Histone deacetylases are promising molecular targets for the development of antitumor agents. A novel series of histone deacetylase inhibitors of the hydroxamic acid type were synthesized for structure-activity studies. Thirteen tricyclic dibenzodiazepine, -oxazepine, and -thiazepine analogues were studied and shown to induce variable degrees of histone H3/H4 and tubulin acetylation in a cellular model of myeloid leukemia sensitive to all-trans retinoic acid (ATRA). Multiparametric correlations between acetylation of the three substrates, tumor cell growth inhibition, and ATRAdependent cytodifferentiation were performed, providing information on the chemical functionalities governing these activities. For two analogues, antitumor activity in the animal was demonstrated.KEYWORDS HDAC inhibitors, hydroxamic acid, retinoic acid, antiproliferative effect, differentiation H istone deacetylase (HDAC) proteins are classified in four groups (class I-IV) based on function and sequence similarity. A common observation in neoplastic cells is high level expression of class I and II HDACs with corresponding hypoacetylation of histones.1 Increased HDAC activity may play a critical role in the pathogenesis of leukemia.2 HDACs of significance for cancer cell biology reside not only in the nucleus but also in the cytoplasm, where they act on substrates other than histones. Within class I, HDACs 1, 2, and 8 are primarily found in the nucleus. Class II HDACs (HDAC 4, 5, 6, 7, 9, and 10) are able to shuttle in and out of the nucleus depending on different signals.3 HDAC 6 is primarily a cytoplasmic enzyme, deacetylating proteins like tubulin, Hsp90, and cortactin. 4 Transformed cells are generally more sensitive to HDAC inhibitor-induced growth inhibition and apoptosis than their normal counterparts.5 Hence, anticancer therapeutic strategies based on HDAC inhibitors have raised significant interest. Some of the most powerful natural and synthetic HDAC inhibitors 6 are derivatives of hydroxamic acid. Here, we describe the chemical synthesis and the pharmacologic characterization of a novel series of hydroxamic acid derivatives characterized by tricyclic dibenzo-diazepine, -oxazepine, and -thiazepine rings. As the catalytic domain of all HDAC isoforms is highly conserved, 7 our approach was to design novel molecules targeting the variable external part of the channel leading to the catalytic center. We studied the effects of a limited number of systematic modifications to the tricyclic core, keeping the hydroxamic group and the linker chain of our molecules constant. The tricyclic core was selected, as structural modifications affecting hydrogen bonding, electronic features, and angles between the two aromatic rings can be easily obtained by accessible chemical modifications. Test compounds (0.01, 0.1, 1.0, 10, and 50 μM) were initially screened using an enzymatic assay measuring the total HDAC activity in HeLa cell extracts, which resulted in the selection of 13 molecules. Scheme 1 illustrates the synthesis and structures o...

The (3S)-3-alkoxypyrroline N-oxides 7 and 27 were easily prepared from l-malic acid and used as starting materials for enantiospecific syntheses of stereodifferentiated polyhydroxyindolizidines. Selection of the appropriate modality (interor intramolecular) for 1,3-dipolar cycloaddition of the cyclic nitrone with 5-hydroxypentenoic acid derivatives gave access to either [1,8a]-trans-or -cis-hydroxyindolizidines 31 and 24, respectively, through elaboration of the primary cycloadducts. Moreover, the choice of the esterification conditions (Ph 3 P/DEAD or DIC/DMAP) used in linking the nitrone and the dipolarophile moieties in the intramolecular approach determined the absolute configuration of the final product, allowing the selective synthesis of both enantiomers, (−)-24 and (+)-24. This strategy required protection of the nitrone functionality to avoid racemization of the unpro-

and N-(2-pyridyl)-C-methylnitrones (3f) to bicyclopropylidene (2) gave the corresponding cycloadducts 5aϪf in 100, 95, 94, 100, 93 and 71% yields, respectively. Treatment of these bisspirocyclopropanated isoxazolidines with trifluoroacetic acid in acetonitrile furnished the corresponding 3-spirocyclopropanated β-lactams 7aϪf in 78, 75, 75, 94, 96 and 96% yields, respectively. The structures of the cycloadduct 5b and of the β-lactam 9a were proved by X-ray crystal structure analyses. Thus, this new method furnishes

The enantiomerically pure indolizidine (−)-21 has been synthesized starting from L-malic acid. The key intermediate 20 has been assembled through an intramolecular 1,3-dipolar cycloaddition of a nitrone generated in situ by retrocycloaddition from isoxazolidine 17 or 18. The configuration of the new three stereocenters was set up with complete control in the cycloaddition step. The presented synthetic route provides a general and highly selective methodology toward indolizidines having the [1,8a]-cis configuration.

Recently we reported on the design and synthesis of a novel class of selective nonpeptide bradykinin (BK) B2 receptor antagonists (J. Med. Chem. 2006, 3602-3613). This work led to the discovery of MEN 15442, an antagonist with subnanomolar affinity for the human B2 receptor (hB2R), which also displayed significant and prolonged activity in vivo (for up to 210 min) against BK-induced bronchoconstriction in the guinea-pig at a dose of 300 nmol/kg (it), while demonstrating only a slight effect on BK-induced hypotension. Here we describe the further optimization of this series of compounds aimed at maximizing the effect on bronchoconstriction and minimizing the effect on hypotension, with a view to developing topically delivered drugs for airway diseases. The work led to the discovery of MEN 16132, a compound which, after intratracheal or aerosol administration, inhibited, in a dose-dependent manner, BK-induced bronchoconstricton in the airways, while showing minimal systemic activity. This compound was selected as a preclinical candidate for the topical treatment of airway diseases involving kinin B2 receptor stimulation.

We recently published the extensive in vivo pharmacological characterization of MEN 16132 (J. Pharmacol. Exp. Ther. 2005, 616-623; Eur. J. Pharmacol. 2005, 528, 7), a member of the sulfonamide-containing human B(2) receptor (hB(2)R) antagonists. Here we report, in detail, how this family of compounds was designed, synthesized, and optimized to provide a group of products with subnanomolar affinity for the hB(2)R and high in vivo potency after topical administration to the respiratory tract. The series was designed on the basis of indications from the X-ray structures of the key structural motifs A and B present in known antagonists and is characterized by the presence of an alpha,alpha-dialkyl amino acid. The first lead (17) of the series was submitted to extensive chemical work to elucidate the structural requirements to increase hB(2) receptor affinity and antagonist potency in bioassays expressing the human B(2) receptor (hB(2)R). The following structural features were selected: a 2,4-dimethylquinoline moiety and a piperazine linker acylated with a basic amino acid. The representative lead compound 68 inhibited the specific binding of [(3)H]BK to hB(2)R with a pKi of 9.4 and antagonized the BK-induced inositolphosphate (IP) accumulation in recombinant cell systems expressing the hB(2)R with a pA(2) of 9.1. Moreover, compound 68 when administered (300 nmol/kg) intratracheally in the anesthetized guinea pig, was able to significantly inhibit BK-induced bronchoconstriction for up to 120 min after its administration, while having a lower and shorter lasting effect on hypotension.

Starting from pyrrole- and indole-2-carboxylic acids 5 a and 5 b, the tri- and tetracyclic N,N-dibenzylcyclopropylamines 7 a and 7 b have been synthesized in 52 and 33 % overall yield, respectively. The synthesis of the enantiopure tetracyclic diamine 10 has been achieved applying the established set of reactions to N-tert-butoxycarbonylindoline-2-carboxylic acid (8) in 46 % overall yield. The amide 15 could not be prepared in the same way starting from the N-tert-butoxycarbonylproline 11. In fact, in the allylation step the stereogenic center was deprotonated and the doubly alkylated amide 13 was formed. However, the desired intermediate 15 could be obtained from L-proline in 49 % yield performing first the N-allylation step, then the introduction of the amide function. From 15, the cyclopropane-annelated pyrrolizidine 16 was obtained in 70 % yield as a mixture of (1aS,6aS,6bR)-16 and (1aR,6aS,6bS)-16 diastereoisomers in a ratio of 1:2.9.

Herein we describe the synthesis of a series of new potent tachykinin NK(2) receptor antagonists by the modulation of the C- and N-terminal moieties of ibodutant (MEN 15596, 1). The N-terminal benzo[b]thiophene ring was replaced by different substituted naphthalenes and benzofurans, while further modifications were evaluated at the C-terminal tetrahydropyran moiety. Most compounds demonstrated a high affinity for the human NK(2) receptor and high in vitro antagonist potency, indicating that a wide range of substituents at both termini can be incorporated in the molecule without detrimental effects on the interactions with the NK(2) receptor. Selected compounds were tested in vivo confirming their activity as NK(2) antagonists. In particular, after both iv and id administration to guinea pig, compound 61 b was able to antagonize NK(2)-induced colonic contractions with a potency and duration-of-action fully comparable to the reference compound 1 (MEN 15596, ibodutant).