Synthetic carboline compounds targeting protein: biophysical and biological perspective.

Pictet-Spengler cyclization method has been adopted for the synthesis of three carboline derived compounds: two compounds with tetrahydro gama- and beta-having CF3 group and amino alkyl chain at delta and alpha position, respectively, and another with guanidine alkyl chain at alpha-position. Structure-activity relationship of the analogues with human serum albumin was studied by fluorescence and Fourier-transform infrared spectroscopy  followed by molecular docking. The data showed maximum affinity of human serum albumin with comp7 (S0-820) followed by comp3 (S0-1040) and least with comp1 (S0-728). The compounds were tested for cytotoxic potencies. Comp3, showed maximum cytotoxicity with GI50 6.2 µM, against HCT-116, followed by comp7, and poor cytotoxicity with comp1. Comp3 and 7 induced oxidative stress mediated autophagy led programmed cell death in HCT-116. Furthermore, the compounds effectively inhibit DNA topoisomerase I activity and showed anti-inflammatory actions. In vivo studies regarding therapeutic protective action of Comp3, as a representative carboline analogue, against colon toxicant, 1,2-dimethylhydrazine dihydrochloride (DMH), showed the efficacy of the compound against organ toxicity. The existing studies on biological evaluation showed that these synthetic compounds may have a major role as anticancer agents having myriad of proven therapeutic applications. Communicated by Ramaswamy H. Sarma.

Synthesis of macrocyclic peptidomimetics via the Ugi-click-strategy.

The Ugi-click-strategy was employed for the synthesis of 12-28 membered 1,2,3-triazole derived macrocyclic peptidomimetics. The Ugi reaction with acid components bearing acetylenic fragments and azidoisocyanides provided the corresponding peptidomimetics in up to 97% isolated yield. The subsequent CuAAC click reaction with these bifunctional substrates containing both acetylene and azide groups was investigated to reveal the influence of the structure of Ugi products on the direction of the click-cyclization. It was demonstrated that this approach allows efficient synthesis of either monomeric (12- and 13-membered) or dimeric (24-, 26- and 28-membered) macrocycles prepared in up to 85% yield. The scope and limitations of this method are discussed.

Trifluoromethylated carboline compounds targeting DNA: Synthesis, binding and anti-proliferative effects on human cancer cell lines.

Three sets of carboline derived compounds were prepared by Pictet-Spengler cyclization. These tetrahydro ß- and γ-carbolines have CF3 group with an additional amino alkyl chains (α- or δ-position) and guanidine alkyl chains (α-position), of varying length. Structure-activity relationship of these molecules with calf thymus DNA was emphasized by fluorescence, ITC, FTIR and viscosity. Binding with DNA resulted in dramatic enhancement and quenching in the fluorescence emission. Gamma-carboline analogs showed maximum DNA binding followed by beta-carboline compounds with amino alkyl chain and least with guanidine alkyl chain compounds. It decreased with increasing chain length. The bindings were entropically driven being more with guanidine alkyl chain analogs. Site preference and mode of binding with partial intercalation and external binding was supported by FTIR and viscosity. Cytotoxic potencies of the compounds were tested on seven different cancer cell lines. The smallest alkyl chain analog attached to gamma position, Comp3, showed maximum cytotoxicity with GI50 6.2 µM, against HCT-116 causing apoptosis, followed by the guanidine alkyl chain compounds, but amino alkyl chain compounds to beta position showed poor cytotoxicity. These results may be of prospective use in a framework to design novel carboline derivatives as antitumor drugs for improved therapeutic applications in future.

Enantioselective synthesis of α-perfluoroalkylated prolines, their 6,7-membered homologues and derivatives.

Enantioselective synthesis of α-perfluoroalkylated cyclic amino acids and their derivatives was elaborated using the organocatalytic Strecker reaction with 5-7 membered cyclic ketimines. The prepared amino nitriles could be transformed into chiral Rf-prolines and their 6,7-membered homologues as well as their corresponding amides and diamines (yields up to 99%, up to >99% ee).

Chiral ß3-isocyanopropionates for multicomponent synthesis of peptides and depsipeptides containing a ß-amino acid fragment.

An efficient three-step synthesis of a novel family of enantiomerically pure isocyanides derived from ß3-isocyanopropionic acids was elaborated. Easily available N-formylated α-amino acids were used as starting materials towards this aim. The 3-step sequence (Arndt-Eistert reaction-Wolff rearrangement-dehydration) resulted in target isonitriles in good yields (up to 97%). As a result a new family of isocyanides bearing a fragment of ß3-amino acids with different functional groups (amides, esters and short peptides) was obtained. It was demonstrated that these new isonitriles can be used in the Ugi and Passerini reactions to prepare short peptides and depsipeptides having a ß-amino acid fragment incorporated.

From Cyclic CF3-ketimines to a Family of Trifluoromethylated Nazlinine and Trypargine Analogues.

An efficient (one- and two-step) synthesis of trifluoromethylated derivatives of the natural alkaloids nazlinine, trypargine, and homotrypargine was elaborated. Trifluoromethyl-substituted 5-7-membered cyclic imines were used as a masked carbonyl component in the Pictet-Spengler reaction with various tryptamines. As a result, this approach opens access to a family of alkaloid-like compounds bearing a CF3 group at position 1 of tetrahydro-ß-carboline.

Synthesis of tetrazole-derived organocatalysts via azido-Ugi reaction with cyclic ketimines.

A new route to tetrazole-derived cyclic amines based on the TMSN3-modified Ugi reaction with 2-substituted cyclic imines was elaborated. The reaction allows the direct preparation of five-, six-, and seven-membered cyclic amines substituted with a tetrazole ring, which are important types of organocatalysts. The scope and limitations of this method are discussed. In the case of the Ugi reaction with benzyl isocyanide, the N-substituted tetrazoles can be easily debenzylated under catalytic hydrogenation conditions to form NH-tetrazoles in quantitative yields. It was demonstrated that both enantiomers of tetrazole-derived cyclic amines can be prepared by resolution with tartaric acid, thereby initiating a simple route to chiral derivatives. One of the obtained chiral tetrazoles was efficiently used as an organocatalyst in the amination reaction.