Benzofused hydroxamic acids: useful fragments for the preparation of histone deacetylase inhibitors. Part 2: 7-fluorobenzothiophenes and benzofurans.

In the search for a new class of histone deacetylase inhibitors, we prepared a series of very simple benzofused hydroxamic acids to find an anchoring fragment of minimal molecular weight: they showed very good ligand efficiencies. Following these findings, classical fragment growing work was performed to increase binding energy and selective cytotoxicity. In the second phase of the work, information from the SARs of the benzothiophene series and data available in literature, we explored the in vitro pharmacological properties of the 6-substituted-7-fluoro-benzothiophene hydroxamates and the 5-susbtituted-benzofuran hydroxamates.

Benzofused hydroxamic acids: useful fragments for the preparation of histone deacetylase inhibitors. Part 1: hit identification.

In the search for a new class of histone deacetylase inhibitors, we prepared a series of simple benzofused hydroxamic acids to find an anchoring fragment of minimal molecular weight. These initial hits, all belonging to the benzothiophene class, showed very good ligand efficiencies. Following these findings, a classical fragment growing approach was performed to increase binding affinity and cytotoxicity.

hNK2 receptor antagonists. The use of intramolecular hydrogen bonding to increase solubility and membrane permeability.

Starting from in-house capped tripeptide libraries, we have developed two series of compounds as potent antagonists of the hNK(2) receptor with a reduced peptide character. These two series maintained a crucial amide bond, which could not be methylated or substituted with classical isostere without a dramatic loss in binding affinity, very likely due conformational changes. We report here the planning, synthesis and evaluation of molecules belonging to the selected chemical series, which contain a strategically placed hydrogen bond acceptor. The aim of the work was to improve membrane permeability via the formation of an intramolecular hydrogen bonding, and at the same time to maintain the structural characteristics geometry and polarity of the amide linkage so as to retain a relevant binding affinity for the biological target.

Alkyl piperidine and piperazine hydroxamic acids as HDAC inhibitors.

We report here the strategy used in our research group to find a new class of histone deacetylase (HDAC) inhibitors. A series of N-substituted 4-alkylpiperazine and 4-alkylpiperidine hydroxamic acids, corresponding to the basic structure of HDAC inhibitors (zinc binding moiety-linker-capping group) has been designed, prepared, and tested for HDAC inhibition. Linker length and aromatic capping group connection were systematically varied to find the optimal geometric parameters. A new series of submicromolar inhibitors was thus identified, which showed antiproliferative activity on HCT-116 colon carcinoma cells.

4-N-Hydroxy-4-[1-(sulfonyl)piperidin-4-yl]-butyramides as HDAC inhibitors.

A series of N-substituted 4-alkylpiperidine hydroxamic acids, corresponding to the basic structure of histone deacetylase (HDAC) inhibitors (zinc binding moiety-linker-capping group) has been previously reported by our group. Linker length and aromatic capping group connection were systematically varied to find the optimal geometric parameters. A new series of submicromolar inhibitors was thus identified, which showed antiproliferative activity on HCT-116 colon carcinoma cells. We report here the second part of the strategy used in our research group to find a new class of HDAC inhibitors, namely the SAR study for the compounds bearing a sulfonyl group on the piperidine nitrogen. In the present work, we have considered both sulfonamides and sulfonyl ureas.

Cinnamic acids and mono-substituted benzoic acids as useful capping groups for the preparation of hNK2 receptor antagonists.

NK(2) antagonists have been reported to be potentially useful for the treatment of a number of chronic diseases, such as asthma, irritable bowel syndrome, cystitis, and depression. Starting from an in-house prepared library of capped dipeptides, we have identified a series of molecules with subnanomolar binding affinity for the hNK(2) receptor. These molecules are composed by three well-defined regions: a planar aromatic acyl system as N-terminal capping group, a rigid and quite lipophilic core, and a flexible and relatively hydrophilic C-terminal capping group. Here we report how we were able to manipulate the N-terminal capping group to obtain significant in vivo activity after i.v. and i.d. administration.

A New Palladium-Catalyzed Intramolecular Allylation to Pyrrolidin-2-ones(1).

A novel palladium(0)-catalyzed cyclization to 3,4-disubstituted pyrrolidin-2-ones has been developed. The new approach relies upon the concomitant generation of stabilized acetamide enolate anions and of a pi-allyl-palladium appendage, properly tethered by a nitrogen atom. Reaction conditions have been optimized for the methoxycarbonyl-stabilized model reaction [(Z)-2 --> 3] and then applied to other substrates. A broad range of acetamide anion stabilizers was shown to allow the desired intramolecular C-C bond formation (MeO(2)C, MeCO, NC, (EtO)(2)PO, PhSO(2)). The cyclizations gave exclusively 5-exo-trig ring closure, thereby affording gamma-lactams. All the cyclizations gave the corresponding 3,4-disubstituted pyrrolidin-2-ones with total diastereoselection. Complete trans preference was unequivocally demonstrated for the model reaction via a NOESY experiment.

Application of Chiral Sulfides to Catalytic Asymmetric Aziridination and Cyclopropanation with In Situ Generation of the Diazo Compound.

Imines and alkenes can be converted into the corresponding aziridines and cyclopropanes (see scheme, PTC=phase-transfer catalyst, Ts=toluene-4-sulfonyl) in good yield with moderate to high d.r. and high ee values using tosylhydrazone salts with catalytic quantities of chiral sulfide (5-20 mol %) and metal catalyst (1 mol %). The process is particularly suited to the synthesis of conformationally locked cyclopropyl amino acids, which can now be prepared in only three steps from commercially available material in 100 % ee.

Catalytic Asymmetric Synthesis of Epoxides from Aldehydes Using Sulfur Ylides with In Situ Generation of Diazocompounds.

A practical, general, and convergent route to epoxides with control of the relative and absolute stereochemistry has been achieved by generating the reactive intermediate (the diazo compound) in situ from tosylhydrazone salts (see scheme, PTC=phase-transfer catalyst, Ts=toluene-4-sulfonyl). High yields (58-82 %), high d.r. (88:12-98:2), and high ee values (87-94 %) have been obtained using a new class of stable chiral sulfides at low catalyst loading (5 mol %) and [Rh2 (OAc)4 ] (0.5 mol %).

Structure-activity relationships of 6-methyl-benzo[b]thiophene-2-carboxylic acid (1-[(S)-1-benzyl-4-[4-(tetrahydropyran-4-ylmethyl)piperazin-1-yl]butylcarbamoyl]cyclopentyl)amide, potent antagonist of the neurokinin-2 receptor.

As part of a project aimed at the identification of a series of small, orally available antagonists for the hNK(2) receptor, starting from one of our capped dipeptide libraries, we succeeded in the chemical optimization of the first identified leads, finally producing a class of molecules with significant activity in our animal model after iv administration. We herein report the results of further chemical modifications made to reduce the overall peptide character of this series and the consequent improvement of their in vivo antagonist activity. The present work identified 6-methylbenzo[b]thiophene-2-carboxylic acid (1-[(S)-1-benzyl-4-[4-(tetrahydropyran-4-ylmethyl)piperazin-1-yl]butylcarbamoyl]cyclopentyl)amide (10i), endowed with subnanomolar potency in all the in vitro tests and being highly potent and of long duration upon in vivo testing after both iv and id dosing.

alpha,alpha-Cyclopentaneglycine dipeptides capped with biaryls as tachykinin NK(2) receptor antagonists.

The NK(2) receptor belongs to the family of tachykinin neurotransmitters. It has been reported to be involved in several pathological conditions, and selective antagonists are potentially useful drugs for the treatment of asthma, irritable bowel syndrome, cystitis, and depression. Starting from in-house capped dipeptide libraries, we were able to identify a number of molecules with sub-nanomolar binding affinity for the hNK(2) receptor. All were characterized by a rigid core structure with a strong constraint induced by an alpha,alpha-cyclopentaneglycine fragment. Herein we report the further elaboration of three initial basic structures. The planar benzothiophene group was substituted with a series of biphenyl and heterobiphenyl moieties that are well tolerated in terms of receptor affinity. The new compounds also maintained good antagonist potency in an in vitro functional assay, and a number of them showed significant in vivo activity after intravenous administration in our guinea pig model.

Generation of a new class of hNK(2) receptor ligands using the 'fragment approach'.

The so called 'fragment approach' was applied in the search for new leads as selective hNK(2) antagonists. A first round of structural space exploration through the use of bond rigidity as scaffold to support the fragments, afforded 27a as 200 nM hNK(2) ligand. Further refinement gave MEN 14933 as a 16 nM hNK(2) ligand, selective versus hNK(1), of a novel class. Conformational analysis was used to study results and plan future work.

Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: mechanistic insights and implications.

Bridged bicyclic sulfide 1 was originally found to provide high levels of asymmetric induction in sulfur ylide-mediated epoxidations. This sulfide possesses chirality in the [2.2.1] thioether moiety and the [2.2.1] camphor-derived carbocyclic moiety. To determine whether the optimal sulfide had been used, a diastereomer of sulfide 1 in which the stereochemistry of the [2.2.1] carbocycle was reversed (sulfide 5) was prepared and studied as an epoxidation catalyst. This diastereomer gave considerably lower levels of asymmetric induction than the original sulfide 1. From computational and x-ray studies it was found that sulfide 5 gave rise to a more hindered ylide, which reacted more reversibly with aldehydes leading to lower enantioselectivity. Conditions that reduced reversibility were also tested and high enantioselectivities were returned for sulfide 5 (similar to sulfide 1). The implications for the synthesis of chiral sulfides for asymmetric epoxidations are discussed.

A new protocol for the in situ generation of aromatic, heteroaromatic, and unsaturated diazo compounds and its application in catalytic and asymmetric epoxidation of carbonyl compounds. Extensive studies to map out scope and limitations, and rationalization of diastereo- and enantioselectivities.

A variety of metalated tosylhydrazone salts derived from benzaldehyde have been prepared and were reacted with benzaldehyde in the presence of tetrahydrothiophene (THT) (20 mol %) and Rh(2)(OAc)(4) (1 mol %) to give stilbene oxide. Of the lithium, sodium, and potassium salts tested, the sodium salt was found to give the highest yield and selectivity. This study was extended to a wide variety of aromatic, heteroaromatic, aliphatic, alpha,beta-unsaturated, and acetylenic aldehydes and to ketones. On the whole, high yields of epoxides with moderate to very high diastereoselectivities were observed. A broad range of tosylhydrazone salts derived from aromatic, heteroaromatic, and alpha,beta-unsaturated aldehydes was also examined using the same protocol in reactions with benzaldehyde, and again, good yields and high diastereoselectivities were observed in most cases. Thus, a general process for the in situ generation of diazo compounds from tosylhydrazone sodium salts has been established and applied in sulfur-ylide mediated epoxidation reactions. The chiral, camphor-derived, [2.2.1] bicyclic sulfide 7 was employed (at 5-20 mol % loading) to render the above processes asymmetric with a range of carbonyl compounds and tosylhydrazone sodium salts. Benzaldehyde tosylhydrazone sodium salt gave enantioselectivities of 91 +/- 3% ee and high levels of diastereoselectivity with a range of aldehydes. However, tosylhydrazone salts derived from a range of carbonyl compounds gave more variable selectivities. Although those salts derived from electron-rich or neutral aldehydes gave high enantioselectivities, those derived from electron-deficient or hindered aromatic aldehydes gave somewhat reduced enantioselectivities. Using alpha,beta-unsaturated hydrazones, chiral sulfide 7 gave epoxides with high diastereoselectivities, but only moderate yields were achieved (12-56%) with varying degrees of enantioselectivity. A study of solvent effects showed that, while the impact on enantioselectivity was small, the efficiency of diazo compound generation was influenced, and CH(3)CN and 1,4-dioxane emerged as the optimum solvents. A general rationalization of the factors that influence both relative and absolute stereochemistry for all of the different substrates is provided. Reversibility in formation of the betaine intermediate is an important issue in the control of diastereoselectivity. Hence, where low diastereocontrol was observed, the results have been rationalized in terms of the factors that contribute to the reduced reversion of the syn betaine back to the original starting materials. The enantioselectivity is governed by ylide conformation, facial selectivity in the ylide reaction, and, again, the degree of reversibility in betaine formation. From experimental evidence and calculations, it has been shown that sulfide 7 gives almost complete control of facial selectivity, and, hence, it is the ylide conformation and degree of reversibility that are responsible for the enantioselectivity observed. A simple test has been developed to ascertain whether the reduced enantioselectivity observed in particular cases is due to poor control in ylide conformation or due to partial reversibility in the formation of the betaine.