sonogashira reaction was also tested.
I H3CO
OH H3CO
Pd(PPh3)2Cl2 CuI
Et3N, CH3CN 99%
C H
OH
H2, Pd/C MeOH
H3CO
OH
95%
OH N
N O C H3 N
N I O C H3
Pd(PPh3)2Cl2
CuI
Et3N, CH3CN 96%
C H
OH
H2, Pd/C MeOH
N N C H3
OH O
78%
Reversing the previous esterification reaction, cyclohexane 1,3,5-cis-tricarboxylic acid was converted into acyl chloride and reacted with several alcohols and amines (obtained from commercial suppliers or synthesized previously).
O O
O O O
O N CH3 C H3
N CH3
CH3 N CH3
C H3
O
O
O O
O
O H3CO
OCH3 OCH3
5
O O
O O
O O
OCH3 H3CO
OCH3
O
O
O O
O O
N N
O C H3
N N O
CH3
N N O
CH3
O O
O O
O
O N
CH3 C H3
N C H3
CH3 N
CH3 CH3
O N H O NH
O NH
COOMe COOMe
MeOOC
O N H O NH
O NH
COOMe COOMe
MeOOC
NO2
NO2 O2N
N
N O
O O
N EtOOC
COOEt
COOEt
NH
NH O
O O
N
H NH
NH O
O O
N H
NH
NH O
O O
N H OCH3
OCH3
H3CO OCH3
OCH3 H3CO
6
Due to solubility problems of the obtained amides, synthesis of the C3 symmetric triazole derivatives was carried out solely by coupling cyclohexane 1,3,5-cis-tricarboxylic acid with an appropriate alcohol. The required triazole alcohols were synthesized from an azide and a terminal alkyne in copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) reaction.
N N
N
O H N3 HC
OH
Cu(OAc)2*H2O PPh3
CH2Cl2
78%
N N
N
N3
OH N
N N
N N N Cu(OAc)2*H2O
PPh3
CH2Cl2 C H
OH
64%
55%
2. NaN3
DMF
∆ 1. MsCl
Et3N CH2Cl2
rt.
N3 N
N O C H3
60%
Cu(OAc)2*H2O PPh3, CH2Cl2 N
N C H3
OH O
C H
OH
2. NaN3
DMF rt.
1. MsCl Et3N CH2Cl2
rt.
N OH N
O C H3
N N N
67%
N N C H3
O Cl
Cl
N N C H3
O Cl
N3 NaN3
DMF rt.
45%
Cu(OAc)2*H2O PPh3, CH2Cl2
C H
OH N N C H3
O Cl
N N N
86% OH
S O O
N CH3 C H3
N H
N3
S O O
N CH3 C H3
N H
N N N
OH
C H
OH
CuI Et3N MeCN/H2O
77% 97%
S O O
N CH3 C H3
Cl
1.) Br-(CH2)2-NH2*HBr CH2Cl2, Et3N 2.) NaN3, MeCN
Cl
C H
OH Cu(OAc)2*H2O
PPh3 CH2Cl2 99%
NaN3
KI aceton/H2O
∆
N3
N N
N OH
71%
Coupling cyclohexane 1,3,5-cis-tricarboxylic acid with the obtained triazole alcohol yielded the expected tripodal derivatives.
7
O
O
O O
O O
N N N
N N N
N N N
O
O O O
O O
N N N
N N N
N N N N
N N N
N N
N N N
O O O
O O O N
N C O H3
N N N
N N O
C H3
N N N
N N
O CH3
N N N
O O
O O
O O N
N O
Cl N C H3
N N
N N
Cl O N
CH3 N N
N N O
Cl N
C H3
N N
8
O
O O O
O S O
O O
N CH3 C H3
NH N
N N
S O
O
N CH3 C H3 NH N N N
S O
O N C H3
CH3
NH
N N N
O
O O O
O O
N N N N
N N
N N N
Internal alkynes from the Sonogashira reaction (see above) were reacted with benzyl azide in ruthenium(II)-catalyzed azide-alkyne cycloaddition resulting 1,4,5-substituted triazoles. In these reactions the two regioisomers were formed, after purification the main product was used for the esterification.
N N N
OH
OCH3 Cp*RuCl(COD)
CH2Cl2
60%
+
N N N
H3CO
OH
18%
OH H3CO
N3
80
OH N
N O C H3
Cp*RuCl(COD) CH2Cl2
N N N
N N OH
CH3 O
+
N N N
OH
N N
O CH3
70% 15%
N3
80
O
O O
O
O O
N N N
OCH3 N
N N H3CO
N N N
H3CO
O O
O
O O
O
N N N
N N CH3
O N
N N N
N C H3
O
N N N
N N
C H3 O
9
Results
The protonation constants of the amino acid derivatives were determined by 1H NMR-pH titration for all tyrosine and p-amino phenylalanine derivatives, and for the trihistidine product as well. (The tritryptophane derivative was not soluble enough for the titration.)
Compound logK1 logK2
3xTyr 10.12±0,01 7.11±0,01
2xTyr 10.04±0,01 7.17±0,01
1xTyr 9.90±0,01 7.22±0,01
3xpAmPhe 7.19±0,01 3.90±0,01
2xpAmPhe 7.24±0,01 3.99±0,01
1xpAmPhe 7.31±0,01 4.12±0,01
3xHis 7.19±0,01 5.06±0,01
3xTrp N/A N/A
For the investigation of the C3 triazoles’ copper(I)-binding ability three different approaches were used. In the first experiment, the possible chelators were tested as ligands in a model CuAAC reaction, where any improvement in the conversion meant to reflect copper(I) complexation. The second experiment was the study of Cu(I) binding by 1H NMR, while mass spectrometry was utilized to confirm the binding event in the gas phase as well.
The conclusion of these tests was that the tripodal derivatives formed 1:1 complexes with copper(I), and the symmetrical structure was crucial for the formation of the stabile complex.
Conclusions
In our organic synthetic work we have created 27 novel C3 symmetric, 8 novel amino acid and 12 novel triazole alcohol derivatives. All structures were verified with 1D and 2D NMR techniques and with HRMS. We have determined the protonation constants of the amino acid derivatives by 1H NMR-pH titrations. Six tripodal triazole derivatives’ Cu(I)-binding capability in model CuAAC reaction was also investigated and the binding event was also confirmed by both NMR and MS experiments.
10
Bibliography of the Candidate's Publications
Publications related to the theme of the PhD thesis:
Neumajer, G.; Sohajda, T.; Darcsi, A.; Tóth, G.; Szente, L.; Noszál, B.; Béni, Sz.
(2012) Chiral recognition of dapoxetine enantiomers with methylated-gamma- cyclodextrin: A validated capillary electrophoresis method. J Pharm Biomed Anal, 62:
42-47. IF: 2.947
Neumajer, G.; Tóth, G.; Béni, Sz.; Noszál, B. (2014) Novel ion-binding C3 symmetric tripodal triazoles: synthesis and characterization. Cent Eur J Chem, 12: 115-125. IF:
1.329 (2013)
Other publications:
Monsieurs, K.; Tapolcsányi, P.; Loones, K. T. J.; Neumajer, G.; De Ridder, D.;
Goubitz, K.; Lemière, G. L. F.; Dommisse, R. A.; Mátyus, P.; Maes, B. U. W. (2007) Is samoquasine A indeed benzo[f]phthalazin-4(3H)-one? Unambiguous, straightforward synthesis of benzo[f]phthalazin-4(3H)-one and its regioisomer benzo[f]phthalazin-1(2H)-one. Tetrahedron, 63: 3870-3881. IF: 2.869
Béni, Sz.; Sohajda, T.; Neumajer, G.; Iványi, R.; Szente, L.; Noszál, B. (2010) Separation and characterization of modified pregabalins in terms of cyclodextrin complexation, using capillary electrophoresis and nuclear magnetic resonance. J Pharm Biomed Anal, 51: 842-852. IF: 2.733
Gaywood, A. P.; Hill, L.; Imam, S. H.; McNab, H.; Neumajer, G; O’Neill, W. J.;
Mátyus, P.: (2010) Cyclisation reactions of some pyridazinylimidoylketenes. New J Chem, 34: 236-242. IF: 2.631
Fejős, I.; Neumajer, G.; Béni, Sz; Jankovics, P.: (2014) Qualitative and quantitative analysis of PDE-5 inhibitors incounterfeit medicines and dietary supplements by HPLC–UVusing sildenafil as a sole reference. J Pharm Biomed Anal, 98: 327-333. IF:
2,829 (2013)
