Conceptual design and cost-efficient environmentally Benign synthesis of beta-lactams

Stereoselective preparation of diverse trans and cis β-lactams following different experimental conditions are executed. A variety of circumstances are critically analyzed. It has been found that the stereochemistry of the products depends on a number of parameters including the conditions of the procedures, composition of the Schiff bases and acid chlorides or equivalents, method of addition of the reactants, temperature of the process and nature of the media. Using some of the compounds and methods as described herein, a number of useful chemical transformations for the preparation of heterocycles are achieved. These methods include indium-catalyzed glycosylation of amino β-lactams, preparation of pyrrole-substituted β-lactams, cycloaddition with sterically congested Schiff bases towards β-lactams, Michael reaction for the preparation of polycyclic oxazepenes and synthesis of two chiral isomers of the thienamycin side chain. Most of the products are obtained stereospecifically and in optically active forms. Many reactions described here are catalytic and therefore, these are environmentally friendly.

O-Isocyanates as Uncharged 1,3-Dipole Equivalents in [3+2] Cycloadditions

1,3-Dipoles are commonly used in [3+2] cycloadditions, whereas isoelectronic uncharged dipole variants remain underdeveloped. In contrast to conventional 1,3-dipoles, uncharged dipole equivalents form zwitterionic cycloadducts, which can be exploited to build further molecular complexity. In this work, the first cycloadditions of oxygen-substituted isocyanates (O-isocyanates) were studied experimentally and by DFT calculations. This unique cycloaddition strategy provides access to a novel class of heterocycle aza-oxonium ylides through intramolecular and intermolecular cycloadditions with alkenes. This allowed a systematic study of the reactivity of the transient aza-oxonium ylide intermediate, which can undergo N-O bond cleavage followed by nitrene C-H insertion, and the formation of β-lactams or isoxazolidinones upon varying the structure of the alkene or O-isocyanate reagents.

Cationic poly-amido-saccharides: stereochemically-defined, enantiopure polymers from anionic ring-opening polymerization of an amino-sugar monomer

We expand the scope of the PAS methodology and evaluate multiple synthetic routes to generate a regioselectively-functionalized 6-amino carbohydrate polymer sharing key properties with natural polysaccharides, including high water-solubility.

Traceless Solid-Phase Organic Synthesis

Traceless solid-phase synthesis represents an ultimate sophisticated synthetic strategy on insoluble supports. Compounds synthesized on solid supports can be released without a trace of the linker that was used to tether the intermediates during the synthesis. Thus, the target products are composed only of the components (atoms, functional groups) inherent to the target core structure. A wide variety of synthetic strategies have been developed to prepare products in a traceless manner, and this review is dedicated to all aspects of traceless solid-phase organic synthesis. Importantly, the synthesis does not need to be carried out on a linker designed for traceless synthesis; most of the synthetic approaches described herein were developed using standard, commercially available linkers (originally devised for solid-phase peptide synthesis). The type of structure prepared in a traceless fashion is not restricted. The individual synthetic approaches are divided into eight sections, each devoted to a different methodology for traceless synthesis. Each section consists of a brief outline of the synthetic strategy followed by a description of individual reported syntheses.

N-Heterocyclic carbene catalyzed dehydrogenative coupling of enals: synthesis of monobactams

The novel NHC-catalyzed dehydrogenative coupling of enals is described to generate a wide range of monobactams.

Synthesis of 3-Substituted-clavams: Antifungal Properties, DD-Peptidase and beta-Lactamase Inhibition

The [2+2]cycloaddition of chlorosulfonyl isocyanate to vinyl and (Z)-propenyl ethers derived from the 2-O-sulfonylated (R)- and (S)-1-(furyl-2')-1,2-ethanediols furnished the 4-alkoxy-azetidin-2-ones with a good to moderate stereoselectivity. The intramolecular alkylation of the beta-lactam nitrogen atom led to the corresponding 3-(furyl-2')- and 6-methyl-3-(furyl-2')-clavams. The transformation of the furyl residue into an alkoxycarbonyl group led to clavams related to the natural compounds. The synthesized clavams exhibited moderate inhibitory activities against DD-peptidase 64-575 and beta-lactamase (penase) as well as antifungal activities.

Synthesis, biological, and chiroptical activity of 3-phenyl-clavams

The [2+2]cycloaddition of chlorosulfonyl isocyanate to simple vinyl ethers derived from the 2-O-sulfonylated (R) and (S) 1-phenyl-1,2-ethanediol leads to 4-alkoxy-azetidin-2-ones with a moderate stereoselectivity. The cycloaddition to analogous (Z)-propenyl ethers proceeds stereospecifically with the retention of the olefin configuration. The intramolecular alkylation of beta-lactam nitrogen atom furnished all possible stereoisomers of 3-phenyl- and 6-methyl-3-phenyl-clavams. The biological and chiroptical activity of synthesized clavams was investigated. The (3R,5R)-diastereomer 30 showed higher inhibition of bacterial enzymes than other related compounds.

Stereoselectivity in formation of oxacephams from 1,3-alkylidene-threitols

The [2+2]cycloaddition of CSI to the (Z)-propenyl ethers derived from respective 1,3-methylidene- and 1,3-ethylidene-threitols, contrary to the corresponding erythritol derivatives, is characterized by a low stereoselectivity and a lack of stereospecificity. On the other hand, the alternative method of the oxacepham formation, based on the 4-vinyloxy-azetidinone, proceeds with an excellent stereoselectivity. The CD-spectroscopy offers an attractive tool for determination of the absolute configuration of the bridgehead carbon atom at the 5-oxacepham skeleton.

Six-membered cyclic sulfites derived from glucofuranose and 1,2,4-butanetriol

Six-membered cyclic sulfites derived from glucofuranose derivatives 5, 6 and from 1-O-tert-butyldimethylsilil-1,2,4-butanetriol 12 were synthesized and separated into pure diastereomers which were in turn subjected to the sequence of reactions leading to the introduction of the terminal vinyl ether fragment. Reactivity and applicability of cyclic sulfites as intermediates in [2+2]cycloaddition of chlorosulfonyl isocyanate (CSI) to vinyl ethers were studied. The cycloaddition to vinyl ethers 19 and 20 proceeded in low yield and low asymmetric induction, in the case of the former, and moderate yield and pronounced asymmetric induction, in the case of the latter. The (1)H-NMR spectra of sulfites 13-16 reveal a preference of the sulfite oxygen atom for the axial position. Thus, well-defined conformation in solution for compounds 13 and 15 and a mixture of the two possible chair forms for sulfites 14 and 16 could be assigned. The stretching frequency of the S-->O bond in stable conformation with an axial sulfite oxygen occurs in the range 1,160-1,210 cm(-1), whereas conformationally mobile sulfites exhibit corresponding absorption above 1,220 cm(-1). The absolute configuration assignments of sulfites 7, 8, 15, 16 and 25-28 were done empirically based on the combined analysis of the NMR, IR, X-ray, and dichroic data. It was demonstrated that the sign of the Cotton effect around 194 nm correlated with the absolute stereochemistry at the sulfur atom in a sulfite chromophore.