Synthetic studies toward macrocidins: an RCM approach for the construction of the central cyclic core

The central macrocyclic core of the macrocidins was constructed using RCM as the key reaction. A preliminary investigation dealing with the key reactions, that is, the Dieckmann cyclization and the RCM, revealed that RCM of the β-ketoamide is better than RCM of the corresponding acyltetramic acid.     

Synthetic studies toward tricyclic cembranoids: a modular approach for the construction of the tricyclic framework of eunicin

The synthesis of a sugar derived allene and its intramolecular silver mediated etherification followed by ring closing metathesis has been explored for building the tricyclic framework of eunicin.     

Synthetic studies toward melotenine A

Attempts to the construction of B/C ring and E ring in melotenine A are described. Based on para-dienone chemistry, a tactical application of tandem aminolysis/aza-Michael addition reaction was made to access highly functionalized building blocks with the pyrrolo[2,3-d]carbazole tetracyclic unit (A/B/C/D ring). Albeit negative results for assembling the dihydroazepine unit (E ring) by using the proposed fragmentation reaction of gem-dihalocyclopropanes, an alternative strategy based on ring closing metathesis was evolved to forge the E ring possessing a twisted 1,3-diene unit embedded in the rigid skeleton of melotenine A.     

Toward a fragment-based approach to MMPs inhibitors: an expedite and efficient synthesis of N-hydroxylactams

Matrix metalloproteinases (MMPs), a class of zinc-enzymes over-activated in many pathologies, such as arthritis and cancer, can be efficiently inhibited by a variety of molecules bearing zinc-binding groups (ZBGs). The hydroxamic acid moiety represents one of the most potent and widely exploited ZBG but the poor target selectivity and in vivo toxicity have tempered the initial enthusiasm for this class of potential therapeutics. These drawbacks might be circumvented, at least in part, by increasing the structural constraints around the hydroxamic moiety. Following this strategy we designed and prepared N-hydroxylactam molecules of different size through a synthetic protocol based on a ring closing metathesis amenable to a fragment-based approach potentially leading to a large molecular diversity.     

Synthetic studies toward the development of novel minoxidil analogs and conjugates with polyamines

Syntheses of novel polyamine-modified minoxidil analogs (PMMs) and minoxidil-polyamine conjugates (MPCs) are described in an effort to improve the biological activity and selectivity of minoxidil and its poor solubility in water.     

Model synthetic studies toward the central 7/8/5 tricarbocyclic core of complex Schisanartane-type nortriterpenoids

A short, flexible approach to a functionally embellished 7/8/5 fused tricyclic scaffold corresponding to the CDEF segment of Schisanartane nortriterpenoids, from commercially available 1,5-cyclooctadiene, is delineated.     

An approach to total synthesis of the cylindricine B pyridoquinoline subclass of tricyclic marine ascidian alkaloids

Employing an intramolecular N-acylketiminium ion/olefin hetero Diels-Alder reaction, and a ring closing metathesis of a vinyl chloride as pivotal steps, it is possible to directly access the pyridoquinoline tricyclic ring system of the marine alkaloids cylindrines B and J.     

Stereoselective synthesis of C1-C5 and C4-C5 linked deoxy disaccharides via a ring closing metathesis protocol

The stereoselective synthesis of C-C linked deoxy disaccharides by a short and efficient route is described. An RCM strategy was adopted for the assembly of the required ring skeleton on the sugar unit, while OsO₄ was used to introduce the vic-diol unit.     

Synthesis of oxaspiropiperidines as a strategy for lowering log D

The syntheses of four new spiropiperidines designed as polar analogs of methyl 2-(3-azaspiro[5.5]undecan-9-yl)acetate are described.     

Synthetic studies on bradykinin antagonist martinellines: construction of a pyrrolo[3,2-c]quinoline skeleton using silicon-tether RCM reaction and allylic amination

The pyrrolo[3,2-c]quinoline consisting of a core structure of martinellines, the first naturally occurring heterocycle, was prepared through silicon-tether ring-closing metathesis reaction and intramolecular allylic amination as key steps.     

Facile synthesis of [(NHC)(NHCewg)RuCl2(CHPh)] complexes

The utility of [(NHC)(PPh₃)RuCl₂(CHPh)] for the facile and efficient synthesis of ten complexes of the type [(NHC)(NHC_ewg)RuCl₂(CHR)] with saturated and unsaturated NHC ligands in 85-94% isolated yield via a simple one step synthesis utilizing [AgI(NHC_ewg)] as NHC_ewg transfer reagents was demonstrated.     

Ring-closing metathesis in the synthesis of fused sultones

Synthesis of seven-membered sultones fused with different carbo- and heterocycles have been developed using ring closing metathesis as the key operation. The required substrates have been easily synthesized from their commercially available corresponding phenols.     

N-ferrocenoyl benzotriazole: A convenient tool for the synthesis of ferrocenoyl esters

A new synthesis methodology has been presented for the preparation of the ferrocenoyl esters. Ferrocene carboxylic acid was derivatized using direct 1H-benzotriazole/SOCl₂ methodology to prepare N-ferrocenoyl benzotriazole as a convenient tool for the functionalization of ferrocene ring. N-ferrocenoyl benzotriazole was reacted with alcohols in mild conditions to prepare ferrocenoyl esters in high purity and in good yield. The solid state structure of benzyl-1-ferrocenoate, 2f, has also been determined by X-ray crystallography. In the crystal structure, intermolecular C-H···O hydrogen bonds link the molecules into a two-dimensional network. The π···π contacts between the cyclopentadiene rings and cyclopentadiene and phenyl rings, [centroid-centroid distances = 3.296(1) and 3.750(1) Å] may further stabilize the structure. Two weak C-H···π interactions are also found.     

Facile ring-opening of N-acylisatins for the development of novel peptidomimetics

A range of novel mono- and bis-glyoxylamide peptidomimetics were prepared via the facile ring-opening of N-acylisatins with amino acids and peptide derivatives. The ring-opening of N-acylisatins with dipeptides and tripeptides was discovered to be the most efficient strategy for the synthesis of second and third generation glyoxylamides.     

First stereoselective total synthesis of Phomolide G and H via RCM protocol

A first total synthetic route has been reported for the synthesis of Phomolide G and H. The syntheses of fragments were initiated from commercially available and inexpensive starting material (R)-epichlorohydrin. The synthesis involves a key Sharpless epoxidation, stereoselective epoxide opening, lactonization and ring closing metathesis (RCM).     

Facile synthesis of 1-substituted 4,5-diaminopyrazoles and its application toward the synthesis of pyrazolo[3,4-b]pyrazines

1-Substituted 5-aminopyrazole-4-carbonylazides were prepared from the appropriate 5-aminopyrazole-4-carboxylates. The acyl azides undergo a Curtius rearrangement followed by quenching with alcohols to form the corresponding carbamates. The 1-substituted 5-amino-4-benzyloxycarbonylaminopyrazoles were unblocked by catalytic hydrogenolysis to give the desired 4,5-diaminopyrazoles. These 4,5-diaminopyrazoles were immediately condensed with glyoxal to afford 1-substituted pyrazolo[3,4-b]pyrazines.     

Facile and rapid regeneration of free amino acids from N-benzyloxycarbonyl-5-oxazolidinones and from N-benzyloxycarbonylamino derivatives by treatment with BCl3 in dichloromethane

Reaction of benzyloxycarbonyl-5-oxazolidinones and of N-benzyloxycarbonylamino acids with BCl₃ in dichloromethane at room temperature affords the corresponding free amino acids.     

Synthetic studies of carzinophilin. Part 3: Synthetic approach toward carzinophilin and successful synthesis of 13-O-desacetyl-12,13-di-O-benzyl-4-O-methylcarzinophilin

The synthetic procedures of the title compound (2), a protected form of carzinophilin (1), were developed. While efforts toward the total synthesis of 1 failed, comparison of the ¹H NMR spectra of 2 and some other related compounds with that of 1 provided definite support for the absolute stereochemistry of 1 which has a complicated history regarding its structure.     

One-pot synthesis of fluorinated 2-amino-pyrimidine-N-oxides. Competing pathways in the four-atom side-chain rearrangements of 1,2,4-oxadiazoles

Trifluoromethylated 2-amino-pyrimidine N-oxides have been synthesized by reaction of the 3-amino-5-methyl-1,2,4-oxadiazole with trifluoromethyl-β-diketones in the presence of perchloric acid, followed by hydrolysis. In this ring-to-ring transformation an initial formation of (unisolated) 1,2,4-oxadiazole-pyrimidinium salts, and subsequent ring-opening at the oxadiazole moiety occurs. Isolation of 2-(hydroxyamino)-pyrimidine from the reaction mixture evidenced the presence of a competing pathway where the N(4) nitrogen of the oxadiazole is involved in the formation of a regioisomeric pyrimidinium salt. The effect of the trifluoromethyl group on the product distribution is discussed. By X-ray analysis, the crystal structure of two different N-oxide regioisomers has been unambiguously ascertained.     

Asymmetric synthesis of spiro 2-pyrrolidin-5-ones, 2-piperidin-6-ones and 1-isoindolin-3-ones. Part 2: N-Acyliminium ion cyclisations with an internal alkene nucleophile

Chiral non-racemic bicyclic and tricyclic oxylactams obtained in two steps from N-(2-hydroxy-1(R)-phenylethyl)-succinimide and phthalimide are cyclised diastereoselectively in formic acid to give spiro[cyclohexane-1,2′-pyrrolidin]-5-ones and spiro[cyclohexane-1,1′-isoindolin]-3-ones, respectively.