Catia Granito

Novel and Recent Synthesis and Applications of β-Lactams

In this chapter, a comprehensive overview of the most significant and interesting contributions published from 2000 until now, concerning the preparation of novel β-lactam structures is presented. Among the different synthetic strategies available, either novel or already known but efficient and versatile methodologies are covered. The simple modifications of one or more substituents linked to the nitrogen N-1, the C-3, and the C-4 carbon atoms of the β-lactam nucleus were considered as an alternative synthetic protocol of more complex and polyfunctionalized molecules. Indeed, it is well known and extensively reviewed that the biological activity of this strained four-membered heterocycle is strictly dependent on the nature of the substituent groups that affect the reactivity towards the molecular active sites, increasing or lowering the possibility of interaction with the substrates. Finally, a synthetic survey of the most significant biological and pharmacological applications of the 2-azetidinones is reported.

Palladium-catalyzed Cyclocarbonylation of Unsaturated Alcohols and Amines. Chemoselective Synthesis of Heterocycle-substituted γ- and δ-Lactones and Lactams

Unsaturated alcohols and amines react with carbon monoxide and hydrogen, in the presence of a catalytic amount of palladium acetate and a phosphine ligand, to afford selectively heterocycle-substituted γ- and δ-lactones and lactams. The distribution of five- and six-membered ring compounds can be modulated by an appropriate combination of solvent and phosphine ligand. The five-membered products are formed in two isomeric forms trans and cis with a modest diasteroselectivity (trans>cis).

Chemoselective construction of novel steroid derivatives.

Alpha-halo-alpha-heteroarylalkyllithiums, generated by deprotonation of the corresponding halides, when added promptly to steroids with C=O or C=NR groups, lead to epoxides and aziridines. The reactions are regio- and stereoselective; in fact, in the presence of more than one C=O group, the oxido or aziridino functions are formed uniquely at the C=O of C-17 (or C-20 depending on its position in the starting molecule), and the C-20(R) stereoisomer is often the only product isolated. Protection of the hydroxyl group present on several considered steroids was required, and it was accomplished through derivatization in acetyl, ether, or lactone.

Stereoselective synthesis of polyfunctionalized aziridines

1,2,3-triHeterocycle-substituted aziridines were prepared by coupling of (α-chloroalkyl) oxazolinyllithium compounds with diheteroaryl imines. The trapping by different electrophiles of the corresponding aziridinyl anions, generated by treatment with strong bases, was investigated. The stereoselectivity of the synthesis and the functionalization reactions was studied highlighting the different stabilizing effects of the heterocycle substituents.

Wittig Rearrangements of (Heteroaryl)alkyl Propargyl Ethers − Synthesis of Allenic and Propargylic Alcohols

(Heteroaryl)alkyl propargyl ethers have been synthesized and treated with nBuLi in THF at −78 °C. The resulting α- or α′-lithio derivatives could be trapped with iodomethane, affording the corresponding α- or α′-methylated products. Treatment in the absence of an external electrophile resulted either in allenic alcohols or in propargylic alcohols, or in mixtures of both compounds, probably arising from competing [1,2]- and [2,3]-Wittig rearrangements, in varying ratios. A high anti diastereoselectivity was observed in the propargylic alcohols produced. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Stereoselective Functionalization of Alkenyl-β-Lactams

Alkenyl-β-lactams, obtained by palladium-catalyzed [2+2] cycloaddition of imines with allyl halides, were functionalized in a stereoselective way by a simple deprotonation with LDA, and subsequent capture of the formed carbanion by various electrophiles. Alkyl, hydroxy and epoxy functionalities were inserted exclusively at the C-3 carbon atom of the β-lactamic system, without performing new cyclizations. High stereoselectivity was noticed with the quenching taking place preferentially at the C α with respect to the C γ carbon atom of the allylic moiety of the azetidinyl anion generated by deprotonation.

Stimulatory effect on pea of Typha Angustifolia L. extracts and their chemical composition

ABSTRACT In this study, the influence of aqueous and organic extracts of different plant parts (flowers, leaves, and stems) of Typha angustifolia on the germination and early seedling growth of field pea (Pisum sativum L.) was evaluated. Chemical composition of extracts of different plant parts of Typha was also determined. Aqueous (20, 40, 60, 80, and 100 g L−1) and organic extracts (at 0.5, 1, and 2 mg mL−1) were applied to the seeds of two pea cultivars, Douce de Provence and Lincoln, placed in Petri dishes. Application of extracts had a beneficial effect on germination and early seedling growth of both pea cultivars. However, aqueous extract of leaves showed the most beneficial effect at 60 and 40 g L−1 for the cultivars Douce de Provence and Lincoln, respectively. The effect could be attributed to the allelochemicals present in the aqueous extracts. Petroleum ether and chloroform extracts of leaves had the most stimulating effect on the germination and early seedling growth of pea. Analysis of Typha extracts indicated the presence of vitamin E in leaves, which could be responsible forthis stimulation. Moreover, Typha leaves also had substantial amount of flavonoids. In conclusion, the allelopathic activity of of Typha was dependent on the plant part, the solvent nature, the concentration of the extracts tested, and on the pea cultivar. Application of leaf extract was the most effective in improving the germination rate and early seedling growth of pea.

Synthesis of Alternative Electron Acceptor Compounds

New perylene monoimides, diimides and bis-diimides have been designed and synthetized. A detailed investigation of the synthesis of these compounds has also been performed in order to highlight the crucial factors for obtaining a specific class of molecules. Specifically, the attention has been focused on the synthesis of the intermediate perylene monoimides which are very useful precursors for many molecules difficult to obtain. Furthemore, two synthetic pathways have been developed for obtaining the bis-diimides variously substituted. These final compounds are predicted to mimic the excellent electron acceptor properties of fullerene derivatives and they can be used as building blocks to form 3D semiconducting materials.