Advances in the synthesis of bioactive unnatural amino acids and peptides.

The key role of proteins and amino acids in the structure and function of living matter has stimulated extensive studies. Modified amino acids with enhanced biological activity, proteolitic stability and bioavailability are of increasing interest in protein design and engineering as drug candidates. In the last few years, several efforts have been devoted to the synthesis of amino acids having unusual side chains and unnatural chirality, commonly referred to as "nonproteinogenic" or "unnatural" amino acids, even though some of them can be isolated from natural sources. In this review we describe recent advances in the amino acid side-chain transformations and backbone modifications by oxidative and fluorination procedures.

Current advances in anti-influenza therapy.

Every year, influenza epidemics cause numerous deaths and millions of hospitalizations, but the most frightening effects are seen when new strains of the virus emerge from different species (e.g. the swine-origin influenza A/H1N1 virus), causing world-wide outbreaks of infection. Several antiviral compounds have been developed against influenza virus to interfere with specific events in the replication cycle. Among them, the inhibitors of viral uncoating (amantadine), nucleoside inhibitors (ribavirin), viral transcription and neuraminidase inhibitors (zanamivir and oseltamivir) are reported as examples of traditional virus-based antiviral strategies. However, for most of them the efficacy is often limited by toxicity and the almost inevitable selection of drug-resistant viral mutants. Thus, the discovery of novel anti-influenza drugs that target general cell signaling pathways essential for viral replication, irrespective to the specific origin of the virus, would decrease the emergence of drug resistance and increase the effectiveness towards different strains of influenza virus. In this context, virus-activated intracellular cascades, finely regulated by small changes in the intracellular redox state, can contribute to inhibit influenza virus replication and pathogenesis of virus-induced disease. This novel therapeutic approach involves advanced cell-based antiviral strategies. In this review current advances in the anti-influenza therapy for both traditional virus-based antiviral strategies as well as for alternative cell-based antiviral strategies are described focusing on the last 10 years. Anti-influenza compounds are classified on the basis of their chemical structure with a special attention to describe their synthetic pathways and the corresponding structure activity relationships.

First synthesis of totally orthogonal protected alpha-(trifluoromethyl)- and alpha-(difluoromethyl)arginines.

The first synthesis of a series of totally orthogonal protected racemic alpha-(trifluoromethyl)- and alpha-(difluoromethyl)arginines is described. The key steps of the synthesis are the mild guanidinylation procedure and the selective hydrogenation of a CC triple bond in the presence of a Cbz-group.

The "Non-Oxidative" pummerer reaction: conclusive evidence for S(N)2-type stereoselectivity, mechanistic insight, and synthesis of enantiopure L-alpha-trifluoromethylthreoninate and D-alpha-trifluoromethyl-allo-threoninate(1)

Enantiopure methyl D-alpha-trifluoromethyl-allo-threoninate 18 and L-alpha-trifluoromethylthreoninate 19 were synthesized using (R)-ethyl p-tolylsulfoxide as chiral alpha-hydroxyethyl anion equivalent. The key step was the S(N)2-type replacement of the sulfinyl auxiliary with a hydroxy group, via trifluoroacetic anhydride promoted "non-oxidative" Pummerer reaction (NOPR) of the diastereomeric intermediate beta-sulfinyl amines 14 and 15, obtained by condensation of (R)-ethyl p-tolylsulfoxide 13 with the N-Cbz imine of methyl trifluoropyruvate 12. The conclusive evidence for S(N)2-type stereoselectivity of the NOPR was achieved by X-ray diffraction of both the starting diastereomer 14 and the p-bromobenzoate 25, obtained from the threoninate 19. NMR monitoring of the NOPR performed on 15 allowed the detection of a transient intermediate, which was identified as the four membered cyclic sigma-sulfurane 27. This intermediate spontaneously rearranged (40 min, rt) into the corresponding sulfenamide 17, probably via an intramolecular displacement of the sulfinyl by a trifluoroacetoxy group, with inversion of configuration at the carbon stereocenter. The same process occurred for the diastereomeric beta-sulfinyl amine 14, but the sulfenamide 16 was formed at a very fast rate, thus precluding NMR detection of the corresponding sigma-sulfurane intermediate 26. One-pot treatment of the diastereomeric sulfenamides 16 and 17 with NaBH(4) afforded very good yields of the corresponding threoninates 18 and 19.

Synthesis and alpha-adrenoceptor blocking activity of the enantiomers of benzyl-(2-chloroethyl)-[2-(2-methoxyphenoxy)-1-methylethyl]amine hydrochloride.

The enantiomers of benzyl-(2-chloroethyl)-[2-(2-methoxyphenoxy) -1-methylethyl]amine hydrochloride (1, CM18) were synthesized and studied pharmacologically for their irreversible antagonism at rat vas deferens alpha-adrenoceptors. In addition, assignment of the absolute configuration of the two enantiomers of 1 was made by X-ray crystallographic analysis performed on the intermediate amine (+)-2 hydrochloride. The enantiomer (R)-(+)-1 [(R)-(+)-CM18] (a) had a 10-fold preferential blocking activity for alpha 1-versus alpha 2-adrenoceptors, (b) discriminated, like racemic 1, between two possible alpha 1-adrenoceptor subsites/subtypes, with a selectivity ratio of 6.5 and (c) was 10-23 times as potent as the (S)-(-)-enantiomer at alpha 2- and alpha 1-adrenoceptors. Thus, it may be a valuable tool for the characterization of rat vas deferens alpha 1-adrenoceptor subtypes.

Pharmacological evaluation of prazosin- and doxazosin-related compounds with modified piperazine ring.

New doxazosin-related compound (1-3) with a N,N'-dimethyl alkanediamine chain replacing the piperazine ring, have been synthesized and their pharmacological properties have been tested together with some prazosin analogues (4-8) bearing either a similar structural modification or a substituted piperazine moiety. In the in vitro study, on alpha 1- and alpha 2-adrenoceptors of rat vas deferens tissues, 1-3 displayed high alpha 1-antagonist activity, 2 and 3 being equipotent to doxazosin but markedly less selective in respect to alpha 2-adrenoceptors. Replacement of the piperazine ring with an alkanediamine chain resulted in a strong fall in alpha 1-selectivity, owing to increased alpha 2-antagonist activity, as in the prazosin-related series. In in vivo studies, the antihypertensive activity of tested compounds was investigated on spontaneously hypertensive rats (SHR) following both intragastric (IG) and intraperitoneal (OP) administration. Among the tested compounds, 7 and 8, which conserved a substituted piperazine ring, proved the most interesting drugs displaying a marked hypotensive effect. The other prazosin- and doxazosin-related compounds, in which an alkanediamine chain replaced the piperazine nucleus, showed an antihypertensive activity markedly lower than that of parent compounds, prazosin (CAS 19216-56-9) and doxazosin (CAS 74191-85-8), although a high alpha 1-antagonist activity in in vitro tests was conserved. These results suggest that the piperazine ring of the prazosin- and doxazosin-related compounds, although not crucial for alpha 1-antagonist activity, may play an important role in the antihypertensive effect, probably by influencing the pharmacokinetic properties of the antagonist.

Synthesis and biological profile of the enantiomers of [4-(4-amino-6,7-dimethoxyquinazolin-2-yl)-cis-octahydroquinoxalin- 1-yl]furan-2-ylmethanone (cyclazosin), a potent competitive alpha 1B- adrenoceptor antagonist.

The enantiomers of [4-(4-amino-6, 7-dimethoxyquinazolin-2-yl)-cis-octahydroquinoxalin-1-yl]-fu ran- 2-ylmethanone (cyclazosin, 1) were synthesized from the chiral furan-2-yl(cis-octahydroquinoxalin-1-yl)methanone [(+)-2 and (-)-2], which were obtained by resolution of the racemic amine with (S)-(+)- and (R)-(-)-mandelic acid. The binding profile of the enantiomers of 1 was assessed at alpha 1-, alpha 2-, D2, and 5-HT1A receptors as well as at native alpha 1A- and alpha 1B- and cloned alpha 1a-, alpha 1b-, and alpha 1d-adrenoceptor subtypes in comparison with prazosin, spiperone, and AH11110A. (+)-1 displayed a 40-90-fold selectivity for the alpha 1B(alpha 1b)-adrenoceptor relative to alpha 1A(alpha 1a) and alpha 1d subtypes. A significant enantioselectivity was observed at the alpha 1A(alpha 1a)-adrenoceptor and particularly at alpha 1d-adrenoceptors since (-)-1 was 11-14- and 47-fold, respectively, more potent than (+)-1. Furthermore the enantiomer (+)-1 displayed selectivities of 1100-, 19000-, and 12000-fold in binding to alpha 1b-adrenoceptors relative to alpha 2-adrenoceptors and 5-HT1A and D2 receptors. These results indicate that (+)-1, [(+)-cyclazosin] is the most potent and selective ligand for the alpha 1B-adrenoceptor subtype so far described and may be a valuable tool in the characterization of alpha 1-adrenoceptor subtypes.

Receptor binding profile of cyclazosin, a new alpha 1B-adrenoceptor antagonist.

The binding profile of cyclazosin, a new prazosin-related alpha 1-adrenoceptor antagonist, at alpha 1-, alpha 2-adrenoceptors, dopamine D2 and 5-HT1A receptors was compared to that of 5-methylurapidil, spiperone, risperidone and other prazosin-related ligands. In addition, cyclazosin was investigated at native and cloned alpha 1-adrenoceptor subtypes. Cyclazosin showed high specificity for alpha 1-adrenoceptors and a 10-15-fold selectivity for alpha 1B (alpha 1b)-adrenoceptors with respect to the alpha 1A (alpha 1a) subtype (pKi values of 9.23-9.57 and 8.18-8.41, respectively). However, it failed to discriminate between cloned alpha 1b and alpha 1d-adrenoceptors (pKi values of 9.23 and 9.28, respectively).

Synthesis and alpha-adrenoreceptor blocking properties of phenoxybenzamine-related (2-chloroethyl)-(2,3-dihydrobenzo[1,4]dioxin- 2-ylmethyl)-(2-phenoxyethyl) amines.

A series of beta-chloroethylamines, structural hybrids of WB 4101, a competitive alpha 1-adrenoreceptor antagonist, and phenoxybenzamine, an irreversible alpha-adrenoreceptor antagonist, has been synthesized and tested in isolated rat vas deferens alpha-adrenoreceptors. Although, for all compounds, apparent blocking potency and alpha 1-selectivity are quite similar to those of phenoxybenzamine, affinity values calculated by taking into account the actual concentration of aziridinium ion in solution, reveal that compounds bearing a 1,4-benzodioxan-2-ylmethyl moiety, display a significantly higher potency for both alpha 1- and alpha 2-adrenoreceptors than compounds having a benzyl group. In addition, two of the compounds, having both methyl and methoxy groups in their structure, show a marked discontinuity in the alpha 1-adrenoreceptor concentration-inhibition curve, with a plateau in the range 30-100 nM. Stereochemical aspects are also shown to play an important role in the binding. The biological results suggest that the two irreversible antagonists may be able to discriminate between two alpha 1-adrenoreceptor subtypes, which are both involved in the noradrenaline-induced contraction of the epididymal portion of rat vas deferens.