Synthesis, biological evaluation and quantitative structure activity relationship analysis of nuclear-substituted pargylines as competitive inhibitors of MAO-A and MAO-B.

A series of nuclear substituted derivatives of pargyline has been prepared and tested (under controlled conditions designed to measure the competitive component of the inhibition) as competitive inhibitors of MAO-A and -B. Adequate correlation of the biological data with the physiochemical constants of substituent groups was obtained only when the m- and p-substituted derivatives were considered separately. Due to the narrow range of activity displayed by the p-substituted derivates when inhibiting MAO-B, meaningful correlations were not found. However, the inhibition of MAO-B by the m-substituted derivatives required the inclusion of the Verloop L parameter for adequate correlation, suggesting that the inhibitor binding site of MAO-B is present within a cavity of more limited lateral dimensions than that present on the MAO-A surface. Inhibition of both MAO-A and -B demonstrated a parabolic relationship between inhibitory activity and pi. Whereas this parabolic relationship showed a maximal value for inhibition of MAO-A (mean pi o = 0.86), inhibition of MAO-B demonstrated a minimal value of pi (pi min = -0.5) i.e. the optimal value of pi for inhibition of MAO-B has not been achieved for this series of compounds but such would be greater than that demonstrated for MAO-A. The Hammett sigma function was important or significant only in the inhibition of MAO-A by the p-substituted derivatives.     

Simple,potent, and selective pyrrole inhibitors of monoamine oxidase types A and B

N-Benzyl- and N-propargyl-1H-pyrrole-2-carboxyamides and some related methylenamines were synthesized and tested for their monoamine oxidase types A and B inhibitory activity. 2-(N-Methyl-N-propargylaminomethyl)-1H-pyrrole (24) was the most potent MAO-A inhibitor of the series [K(i)(MAO-A) = 0.0054 microM], but it was not selective. Inhibitors N-4-fluorobenzyl-1H-pyrrole-2-carboxamide (12) and N-cyclohexylmethyl-1H-pyrrole-2-carboxamide (25) showed the highest MAO-A selectivity indexes (SI) corresponding to 2025 and >2500, respectively, while 2-(N-methyl-N-benzylaminomethyl)-1H-pyrrole (21) was the most selective MAO-B inhibitor, having an SI of 0.0057.     

Studies on the monoamine oxidase inhibitors of medicinal plants I. Isolation of MAO-B inhibitors fromChrysanthemum indicum

Fourteen kinds of medicinal plants were screened for determining inhibitory activities on monoamine oxidase B. The extracts ofArtemisia Messer-Schmidtiana (herba),Chrysanthemum indicum (flos),Ericibe obtusifolia (radix et rhizoma) andSophora japonica (flos) strongly inhibited the enzyme. Among them, Chrysanthemi flos was chosen for elucidating its active principles, and some flavonoids were isolated and identified as acacetin (I), 5,7-dihydroxy chromone (II), diosmetin (III), apigenin (IV), eriodictyol (V) and luteolin (VI). IC₅₀-dihydroxy chromone (II), diosmetin (III), apigenin (IV), eriodictyol (V) and luteolin (VI). IC₅₀ were determined as following: I, 2.46; II, 0.19; III. 2.11mM, and the others showed weak inhibition.     

Synthesis of novel MPTP analogs as potential monoamine oxidase B (MAO-B) inhibitors.

The nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetahydropyridine (MPTP) is an excellent substrate and a weak inactivator of the flavoenzyme monoamine oxidase B (MAO-B). In an attempt to develop novel mechanism-based inactivators of MAO-B, we have synthesized analogs of MPTP bearing a variety of functional groups at either the N or the C(4) position and have examined their interactions with a purified MAO-B preparation isolated from beef liver. The substituents selected include allyl, propargyl, ethenyl, ethynyl, and cyclobutyl, that is, functionalities which were considered potential sources of enzyme generated electrophilic or radical intermediates that might alkylate and inactivate the enzyme. None of the C(4)-substituted compounds displayed significant enzyme inhibitor properties although some proved to be good substrates. In the N-substituted MPTP series only the 4-phenyl-1-propargyl analog was a good inhibitor. The time- and concentration-dependent inhibition of MAO-B displayed by this compound is consistent with a mechanism-based inactivation pathway and the catalytic mechanism currently held for monoamine oxidases. The results of these studies provide additional insights into the steric features of the active site of MAO-B and predict that the area in which the C(4) substituent of the tetrahydropyridine ring resides lacks a reactive nucleophilic group.     

Stereoselectivity and isoenzyme selectivity of monoamine oxidase inhibitors. Enantiomers of amphetamine, N-methylamphetamine and deprenyl

The enantiomers of amphetamine, N-methylamphetamine and deprenyl were studied, using a solubilised rat liver mitochondrial monoamine oxidase (MAO) preparation, as competitive inhibitors of MAO-A and MAO-B (5-hydroxytryptamine and beta-phenylethylamine as substrate respectively). Only in the case of deprenyl enantiomers inhibiting MAO-B was a preference shown towards the [R]-configuration enantiomer justifying the use of [R]-(-)-deprenyl (as compared to the racemate) for the specific inhibition of MAO-B. Recalculation of the observed Ki values in terms of the base form of the inhibitor indicated that the activity of all enantiomers fell within a narrow, approximately 25-fold range when inhibiting MAO-B. The selectivity of inhibition of MAO-B by [R]-(-)-deprenyl cannot therefore be attributed to any specific structural features of the MAO-B isoenzyme form but rather to a lack of affinity of this enantiomer towards MAO-A.     

Substrate selectivity of monoamine oxidase A, monoamine oxidase B, diamine oxidase, and semicarbazide-sensitive amine oxidase in COS-1 expression systems

The substrate selectivity of monoamine oxidase A (MAO-A), monoamine oxidase B (MAO-B), diamine oxidase (DAO), and semicarbazide-sensitive amine oxidase (SSAO) was investigated in the absence of chemical inhibitors using the COS-1 cells expressed with respective amine oxidase. Serotonin (5-hydroxytryptamine), 1-methylhistamine, and histamine were preferentially oxidized by MAO-A, SSAO, and DAO, respectively, at a low substrate concentration. In contrast, benzylamine, tyramine, and beta-phenylethylamine served as substrates for all of MAO-A, MAO-B, and SSAO. Each amine oxidase showed broad substrate selectivity at a high substrate concentration. The cross-inhibition was remarkable in MAO-A and MAO-B, especially in MAO-A, but not in SSAO and DAO. A study of the substrate selectivity of amine oxidases should include consideration of the effects of substrate concentration and specific chemical inhibitors.     

The evaluation of isatin analogues as inhibitors of monoamine oxidase

The small molecule, isatin, is a well-known reversible inhibitor of the monoamine oxidase (MAO) enzymes with IC₅₀ values of 12.3 and 4.86 μM for MAO-A and MAO-B, respectively. While the interaction of isatin with MAO-B has been characterized, only a few studies have explored structure–activity relationships (SARs) of MAO inhibition by isatin analogues. The current study therefore evaluated a series of 14 isatin analogues as in vitro inhibitors of human MAO-A and MAO-B. The results indicated good potency MAO inhibition for some isatin analogues with five compounds exhibiting IC₅₀ < 1 μM. 4-Chloroisatin ( 1b ) and 5-bromoisatin ( 1f ) were the most potent inhibitors with IC₅₀ values of 0.812 and 0.125 μM for MAO-A and MAO-B, respectively. These compounds were also found to be competitive inhibitors of MAO-A and MAO-B with K_i values of 0.311 and 0.033 μM, respectively. Among the SARs, it was interesting to note that C5-substitution was particularly beneficial for MAO-B inhibition. MAO inhibitors are established drugs for the treatment of neuropsychiatric and neurodegenerative disorders, while potential new roles in prostate cancer and cardiovascular disease are being investigated.     

Design, synthesis, and biological evaluation of semicarbazide-sensitive amine oxidase (SSAO) inhibitors with anti-inflammatory activity

In an attempt to examine the effect of inhibition of semicarbazide-sensitive amine oxidase (SSAO; EC 1.4.3.6, also known as VAP-1) as a novel anti-inflammatory target, the structure/mechanism based design and synthesis of a series of novel hydrazino-containing small molecules are described. The in vitro biological results show that compounds 4a,c are highly potent SSAO inhibitors with notable selectivity toward SSAO over monoamine oxidases A and B (MAO-A and MAO-B). SAR studies based on compound 4c were performed, and the results are discussed. The most potent and selective compound, 4a (IC(50) = 2 nM), is an orally active, competitive, and apparently irreversible inhibitor of SSAO that is effective at reducing disease incidence and severity in an in vivo animal disease model of multiple sclerosis.     

Synthesis and biological evaluation of D-amino acid oxidase inhibitors

D-amino acid oxidase (DAAO) catalyzes the oxidation of D-amino acids including d-serine, a full agonist at the glycine site of the NMDA receptor. A series of benzo[ d]isoxazol-3-ol derivatives were synthesized and evaluated as DAAO inhibitors. Among them, 5-chloro-benzo[ d]isoxazol-3-ol (CBIO) potently inhibited DAAO with an IC50 in the submicromolar range. Oral administration of CBIO in conjunction with d-serine enhanced the plasma and brain levels of d-serine in rats compared to the oral administration of d-serine alone.     

New potent bisubstrate inhibitors of histone acetyltransferase p300: design, synthesis and biological evaluation

Bisubstrate-type compound Lys-CoA has been shown to inhibit the p300 histone acetyl transferase activity efficiently and may constitute a lead compound for a novel class of anticancer therapeutics. Based on this strategy, we synthesized a series of CoA derivatives and evaluated these molecules for their activity as p300 histone acetyltransferases inhibitor. The best activity was obtained with compound 3 bearing a C-5 spacing linker that connects the CoA moiety to a tert-butyloxycarbonyl (Boc) group. Based on docking simulations, this inhibitor exhibits favorable interactions with two binding areas, namely pockets P1 and P2, within the active site.     

Design, synthesis, and biological evaluation of potent c-Met inhibitors

c-Met is a receptor tyrosine kinase that plays a key role in several cellular processes but has also been found to be overexpressed and mutated in different human cancers. Consequently, targeting this enzyme has become an area of intense research in drug discovery. Our studies began with the design and synthesis of novel pyrimidone 7, which was found to be a potent c-Met inhibitor. Subsequent SAR studies identified 22 as a more potent analog, whereas an X-ray crystal structure of 7 bound to c-Met revealed an unexpected binding conformation. This latter finding led to the development of a new series that featured compounds that were more potent both in vitro and in vivo than 22 and also exhibited different binding conformations to c-Met. Novel c-Met inhibitors have been designed, developed, and found to be potent in vitro and in vivo.     

Novel malyngamide structural analogs: synthesis and biological evaluation

In the course of our search for new anticancer agents, a series of novel malyngamide derivatives were synthesized by sharpless asymmetric epoxidation, followed by Julia-Kocinski olefination reactions as key reaction sequence. Anticancer activities of all these derivatives were screened against IMR-32, SF-295, SKNSH, HeLa, Colon-502713, SW-620, and Hop-62 cell lines for the first time.     

Aminoacyl-anthraquinone conjugates as telomerase inhibitors: synthesis, biophysical and biological evaluation

The telomerase-telomere complex is a prospective anticancer target. To inhibit enzyme activity by induction of G-quadruplex in human telomeres, we have synthesized a small library of 2,6- and 2,7-amino-acyl/ peptidyl anthraquinones with diverse connecting linkers, charge, lipophilicity and bulk. The test compounds modulated G-quadruplex stability to different extents and showed clear preference for quadruplex over duplex DNA. Telomerase inhibition correlated with G-quadruplex stabilization. A SAR analysis showed that type of linkage between the linker and the anthraquinone, together with the position of the side chains and the nature of the amino acid components play a major role both in stabilizing G-quadruplex and producing telomerase inhibition. Short-term cytotoxic activity was poor. However, after prolonged exposure to effective G-quadruplex binders, cells became senescent. These results are of help in the rational design of more efficient G-quadruplex stabilizers, possibly endowed with cancer cell-selective antiproliferative effects.     

Monoamine oxidase inhibitors and whole blood, platelet and plasma monoamine oxidase.

1. Whole lysed blood monoamine oxidase activity using benzylamine as substrate, represents an addition of platelet and plasma activity. 2. Enzyme activity measured in whole lysed blood in the presence of 10(-4)M pargyline gave a value equivalent to plasma monoamine oxidase, and by subtraction gives a value for platelet enzyme activity. 3. This method of measuring platelet and plasma monoamine oxidase activities from a single whole blood sample, has the advantage of not requiring physical separation of the blood fraction.