Evaluation of P(L)LA-PEG-P(L)LA as processing aid for biodegradable particles from gas saturated solutions (PGSS) process.

A series of biodegradable P(L)LA-PEG1.5 kDa-P(L)LA copolymers have been synthesized and compared as processing aid versus Poloxamer 407 (PEO-PPO-PEO), in the formulation of protein encapsulated microparticles, using supercritical carbon dioxide (scCO2). Bovine serum albumin (BSA) loaded microcarriers were prepared applying the particles from the gas saturated solutions (PGSS) technique using scCO2 and thus, avoiding the standard practice of organic solvent encapsulation. Four triblock copolymers were synthesized and characterized, particularly in terms of thermal properties and behaviour when exposed to scCO2. The effects of the inclusion of these copolymers in the formulation of poly(α-hydroxy acids) based microparticles - e.g. poly(D,L-lactic-co-glycolic acid) (PLGA) and poly(D,L-lactide) (PLA) - were analysed in terms of yield, particle size, morphology and drug release. The use of P(L)LA-PEG1.5 kDa-P(L)LA triblock copolymers were found to increase the yield of the PGSS-based process and to decrease the size of the microparticles produced, in comparison with the formulation containing the Poloxamer 407. Moreover the microparticles formulated with the triblock copolymers possessing the higher hydrophobic character were able to maintain a controlled drug release profile.

Ibuprofen and lipoic acid diamide as co-drug with neuroprotective activity: pharmacological properties and effects in beta-amyloid (1-40) infused Alzheimer's disease rat model.

Both oxidative stress and inflammation are elevated in brains of Alzheimer's disease patients, but their pathogenic significance still remains unclear. Current evidence support the hypothesis that non-steroidal anti-inflammatory drugs (NSAIDs) and antioxidant therapy might protect against the development of Alzheimer's disease, and ibuprofen has the strongest epidemiological support. In the present work our attention was focused on (R)-alpha-lipoic acid considered as a potential neuroprotective agent in Alzheimer's disease therapy. In particular, we investigated a new co-drug (1) obtained by joining (R)-alpha-lipoic acid and ibuprofen via a diamide bond, for evaluating its potential to antagonize the deleterious structural and cognitive effects of beta-amyloid (1-40) in an infused Alzheimer's disease rat model. Our results indicated that infusion of beta-amyloid (1-40) impairs memory performance through a progressive cognitive deterioration; however, ibuprofen and co-drug 1 seemed to protect against behavioural detriment induced by simultaneous administration of beta-amyloid (1-40) protein. The obtained data were supported by the histochemical findings of the present study: beta-amyloid protein was less expressed in 1-treated than in ibuprofen and (R)-alpha-lipoic acid alone-treated cerebral cortex. Taken together, the present findings suggest that co-drug 1 treatment may protect against the cognitive dysfunction induced by intracerebroventricular infusion of beta-amyloid (1-40) in rats. Thus, co-drug 1 could prove useful as a tool for controlling Alzheimer's disease-induced cerebral amyloid deposits and behavioural deterioration.

Dopamine D5 receptors: a challenge to medicinal chemists.

Due to the lack of highly selective dopamine D(1) or D(5) receptor ligands, only few data about activation or blocking of these receptor subtypes are available. The present review collects the available information about molecules with notable affinity for D(5) receptor subtype with the purpose to help the researchers to design novel D(5) selective ligands, whose discovery may enrich the knowledge about the physiological function of such a receptor, provide information about its topography, as well as lead to novel potential therapeutic tools.

Glycosyl and polyalcoholic prodrugs of lonidamine.

Polyhydric alcohol derivatives of the anticancer agent lonidamine (LND) have been synthesized. The increased water solubility showed by prodrugs 4, 7, and 25 together with their logP values (2.19, 2.55, and 2.54, respectively) and chemical stability might be beneficial for prodrugs absorption after oral administration. Moreover, the new prodrugs undergo enzymatic hydrolysis in plasma and release LND demonstrating that they are promising candidates for in vivo investigations.

Synthesis and pharmacological evaluation of 4-phenoxy-1,2,3,4-tetrahydroisoquinolines and 4,5,6,6a-tetrahydrochromeno[2,3,4-de]isoquinolines.

The novel 4-phenoxy-1,2,3,4-tetrahydroisoquinolines 6a-c and their rigid congeners 4,5,6,6a-tetrahydro-chromeno[2,3,4-de]isoquinolines 7a,b were synthesized in order to obtain dopamine D2-like receptor ligands. The new compounds were evaluated for their in vitro binding affinities, in vivo behavioral activities on rats, and for their effects on rat brain neurochemistry. Compounds 6b (toward both D2 and D3 dopamine receptors) and 7a,b (toward D3 only dopamine receptors) showed the most significant affinities. However none of the new compounds was able to stimulate behavioral activity in non pre-treated rats, nor to influence brain neurochemistry.

Synthesis and preliminary pharmacological evaluation of 5-hydroxy- and 5,6-dihydroxy-1,2,3,7,12,12a-hexahydrobenzo[5,6]cyclohepta[1,2,3-ij]isoquinoline derivatives as dopamine receptor ligands.

A series of 5-hydroxy- and 5,6-dihydroxy-1,2,3,7,12,12a-hexahydrobenzo[5,6]cyclohepta[1,2,3-ij]isoquinoline derivatives (5a--e and 6a--e) were synthesized as conformationally rigid analogues of 1-benzyltetrahydroisoquinoline and evaluated for their affinity at D(1) and D(2) dopamine receptors. All compounds showed lower D(1) and D(2) affinities than dopamine. The 5-hydroxy-1-methyl-2,3,12,12a-hexahydrobenzo[5,6]cyclohepta[1,2,3-ij]isoquinoline 5a and the 5,6-dihydroxy analogue 6a showed D(2) agonist activity. This was proved by their effects on prolactin release from primary cultures of rat anterior pituitary cells. Molecular modeling studies showed that the geometric parameters (namely the distances from meta and para hydroxyl oxygens to the nitrogen and the height of nitrogen from the hydroxylated phenyl ring plane) of the dopaminergic pharmacophore embedded in our compounds have lower values in comparison with those observed in D(1) and D(2) selective ligands.

Dimeric L-dopa derivatives as potential prodrugs.

A series of dimeric derivatives (+)-1, and (+)-2, and (+)-3a-d of L-Dopa diacetyl esters was synthesized and evaluated as potential L-Dopa prodrugs with improved physicochemical properties. All the new compounds showed chemical stability in aqueous buffer solutions (pH 1.3 and 7.4). A relatively slow release of L-Dopa in human plasma was observed.

Synthesis of L-(+)-3-(3-hydroxy-4-pivaloyloxybenzyl)-2,5-diketomorpholine as potential prodrug of L-dopa.

The synthesis and in vitro chemical and enzymatic stability of L-(+)-3-(3-hydroxy-4-pivaloyloxybenzyl)-2,5-diketomorpholine (9) as L-Dopa prodrug are described. Prodrug 9 possesses a good lipophilicity (log P = 2.153 +/- 0.017), is stable in aqueous buffer solutions (pH 1.3 and 7.4), and in 80% rat and human plasma it is turned into L-Dopa.

Binding and preliminary evaluation of 5-hydroxy- and 10-hydroxy-2,3, 12,12a-tetrahydro-1H-[1]benzoxepino[2,3,4-ij]isoquinolines as dopamine receptor ligands.

The N-methyl, N-ethyl, and N-n-propyl derivatives of 5-hydoxy- and 10-hydroxy-2,3,12,12a-tetrahydro-1H-[1]benzoxepino[2,3, 4-ij]isoquinolines were prepared as monophenolic ligands for the dopamine receptor and evaluated for their affinity at D(1)-like and D(2)-like subtypes. All compounds showed very low D(1) affinities. This could be ascribed to the absence of a catechol nucleus or of the beta-phenyldopamine pharmacophore. Only the N-methyl-5-hydroxy- (5a), N-methyl-10-hydroxy- (6a), and N-methyl-4-bromo-10-methoxy-2,3, 12,12a-tetrahydro-1H-[1]benzoxepino[2,3,4-ij]isoquinolines (26a) bound the D(2) receptors with low affinity, in the same range as dopamine. In compounds 5a and 6a, the 2-(3-hydroxyphenyl)ethylamine moiety does not meet the requirements of the D(2) agonist pharmacophore: namely, the 2-(3-hydroxyphenyl)ethylamine does not reach the trans, fully extended conformation. The three compounds did not interact with recombinant human D(4) receptors, and only 5a showed low affinity for rat recombinant D(3) receptors. Analysis of the influence of Na(+) on [(3)H]spiperone binding showed that 5a displays a potential dopamine D(2) agonist profile, whereas 6a probably has a dopamine D(2) antagonist activity. The D(2) agonist activity of 5a was proved by the effects on prolactin release from primary cultures of rat anterior pituitary cells.

Synthesis, resolution, and preliminary evaluation of trans-2-amino-6(5)-hydroxy-1-phenyl-2,3-dihydro-1H-indenes and related derivatives as dopamine receptors ligands.

The present work reports the synthesis of enantiomeric pairs of the trans-2-amino-6-hydroxy-1-phenyl-2,3-dihydro-1H-indene [(+)-14a, (-)-14a] and trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1 H-indene [(+)-14b, (-)-14b] and their N,N-di-n-propyl [(+)-and (-)-15a,b], N-methyl-N-allyl [(+)-and (-)-16a,b], and N-methyl-N-n-propyl [(+) and (-)-17a,b] derivatives obtained by a combination of stereospecific reactions and optical resolution. The new compounds were evaluated for their affinity at the dopamine D1 and D2 receptors. The amines (+)- and (-)-14a, incorporating the D1 pharmacophore 2-phenyl-2-(3-hydroxyphenyl)ethylamine in a trans extended conformation, and their derivatives displayed D1 and D2 affinity in the nanomolar range. On the other hand, the enantiomers (+)- and (-)-14b, (+)- and (-)-15b displayed high affinity and selectivity for the D1 receptor. In a preliminary behavioral study on rats (+)-14b, and to a greater extent (+)-15b, promoted episodes of intense grooming, thus indicating that they act as central D1 agonists. The trans-2-amino-5-hydroxy-1-phenyl-2,3-dihydro-1H-indenes (+)-14b and (+)-15b represent selective D1 agonists lacking a catechol group, which should meet the prerequisites for a central nervous system penetration.

Activity of N-(2-phenylethyl)-N-n-propyl-2-(3-hydroxyphenyl) ethylamine derivatives as dopamine receptor ligands.

The N-n-propyl-N-(2-phenylethyl)-2-(3-hydroxyphenyl)ethylamine (1, RU 24213) had been previously identified as selective agonist of DA D2 receptor subtype. In this paper we describe the synthesis and in vitro binding affinities of several derivatives of 1 substituted with fluorine, chlorine and methyl or hydroxy groups on the phenyl ring of the N-2-phenylethyl moiety. The results obtained indicate that these substitutions do not improve the D2 binding affinity. The introduction on the phenyl ring of two fluorine or chlorine atoms decreases with D1 affinity, and the dichloro derivatives are highly selective for the D2 receptor. Preliminary behavioural tests confirm that the dichloro derivatives behave as D2 selective agonists.

Synthesis and dopamine receptor binding of 4-(2-aminoethyl)-1H-pyrazole and its N,N-dialkyl derivatives.

The agnostic activity of Quinpirole (3a) at the D2 dopamine (DA) receptor suggested that the dopaminergic pharmacophore embedded in 3a was the 4-(2-aminoethyl)-1H-pyrazole (5) moiety. On that basis we have synthesized some derivatives of 5 bearing on the amino group alkyl and alkylaryl substituents. The affinities of 5 and its derivatives for the D1 and D2 DA receptor subtypes were evaluated in rat striatum by binding assays. None of these compounds show affinity for the D1 receptor. In the D2 binding assay only the N,N-di-(2-phenylethyl) (5i) and N-n-propyl-N-[2-(3-hydroxyphenyl)ethyl] (5j) derivatives show affinities comparable to that of Quinpirole. These results do not support the postulate that the 4-(2-aminoethyl)-1H-pyrazole is a bioisostere of the catechol nucleus of DA.

Synthesis and pharmacological characterization of 2-(4-chloro-3-hydroxyphenyl)ethylamine and N,N-dialkyl derivatives as dopamine receptor ligands.

2-(4-Chloro-3-hydroxyphenyl)ethylamine (4) and some derivatives were synthesized as dopamine (DA) receptor ligands. Amine 4 retains the dopaminergic pharmacophore 2-(3-hydroxyphenyl)-ethylamine, and the chlorine atom replaces the "para" hydroxyl group of DA. The derivatives 18a-e were obtained by introducing on the nitrogen of amine 4 the n-propyl and 2-phenylethyl or 3-phenylpropyl groups which can be accommodated by the D-2 receptor lipophilic sites 3C and pi 3, respectively. The affinity and selectivity of these compounds for D-1 and D-2 subtypes was determined in radioligand competition assays for the DA receptors of rat striatum membranes using [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) as radioligands. The amine 4 shows about 7-fold lower affinity than DA for both sites and is not able to discriminate between the two subtypes of DA receptors. The introduction of two n-propyl groups (18a) on the nitrogen atom reduces by one-half and doubles the affinity for D-1 and D-2 binding sites, respectively. The substitution of an n-propyl group with different alkylphenyl groups, to give compounds 18b-e, increases the affinity for the D-2 subtype from 19-fold to 36-fold. These compounds have the same affinity at the D-2 site as the DA agonist N-n-propyl-N-(2-phenylethyl)-2-(3-hydroxyphenyl)-ethylamine (2a) and are about 20 times more selective than DA for this binding site. In the assay for D-2 receptor mediated inhibition of adenylate cyclase activity, all the tested compounds behaved as D-2 agonists; N-n-propyl-N-[2(4-hydroxyphenyl)ethyl]- (18d) and N-n-propyl-N-(2-phenyl-ethyl)-2-(4-chloro-3-hydroxyphenyl)ethylamine (18b) were more effective than DA or 2a. On the other hand, all compounds were less effective than DA in stimulation of adenylate cyclase activity in rat striatal homogenates, a kind of effect which is mediated by the D-1 subtype of DA receptors. These results suggest that the nitrogen substitution enhances the affinity and selectivity for the D-2 receptor. In the adenylate cyclase assay, the compounds behave as potent D-2 agonists.

Structure-activity relationships of N-n-propyl-2-(4-fluoro-3-hydroxyphenyl)ethylamine derivatives as dopamine receptor ligands.

A series of N-n-propyl-2-(4-fluoro-3-hydroxyphenyl)ethylamine derivatives obtained by introducing on nitrogen atom a 2-phenylethyl moiety (with aromatic nucleus substituted at 3 or 4 position with fluorine, chlorine or hydroxy and methyl groups), as well as a 2-cyclohexylethyl or 3-phenylpropyl groups were synthesized. These substituents can interact with the D2 accessory binding site pi 3. The affinities of new compounds for D1 and D2 subtypes of dopamine (DA) receptor were measured in a test involving displacement of [3H]SCH 23390 and [3H]spiperone, respectively, from homogenates of rat striatum. The new derivatives are selective for D2 sites, and are more potent than the parent compound N-n-propyl-N-(2-phenylethyl)-2-(4-fluoro-3-hydroxyphenyl)ethylamine 2a. The N-n-propyl-N-[2-(4-hydroxyphenyl)ethyl]-2-(4-fluoro-3-hydroxyphenyl) ethylamine (11f) is the most potent and selective member in the series. Other derivatives are less effective but are as potent as the D2 agonist RU 24213. The results indicate that the pi 3 site is a rather large lipophilic pocket which can accommodate not only aromatic nuclei, but also the cyclohexyl group.

Synthesis and dopamine receptor affinities of 6-amino-5,6,7,8-tetrahydroquinoline derivatives.

Some N,N-dialkylderivatives of 6-amino-5,6,7,8-tetrahydroquinoline were synthesized. The affinity of new compounds for dopamine binding sites was measured in a test involving displacement of [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) from homogenized rat striatal tissue. While no compound was effective in displacing [3H]SCH 23390, in the binding assays on the D-2 receptor all tetrahydroquinolines displaced [3H]spiperone from specific binding sites, the compounds with a N-n-propyl-N-phenylethylamino group (18) or N,N-di n-propylamino group (16) being the most potent.