Psymberin, a potent sponge-derived cytotoxin from Psammocinia distantly related to the pederin family

[structure: see text] Bioassay-guided fractionation of the sponge Psammocinia sp. afforded psymberin (1) possessing 5S,8S,9S,11R,13R,15S,16R,17R stereochemistry. Psymberin exhibits structural similarities to the pederin family metabolites. The potent cytotoxicty and unique structural features of 1 make it a promising lead for therapeutic development.     

Kibdelones: novel anticancer polyketides from a rare Australian actinomycete

The kibdelones are a novel family of bioactive heterocyclic polyketides produced by a rare soil actinomycete, Kibdelosporangium sp. (MST-108465). Complete relative stereostructures were assigned to kibdelones A-C (1-3), kibdelone B rhamnoside (5), 13-oxokibdelone A (7), and 25-methoxy-24-oxokibdelone C (8) on the basis of detailed spectroscopic analysis and chemical interconversion, as well as mechanistic and biosynthetic considerations. Under mild conditions, kibdelones B (2) and C (3) undergo a facile equilibration to kibdelones A-C (1-3), while kibdelone B rhamnoside (5) equilibrates to a mixture of kibdelone A-C rhamnosides (4-6). A plausible mechanism for this equilibration is proposed and involves air oxidation, quinone/hydroquinone redox transformations, and a choreographed sequence of keto/enol tautomerizations that aromatize ring C via a quinone methide intermediate. Kibdelones exhibit potent and selective cytotoxicity against a panel of human tumor cell lines and display significant antibacterial and nematocidal activity.     

Discovery of a potent and orally available acyl-CoA: cholesterol acyltransferase inhibitor as an anti-atherosclerotic agent: (4-phenylcoumarin)acetanilide derivatives

Acyl-CoA: cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes cholesterol esterification. ACAT inhibitors are expected to be potent therapeutic agents for the treatment of atherosclerosis. A series of potent ACAT inhibitors based on an (4-phenylcoumarin)acetanilide scaffold was identified. Evaluation of the structure-activity relationships of a substituent on this scaffold, with an emphasis on improving the pharmacokinetic profile led to the discovery of 2-[7-chloro-4-(3-chlorophenyl)-6-methyl-2-oxo-2H-chromen-3-yl]-N-[4-chloro-2-(trifluoromethyl)phenyl]acetamide (23), which exhibited potent ACAT inhibitory activity (IC50=12 nM) and good pharmacokinetic profile in mice. Compound 23 also showed regressive effects on atherosclerotic plaques in apolipoprotein (apo)E knock out (KO) mice at a dose of 0.3 mg/kg per os (p.o.).     

Synthesis of novel curcumin analogues and their evaluation as selective cyclooxygenase-1 (COX-1) inhibitors

Curcumin, a major yellow pigment and active component of turmeric, has been shown to possess anti-inflammatory and anti-cancer activities. Recent studies have indicated that cyclooxygenase-1 (COX-1) plays an important role in inflammation and carcinogenesis. In order to find more selective COX-1 inhibitors a series of novel curcumin derivatives was synthesized and evaluated for their ability to inhibit this enzyme using in vitro inhibition assays for COX-1 and COX-2 by measuring PGE(2) production. All curcumin analogues showed a higher rate of COX-1 inhibition. The most potent curcumin compounds were (1E,6E)-1,7-di-(2,3,4-trimethoxyphenyl)-1,6-heptadien-3,5-dione (4) (COX-1: IC(50) = 0.06 microM, COX-2: IC(50) > 100 microM, selectivity index>1666) and (1E,6E)-methyl 4-[7-(4-methoxycarbonyl)phenyl]-3,5-dioxo-1,6-heptadienyl]benzoate (6) (COX-1: IC(50) = 0.05 microM, COX-2: IC(50) > 100 microM, selectivity index > 2000). Curcumin analogues therefore represent a novel class of highly selective COX-1 inhibitors and promising candidates for in vivo studies.     

Inhibitory effect of validamine, valienamine and valiolamine on activities of carbohydrases in rat small intestinal brush border membranes

Three pseudo-aminosugars, validamine, valienamine and valiolamine, produced by Streptomyces hygroscopicus subsp. limoneus showed potent inhibitory action on rat small intestinal carbohydrase activities such as sucrase, maltase, glucoamylase, isomaltase and trehalase activities, but negligible action on lactase activity and pancreatic alpha-amylase activity. Where inhibition was seen, kinetic analysis showed fully competitive inhibition of the carbohydrase activities by all three inhibitors. Valiolamine has more potent carbohydrase inhibitory activity than validamine or valienamine, and the apparent Ki values of valiolamine for sucrase, maltase, glucoamylase, isomaltase and trehalase activities were 3.2 x 10(-7), 2.9 x 10(-6), 1.2 x 10(-6), 9.1 x 10(-7) and 4.9 x 10(-5) M, respectively, which are 10(-5) to 10(-3) times smaller than the apparent Km values.     

Potent active site-directed inhibition of steroid sulphatase by tricyclic coumarin-based sulphamates

BACKGROUND: There is now abundant evidence that inhibition of steroid sulphatase alone or in conjunction with inhibition of aromatase may enhance the response of postmenopausal patients with hormone-dependent breast cancer to this type of endocrine therapy. Additionally, sulphatase inhibition has been proposed to be of potential therapeutic benefit in the immune system and for neuro-degenerative diseases. After the finding that our first highly potent active site-directed steroid sulphatase inhibitor, oestrone-3-O-sulphamate (EMATE), was highly oestrogenic, we proposed non-steroidal coumarin sulphamates such as 4-methylcoumarin-7-O-sulphamate (COUMATE) as alternative non-steroidal steroid sulphatase inhibitors. In this work, we describe how tricyclic coumarin-based sulphamates have been developed which are even more potent than COUMATE, are non-oestrogenic and orally active. We also discuss potential mechanisms of action. RESULTS: 4-Ethyl- (4), 4-(n-propyl)- (6), 3-ethyl-4-methyl- (8), 4-methyl-3-(n-propyl)coumarin-7-O-sulphamate (11); the tricyclic derivatives 665COUMATE (13), 666COUMATE (15), 667COUMATE (17), 668COUMATE (20) and the tricyclic oxepin sulphamate (22) were synthesised. In a placental microsome preparation, all of these analogues were found to be more active than COUMATE in the inhibition of oestrone sulphatase, with the most potent inhibitor being 667COUMATE which has an IC(50) of 8 nM, some 3-fold lower than that for EMATE (25 nM). In addition, 667COUMATE was also found to inhibit DHEA-sulphatase some 25-fold more potently than EMATE in a placental microsome preparation. Like EMATE, 667COUMATE acts in a time- and concentration-dependent manner, suggesting that it is an active site-directed inhibitor. However, in contrast to EMATE, 667COUMATE has the important advantage of not being oestrogenic. In addition, we propose several diverse mechanisms of action for this active site-directed steroid sulphatase inhibitor in the light of recent publications on the crystal structures of human arylsulphatases A and B and the catalytic site topology for the hydrolysis of a sulphate ester. CONCLUSIONS: A highly potent non-steroidal, non-oestrogenic and irreversible steroid sulphatase inhibitor has been developed. Several mechanisms of action for an active site-directed steroid sulphatase inhibitor are proposed. With 667COUMATE now in pre-clinical development for clinical trial, this should allow the biological and/or clinical significance of steroid sulphatase inhibitors in the treatment of postmenopausal women with hormone-dependent breast cancer and other therapeutic indications to be fully evaluated.     

Design, synthesis and biological activity of cyclohexane-bearing C-glucoside derivatives as SGLT2 inhibitors

Seven cyclohexane-bearing C-glucoside derivatives (7, 9, 12, 13 and 17-19) were designed and synthesized as SGLT2 inhibitors starting from a potent SGLT2 inhibitor we discovered in earlier work, (1S)-1-deoxy-1-[4-methoxy-3-(trans-n-propylcyclohexyl)methylphenyl]-D-glucose (1). The in vitro and in vivo biological activities were evaluated by hSGLT2/hSGLT1 inhibition and urinary glucose excretion (UGE), respectively. Among the synthesized compounds 12, the 6-deoxy derivative of 1 was the most active and selective SGLT2 inhibitor (IC50 = 1.4 nmol/L against hSGLT2; selectivity = 1576). Compound 12 was a potent SGLT2 inhibitor, which could induce more urinary glucose than 1 and dapagliflozin in UGE.     

Synthesis and structure-activity relationship of N-arylrolipram derivatives as inhibitors of PDE4 isozymes

Structure activity studies of N-phenylrolipram derivatives have led to the identification of highly potent PDE4 inhibitors. The potential of these inhibitors for cellular activity was routinely assessed in an assay of fMLP induced oxidative burst in human eosinophils. Since first generation PDE4 inhibitors have been plagued with a number of unwanted side effects, parallel structure activity studies for competition with the [3H]-rolipram binding site in rat brain were performed. In this fashion 5-[4-(3-cyclopentyloxy-4-methoxyphenyl)-2-oxo-pyrrolidin-1-yl]-3-(3-methoxybenzyloxy)benzoic acid N',N'-dimethylhydrazide (22) was identified as a potent inhibitor of PDE4 which exhibits >1000 fold selectivity versus PDE3, and is a nanomolar inhibitor in all the cellular assays tested. Studies on the stereoselectivity of PDE4 inhibition of this class of rolipram based compounds revealed, that for example (S)-11 is a more potent inhibitor than (R)-11. This effect can also be observed in primary human cells where the (S)-enantiomer is about 10 fold more potent than the corresponding (R)-enantiomer.     

Potent and selective inhibition of SH3 domains with dirhodium metalloinhibitors

Src-family kinases (SFKs) play important roles in human biology and are key drug targets as well. However, achieving selective inhibition of individual Src-family kinases is challenging due to the high similarity within the protein family. We describe rhodium(ii) conjugates that deliver both potent and selective inhibition of Src-family SH3 domains. Rhodium(ii) conjugates offer dramatic affinity enhancements due to interactions with specific and unique Lewis-basic histidine residues near the SH3 binding interface, allowing predictable, structure-guided inhibition of SH3 targets that are recalcitrant to traditional inhibitors. In one example, a simple metallopeptide binds the Lyn SH3 domain with 6 nM affinity and exhibits functional activation of Lyn kinase under biologically relevant concentrations (EC₅₀ ∼ 200 nM).     

KNI-102, a novel tripeptide HIV protease inhibitor containing allophenylnorstatine as a transition-state mimic.

HIV-1 protease inhibitors containing allophenylnorstatine [Apns; (2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid]-Pro (syn diastereomer) as a transition-state mimic were established to be potent and highly selective. Z-Asn-Apns-Pro-NHBut (KNI-102) is the only tripeptide exhibiting substantial anti-HIV activity and may be of minimum size for potent, selective inhibition of HIV protease. Ready availability due to its simple chemical structure and stability should make it valuable for studies of the development of metabolically stable anti-AIDS drugs.     

Probing sponge-derived terpenoids for human 15-lipoxygenase inhibitors

A human 15-lipoxygenase (15-HLO) assay has been employed to discover new marine-sponge-derived bioactive compounds. Extracts from two different sponges, Jaspis splendens (order Choristida, family Jaspidae) and Suberea sp. (order Verongida, family Aplysinellidae), exhibited potent IC(50) values of 0.4 and 0.1 microg/mL, respectively. Both are sources of terpenoids, and the former is a known source of (+)-jasplakinolide (7), which is inactive as a 15-HLO inhibitor. The terpenoids included (+)-(5S,6S)-subersin (1, IC(50) > 100 microM), (-)-(5R,10R)-subersic acid (2, IC(50) = 15 microM), jaspaquinol (3, IC(50) = 0.3 microM), and (-)-jaspic acid (4, IC(50) = 1.4 microM). Structure elucidations and lipoxygenase activity studies of these compounds are reported.     

Structure-activity relationship of orally potent tripeptide-based HIV protease inhibitors containing hydroxymethylcarbonyl isostere

We designed and synthesized a new class of peptidomimetic human immunodeficiency virus protease inhibitors containing a unique unnatural amino acid, allophenylnorstatine [Apns; (2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid], with a hydroxymethylcarbonyl isostere as the active moiety. From a structure-activity relationship study of HIV-1 protease inhibition, enzyme selectivity for other aspartyl proteases, the antiviral activity and pharmacokinetics in rats, 24c (KNI-227) and 24d (KNI-272, our first clinical candidate) were found to be selective and orally potent HIV protease inhibitors. Moreover, an improvement of the pharmacokinetic features of KNI-272 provided two long-lasting and highly bioavailable compounds (24g: JE-2178, 24h: JE-2179).     

A search for BACE inhibitors reveals new biosynthetically related pyrrolidones, furanones and pyrroles from a southern Australian marine sponge, Ianthella sp

Fractionation of a southern Australian marine sponge, Ianthella sp., yielded sixteen metabolites including a new class of pyrrolidone, ianthellidones A-F (1-6), a new class of furanone, ianthellidones G-H (7-8), new and known lamellarins, lamellarins O1 (9), O2 (10), O (11) and Q (12), plus the known 4-hydroxybenzaldehyde (13), 4-hydroxybenzoic acid (14), 4-methoxybenzoic acid (15) and ethyl 4-hydroxybenzoate (16). Structures for all Ianthella metabolites were determined by detailed spectroscopic analysis, supported by a plausible biosynthetic relationship. The ianthellidones were non-cytotoxic towards two human colon cancer cell lines (SW620 and SW620 Ad300), as well as Gram +ve and Gram -ve bacteria, and a fungus. Ianthellidone F (6) and lamellarins O2 (10) and O (11) displayed modest BACE inhibitory properties (IC(50) > 10 μM), while lamellarin O1 (9) was more potent (IC(50) < 10 μM). Lamellarin O (11) exhibited modest cytotoxicity towards SW620 and SW620 Ad300 cell lines (IC(50) > 22 μM), was an inhibitor of the multi-drug resistance efflux pump P-glycoprotein, and displayed selective growth inhibitory activity against the Gram +ve bacterium Bacillus subtilis (ATCC 6633) (IC(50) 2.5 μM).     

Inhibitory activities and inhibition specificities of caffeic acid derivatives and related compounds toward 5-lipoxygenase

Various caffeic acid derivatives were synthesized, and their effects on 5-lipoxygenase (5-LO), 12-lipoxygenase (12-LO) and prostaglandin (PG) synthase activities were investigated. Among them, caffeic acid octyl amide (5) and 1-(3,4-dihydroxyphenyl)-1-octen-3-one (11) showed very potent inhibitory activities toward 5-LO with IC50 values of 4.2 x 10(-8) and 3.5 x 10(-8) M, respectively. They were very selective inhibitors for 5-LO. Compound 11 showed non-competitive inhibition, and the two adjacent hydroxy groups attached to the benzene ring, as well as the hydrophobic alkyl side chain, were required for its strong binding to 5-LO.     

Design,synthesis, and evaluation of gluten peptide analogs as selective inhibitors of human tissue transglutaminase

Recent studies have implicated a crucial role for tissue transglutaminase (TG2) in the pathogenesis of Celiac Sprue, a disorder of the small intestine triggered in genetically susceptible individuals by dietary exposure to gluten. Proteolytically stable peptide inhibitors of human TG2 were designed containing acivicin or alternatively 6-diazo-5-oxo-norleucine (DON) as warheads. In biochemical and cell-based assays, the best of these inhibitors, Ac-PQP-(DON)-LPF-NH(2), was considerably more potent and selective than other TG2 inhibitors reported to date. Selective pharmacological inhibition of extracellular TG2 should be useful in exploring the mechanistic implications of TG2-catalyzed modification of dietary gluten, a phenomenon of considerable relevance in Celiac Sprue.     

Polyhydroxylated bicyclic isoureas and guanidines are potent glucocerebrosidase inhibitors and nanomolar enzyme activity enhancers in Gaucher cells

Four diastereomeric series of N-alkylated [6+5] bicyclic isoureas having hydroxyl substituents mimicking glucose hydroxyl groups have been synthesized as potential β-glucocerebrosidase (GCase) inhibitors with the aim of developing pharmacological chaperones for enzyme deficiency in Gaucher disease (GD). The bicyclic compounds differ either by the configuration of the ring fusion carbon atoms or by the nature of the N-alkyl substituents. When assayed for effects on GCase activity, the isoureas displayed selective inhibition of GCase with low micromolar to nanomolar IC(50)'s in isolated enzyme experiments. One of the series of isoureas, a family having a specific cis ring fusion, exhibited strong inhibition of recombinant GCase activity with K(i) values in the 2-42 nM range. In addition, the [6+5] bicyclic guanidine derivatives with a substitution pattern analogous to the most active isoureas were also found to be potent inhibitors of GCase with K(i) values between 3 and 10 nM. Interestingly, the active bicyclic isoureas and guanidines also behaved as GCase inhibitors in wild-type human fibroblasts at nanomolar concentrations. The potential of these compounds as pharmaceutical chaperones was determined by analyzing their capacity for increasing GCase activity in GD lymphoblasts derived from N370S and L444P variants, two of the most prevalent Gaucher mutations. Six compounds were selected from the different bicyclic isoureas and guanidines obtained that increased GCase activity by 40-110% in N370S and 10-50% in L444P cells at low micromolar to nanomolar concentrations following a 3 day incubation. These results describe a promising series of potent GCase ligands having the cellular properties required for pharmacological chaperones.     

Synthesis of 5'-methylenearisteromycin and its 2-fluoro derivative with potent antimalarial activity due to inhibition of the parasite S-adenosylhomocysteine hydrolase

5'-methylenearisteromycin 5 and its 2-fluoro derivative 6, which were designed as antimalarial agents because of their AdoHcy hydrolase inhibition, were synthesized from D-ribose, using a stereoselective intramolecular radical cyclization as the key step to construct the carbocyclic structure. These compounds were evaluated as AdoHcy hydrolase inhibitors with the recombinant human and malarial parasite enzymes. Although 5 and 6 were both potent inhibitors of the malarial parasite AdoHcy hydrolase, the 2-fluoro derivative 6 proved to be superior due to its lower inhibitory effect on the human enzyme. In addition, 6 was identified as a potent antimalarial agent using an in vitro assay system with Plasmodium falciparum.     

Cyclodextrin-mediated crystallization of acid β-glucosidase in complex with amphiphilic bicyclic nojirimycin analogues

Cyclodextrin-based host-guest chemistry has been exploited to facilitate co-crystallization of recombinant human acid β-glucosidase (β-glucocerebrosidase, GlcCerase) with amphiphilic bicyclic nojirimycin analogues of the sp(2)-iminosugar type. Attempts to co-crystallize GlcCerase with 5-N,6-O-[N'-(n-octyl)iminomethylidene]nojirimycin (NOI-NJ) or with 5-N,6-S-[N'-(n-octyl)iminomethylidene]-6-thionojirimycin (6S-NOI-NJ), two potent inhibitors of the enzyme with promising pharmacological chaperone activity for several Gaucher disease-associated mutations, were unsuccessful probably due to the formation of aggregates that increase the heterogeneity of the sample and affect nucleation and growth of crystals. Cyclomaltoheptaose (β-cyclodextrin, βCD) efficiently captures NOI-NJ and 6S-NOI-NJ in aqueous media to form inclusion complexes in which the lipophilic tail is accommodated in the hydrophobic cavity of the cyclooligosaccharide. The dissociation constant of the complex of the amphiphilic sp(2)-iminosugars with βCD is two orders of magnitude higher than that of the corresponding complex with GlcCerase, allowing the efficient transfer of the inhibitor from the βCD cavity to the GlcCerase active site. Enzyme-inhibitor complexes suitable for X-ray analysis were thus grown in the presence of βCD. In contrast to what was previously observed for the complex of GlcCerase with the more basic derivative, 6-amino-6-deoxy-5-N,6-N-[N'-(n-octyl)iminomethylidene]nojirimycin (6N-NOI-NJ), the β-anomers of both NOI-NJ and 6S-NOI-NJ were seen in the active site, even though the α-anomer was exclusively detected both in aqueous solution and in the corresponding βCD:sp(2)-iminosugar complexes. Our results further suggest that cyclodextrin derivatives might serve as suitable delivery systems of amphiphilic glycosidase inhibitors in a biomedical context.     

An inhibitor of sequence-specific proteolysis that targets the substrate rather than the enzyme

BACKGROUND: Traditional protease inhibitors target the active site of the enzyme. However, since most proteases act on multiple substrates, even the most specific protease inhibitors will affect the levels of a number of different proteins. However, if substrate-targeted inhibitors could be developed, much higher levels of specificity could be achieved. In theory, compounds that bind the cleavage site of a particular substrate could block its interaction with a protease without having any effect on the processing of other substrates of that protease. RESULTS: A model system is presented that demonstrates the feasibility of substrate-targeted inhibition of proteolysis. A peptide selected genetically to bind a 14-residue epitope that encompasses the cleavage site of human pro-IL-1beta was shown to inhibit interleukin-converting enzyme (ICE)-mediated proteolysis of model substrates containing the 14-mer target sequence. However, the peptide had no effect on the cleavage of other ICE substrates with different amino acids flanking the minimal cleavage site. CONCLUSIONS: This study demonstrates the feasibility of substrate-targeted inhibition of proteolysis. More potent compounds must be developed before substrate-targeted inhibitors can be used routinely. Nonetheless, this novel strategy for protease inhibition seems promising for the development of extremely selective molecules with which to manipulate the maturation of many important pro-hormones, -cytokines and -proteins.