Synthesis of 5/7-, 5/8- and 5/9-bicyclic lactam templates as constraints for external beta-turns

Synthesis of Conformationally Constrained Dipeptide Mimetics with Azabicyclo[4,3,0]nonanone and Azabicyclo[5,3,0]decanone Scaffolds

A general and efficient method for the synthesis of azabicyclo[4,3,0]nonanone and azabicyclo[5,3,0]decanone amino acid derivatives was developed with the palladium-catalyzed coupling of intermediates 9 and 10 with BocNH₂ and Boc₂NH and the following reduction of the C-C double bond by hydrogenation as the key steps. The exploration of the synthesis of C₆-substituted dipeptide mimetics from 9 and 10 using Suzuki coupling as the key reaction has also been performed.

Continuous-flow thermolysis for the preparation of vinylglycine derivatives

Syn sulfoxide elimination was carried out under continuous-flow conditions in a mesofluidic thermolysis reactor. The design of the reactor enabled accurate control of reaction time and conditions, affording a convenient scale-independent procedure for the production of N,C-protected vinylglycine derivatives. Thermolysis at 270 °C under 1000 psi of pressure in superheated toluene enabled typical daily outputs ranging from 11 to 46 g per day with excellent selectivities and ee (>97%). The various competitive reaction pathways were studied and rationalized according to a computational study.

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with α,β-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic α-amino acids, directly usable for the synthesis of customized peptides.

Towards a KCC2 blocker pharmacophore model

A multi-disciplinary approach was used to identify the first pharmacophore model for KCC2 blockers: several physico-chemical studies such as XRD and NMR were combined to molecular modelling techniques, SAR analysis and synthesis of constrained analogues in order to determine a minimal conformational space regrouping few potential bioactive conformations. These conformations were further compared to the conformational space of a different series of KCC2 blockers in order to identify the common pharmacophoric features. The synthesis of more potent analogues in this second series confirmed the usefulness of this KCC2 blocker pharmacophore model.

Nonpeptidic and potent small-molecule inhibitors of cIAP-1/2 and XIAP proteins

A series of compounds were designed and synthesized as antagonists of cIAP-1/2 and XIAP based upon our previously identified lead compound SM-122 (1). The most potent of these (7) binds to XIAP, cIAP-1, and cIAP-2 proteins with K(i) values of 36, <1, and <1.9 nM, respectively. Consistent with its potent binding affinities to IAPs, 7 effectively antagonizes XIAP in a cell-free caspase-9 functional assay, efficiently induces cIAP-1 degradation in cells at concentrations as low as 10 nM, and triggers activation of caspases and PARP cleavage in the MDA-MB-231 breast cancer cell line. Compound 7 potently inhibits cell growth in the MDA-MB-231 cancer cell line with an IC(50) value of 200 nM and is 9 times more potent than compound 1.

Total synthesis and evaluation of Wnt signal inhibition of melleumin A and B, and their derivatives

The total synthesis of melleumin A (1), a novel cyclic depsipeptide isolated from the myxomycete Physarum melleum, and 3-epi-melleumin A (6) was achieved. Melleumin A-like compounds were also designed and synthesized; analysis of these melleumin A-like compounds showed moderate Wnt signal inhibition. Comparison of the inhibition activity of melleumin B and its three epimers, melleumin A, 3-epi-melleumin A and three melleumin A-like compounds led to further investigation of the structural conformation of the active molecules. The scaffold of melleumin is a potential target in the search for "peptide-like" Wnt signaling inhibitors.

Total synthesis of syringolin A and B

Total syntheses of two recently discovered proteasome inhibitors, syringolin A and B, are reported. The key to our approach was creation of the alpha,beta-unsaturated 12-membered lactam via intramolecular Horner-Wadsworth-Emmons reaction. Such reactions have been broadly used to prepared macrolactones, but this work presents a rarer example of its application to macrolactams. The final steps involved attachment of the bis(valinyl)urea side chain using peptide coupling procedures, including a method based on the unprotected valine N-carboxy anhydride. The additional alkene of syringolin A was created through cross-metathesis.

Enantioselective rhodium-catalyzed [4+2+2] cycloaddition of dienyl isocyanates for the synthesis of bicyclic azocine rings

A highly enantioselective rhodium-catalyzed [4+2+2] cycloaddition of terminal alkynes and dienyl isocyanates has been developed. The cycloaddition provides a rapid entry to highly functionalized and enantioenriched bicyclic azocines. This reaction represents the first [4+2+2] cycloaddition strategy to construct nitrogen-containing eight-membered rings.

Structure-based design, synthesis, evaluation, and crystallographic studies of conformationally constrained Smac mimetics as inhibitors of the X-linked inhibitor of apoptosis protein (XIAP)

Small molecules designed to mimic the binding of Smac protein to X-linked inhibitor of apoptosis protein (XIAP) are being pursued as a promising new class of anticancer drugs. Herein, we report the design, synthesis, and comprehensive structure-activity relationship studies of a series of conformationally constrained bicyclic Smac mimetics. Our studies led to the discovery of a number of highly potent and cell-permeable Smac mimetics and yielded important new insights into their structure-activity relationship for their binding to XIAP and for their activity in inhibition of cancer cell growth. Determination of the crystal structure of one potent Smac mimetic, compound 21, in complex with XIAP BIR3 provides the structural basis for its high-affinity binding to XIAP and for the design of highly potent Smac mimetics.

Design, synthesis, and characterization of a potent, nonpeptide, cell-permeable, bivalent Smac mimetic that concurrently targets both the BIR2 and BIR3 domains in XIAP

XIAP is a central apoptosis regulator that inhibits apoptosis by binding to and inhibiting the effectors caspase-3/-7 and an initiator caspase-9 through its BIR2 and BIR3 domains, respectively. Smac protein in its dimeric form effectively antagonizes XIAP by concurrently targeting both its BIR2 and BIR3 domains. We report the design, synthesis, and characterization of a nonpeptide, cell-permeable, bivalent small-molecule (SM-164) which mimics Smac protein for targeting XIAP. Our study shows that SM-164 binds to XIAP containing both BIR domains with an IC50 value of 1.39 nM, being 300 and 7000 times more potent than its monovalent counterparts and the natural Smac AVPI peptide, respectively. SM-164 concurrently interacts with both BIR domains in XIAP and functions as an ultrapotent antagonist of XIAP in both cell-free functional and cell-based assays. SM-164 targets cellular XIAP and effectively induces apoptosis at concentrations as low as 1 nM in the HL-60 leukemia cell line. The potency of bivalent SM-164 in binding, functional, and cellular assays is 2-3 orders of magnitude higher than its corresponding monovalent Smac mimetics.

Structural diversity of bicyclic amino acids

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.