Modification of constrained peptides by ring-closing metathesis reaction

Design and synthesis of hetero-steroids via ring-closing metathesis: Biological studies towards in vitro anticancer activity

Here, we report a synthetic approach to hetero-steroids and also studied their biological activities as anticancer agents. A novel class of oxacycles containing estrone moiety were synthesized in this report. Allyl ether derived from estrone underwent Claisen rearrangement (CR) and again O-allylation and subsequent ring-closure gave A-ring-furan and oxepine fused derivatives in high yields. We used double bond isomerization and ring-closing metathesis (RCM) as key steps to assemble hetero steroids containing a mixture of regio isomers like benzofurans and benzoxepine moieties. The novel benzofuran and benzoxepine-based hybrid steroid derivatives were subjected to in vitro cytotoxicity analysis and were found to exert cancer cell-specific activity.

Annulation Tactics of cis-syn-cis Triquinanes by Allylsilanes: Application of Hosomi-Sakurai Reaction Conditions

A stereoselective [3+2] cycloaddition approach to functionalized pentaquinanes starting from cis-syn-cis triquinanes, derived from Cookson's diones, is reported. This transformation involves generation of six new stereocenters in a single step leading to cis-anti-cis-syn-cis-anti-cis polyquinane systems. Our method prevents transannular cyclizations which are prevalent in these moieties. The structure and stereochemistry of target molecules are well-characterized based on NMR data and X-ray diffraction studies.

Modular Approach to Benzofurans, 2H-Chromenes and Benzoxepines via Claisen Rearrangement and Ring-Closing Metathesis: Access to Phenylpropanoids

Benzofurans, 2 H -chromenes and benzoxepines are key structural elements present in several natural products and pharmaceuticals. Here, we describe an easy-to-execute strategy for the synthesis of benzofurans, 2 H -chromenes and benzoxepines, by employing Claisen rearrangement and ring-closing metathesis as key steps. A variety of phenols were converted into useful oxacycles in good to excellent yields. The ring-closing metathesis approach has been used to produce phenylpropanoid natural products. Examples described here include, the naturally occurring benzofurans such as 7-methoxywutaifuranal, 7-methoxywutaifuranol, 7-methoxywutaifuranate and the O -prenylated natural products like boropinic acid, boropinols A and C.

One-pot thiol-free synthetic approach to sulfides, and sulfoxides selectively

A facile and efficient thiol-free one-pot method for direct synthesis of sulfides and sulfoxides under green conditions without using any metal catalyst is reported. For this purpose, we used benzyl bromides as starting materials in the presence of potassium thioacetate (PTA) and Oxone® which are low-cost, and readily accessible chemicals. This method is highly compatible with a variety of functional groups and delivered a series of sulfides, bis-sulfides, and sulfoxides in good yields. The selective formation of sulfoxides over sulfones is discussed via a mechanism.

A facile and efficient thiol-free one-pot method for direct synthesis of sulfides and sulfoxides under green conditions without using any metal catalyst is reported.

A Modular Approach to Angularly Fused Polyquinanes via Ring-Rearrangement Metathesis: Synthetic Access to Cameroonanol Analogues and the Basic Core of Subergorgic Acid and Crinipellin

We describe a modular approach to angularly fused polyquinanes that are core units of many natural products such as cameroonanol, subergorgic acid, and crinepellin, etc. in excellent yields by employing atom-economic ring-rearrangement metathesis as a key step. Our work highlights, the synthesis of cameroonanol analogues 1-6 and their ester derivatives by using the stereoselective reduction of the carbonyl group by using DIBAL-H- and DCC-mediated coupling as the key reactions. The subergorgic acid core 7 was produced by LDA-mediated kinetically controlled regio- and stereoselective ring-junction allylation as a critical step. Moreover, it is worth mentioning that the present strategy relies on a less explored exo-dicyclopentadiene-1-one (8) and produces highly congested polycyclic frameworks containing up to seven contiguous stereogenic centers including quaternary carbons up to two. All of the new molecules were characterized by NMR data. The structure and relative stereochemistry of some compounds were confirmed by chemical methods and further supported by single-crystal X-ray diffraction studies. The newly reported tri- and tetraquinane skeletons are present in many naturally occurring bioactive polyquinanes. Hence, this strategy is useful for designing various "druglike molecules" and expands the chemical space of cyclopentanoids that are useful in medicinal chemistry.

Design, Synthesis and Late-Stage Modification of Indane-Based Peptides via [2+2+2] Cyclotrimerization

Here, we prepared several dipeptides containing 2-aminoindane-2-carboxylic acid (Aic) and carried out further synthetic transformations. Synthesis and purification of modified peptides by using [2+2+2] cyclotrimerization is a challenging task. We are able to modify the unusual amino acids and peptide derivatives by late-stage incorporation of benzylhalo functionality. To incorporate benzylhalo moiety we used [2+2+2] cyclotrimerization in the presence of Mo(CO)₆ . These halo derivatives are potential substrates for further modification by Sonogashira reaction, Suzuki-Miyaura cross-coupling, sultine formation, and the Diels-Alder reaction sequence.

Synthetic Strategies to Diverse Polyquinanes via Olefin Metathesis: Access to the Basic Core of Crinipellin, Presilphiperfolanol, and Cucumin

A rapid and useful synthetic approach to various polyquinane-based natural products was accomplished efficiently by employing ring-rearrangement metathesis and ring-closing metathesis as key steps. Here, we report the synthesis of stereochemically well-defined cis-anti-cis triquinanes (1, 2), tetraquinanes (3, 4), a novel pentaquinane 5, and fused [5-5-5-6] tetracyclic systems (6, 7) that are present in crinipellin, presilphiperfolanol, cucumin, etc. Hence, the current strategy may be suitable for the synthesis of various complex natural and unnatural cyclopentanoid targets. Moreover, our approach to the newly synthesized pentaquinane 5 has paved the way for various complex polyquinanes/molecules having significant applications in theoretical and medicinal chemistry.

Synthesis of C 3-symmetric star-shaped molecules containing α-amino acids and dipeptides via Negishi coupling as a key step

We demonstrate a new synthetic strategy toward star-shaped C₃-symmetric molecules containing α-amino acid (AAA) derivatives and dipeptides. In this regard, trimerization and Negishi cross-coupling reactions are used as the key steps starting from readily available 4’-iodoacetophenone and L-serine. These C₃-symmetric molecules containing AAA moieties are useful to design new ligands suitable for asymmetric synthesis and peptide dendrimers.

Design and Synthesis of Polycycles, Heterocycles, and Macrocycles via Strategic Utilization of Ring-Closing Metathesis

In this perspective, we summarize new synthetic approaches for the construction of various polycyclic compounds involving ring-closing metathesis as a key step. In this regard, we used ring-closing metathesis in combination with other popular reactions like Suzuki-Miyaura coupling, Claisen rearrangement, Fischer indolization, Grignard addition, Diels-Alder reaction, and [2+2] cycloaddition reaction etc. To this end, a variety of functional molecules such as α-amino acids, cyclophanes, heterocycles, propellanes, spirocycles, and macrocycles have been prepared. The strategies developed and the molecules prepared here play a key role in designing new materials and also act as lead compounds in drug design. The strategies and tactics developed here are useful to design polycycles, macrocycles, and heterocycles of diverse ring systems.

Design and synthesis of hybrid cyclophanes containing thiophene and indole units via Grignard reaction, Fischer indolization and ring-closing metathesis as key steps

We demonstrate a new synthetic strategy to cyclophanes containing thiophene and indole moieties via Grignard addition, Fischer indolization and ring-closing metathesis as key steps.

On the two-component microwave-mediated reaction of isonitriles with carboxylic acids: regarding alleged formimidate carboxylate mixed anhydrides

Microwave induced two-component coupling (2CC) reaction of carboxylic acids with isonitriles gives rise to various N-formylamides. The formimidate carboxylate mixed anhydride (FCMA) is proposed as the reactive intermediate, which undergoes 1,3-O-->N acyl transfer to give the observed product. The formation and survival of the labile FCMA system has been evaluated.

Chemotactic tripeptides incorporating at position 2 alpha-aminoacid residues with unsaturated side chains

New N-For-Met-Leu-Phe-OMe (fMLF-OMe) analogues incorporating three different gamma-delta-didehydro-alpha-aminoacid residues (namely: Alg = (S)-Allylglycine; Dag = Diallylglycine; Cpg = 1-Aminocyclopent-3-ene-1-carboxylic acid) replacing the native (S)-Leucine have been synthesized and their activity towards human neutrophils has been evaluated in comparison with that shown by the reference tripeptide fMLF-OMe. Chemotaxis, lysozyme release and superoxide anion production have been measured. (1)H NMR titration experiments and NOESY spectrum of the Cpg containing model 10 have been discussed in order to ascertain the preferred solution conformations. A fully extended (C(5)) conformation at position 2 and a folded conformation with two consecutive gamma-turns (C(7) structure) have been proposed for the Dag and Cpg containing tripeptides, respectively.

Metal-catalysed tandem metathesis-hydrogenation reactions for the synthesis of carba analogues of cyclic peptides

Dicarba cyclic peptide analogues of the cystine-containing octapeptides octreotide, lanreotide, and vapreotide, all known somatostatin analogues, have been synthesized via an on-resin homogeneous metal-catalysed sequence involving ruthenium-catalysed ring-closing metathesis followed by rhodium-catalysed hydrogenation.Key words: dicarba-analogues of cystine-containing peptides, octreotide, vapreotide, and lanreotide; tandem ring-closing metathesis and hydrogenation.

Application of the Suzuki-Miyaura cross-coupling reaction for the modification of phenylalanine peptides

We have demonstrated an exceptionally simple and a useful methodology for modification of unusual phenylalanine peptides by adapting the building block approach using the Suzuki-Miyaura cross-coupling reaction as a key step. This strategy gave a good overall yield of various modified tri- and pentapeptides that may be useful to prepare various biologically active peptides in a short period of time.

A new approach for modification of phenylalanine peptides by Suzuki-Miyaura coupling reaction

For the first time, we have modified phenylalanine peptides by the Suzuki-Miyaura coupling reaction which may be useful in developing combinatorial libraries of peptidomimetics.