A new class of HIV-1 integrase inhibitors: the 3,3,3', 3'-tetramethyl-1,1'-spirobi(indan)-5,5',6,6'-tetrol family

Asymmetric Photoaerobic Lactonization and Aza-Wacker Cyclization of Alkenes Enabled by Ternary Selenium-Sulfur Multicatalysis

An adaptable, sulfur-accelerated photoaerobic selenium-π-acid ternary catalyst system for the enantioselective allylic redox functionalization of simple, nondirecting alkenes is reported. In contrast to related photoredox catalytic methods, which largely depend on olefinic substrates with heteroatomic directing groups to unfold high degrees of stereoinduction, the current protocol relies on chiral, spirocyclic selenium-π-acids that covalently bind to the alkene moiety. The performance of this ternary catalytic method is demonstrated in the asymmetric, photoaerobic lactonization and cycloamination of enoic acids and unsaturated sulfonamides, respectively, leading to an averaged enantiomeric ratio (er) of 92:8. Notably, this protocol provides for the first time an asymmetric, catalytic entryway to pharmaceutically relevant 3-pyrroline motifs, which was used as a platform to access a 3,4-dihydroxyproline derivative in only seven steps with a 92:8 er.

Organocatalytic Enantioselective Intramolecular Michael Addition by In Situ Generated Aminoisobenzofulvenes: Construction of Spiro Quaternary Carbon Stereocenters

An unprecedented enantioselective organocatalytic spirocyclization strategy is presented by in situ generation of aminoisobezofulvenes. The reaction sequence involves a reductive Michael/aldol-condensation/Michael addition cascade by iminium-enamine catalysis. The key success of this spirocyclization was the formation of intermediatory nucleophilic aminoisobenzofuvenes accountable for intramolecular Michael addition. Benzospirononanes featuring an all carbon qauternary spirocenter were obtained using proline-derived amino-organocatalyst in moderate to good yields and excellent diastereo- and enantioselectivities (up to >20 : 1 dr, and 99 % ee). Post-methodological manipulation of benzospirononanes was also demonstrated.

Controlling Spin Crossover in a Family of Dinuclear Fe(III) Complexes via the Bis(catecholate) Bridging Ligand

Spin crossover (SCO) complexes can reversibly switch between low spin (LS) and high spin (HS) states, affording possible applications in sensing, displays, and molecular electronics. Dinuclear SCO complexes with access to [LS-LS], [LS-HS], and [HS-HS] states may offer increased levels of functionality. The nature of the SCO interconversion in dinuclear complexes is influenced by the local electronic environment. We report the synthesis and characterization of [{FeIII(tpa)}2spiro](PF6)2 (1), [{FeIII(tpa)}2Br4spiro](PF6)2 (2), and [{FeIII(tpa)}2thea](PF6)2 (3) (tpa = tris(2-pyridylmethyl)amine, spiroH4 = 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-5,5',6,6'-tetraol, Br4spiroH4 = 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-4,4',7,7'-tetrabromo-5,5',6,6'-tetraol, theaH4 = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene), utilizing non-conjugated bis(catecholate) bridging ligands. In the solid state, magnetic and structural analysis shows that 1 remains in the [HS-HS] state, while 2 and 3 undergo a partial SCO interconversion upon cooling from room temperature involving the mixed [LS-HS] state. In solution, all complexes undergo SCO from [HS-HS] at room temperature, via [LS-HS] to mixtures including [LS-LS] at 77 K, with the extent of SCO increasing in the order 1 < 2 < 3. Gas phase density functional theory calculations suggest a [LS-LS] ground state for all complexes, with the [LS-HS] and [HS-HS] states successively destabilized. The relative energy separations indicate that ligand field strength increases following spiro4- < Br4spiro4- < thea4-, consistent with solid-state magnetic and EPR behavior. All three complexes show stabilization of the [LS-HS] state in relation to the midpoint energy between [LS-LS] and [HS-HS]. The relative stability of the [LS-HS] state increases with increasing ligand field strength of the bis(catecholate) bridging ligand in the order 1 < 2 < 3. The bromo substituents of Br4spiro4- increase the ligand field strength relative to spiro4-, while the stronger ligand field provided by thea4- arises from extension of the overlapping π-orbital system across the two catecholate units. This study highlights how SCO behavior in dinuclear complexes can be modulated by the bridging ligand, providing useful insights for the design of molecules that can be interconverted between more than two states.

Super-heat resistant, transparent and low dielectric polyimides based on spirocyclic bisbenzoxazole diamines with Tg > 450°C

Maintaining ultra-high heat resistance and sufficient colorless transparency at the same time is a challenge for polymer materials because of conflicting design principles, but such materials are urgently needed for...

Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis

Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.

Copper-Catalyzed Asymmetric Borylacylation of Styrene and Indene Derivatives

The enantioselective copper-catalyzed borylacylation of aryl olefins with acyl chlorides and bis-(pinacolato)diboron is reported. This three-component reaction involves an enantioselective syn-borylcupration of the aryl olefin, followed by a nucleophilic attack on the acyl chloride. This reaction proceeds with a 2 mol % catalyst loading and is generally completed within 30 min at room temperature. Because the boron moiety can be converted into versatile functional groups and the carbonyl group is a ubiquitous functional group, the resulting chiral β-borylated ketones are versatile intermediates in organic synthesis.

Copper-catalyzed asymmetric tandem borylative addition and aldol cyclization

A highly enantioselective asymmetric copper-catalyzed tandem conjugate addition/aldol cyclization of electron-deficient olefins with B₂pin₂ was developed, which provided a rapid access to indanes bearing three consecutive chiral stereogenic centers.

Synthesis and application of a new hexamethyl-1,1′-spirobiindane-based chiral bisphosphine (HMSI-PHOS) ligand in asymmetric allylic alkylation

A new class of hexamethyl-1,1′-spirobiindane-based chiral bisphosphine ligand was synthesized and used in Pd-catalyzed asymmetric allylic alkylation reactions.

Palladium-catalyzed arene C–H activation/ketone C–H functionalization reaction: route to spirodihydroindenones

A novel palladium and norbornene catalyzed arene C–H activation method to synthesize various spirodihydroindenone derivatives is developed.

Gold-catalysed facile access to indene scaffolds via sequential C–H functionalization and 5-endo-dig carbocyclization

The concise synthesis of functionalized indene derivatives via the gold(i)-catalysed cascade C–H functionalization/conia-ene type reaction of electron-rich aromatics with o-alkynylaryl α-diazoesters has been developed.

Lewis acid catalyzed Nazarov type cyclization for the synthesis of a substituted indane framework: total synthesis of (±)-mutisianthol

A new synthetic route has been developed for the synthesis of a substituted indane derivative using Lewis acid catalyzed modified Nazarov type cyclization, which was further applied in the total synthesis of mutisianthol and epi-mutisianthol in a nine step longest linear sequence.

Inhibitors of human immunodeficiency virus type I integration

PURPOSE OF REVIEW

The virally encoded enzyme integrase plays a critical role in HIV-1 replication and has long been considered a promising target for the development of agents to treat HIV-1 infection. It is only recently, however, that the efficacy of integrase inhibitors has been demonstrated in experimental animal model systems of retroviral infection, and in HIV-1 infected subjects. Several compounds that have shown potent efficacy in short-term monotherapy studies have initiated phase two and three clinical studies in 2006.

RECENT FINDINGS

Although the first inhibitors in this new class of antiretroviral therapy are in the earliest stages of clinical development, the study of integrase function and inhibitor mechanism, as well as recent insights on resistance to prototypical inhibitors in vitro, have important implications for the discovery and development of these agents.

SUMMARY

This review will summarize the role of integrase in HIV-1 infection, the mechanism of integrase inhibitors, and the results of resistance studies on preclinical compounds which suggest there may be multiple opportunities for developing inhibitors against this essential HIV-1 target.

Gold catalysis: domino reaction of en-diynes to highly substituted phenols

By Sonogashira coupling of 1,7-heptadiynes and 1,8-octadiynes with 2-iodoallyl alcohols, various substrates that bear a 2-alkynylallyl alcohol moiety tethered to an additional alkyne were prepared in one step. Subjection to nitrogen acyclic carbene (NAC)/gold(I) catalysts delivered highly substituted phenols in an efficient domino reaction. Furan derivatives were formed as intermediates; this was proven by in situ NMR spectroscopy. The uncommon substitution pattern of these furans opens the way for a selective formation of phenols that contain the hydroxyl group in the meta position to the ring junction, which previously was not possible by gold-catalyzed furan-yne cyclization. Furthermore, interesting mechanistic insights were obtained by products derived from secondary allyl alcohols. In this case, in addition to the phenolic compounds, a ketone is formed by 1,2-alkyl shift.

A cooperative and specific DNA-binding mode of HIV-1 integrase depends on the nature of the metallic cofactor and involves the zinc-containing N-terminal domain

HIV-1 integrase catalyzes the insertion of the viral genome into chromosomal DNA. We characterized the structural determinants of the 3′-processing reaction specificity—the first reaction of the integration process—at the DNA-binding level. We found that the integrase N-terminal domain, containing a pseudo zinc-finger motif, plays a key role, at least indirectly, in the formation of specific integrase–DNA contacts. This motif mediates a cooperative DNA binding of integrase that occurs only with the cognate/viral DNA sequence and the physiologically relevant Mg²⁺ cofactor. The DNA-binding was essentially non-cooperative with Mn²⁺ or using non-specific/random sequences, regardless of the metallic cofactor. 2,2′-Dithiobisbenzamide-1 induced zinc ejection from integrase by covalently targeting the zinc-finger motif, and significantly decreased the Hill coefficient of the Mg²⁺-mediated integrase–DNA interaction, without affecting the overall affinity. Concomitantly, 2,2′-dithiobisbenzamide-1 severely impaired 3′-processing (IC₅₀ = 11–15 nM), suggesting that zinc ejection primarily perturbs the nature of the active integrase oligomer. A less specific and weaker catalytic effect of 2,2′-dithiobisbenzamide-1 is mediated by Cys 56 in the catalytic core and, notably, accounts for the weaker inhibition of the non-cooperative Mn²⁺-dependent 3′-processing. Our data show that the cooperative DNA-binding mode is strongly related to the sequence-specific DNA-binding, and depends on the simultaneous presence of the Mg²⁺ cofactor and the zinc effector.

Design, synthesis and anti-HIV integrase evaluation of 4-oxo-4H-quinolizine-3-carboxylic acid derivatives

4-Oxo-4H-quinolizine-3-carboxylic acid derivatives bearing sulfamido, carboxylamido, benzimidazole and benzothiazole substituents have been designed and synthesized. The structures of these new compounds were confirmed by ¹H-NMR, ¹³C- NMR, IR and ESI (or HRMS) spectra. Compounds were screened for possible HIV integrase inhibitory activity.

Integrase and integration: biochemical activities of HIV-1 integrase

Integration of retroviral DNA is an obligatory step of retrovirus replication because proviral DNA is the template for productive infection. Integrase, a retroviral enzyme, catalyses integration. The process of integration can be divided into two sequential reactions. The first one, named 3'-processing, corresponds to a specific endonucleolytic reaction which prepares the viral DNA extremities to be competent for the subsequent covalent insertion, named strand transfer, into the host cell genome by a trans-esterification reaction. Recently, a novel specific activity of the full length integrase was reported, in vitro, by our group for two retroviral integrases (HIV-1 and PFV-1). This activity of internal cleavage occurs at a specific palindromic sequence mimicking the LTR-LTR junction described into the 2-LTR circles which are peculiar viral DNA forms found during viral infection. Moreover, recent studies demonstrated the existence of a weak palindromic consensus found at the integration sites. Taken together, these data underline the propensity of retroviral integrases for binding symmetrical sequences and give perspectives for targeting specific sequences used for gene therapy.

From Simple Ugi Adducts to Indanes and δ-Amidomalonates: New Manganese(III)-Induced Radical Cascades

A complete change of the traditional Ugi adducts framework has been obtained using new radical cascades as Ugi post-condensation reactions. Indanes and delta-amidomalonates were thus obtained in a one-pot procedure from aromatic aldehydes under a sequence involving Ugi addition followed by treatment of the adducts with Mn(III) and malonate or beta-ketoester. The radical step probably involves an intramolecular aryl transfer followed by an oxidative cleavage and final cyclization to indanes.

Development of integrase inhibitors for treatment of AIDS: An overview

HIV-1 integrase (IN) is an essential enzyme for retroviral replication. It is involved in the integration of HIV DNA into host chromosomal DNA. The unique properties of IN makes it an ideal target for drug design. First, there appears to have no functional equivalent in human cells and the reactions catalyzed by IN are unique. Second, IN is absolutely required for viral replication and mutations in a number of key residues block the viral replication. Third, IN has been validated as a legitimate target and the results from the molecules like S-1,360, JKT-303 which are under phase II/III clinical trials suggest synergistic effect with reverse transcriptase (RT) and protease (PR) inhibitors. During the past 10 years a plethora of inhibitors have been identified and some were shown to be selective against IN and block viral replication. The classes under which inhibitors of integrase can be classified are catechol-containing hydroxylated aromatics, diketoacid-containing aromatics, quninolines and others (non-catechol containing). In the present article we review all the recent small molecules reported to inhibit recombinant HIV-1 IN under these heads. It seems likely that the efficient use of HIV IN as target for rational design can give potent anti-HIV agents, which can be used alone or in combination regimens with other classes of anti-HIV drugs.

BINOL-Based FoldamersAccess to Oligomers with Diverse Structural Architectures

In this article, we report on the synthesis and conformation of a new family of aromatic oligoamide foldamers based on binaphthol (BINOL) monomers. A series of oligomers with differing chirality of the individual BINOL building blocks and mixed sequences of alternate BINOL and pyridyl building blocks has been synthesized and structurally characterized. NMR and quantum chemical calculations on the basis of ab initio MO theory were performed to obtain insight into the conformational features of these oligomers. It is shown that the combination of these inherently chiral aromatic building blocks provides a novel access to a wide variety of conformationally ordered synthetic oligomers with diverse and dazzling structural architectures distinct from those classically observed.

Synthesis and HIV-1 integrase inhibitory activities of caffeic acid dimers derived from Salvia officinalis

The synthesis of two caffeoyl-coumarin conjugates, derived from sagecoumarin, has been accomplished, starting from ferulic acid, isoferulic acid and sesamol. Both compounds exhibited potent inhibitory activities at micromolar concentrations against HIV-1 integrase in 3'-end processing reaction but were less effective against HIV-1 replication in a single-round infection assay of HeLa-beta-gal-CD4+ cells.

Synthesis and biological evaluation of geminal disulfones as HIV-1 integrase inhibitors

Integration of HIV-1 viral DNA into the host genome is carried out by HIV-integrase (IN) and is a critical step in viral replication. Although several classes of compounds have been reported to inhibit IN in enzymatic assays, inhibition is not always correlated with antiviral activity. Moreover, potent antiviral IN inhibitors such as the chicoric acids do not act upon the intended enzymatic target but behave as entry inhibitors instead. The charged nature of the chicoric acids contributes to poor cellular uptake, and these compounds are further plagued by rapid ester hydrolysis in vivo. To address these critical deficiencies, we designed neutral, nonhydrolyzable analogues of the chicoric acids. Herein, we report the synthesis, enzyme inhibition studies, and cellular antiviral data for a series of geminal disulfones. Of the 10 compounds evaluated, 8 showed moderate to high inhibition of IN in purified enzyme assays. The purified enzyme data correlated with antiviral assays for all but two compounds, suggesting alternative modes of inhibition. Time-of-addition studies were performed on these analogues, and the results indicate that they inhibit an early stage in the replication process, perhaps entry. In contrast, the most potent member of the correlative group shows behavior consistent with IN being the cellular target.

Cluster analysis and three-dimensional QSAR studies of HIV-1 integrase inhibitors

Three-dimensional quantitative structure-activity relationship (3D QSAR) and cluster analysis were applied to a variety of HIV-1 integrase inhibitors. One structure was chosen from each of 11 classes of inhibitors to represent the whole class in descriptor-based cluster analysis. The 11 classes of inhibitors were classified into two groups. The molecular field analysis (MFA) models for these two clusters had r2 values of 0.90 and 0.95 and q2 values of 0.85 and 0.91 that were noticeably enhanced from those of conventional QSAR models. The five test compounds, which were proposed to have a common binding site near the metal in HIV-1 integrase based on docking studies by Sotriffer et al., were utilized to compare the predictive capability of MFA and conventional QSAR models. Among these five compounds, only L-chicoric acid belongs to cluster 1 and the other four belong to cluster 2. MFA models give better overall predictions and more importantly the activity of these test compounds is better predicted by the MFA model derived from the cluster each test compound belongs to. The necessity of dividing the inhibitors into two groups to obtain predictive QSAR models supports the likelihood of two separate binding sites.

QSAR studies of HIV-1 integrase inhibition

Compounds from a wide variety of structural classes inhibit HIV-1 integrase. However, a single unified understanding of the relationship between the structures and activities of these compounds still eludes researchers. We report herein the development of QSAR models for integrase inhibition. The genetic function approximation (GFA) was utilized to select descriptors for the development of the QSAR models. The best QSAR model derived for the complete set of 11 structural classes had a correlation coefficient (r(2)) of only 0.54 and a cross-validated correlation coefficient (q(2)) of only 0.42. This indicated that the compounds studied may differ in the exact relationship between structure and inhibition, perhaps through interactions with different subsets of amino acids in the binding pocket, or through the presence of non-overlapping binding pockets. Descriptor-based cluster analysis indicated that the 11 structural classes of integrase inhibitors studied belonged to two clusters, one consisting of five structural classes, and the other six. QSAR models for these two clusters had r(2) values of 0.79 and 0.82 and q(2) values of 0.71 and 0.74, a significant improvement over models obtained for the complete set of compounds. The two models were applied to predict the activities of compounds from the same structural classes as those used to build the models, giving r(2) values of 0.65 and 0.78. The models were also used to predict the activities of compounds shown in crystallographic or docking studies to interact near the active site metal ion. The model describing the larger cluster of structural classes was better able to reproduce the biological activities of these five structures with an average percent residual error of 7.9 compared with the 19.3% residual error for predictions from the other model. This indicated that the six structural classes comprising the larger cluster may bind near the metal ion in a fashion similar to that observed in one publicly available co-crystal structure of an inhibitor bound to HIV-1 integrase. Flexible alignment of inhibitors in the two clusters found different pharmacophores that are consistent with previously published pharmacophores developed on the basis of individual structural classes that have produced novel inhibitory compounds. Thus we expect that these two QSAR models can be used in the search for novel HIV-1 integrase inhibitors as well as to provide insight into the binding modes of such diverse chemical compounds.

Synthesis and HIV-1 integrase inhibitory activities of catechol and bis-catechol derivatives

Fourteen catechol and bis-catechol derivatives have been synthesised and tested for their HIV-1 inhibitory activities. The six more active molecules have been tested for their antiviral activity and cytotoxicity. We have found that bis-catechols 1 and 2 are the most active HIV-1 integrase inhibitor whereas the best antiviral compound is 4.

DNA binding induces dissociation of the multimeric form of HIV-1 integrase: a time-resolved fluorescence anisotropy study

Self-assembly of HIV-1 integrase (IN) in solution has been studied previously by time-resolved fluorescence, using tryptophan anisotropy decay. This approach provides information on the size of macromolecules via the determination of rotational correlation times (theta). We have shown that, at submicromolar concentration, IN is characterized by a long rotational correlation time (theta(20 degrees C) = 90-100 ns) corresponding to a high-order oligomeric form, likely a tetramer. In the present work, we investigated the self-assembly properties of the DNA-bound IN by using three independent fluorophores. Under enzymatic assay conditions (10(-7) M IN, 2 x 10(-8) M DNA), using either fluorescein-labeled or fluorescent guanosine analog-containing oligonucleotides that mimic a viral end long terminal repeat sequence, we found that the DNA-IN complex was characterized by shorter theta(20 degrees C) values of 15.5-19.5 and 23-27 ns, calculated from experiments performed at 25 degrees C and 37 degrees C, respectively. These results were confirmed by monitoring the Trp anisotropy decay as a function of the DNA substrate concentration: the theta of IN shifted from 90-100 ns to lower values (<30 ns) upon increasing the DNA concentration. Again, the normalized theta(20 degrees C) values were significantly higher when monitored at 37 degrees C as compared with 25 degrees C. These results indicate that upon binding the viral DNA end, the multimeric enzyme undergoes a dissociation, most likely into a homogeneous monomeric form at 25 degrees C and into a monomer-dimer equilibrium at 37 degrees C.

Active site binding modes of HIV-1 integrase inhibitors

Using the crystal structure of the first complex of the HIV-1 integrase catalytic core domain with an inhibitor bound to the active site, structural models for the interaction of various inhibitors with integrase were generated by computational docking. For the compound of the crystallographic study, binding modes unaffected by crystal packing have recently been proposed. Although a large search region was used for the docking simulations, the ligands investigated here are found to bind preferably in similar ways close to the active site. The binding site is formed by residues 64-67, 116, 148, 151-152, 155-156, and 159, as well as by residue 92 in case of the largest ligand of the series. The coherent picture of possible interactions of small-molecule inhibitors at the active site provides an improved basis for structure-based ligand design. The recurring motif of tight interaction with the two lysine residues 156 and 159 is suggested to be of prime importance.