The Finally Rewarding Search for A Cytotoxic Isosteviol Derivative.

Acid hydrolysis of stevioside resulted in a 63% yield of isosteviol (1), which served as a starting material for the preparation of numerous amides. These compounds were tested for cytotoxic activity, employing a panel of human tumor cell lines, and almost all amides were found to be non-cytotoxic. Only the combination of isosteviol, a (homo)-piperazinyl spacer and rhodamine B or rhodamine 101 unit proved to be particularly suitable. These spacered rhodamine conjugates exhibited cytotoxic activity in the sub-micromolar concentration range. In this regard, the homopiperazinyl-spacered derivatives were found to be better than those compounds with piperazinyl spacers, and rhodamine 101 conjugates were more cytotoxic than rhodamine B hybrids.

Comparing C2=O and C2=S Barbiturates: Different Hydrogen-Bonding Patterns of Thiobarbiturates in Solution and the Solid State.

Carbonyl-centered hydrogen bonds with various strength and geometries are often exploited in materials to embed dynamic and adaptive properties, with the use of thiocarbonyl groups as hydrogen-bonding acceptors remaining only scarcely investigated. We herein report a comparative study of C2=O and C2=S barbiturates in view of their differing hydrogen bonds, using the 5,5-disubstituted barbiturate B and the thiobarbiturate TB as model compounds. Owing to the different hydrogen-bonding strength and geometries of C2=O vs. C2=S, we postulate the formation of different hydrogen-bonding patterns in C2=S in comparison to the C2=O in conventional barbiturates. To study differences in their association in solution, we conducted concentration- and temperature-dependent NMR experiments to compare their association constants, Gibbs free energy of association ∆Gassn., and the coalescence behavior of the N-H‧‧‧S=C bonded assemblies. In Langmuir films, the introduction of C2=S suppressed 2D crystallization when comparing B and TB using Brewster angle microscopy, also revealing a significant deviation in morphology. When embedded into a hydrophobic polymer such as polyisobutylene, a largely different rheological behavior was observed for the barbiturate-bearing PB compared to the thiobarbiturate-bearing PTB polymers, indicative of a stronger hydrogen bonding in the thioanalogue PTB. We therefore prove that H-bonds, when affixed to a polymer, here the thiobarbiturate moieties in PTB, can reinforce the nonpolar PIB matrix even better, thus indicating the formation of stronger H-bonds among the thiobarbiturates in polymers in contrast to the effects observed in solution.

First Isolation and Structure Elucidation of GDNT-ß-Glu - Tetraether Lipid Fragment from Archaeal Sulfolobus Strains.

Due to their special chemical structure, tetraether lipids (TEL) represent essential elements of archaeal membranes, providing these organisms with extraordinary properties. Here we describe the characterization of a newly isolated structural element of the main lipids. The TEL fragment GDNT-ß-Glu was isolated from Sulfolobus metallicus and characterized in terms of its chemical structure by NMR- and MS-investigations. The obtained data are dissimilar to analogically derived established structures - in essence, the binding relationships in the polar head group are re-determined and verified. With this work, we provide an important contribution to the structure elucidation of intact TEL also contained in other Sulfolobus strains such as Solfulobus acidocaldarius and Sulfolobus solfataricus.

A simple but unusual rearrangement of an oleanane to a taraxerane-28,14 ß -olide.

Reaction of 3-O-acetyl-oleanolic acid (3) with formic acid/hydrogen peroxide at 100 °C for several hours provides an extraordinary but simple pathway to a taraxeran-28,14 ß -olide type triterpenoid while the same reaction at 0 °C occurred without re-arrangement of the carbon skeleton, and an oleanane-28,13 ß -olide was obtained instead. The products from these reactions were subjected to a cytotoxicity screening employing several human tumor cell lines showing the latter compound not cytotoxic while the former was cytotoxic especially for MCF-7 (breast adenocarcinoma), and FaDu (hypopharyngeal carcinoma) cells. The highest cytotoxicity, however, was observed for 3 ß, 12α, 13 ß -trihydroxy-oleanan-28-oic acid (6) holding with EC50 = 4.2 µM for MCF-7 tumor cells.

Novel effective antibacterial small-molecules against Staphylococcus and Enterococcus strains.

Background: Resistance developments against established antibiotics are an emerging problem for antibacterial therapies. Novel antibiotics are urgently needed. Materials & methods: We developed novel small-molecule antibacterials which are easily accessible in a simple one-pot synthesis. The central cyclopentaindole core is substituted with two indole residues. Various indole and cyclopentane substituents have been introduced. Additionally, first indole substituted propene compounds as ring-open variants of the cyclopentaindoles have been yielded and evaluated as antibacterials against Staphylococcus aureus and Enterococcus strains. Results: Most effective compounds have been those with a bromo cyclopentane and a chloro indole substitution. First lead compounds were identified with promising activities similar to that observed in vitro for last resort antibiotics, so that the novel compounds enriche the pool of perspective small-molecule antibacterial drug candidates.

In the Mists of a Fungal Metabolite: An Unexpected Reaction of 2,4,5-Trimethoxyphenylglyoxylic Acid.

The reactions of phenylglyoxylic acids during the synthesis and biological evaluation of fungal metabolites led to the discovery of hitherto unknown compounds with a p-quinone methide (p-QM) structure. The formation of these p-QMs using 13C-labelled starting materials revealed a key-step of this reaction being a retro-Friedel-Crafts alkylation.

Ugi multicomponent-reaction: Syntheses of cytotoxic dehydroabietylamine derivatives.

Isocyanide-based multicomponent reactions - especially the standard four component Ugi reaction - provide an easy and powerful access to compounds with an auspicious pharmacological potential. Therefore, a set of 16 novel derivatives of the diterpene dehydroabietylamine was synthesized by the Ugi-4CR. The subsequent screening of the synthesized α-acylamino carboxamides in colorimetric sulforhodamine B assays revealed an in vitro cytotoxicity towards several human tumor cell lines. Particularly, the rhodamine B conjugates 14-16 showed a remarkable cytotoxic activity, characterized by EC50 values in a low three-digit nanomolar range. The screening of rhodamine B amide 17 that was obtained for comparison by a Schotten-Baumann reaction showed that the linkage of the rhodamine B moiety and the diterpene influences significantly its cytotoxic potency. While 14 was highly cytotoxic and acted as a mitocan, compound 17 was not cytotoxic at all. This observation underlines the importance of the type of coupling between the diterpene and the rhodamine part. The presence of a rhodamine B moiety in the molecules doesn't necessarily guarantee that the compound is cytotoxic.

Homopiperazine-rhodamine B adducts of triterpenoic acids are strong mitocans.

Parent pentacyclic triterpenoic acids such as ursolic-, oleanolic, glycyrrhetinic, betulinic and boswellic acid were converted into their acetylated piperazinyl amides that were coupled with rhodamine B. SRB assays to evaluate their cytotoxicity showed all of these triterpene-homopiperazinyl-rhodamine adducts 16-20 being highly cytotoxic for a panel of human tumor cell lines even in nanomolar concentrations while being significantly less cytotoxic for non-malignant cells. Interestingly enough, these compounds were even more cytotoxic than previously prepared piperazinyl analogs, thus making the homopiperazinyl spacer a very interesting scaffold for the development of biologically active compounds. Extra staining experiments showed that the cytostatic effect of compounds 18 and 20 onto A2780 cancer cells is due to their ability to act as a mitocan.

Betulinic acid derived hydroxamates and betulin derived carbamates are interesting scaffolds for the synthesis of novel cytotoxic compounds.

The betulinic acid-derived hydroxamates 5-18, the amides 19-24, and betulin-derived bis-carbamates 25-28 as well as the carbamates 31-40 and 44-48 were prepared and evaluated for their antiproliferative activity in a photometric sulforhodamine B (SRB) assay against several human cancer cell lines and nonmalignant mouse fibroblasts (NIH 3T3). While for 3-O-acetyl hydroxamic acid 5 EC50 values as low as EC50 = 1.3 µM were found, N,O-bis-alkyl substituted hydroxamates showed lowered cytotoxicity (EC50 = 16-20 µM). In general, hydroxamic acid derivatives showed only reduced selectivity for tumor cells, except for allyl substituted compound 13 (EC50 = 5.9 µM for A2780 human ovarian carcinoma cells and EC50 > 30 µM for nonmalignant mouse fibroblasts). The cytotoxicity of betulinic acid derived amides 19-24 and of betulin derived bis-carbamates 25-28 was low, except for N-ethyl substituted 25. Hexyl substituted 39 showed EC50 = 5.6 µM (518A2 cells) while for mouse fibroblasts EC50 > 30 was determined.

Orthogonal Modification of Polymers via Thio-Bromo "Click" Reaction and Supramolecular Chemistry: An Easy Method Toward Head-to-Tail Self-Assembled Supramolecular Polymers.

Heterotelechelic poly(n-butyl acrylate)s (PnBuA) bearing two different and complementing supramolecular groups (namely, barbiturate (Ba) and the Hamilton wedge (HW)) at their α-end and ω-end (Ba-PnBuA-HW) were prepared by a combination of the reversible addition-fragmentation chain transfer (RAFT) process and the thio-bromo click reaction. The successful synthesis of the heterotelechelic H-bonding polymer Ba-PnBuA-HW (Mn,NMR = 7700 g/mol, Mn,SEC = 7500 g/mol, PDI = 1.25) was proven by a combination of 1H NMR and MALDI-TOF mass spectrometry. Self-assembly of the resulting heterotelechelic H-bonding polymers (Ba-PnBuA-HW) in a head-to-tail fashion driven by multiple H-bondings in solution and in the bulk was proven by temperature-dependent 1H NMR, concentration-dependent DOSY NMR studies, and rheological measurements.

Resveratrol derived butyrylcholinesterase inhibitors.

Novel polyhydroxylated (E)-stilbenes were synthesized by Mizoroki-Heck reactions and tested for their ability to inhibit the enzymes acetyl- and butyrylcholinesterase. Several of them are good inhibitors of butyrylcholinesterase; one of them carrying an extra fluorine substituent is a 94-fold stronger inhibitor of butyrylcholinesterase than of acetylcholinesterase.

Does one keto group matter? Structure-activity relationships of glycyrrhetinic acid derivatives modified at position C-11.

Several triterpenoic acids display a remarkable cytotoxicity on tumor cells. Glycyrrhetinic acid - the main content of the licorice root - possesses an apoptotic effect on tumor cells. Previous studies pointed out the presence of a keto group at position C-11 in glycyrrhetinic acid derivatives as the main reason for its apoptotic activity. Several pairs of derivatives were synthesized differing only at position C-11. These compounds were tested in a sulforhodamine B colorimetric assay for cytotoxicity screening on 12 tumor cell lines and mouse embryonic fibroblasts (NIH3T3). Our results show that there is no direct relation between the existence of the C-11 keto group and the apoptotic activity of the compounds.

Conversions at C-30 of glycyrrhetinic acid and their impact on antitumor activity.

The extracts of the roots of licorice have been used in traditional and folk medicine to treat a broad variety of maladies. The main ingredient of these extracts is glycyrrhicinic acid. Its aglycon, glycyrrhetinic acid, has many biological activities, among them a pronounced cytotoxicity against tumor cells. In this study we varied glycyrrhetinic acid at position C-30 to get "simple" derivatives, for example esters, amides and a nitrile. The influence of these changes on the cytotoxic activity is noteworthy and was determined by a colorimetric sulphorhodamine B test using 7 human tumor cell lines and mouse embryonic fibroblasts (NIH3T3) for comparison. A Trypan blue test as well as an acridine orange/ethidium bromide test was used to discover the ability of the compounds to induce apoptosis.

Synthesis and biological evaluation of antitumor-active arglabin derivatives.

Arglabin derivatives varied at the endo- or exo-cyclic double bond were synthesized and studied in a colorimetric sulforhodamine B assay for their cytotoxicity. Variations on the endocyclic double bond led to compounds of reduced cytotoxicity whereas derivatives from the reaction of the α-methylene-γ-butyrolactone moiety led to compounds of similar or only slightly reduced cytotoxicity but different, cell line-dependent selectivity. In addition, arglabin is an excellent starting material for the synthesis of the guaianolide arborescin.

Synthesis and antitumor activity of ring A modified glycyrrhetinic acid derivatives.

Triterpenoic acids show many pharmacological effects, among them an antiinflammatory or an antitumor activity. One of these, glycyrrhetinic acid (1) is of interest because of its antitumor profile. Glycyrrhetinic acid is not only cytotoxic but also triggers apoptosis in various human tumor cell lines. To improve the cytotoxicity of parent 1 we set out to synthesize new derivatives of it--differing in structure and lipophilicity. These compounds were tested in a sulforhodamine B assay for cytotoxicity, and screened for their ability to induce apoptosis using an acridine orange/ethidium bromide assay and trypan blue staining. The most active compound, 34, a benzyl glycyrrhetinate holding an extra 3-N-(3-aminopropyl)glycyl substituent showed IC(50) between 1.96 and 5.14 µm for five human cancer cell lines and triggers apoptosis in 80% of the cells.

Improvement of the cytotoxicity and tumor selectivity of glycyrrhetinic acid by derivatization with bifunctional amino acids.

Glycyrrhetinic acid (GA) is a major ingredient of the dried extract of licorice roots; its antitumor activity is low compared to other members of the triterpenoic family. For example, oleanolic acid, betulin or betulinic acid are more cytotoxic with a pronounced activity for tumor cells. GA, however, is easily to earn, cheap and shows apoptotic effects on tumor cells--like the other triterpenoic acids. These facts bring GA and derivatives in the focus of our scientific interest. Here we tried to improve the poor cytotoxicity of GA by simple derivatization. Thus, we selected various glutamyl and aspartyl substituents for the synthesis of C(3) esters of GA methyl ester. A short (3-5 steps) synthesis was elaborated that allowed to access more effective compounds. One compound, methyl 3ß 3-(O-benzyl-L-glutamyl)-11-oxo-olean-12-en-30-oate (5), having a glutamyl substituent with a benzyl protected side chain showed up to 67-fold higher cytotoxicity and an up to 140-fold better selectivity towards tumor cells than parent GA. All compounds were evaluated by a sulforhodamine B assay as well as by a trypan blue test and extra acridine orange/ethidium bromide tests for apoptosis.

Amplification of the inhibitory activity and reversal of the selectivity of miglitol by C(2')-monofluorination.

Selective monofluorination of the α-glycosidase inhibitor and antidiabetic agent miglitol at positions C(2') or C(6) creates competitive inhibitors of glycosidases. Introducing a fluorine substituent at position C(6) results in a reduced binding to the enzyme whereas fluorination at C(2') produces an inhibitor with an activity four times higher than the parent compound. This compound is selective for the α-galactosidase from green coffee beans. Its screening against a panel of human cell lines showed a low cytotoxicity, therefore, making this compound an interesting candidate for further clinical investigations.

Synthesis and biological activity of some antitumor active derivatives from glycyrrhetinic acid.

Aminoalkyl substituted derivatives were synthesized starting from glycyrrhetinic acid methyl ester and screened for antitumor activity in a panel of 15 human cancer cell lines by an SRB assay. The most compound 7 possesses an aminohexyl side chain, induces apoptosis and shows IC50 values of 0.6-3.0 µM.

Synthesis, cytotoxicity and liposome preparation of 28-acetylenic betulin derivatives.

Several novel betulin derivatives were prepared and evaluated for their antitumor activity. 3-O-acetylbetulinic aldehyde served as an ideal starting material for the synthesis of 28-acetylenic derivatives. These compounds were further transformed into pyrazoles and 1,2,3-triazoles. Also, the synthesis of 3-amino substituted butenolides was carried out. The compounds were screened for their antitumor activity in a panel of 15 human cancer cell lines in a sulforhodamine B (SRB) assay. Several compounds showed a noteworthy antitumor activity. In addition, the possibility of encapsulation into liposomes was examined, thereby resulting in an increased cytotoxicity. The results from a trypan-blue test and from DNA laddering provided evidence for an apoptotic cell death.

Synthesis of an antitumor active endoperoxide from 11-keto-beta-boswellic acid.

An endoperoxide was synthesized starting from 11-keto-beta-boswellic acid and screened for antitumor activity in a panel of 15 human cancer cell lines by an SRB assay. The compound induces apoptosis and shows an average IC(50) value of 0.4-4.5 microM.