An easy and stereoselective synthesis of N-Boc-dolaproine via the Baylis-Hillman reaction

In this communication we report a stereoselective total synthesis of N-Boc-dolaproine (Dap), an amino acid residue of the antineoplastic pentapeptide Dolastatin 10. Our strategy is based on a Baylis-Hillman reaction between N-Boc-prolinal and methyl acrylate, followed by a diastereoselective double bond hydrogenation and hydrolysis of the ester function.     

Calixarene complexes with metal ions

Selected complexes of metal ions are presented showing their syntheses and possible applications, an attention was paid to their usefulness in chemosensors design and in the environmental protection.     

Catalytic Oxidative Cyclocondensation of o‐Aminophenols to 2‐Amino‐3H‐phenoxazin‐3‐ones

The catalytic oxidative cyclocondensation of the o‐aminophenols 1a–f was investigated. The oxidants used were air/laccase, H₂O₂/horseradish peroxidase, H₂O₂/ebselen (3), and TBHP/diphenyl diselenide 4. The products obtained were 2‐amino‐3H‐phenoxazin‐3‐one—questiomycin A, its derivative 2b, and cinnabarinic acid and actinocin (2c,d). Substrates with methyl groups at 4 and 5 positions of benzene ring were converted to different dihydrophenoxazinones 2g,h. Compounds having chlorine atoms at the same positions underwent oxidation to planar phenoxa-zinones 2e,f with elimination of one hydrochloride molecule.     

Metallofullerenes

Summary Endohedral and exohedral metallofullerenes, including metal-doped fullerenes, organometallic fullerenes and fullerene metal complexes, are described in the context of their syntheses and properties.     

Lower rim substituted tert-butylcalix[4]arenes. Part 8: Calix[4]arenes with dialkoxyphosphoryl functions. Synthesis and complexing properties

New compounds: 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diisopropoxyphosphorylpropoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-methoxyethoxyphosphorylpropoxy)calix[4]arene (2) were synthesized and their ionophoric properties in ion-selective membrane electrodes were studied in comparison with already described by us 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diethoxyphophorylpropoxy)calix[4]arene (3). Complexes of 1 with calcium(II), lanthanum(III), europium(III) and gadolinium(III) nitrates were prepared in direct reaction of the ligand and appropriate metal salts. They were characterized by spectral data (IR, UV/Vis, luminescence, NMR, ESI-MS) and elemental analysis. The similarity in complexing behavior of the (dialkoxyphosphoryl)propoxy-calix[4]arenes toward calcium and some lanthanides was observed.     

Coordination modes of 2-mercapto-1,3-benzothiazolate in gallium and indium complexes

2-Mercapto-1,3-benzothiazole (mbztH) may act as a chelating or bridging ligand. In this study, reactions of mbztH with Me₃Ga and Me₃In were examined. The products were characterized by NMR spectroscopy, elemental analyses, melting point, and molecular weight determinations. Formation of mononuclear chelating complexes Me₂M(mbzt) (M = Ga, In) was observed in solutions. Crystallization of Me₂M(mbzt) yielded uncommon non-symmetrical dinuclear complexes Me₄M₂(mbzt)₂, in which one metal is bonded to two sulfurs and the other to two nitrogens.     

Immediate extensions of filtered rings

Summary A separated filtered ring has a maximally complete immediate extension. This is an analogue of Krull Theorem from valuation ring theory in the frame of filtered rings.

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Riassunto Un anello separato filtrato ha una immediata estensione massimale completa. Questo risultato è un analogo del teorema di Krull della teoria degli anelli di valutazione nell’ambito degli anelli filtrati.