Nano-assembly of cytotoxic amides of moronic and morolic acid.

Moronic acid and morolic acid, less frequently studied plant triterpenoids, were subjected to derivation with several structural modifiers, namely, piperazine-, pyrazine-, 1H-indole- and L-methionine-based compounds. Derivation was targeted to design and prepare novel compounds capable of nano-assembling and/or displaying cytotoxicity. Formation of nanostructures has been proven for several novel target compounds that formed different types of nanostructures, either in chloroform or in water. Isometric nanoparticles with broad size distributions (12 and 25), distorted single sheets (23) or very large thin warped films (13) were formed in chloroform solutions. Sheet-like nanostructures (12 and 23), and sphere-like nanostructures (hydrogen bonding connected nanoparticles; 3, 5, 13, 21 and 25) were formed in water suspensions. Cytotoxicity was also investigated and compared with that of the parent triterpenoids, showing enhanced effect of 18 that was the most successful derivative of the prepared series with sufficient balance between its cytotoxicity in CEM (IC50 = 11.7 ± 2.4 µM), HeLa (IC50 = 9.0 ± 0.7 µM) and G-361 (IC50 = 10.6 ± 5.5 µM) cancer cell lines, and toxicity in BJ (IC50 = 43.3 ± 1.5 µM). The calculated selectivity index values for 18 are SI = 3.9 (CEM), 4.8 (HeLa) and 4.4 (G-361). Additional compounds displaying cytotoxicity were 5, 7, 9 and 15, all of them showed comparable cytotoxicity with 18, in the investigated cancer cell lines; however, they were more toxic in BJ than 18.

Novel cytotoxic 1,10-phenanthroline-triterpenoid amphiphiles with supramolecular characteristics capable of coordinating 64Cu(II) labels.

1,10-Phenanthroline was decorated with triterpenoid-based substituents bearing additional spermine units to form amphiphilic molecules. The synthetic procedure designed for the new phenanthroline-triterpenoid amphiphiles is described in detail. Besides 1,10-phenanthroline, all target structures bear 1,4-disubstituted 1,2,3-triazole rings. The target compounds self-assembled into either helical-like or sheet-like nanostructures, depending on the structure of the target molecule, either based on betulinic acid or oleanolic acid, and on the way of binding spermine subunits to the rest of the molecules. They also proved their ability to coordinate 64Cu(II) ions. Finally, the target compounds showed cytotoxicity that was partly dependent on the formation of nanostructures.

Rapid Self-Healing and Thixotropic Organogelation of Amphiphilic Oleanolic Acid-Spermine Conjugates.

Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid-triazole-spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show rapid self-recovery (up to 96% of the initial storage modulus) and sol ⇔ gel transition under several cycles. Interestingly, rheological flow curves reveal the thixotropic behavior of the gels. To the best of our knowledge, this kind of behavior was not shown in the literature before, neither for a triterpenoid nor for its derivatives. Conjugate 4, having a bolaamphiphile-like structure, was found to be a nongelator. Our results indicate that the position and number of spermine units alter the gelation properties, gel strength, and their self-assembly behavior. Preliminary cytotoxicity studies of the target compounds 2-4 in four human cancer cell lines suggest that the position and number of spermine units affect the biological activity. Our results also encourage exploring other triterpenoids and their derivatives as sustainable, renewable, and biologically active building blocks for multifunctional soft organic nanomaterials.

Synthesis and Pharmacological Effects of Diosgenin-Betulinic Acid Conjugates.

The target diosgenin-betulinic acid conjugates are reported to investigate their ability to enhance and modify the pharmacological effects of their components. The detailed synthetic procedure that includes copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (click reaction), and palladium-catalyzed debenzylation by hydrogenolysis is described together with the results of cytotoxicity screening tests. Palladium-catalyzed debenzylation reaction of benzyl ester intermediates was the key step in this synthetic procedure due to the simultaneous presence of a 1,4-disubstituted 1,2,3-triazole ring in the molecule that was a competing coordination site for the palladium catalyst. High pressure (130 kPa) palladium-catalyzed procedure represented a successful synthetic step yielding the required products. The conjugate 7 showed selective cytotoxicity in human T-lymphoblastic leukemia (CEM) cancer cells (IC50 = 6.5 ± 1.1 µM), in contrast to the conjugate 8 showing no cytotoxicity, and diosgenin (1), an adaptogen, for which a potential to be active on central nervous system was calculated in silico. In addition, 5 showed medium multifarious cytotoxicity in human T-lymphoblastic leukemia (CEM), human cervical cancer (HeLa), and human colon cancer (HCT 116). Betulinic acid (2) and the intermediates 3 and 4 showed no cytotoxicity in the tested cancer cell lines. The experimental data obtained are supplemented by and compared with the in silico calculated physico-chemical and absorption, distribution, metabolism, and excretion (ADME) parameters of these compounds.

Ascorbigen A-NMR identification.

The connectivities of all atoms in ascorbigen A, an important metabolite, were determined unambiguously for the first time. The connectivity between carbon atoms was established by 2D INADEQUATE, and one-bond 13 C-13 C coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The 13 C-13 C coupling in one of the pairs was proved by a modification of standard INADEQUATE; however, the signals from the other pair were too weak to be observed. The connectivity within the two strongly coupled C-C pairs was confirmed by a combination of COSY and gHSQC; the latter experiment also identified all C-H bonds. The proton nuclear magnetic resonance (1 H NMR) spectra in dry dimethyl sulfoxide allowed identification and assignment of the signals due to NH and OH protons. The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, agrees with the structure suggested for ascorbigen A in 1966. The density functional theory (DFT) calculations showed that among 16 possible stereoisomers, only two complied with the almost zero value of the measured 3 J(H6-H6a). Of the two stereoisomers, 3S,3aS,6S,6aR and 3R,3aR,6R,6aS, the latter was excluded on synthetic grounds. The nuclear Overhauser effect measurements unveiled close proximity between H2' proton of the indole and the H6a proton of the tetrahydrofuro[3,2-b]furan part. Detailed structural interpretation of the measured NMR parameters by means of DFT NMR was hampered by rotational flexibility of the indole and tetrahydrofuro[3,2-b]furan parts and inadequacy of Polarizable Continuum Model (PCM) solvent model.

Diquats with Robust Chirality: Facile Resolution, Synthesis of Chiral Dyes, and Application as Selectors in Chiral Analysis.

Diquats with extremely high racemization barriers with ΔG≠theor of 233 kJ mol-1 at 180 °C are described. Reported configurational robustness is due to a combination of two structural features: the rigid o-xylylene tether connecting the nitrogen atoms and the presence of two substituents in the bay region of the bipyridinium scaffold. The straightforward synthesis of diquats, plus facile resolution and derivatization make them attractive for chiral application studies. This is demonstrated by: 1) synthesis of the first non-racemic diquat dyes with pronounced chiroptical properties, and 2) capability of diquats to interact stereospecifically with chiral molecules. This suggests potential for diquat derivatives to be used as chiral selectors in separation methods.

Dutch Resolution of a configurationally stable [5]helquat.

Synthesis and nontrivial optical resolution of a helicene-like dication, helquat 1, has been accomplished. Starting with gram scale of the racemic helquat 1 sample, Dutch Resolution using family of 3 tartrate anions was key to achieve successful separation of M and P helical enantiomers of 1. Hundreds of milligrams of each enantiomer of this configurationally stable C2 -symmetric helquat have been obtained. Racemization barrier of 1 has been determined. To our knowledge this is the first report on Dutch Resolution performed with a helicene-like compound. Moreover, there are no literature precedents for Dutch Resolution of chiral quaternary ammonium cations.

Tunable Chiral Second-Order Nonlinear Optical Chromophores Based on Helquat Dications.

Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron donor groups attached to helquat (Hq) acceptors. These Hq derivatives have been characterized as their TfO- salts by using various techniques including NMR and electronic absorption spectroscopies. UV-vis spectra show intense, relatively low energy absorptions with λmax ≈ 400-600 nm, attributable to intramolecular charge-transfer (ICT) excitations. Single-crystal X-ray structures have been solved for two of the chromophores, one as its PF6- salt, revealing centrosymmetric packing arrangements (space groups Pbca and P1̅). Molecular quadratic nonlinear optical (NLO) responses have been determined directly by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and indirectly via Stark (electroabsorption) spectroscopy for the low energy absorption bands. The obtained static first hyperpolarizabilities ß0 range from moderate to large: (9-140) × 10-30 esu from HRS in MeCN and (44-580) × 10-30 esu from the Stark data in PrCN. The magnitude of ß0 increases upon either extending the π-conjugation length or replacing a methoxy with a tertiary amino electron donor substituent. Density functional theory (DFT) and time-dependent DFT calculations on selected tertiary amino chromophores confirm that the low energy absorptions have ICT character. Relatively good agreement between the simulated and experimental UV-vis absorption spectra is achieved by using the CAM-B3LYP functional with the 6-311G(d) basis set. The ßtot values predicted by using DFT at the same level of theory are large ((472-1443) × 10-30 esu in MeCN). Both the theoretical and experimental results show that para-conjugation between Hq and electron donor fragments is optimal, and enlarging the Hq unit is inconsequential with respect to the molecular quadratic NLO response.

Synthesis of Long Oxahelicenes by Polycyclization in a Flow Reactor.

A series of oxahelicenes composed of ortho/meta-annulated benzene/pyridine and 2H-pyran rings were synthesized on the basis of the cobalt(I)-mediated (or rhodium(I)- or nickel(0)-mediated) double, triple, or quadruple [2+2+2] cycloisomerization of branched aromatic hexa-, nona-, or dodecaynes, thus allowing the construction of 6, 9, or 12 rings in a single operation. The use of a flow reactor was found to be beneficial for the multicyclization reactions. The stereogenic centers present in some of the oligoynes steered the helical folding in such a way that the final oxa[9]-, [13]-, [17]- and [19]helicenes were obtained in both enantiomerically and diastereomerically pure form. Specifically, the oxa[19]helicenes beat the current record in the length of a helicene backbone. Single-molecule conductivity was studied by the mechanically controllable break-junction method with a pyridooxa[9]helicene.

[2+2+2] Cycloisomerisation of Aromatic Cyanodiynes in the Synthesis of Pyridohelicenes and Their Analogues.

We have developed a methodology for the synthesis of pyridohelicenes and their analogues based on the Ni(0) -, Co(I) - or Rh(I) -mediated intramolecular [2+2+2] cycloisomerisation of cyanodiynes. It allows for folding the linear precursors into the corresponding helical backbones comprising the newly formed pyridine unit in their central part. Along with racemic pyrido[n]helicenes (n=5,6,7) and their derivatives, both enantio- and diastereomerically pure pyrido[n]helicene-like molecules (n=5,6) were prepared by employing the chiral substrate-controlled cyclisation of the corresponding enantiopure cyanodiynes.

Helquat Dyes: Helicene-like Push-Pull Systems with Large Second-Order Nonlinear Optical Responses.

Helquat dyes combine a cationic hemicyanine with a helicene-like motif to form a new blueprint for chiral systems with large and tunable nonlinear optical (NLO) properties. We report a series of such species with characterization, including determination of static first hyperpolarizabilities ß0 via hyper-Rayleigh scattering and Stark spectroscopy. The measured ß0 values are similar to or substantially larger than that of the commercial chromophore E-4'-(dimethylamino)-N-methyl-4-stilbazolium. Density functional theory (DFT) and time-dependent DFT calculations on two of the new cations are used to probe their molecular electronic structures and optical properties. Related molecules are expected to show bulk second-order NLO effects in even nonpolar media, overcoming a key challenge in developing useful materials.

An Ultimate Stereocontrol in Asymmetric Synthesis of Optically Pure Fully Aromatic Helicenes.

The role of the helicity of small molecules in enantioselective catalysis, molecular recognition, self-assembly, material science, biology, and nanoscience is much less understood than that of point-, axial-, or planar-chiral molecules. To uncover the envisaged potential of helically chiral polyaromatics represented by iconic helicenes, their availability in an optically pure form through asymmetric synthesis is urgently needed. We provide a solution to this problem present since the birth of helicene chemistry in 1956 by developing a general synthetic methodology for the preparation of uniformly enantiopure fully aromatic [5]-, [6]-, and [7]helicenes and their functionalized derivatives. [2 + 2 + 2] Cycloisomerization of chiral triynes combined with asymmetric transformation of the first kind (ultimately controlled by the 1,3-allylic-type strain) is central to this endeavor. The point-to-helical chirality transfer utilizing a traceless chiral auxiliary features a remarkable resistance to diverse structural perturbations.

Studies on supramolecular gel formation using DOSY NMR.

Herein, we present the results obtained from our studies on supramolecular self-assembly and molecular mobility of low-molecular-weight gelators (LMWGs) in organic solvents using pulsed field gradient (PFG) diffusion ordered spectroscopy (DOSY) NMR. A series of concentration-dependent DOSY NMR experiments were performed on selected LMWGs to determine the critical gelation concentration (CGC) as well as to understand the behaviour of the gelator molecules in the gel state. In addition, variable-temperature DOSY NMR experiments were performed to determine the gel-to-sol transition. The PFG NMR experiments performed as a function of gradient strength were further analyzed using monoexponential DOSY processing, and the results were compared with the automated Bayesian DOSY transformation to obtain 2D plots. Our results provide useful information on the stepwise self-assembly of small molecules leading to gelation. We believe that the results obtained from these experiments are applicable in determining the CGC and gel melting temperatures of supramolecular gels.

Search for conglomerate in set of [7]helquat salts: multigram resolution of helicene-viologen hybrid by preferential crystallization.

Investigation of a set of 12 [7]helquat salts by X-ray crystal diffraction led to identification of conglomerate behavior in bis(trifluoroacetate) salt [2][CF(3)CO(2)](2). This is to demonstrate that a systematic search for conglomerates can be performed for a given helicenoid enabling straightforward multigram resolution via preferential crystallization. Subsequently, preferential crystallization of this chiral helicene-viologen hybrid has been established to obtain pure P and M enantiomers on a multigram scale, 5 g each. Furthermore, preparation of nonracemic samples of [7]helquat 2 via diastereomeric (R,R)-dibenzoyltartrate salts is described, and determination of absolute configuration and racemization barrier is also reported.

An organometallic route to long helicenes.

Along with the recent progress in the development of advanced synthetic methods, the chemical community has witnessed an increasing interest in promising carbon-rich materials. Among them, helicenes are unique 3D aromatic systems that are inherently chiral and attractive for asymmetric catalysis, chiral recognition and material science. However, there have been only limited attempts at synthesizing long helicenes, which represent challenging targets. Here, we report on an organometallic approach to the derivatives of undecacyclic helicene, which is based on intramolecular [2 + 2 + 2] cycloisomerization of aromatic hexaynes under metal catalysis closing 6 new cycles of a helicene backbone in a single operation. The preparation of nonracemic compounds relied on racemate resolution or diastereoselective synthesis supported by quantum chemical (density functional theory) calculations. The fully aromatic [11]helicene was studied in detail including the measurement and theoretical calculation of its racemization barrier and its organization on the InSb (001) surface by STM. This research provides a strategy for the synthesis of long helical aromatics that inherently comprise 2 possible channels for charge transport: Along a pi-conjugated pathway and across an intramolecularly pi-pi stacked aromatic scaffold.

Nitrogen heteroaromatic cations by [2+2+2] cycloaddition.

A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at -0.7 V and oxidation at -0.05 V).

Stigmasterol-based novel low molecular weight/mass organic gelators.

Conjugates consisting of stigmasterol and L-phenylalanine, interconnected through short-chained dicarboxylic acyls by ester and amide bonds, respectively, were synthesized as potential low molecular weight/mass organic gelators (LMWGs/LMMGs). Their physico-chemical properties were subjected to investigation, especially their ability to form gels reversibly based on changes of the environmental conditions. Other self-assembly properties detectable by UV-VIS traces were measured in systems consisting of two miscible solvents (water/acetonitrile) with varying solvent ratios and using constant concentrations of the studied compounds. Partition and diffusion coefficients and solubility in water were calculated for the target conjugates. The conjugate 3a was the only compound from this series capable of forming a gel in 1-octanol. All three conjugates 3a-3c displayed supramolecular characteristics in the UV-VIS spectra.

Biotransformation of (1S)-2-carene and (1S)-3-carene by Picea abies suspension culture.

Biotransformation of (1S)-2-carene and (1S)-3-carene by Picea abies suspension culture led to the formation of oxygenated products. (1S)-2-Carene was transformed slowly and the final product was identified as (1S)-2-caren-4-one. On the other hand, the transformation of (1S)-3-carene was rapid and finally led to the formation of (1S)-3-caren-5-one and (1S)-2-caren-4-one as equally abundant major products. The time-course of the reaction indicates that some products abundant at the beginning of the reaction (e.g. (1S, 3S, 4R)-3,4-epoxycarane and (1R)-p-mentha-1(7),2-dien-8-ol) were consumed by a subsequent transformations. Thus, a precise selection of the biotransformation time may be used for a production of specific compounds.

Novel Oleanolic Acid-Tryptamine and -Fluorotryptamine Amides: From Adaptogens to Agents Targeting In Vitro Cell Apoptosis.

BACKGROUND: Oleanolic acid is a natural plant adaptogen, and tryptamine is a natural psychoactive drug. To compare their effects of with the effect of their derivatives, tryptamine and fluorotryptamine amides of oleanolic acid were designed and synthesized. METHODS: The target amides were investigated for their pharmacological effect, and basic supramolecular self-assembly characteristics. Four human cancer cell lines were involved in the screening tests performed by standard methods. RESULTS: The ability to display cytotoxicity and to cause selective cell apoptosis in human cervical carcinoma and in human malignant melanoma was seen with the three most active compounds of the prepared series of compounds. Tryptamine amide of (3ß)-3-(acetyloxy)olean-12-en-28-oic acid (3a) exhibited cytotoxicity in HeLa cancer cell lines (IC50 = 8.7 ± 0.4 µM) and in G-361 cancer cell lines (IC50 = 9.0 ± 0.4 µM). Fluorotryptamine amides of (3ß)-3-(acetyloxy)olean-12-en-28-oic acid (compounds 3b and 3c) showed cytotoxicity in the HeLa cancer cell line (IC50 = 6.7 ± 0.4 µM and 12.2 ± 4.7 µM, respectively). The fluorotryptamine amide of oleanolic acid (compound 4c) displayed cytotoxicity in the MCF7 cancer cell line (IC50 = 13.5 ± 3.3 µM). Based on the preliminary UV spectra measured in methanol/water mixtures, the compounds 3a-3c were also found to self-assemble into supramolecular systems. Conclusions: An effect of the fluorine atom present in the molecules on self-assembly was observed with 3b. Enhanced cytotoxicity has been achieved in 3a-4c in comparison with the effect of the parent oleanolic acid (1) and tryptamine. The compounds 3a-3c showed a strong induction of apoptosis in HeLa and G-361 cells after 24 h.

Triterpenoid-PEG Ribbons Targeting Selectivity in Pharmacological Effects.

(1) Background: To compare the effect of selected triterpenoids with their structurally resembling derivatives, designing of the molecular ribbons was targeted to develop compounds with selectivity in their pharmacological effects. (2) Methods: In the synthetic procedures, Huisgen 1,3-dipolar cycloaddition was applied as a key synthetic step for introducing a 1,2,3-triazole ring as a part of a junction unit in the molecular ribbons. (3) Results: The antimicrobial activity, antiviral activity, and cytotoxicity of the prepared compounds were studied. Most of the molecular ribbons showed antimicrobial activity, especially on Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis, with a 50-90% inhibition effect (c = 25 µg·mL-1). No target compound was effective against HSV-1, but 8a displayed activity against HIV-1 (EC50 = 50.6 ± 7.8 µM). Cytotoxicity was tested on several cancer cell lines, and 6d showed cytotoxicity in the malignant melanoma cancer cell line (G-361; IC50 = 20.0 ± 0.6 µM). Physicochemical characteristics of the prepared compounds were investigated, namely a formation of supramolecular gels and a self-assembly potential in general, with positive results achieved with several target compounds. (4) Conclusions: Several compounds of a series of triterpenoid molecular ribbons showed better pharmacological profiles than the parent compounds and displayed certain selectivity in their effects.