Synthesis of antibacterial 1,3-diyne-linked peptoids from an Ugi-4CR/Glaser coupling approach.

A library of ten 1,3-diyne-linked peptoids has been synthesized through an Ugi four-component reaction (U-4CR) followed by a copper-catalysed alkyne homocoupling (Glaser reaction). The short and chemoselective reaction sequence allows generating diverse (pseudo) dimeric peptoids. A combinatorial version allows the one-pot preparation of, e.g., six-compound-libraries of homo- and heterodimers verified by ESI-MS and HPLC. In a preliminary evaluation, some compounds display moderate activity against the Gram-positive bacterium Bacillus subtilis.

The enzyme 3-hydroxykynurenine transaminase as potential target for 1,2,4-oxadiazoles with larvicide activity against the dengue vector Aedes aegypti.

The mosquito Aedes aegypti is the vector agent responsible for the transmission of yellow fever and dengue fever viruses to over 80 million people in tropical and subtropical regions of the world. Exhaustive efforts have lead to a vaccine candidate with only 30% effectiveness against the dengue virus and failure to protect patients against the serotype 2. Hence, vector control remains the most viable route to dengue fever control programs. We have synthesized a class of 1,2,4-oxadiazole derivatives whose most biologically active compounds exhibit potent activity against Aedes aegypti larvae (ca. of 15 ppm) and low toxicity in mammals. Exposure to these larvicides results in larvae pigmentation in a manner correlated with the LC50 measurements. Structural comparisons of the 1,2,4-oxadiazole nucleus against known inhibitors of insect enzymes allowed the identification of 3-hydroxykynurenine transaminase as a potential target for these synthetic larvicides. Molecular docking calculations indicate that 1,2,4-oxadiazole compounds can bind to 3-hydroxykynurenine transaminase with similar conformation and binding energies as its crystallographic inhibitor 4-(2-aminophenyl)-4-oxobutanoic acid.

The multicomponent approach to N-methyl peptides: total synthesis of antibacterial (-)-viridic acid and analogues.

Two syntheses of natural viridic acid, an unusual triply N-methylated peptide with two anthranilate units, are presented. The first one is based on peptide-coupling strategies and affords the optically active natural product in 20% overall yield over six steps. A more economical approach with only four steps leads to the similarly active racemate by utilizing a Ugi four-component reaction (Ugi-4CR) as the key transformation. A small library of viridic acid analogues is readily available to provide first SAR insight. The biological activities of the natural product and its derivatives against the Gram-negative bacterium Aliivibrio fischeri were evaluated.

Synthesis of (-)-julocrotine and a diversity oriented Ugi-approach to analogues and probes.

An improved total synthesis of (-)-julocrotine in three steps from Cbz-glutamine, in 51% overall yield, is presented. To demonstrate the potential of the heterocyclic moiety for diversity oriented synthesis, a series of (-)-julocrotine analogues was synthesized by employing the heterocyclic precursor as an amino input in Ugi four-component reactions (Ugi-4CR) [1].

3-[3-(3-Fluoro-phen-yl)-1,2,4-oxadiazol-5-yl]propionic acid.

In the title compound, C(11)H(9)FN(2)O(3), the benzene ring is almost coplanar with the heterocyclic ring, making a dihedral angle of 14.0 (1)°. The plane of the carboxyl group is rotated by 14.7 (3)° with respect to the 1,2,4-oxadiazole ring plane. The aliphatic chain exhibits a standard zigzag arrangement. Two inter-molecular O-H⋯O hydrogen bonds between the carboxyl groups related by an inversion centre promote a dimeric structure formation. The dimers are stacked along the crystallographic a axis.

A handy and solventless direct route to primary 3-[3-aryl)-1,2,4-oxadiazol-5-yl]propionamides using microwave irradiation.

A one-step, simple and straightforward synthesis of the title amides from the corresponding carboxylic acids, urea and imidazole under microwave irradiation is described.

First ultrasound-mediated one-pot synthesis of N-substituted amides.

Ultrasound irradiation, an efficient and innocuous technique of reagent activation for synthesizing organic compounds, has been applied with success to transform seven carboxylic acids to fourteen secondary amides in good to excellent yields. The reaction has worked well either with aryl or alkyl carboxylic acids as well as with aromatic or aliphatic amines. This methodology is expeditious and reliable for preparing secondary carboxamides which in many cases are embedded in the C-5 side-chain of 1,2,4-oxadiazoles (14, 15, 17-27). The elemental analyses of new compounds (19-27) in conjunction with the spectral data of all synthesized amides gave an idea about their structures, while the crystallographic data of one of the compounds (26) supplied information concerning the configurational behavior of the amidic part and also the conformational aspect of the entire molecule in the crystalline state.

Synthesis and cytotoxic profile of glycosyl-triazole linked to 1,2,4-oxadiazole moiety at C-5 through a straight-chain carbon and oxygen atoms.

The convergent synthesis of an unusual (but simple) class of compounds 5a-g has been achieved by the copper-catalyzed [3+2] cycloaddition reaction of 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl azide 4 with propynyl 3-[3-(aryl)-1,2,4-oxadiazol-5-yl] propionates 3a-g. The formerly known azide 4 has been prepared according to the literature procedure; however, the synthesis of esters 3a-g is being reported for the first time. The infrared as well as (1)H NMR spectra of all new products are in agreement with their proposed structures. By carrying out the nOe experiment of one of the final compounds 5a, we have been able to establish that only the 1,4-regioisomers have been formed in the cycloaddition reaction. All final products presented weak cytotoxic activity, but 5e and 5g had somewhat better behaviour showing 22-25% cell growth inhibition against two cell strains: NCI-H(292) (lung carcinoma) and HEp-2 (larynx carcinoma).