Antonio Guarna

1,3-Aminoalcohols by reductive cleavage of isoxazolidines with molybdenum hexacarbonyl

Abstract Isoxazolidines are reductively cleaved to 1,3-aminoalcohols by reacting with Mo(CO) 6 and water. Reaction conditions are simple, mild and selective giving good yields of highly functionalized products with complete retention of configuration of the stereocenters. The reduction fails when steric hindrance is experienced by the nitrogen atom.

A New Family of Cinchona-Derived Amino Phosphine Precatalysts: Application to the Highly Enantio- and Diastereoselective Silver-Catalyzed Isocyanoacetate Aldol Reaction

A new class of readily accessible chiral amino-phosphine precatalysts derived from 9-amino(9-deoxy) epicinchona alkaloids has been developed. In combination with Ag(I) salts, these amino-phosphines performed as effective cooperative Brønsted base/Lewis acid catalysts in the asymmetric aldol reaction of isocyanoacetate nucleophiles. Under optimal conditions, high diastereoselectivities (up to 98%) and enantioselectivities (up to 98%) were obtained.

Structural diversity of bicyclic amino acids

Summary.Over the years biomedical research has been constantly oriented towards the development of new therapeutics based on bioactive peptides and their analogues. In particular, the generation of compounds having structures and functions similar to bioactive peptides, named “peptidomimetics”, raised much interest among organic and medicinal chemists due to the possibility by using such compounds to improve both potency and stability of peptidic lead compounds. In the context of this research area, unnatural amino acids are of great interest in drug discovery, and their use as new building blocks for the development of peptidomimetics with high diversity level and possessing high-ordered structures is of special interest. In particular, medicinal chemistry has taken advantage of the use of amino acid homologues and of cyclic and polycyclic templates to introduce elements of diversity for the generation of new molecules as drug candidates. Bicyclic amino acids have been developed as reverse turn mimetics and dipeptide isosteres, and the constraint imposed by their structures has been reported as a tool for controlling the conformational preferences of modified peptides. Moreover, synthetic efforts have been driven to the generation of diverse structures based on the modulation of ring size and scaffold decoration by suitable functional groups. Herein is reported an overview of different classes of bicyclic amino acids, taking into account the strategies to achieve structurally diverse templates, and some implications in medicinal chemistry are also disclosed.

Click-chemistry-derived triazole ligands of arginine-glycine-aspartate (RGD) integrins with a broad capacity to inhibit adhesion of melanoma cells and both in vitro and in vivo angiogenesis.

A click chemistry approach was applied for the discovery of triazole-based arginine-glycine-aspartate (RGD) mimetics by Cu(I)-catalyzed 1,3-dipolar alkyne-azide coupling reaction, which showed binding affinity properties toward α(v)β(3)/α(v)β(5) integrins. Biological assays showed compound 18 capable of binding α(v)β(3) integrin with nanomolar affinity according to a two-sites model, and molecular modeling studies revealed a peculiar π-stacking interaction between the triazole ring and Tyr178 side chain. Accordingly, compound 18 inhibited the adhesion of integrin-expressing human melanoma cells to RGD-containing proteins of the extracellular matrix, such as vitronectin, fibronectin, and osteopontin, and also angiogenesis in in vitro and in vivo experimental models. The relevant biological effects exerted by compound 18 suggest its potential application as an antiangiogenic agent in the diagnosis and therapy of tumors where α(v)β(3) integrin expression is up-regulated.

Selective non-steroidal inhibitors of 5α-reductase type 1

The enzyme 5α-reductase (5αR) catalyses the reduction of testosterone (T) into the more potent androgen dihydrotestosterone (DHT). The abnormal production of DHT is associated to pathologies of the main target organs of this hormone: the prostate and the skin. Benign prostatic hyperplasia (BPH), prostate cancer, acne, androgenetic alopecia in men, and hirsutism in women appear related to the DHT production. Two isozymes of 5α-reductase have been cloned, expressed and characterized (5αR-1 and 5αR-2). They share a poor homology, have different chromosomal localization, enzyme kinetic parameters, and tissue expression patterns. Since 5αR-1 and 5αR-2 are differently distributed in the androgen target organs, a different involvement of the two isozymes in the pathogenesis of prostate and skin disorders can be hypothesized. High interest has been paid to the synthesis of inhibitors of 5α-reductase for the treatment of DHT related pathologies, and the selective inhibition of any single isozyme represents a great challenge for medical and pharmaceutical research in order to have more specific drugs. At present, no 5αR-1 inhibitor is marketed for the treatment of 5αR-1 related pathologies but pharmaceutical research is very active in this field. This paper will review the major classes of 5αR inhibitors focusing in particular on non-steroidal inhibitors and on structural features that enhance the selectivity versus the type 1 isozyme. Biological tests to assess the inhibitory activity towards the two 5αR isozymes will be also discussed.

Low molecular weight, non-peptidic agonists of TrkA receptor with NGF-mimetic activity

Exploitation of the biologic activity of neurotrophins is desirable for medical purposes, but their protein nature intrinsically bears adverse pharmacokinetic properties. Here, we report synthesis and biologic characterization of a novel class of low molecular weight, non-peptidic compounds with NGF (nerve growth factor)-mimetic properties. MT2, a representative compound, bound to Trk (tropomyosin kinase receptor)A chain on NGF-sensitive cells, as well as in cell-free assays, at nanomolar concentrations and induced TrkA autophosphorylation and receptor-mediated internalization. MT2 binding involved at least two amino-acid residues within TrkA molecule. Like NGF, MT2 increased phosphorylation of extracellular signal-regulated kinase1/2 and Akt proteins and production of MKP-1 phosphatase (dual specificity phosphatase 1), modulated p38 mitogen-activated protein kinase activation, sustained survival of serum-starved PC12 or RDG cells, and promoted their differentiation. However, the intensity of such responses was heterogenous, as the ability of maintaining survival was equally possessed by NGF and MT2, whereas the induction of differentiation was expressed at definitely lower levels by the mimetic. Analysis of TrkA autophosphorylation patterns induced by MT2 revealed a strong tyrosine (Tyr)490 and a limited Tyr785 and Tyr674/675 activation, findings coherent with the observed functional divarication. Consistently, in an NGF-deprived rat hippocampal neuronal model of Alzheimer Disease, MT2 could correct the biochemical abnormalities and sustain cell survival. Thus, NGF mimetics may reveal interesting investigational tools in neurobiology, as well as promising drug candidates.

A new synthesis of (2S)-4-oxopipecolic acid by thermal rearrangement of enantiopure spirocyclopropaneisoxazolidine

Abstract A novel synthesis of (2S)-4-oxo-pipecolic acid is reported. The synthetic route employs as a key step the diastereoselective cycloaddition of the N-glycosylnitrone 7 to methylenecyclopropane followed by thermal rearrangement of the spirocyclopropaneisoxazolidine 8a . Stereoselective reduction of the N-BOC methyl ester of 4-oxopipecolic acid by L-selectride ® gives the protected cis-4-hydroxy-pipecolic acid 14 .

The TLR7 Ligand 9-Benzyl-2-Butoxy-8-Hydroxy Adenine Inhibits IL-17 Response by Eliciting IL-10 and IL-10–Inducing Cytokines

This study evaluates the ability of a novel TLR7 ligand (9-benzyl-2-butoxy-8-hydroxy adenine, called SA-2) to affect IL-17 response. The SA-2 activity on the expression of IL-17A and IL-17–related molecules was evaluated in acute and chronic models of asthma as well as in in vivo and in vitro α-galactosyl ceramide (α-GalCer)-driven systems. SA-2 prepriming reduced neutrophils in bronchoalveolar lavage fluid and decreased methacoline-induced airway hyperresponsiveness in murine asthma models. These results were associated with the reduction of IL-17A (and type 2 cytokines) as well as of molecules favoring Th17 (and Th2) development in lung tissue. The IL-17A production in response to α-GalCer by spleen mononuclear cells was inhibited in vitro by the presence of SA-2. Reduced IL-17A (as well as IFN-γ and IL-13) serum levels in mice treated with α-GalCer plus SA-2 were also observed. The in vitro results indicated that IL-10 produced by B cells and IL-10–promoting molecules such as IFN-α and IL-27 by dendritic cells are the major player for SA-2–driven IL-17A (and also IFN-γ and IL-13) inhibition. The in vivo experiments with anti-cytokine receptor Abs provided evidence of an early IL-17A inhibition essentially due to IL-10 produced by resident peritoneal cells and of a delayed IL-17A inhibition sustained by IFN-α and IL-27, which in turn drive effector T cells to IL-10 production. These findings suggest that such TLR7 agonist downregulating Th17 (as well as Th2) response has to be considered a valid candidate for novel vaccine formulations in allergy.

The isoxazoline-5-spirocyclopropane route to (±)-Pumiliotoxin C

Abstract A new total synthesis of (±)-Pumiliotoxin C has been achieved by the key thermal rearrangement of an appropriate 5-spirocyclopropane isoxazoline.

Rearrangement of isoxazoline-5-spiro derivatives. Part 7. Thermal rearrangement of 4,5-dihydro and tetrahydroisoxazole-5-spirocyclobutanes to azepin-4-one derivatives☆

Abstract Some representative 4,5-dihydro and tetrahydroisoxazole 5-spirocyclobutanes have been synthesized by 1,3-dipolar cycloaddition of alkylidenecyclobutanes to nitrile oxides and nitrones, respectively. When subjected to flash vacuum thermolysis conditions, the spiranic cycloadducts rearranged to afford mainly the desired azepin-4-one derivatives. In addition, the isoxazoline cycloadducts gave unexpected by-products, which were identified as 1-alkenyl-2-pyrrolidinones. Analogies and differences with respect to the lower homologue cyclopropanes are evidenced in both cycloaddition and rearrangement reactions.