Stereoselective oxidation of phenoxathiin-based thiacalix[4]arenes - stereomutation of sulfoxide groups.

A phenoxathiin-based macrocycle represents an inherently chiral building block, well accessible in two steps from the starting thiacalix[4]arene. The oxidized derivatives bearing one sulfoxide group and three sulfonyl groups were found to exhibit unexpected stereochemical preferences of the sulfoxide group during transformations. The sulfoxide moiety is always pointing out of the cavity (SO out), while the opposite (SO in) configuration was never obtained by direct oxidation. In order to achieve full oxidation to sulfone, the configuration of the sulfoxide group must first be changed by a photochemical inversion before the final oxidation occurs. The phenomenon of stereomutation of the sulfoxide group in the thiacalixarene series was studied using a combination of experimental (NMR and single crystal X-ray analysis) and theoretical (DFT) approaches.

Synthesis of upper rim-double-bridged calix[4]arenes bearing seven membered rings and related compounds.

Meta/meta- and meta/para-disubstituted organomercury calix[4]arenes in the cone conformation were transformed into corresponding amino derivatives. Acylation and subsequent intramolecular cyclization using the Bischler-Napieralski reaction provided, in the case of the meta/meta-series, double bridged calixarenes possessing seven membered rings on the upper rim. A similar synthetic strategy applied to meta/para-isomers allowed for the isolation of monobridged compounds bearing an additional trifluoroacetamido group located distally to seven-membered rings. Both series represent inherently chiral systems, which were successfully resolved using preparative chiral HPLC. The pure enantiomers exhibited a recognition ability towards selected chiral guest molecules as documented by the 1H NMR titration experiments. The absolute configuration of the phenyl-substituted enantiomer (meta/meta-) was confirmed by single crystal structure determination (X-ray).

Unexpected cleavage of upper rim-bridged calix[4]arenes leading to linear oligophenolic derivatives.

Regioselective meta-mercuration followed by Pd-catalysed intramolecular bridging gave birth to a novel type of calixarene bearing a single bond bridge between the meta positions of the neighboring aromatic subunits. These bridged derivatives possess extremely distorted cavities that imply possible amended properties over common calix[4]arenes. This new type of calixarene reactivity can be documented by acid-/electrophile-mediated cleavage of the basic macrocyclic skeleton leading to open oligomeric structures-the behavior of which has never been observed before in classic calix[4]arenes bearing alkoxy groups on the lower rim.

Application of RDC enhanced NMR spectroscopy in structural analysis of thiacalix[4]arene derivatives.

Thiacalix[4]arene spirodienone was rearranged into the corresponding phenoxathiin-based macrocycle. Alkylation of this inherently chiral system to achieve its immobilization led to a mixture of only two (out of four theoretically possible) stereoisomers. As standard NOE and dynamic NMR experiments did not lead to unambiguous determination of the structures we applied the Residual Dipolar Coupling constant (RDC) method. Poly-γ-ethyl-l-glutamate (PELG) and poly-γ-benzyl-l-glutamate (PBLG) were found to be easily applicable lyotropic liquid crystalline alignment media for the conformational analysis of thiacalixarene derivatives. Using these media the 1,2-alternate and the partial cone conformations were determined unequivocally.

Mercuration of thiacalix[4]arenes in the cone and 1,3-alternate conformations.

The first mercuration in the thiacalixarene series using thiacalix[4]arenes immobilized in the cone or 1,3-alternate conformations gave a mixture of two monomercurated regioisomers (meta and para) in approx. 4 : 1 and 2 : 1 ratios, respectively. The organomercurial intermediates show unusual solid-state behaviour, as evidenced by the formation of η(6) complexes, and can be easily transformed into halogen-substituted derivatives, so far inaccessible in thiacalixarene chemistry. This paves the way towards the synthesis of inherently chiral thiacalixarene-based receptors with an unusual substitution pattern.

Photophysical properties and photoinduced electron transfer within host-guest complexes of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin with water-soluble calixarenes and cyclodextrins.

We report the formation of host-guest complexes between water-soluble calix[n]arene-p-tetrasulfonates (n = 4, 6, 8) or 2-hydroxypropyl-cyclodextrins (alpha-, beta-, gamma-) and the tetratosylate salt of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). The binding constants ranging between 10(2) and 10(5) M-1 were calculated from the absorption and fluorescence changes. Calix[4]arene-p-tetrasulfonate has a high binding affinity and forms with TMPyP a 1:1 complex, whereas other calixarenes bind two molecules of TMPyP. Electrostatic attraction is the dominating binding mode. Binding to calixarenes leads to a considerable decrease of the quantum yields of the triplet and excited singlet states and to shortening of the singlet and triplet lifetimes of TMPyP. The quenching mechanism is attributed to electron transfer between calixarene phenolates and excited TMPyP. Photoinduced electron transfer within a novel supramolecular complex calixarene/TMPyP (electron donor)/methyl viologen (electron acceptor) has been proven by absorption and fluorescence measurements. Electrostatic attraction between the cationic donor and cationic acceptor, on the one hand, and the anionic host, on the other, overcomes the electrostatic repulsion forces. In contrast, the interaction of cyclodextrin with TMPyP is hydrophobic in nature and only slightly influences the photophysical properties of TMPyP. The different behavior of TMPyP bound to either of the hosts has been assigned to the specific effects of the dominant binding modes, viz. the electrostatic attraction for calixarenes and the hydrophobic interactions for inclusion complexes with cyclodextrins.

[Azabischalcones--a new class of potential antitubercular agents]. / Azabischalkony--nová trída potenciálních antituberkulotik.

A series of substituted azabischalcones Ia-Ip, monochalcone II and dihydroxyderivative III has been prepared and examined for their in vitro activity against Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium avium, Mycobacterium fortuitum as well as INH-resistant strains. Several compounds under study have the same activity as INH and greater than PAS, Contebene, Ethionamide. The results are summarized in Table 1. In the case of compound Ie, its in vivo activity was studied against M. tuberculosis as well (see Table 2). The toxicity of compounds under study is very low--2000 mg/kg/mouse.