New taxane derivatives: synthesis of baccatin[14,1-d]furan-2-one nucleus and its condensation with the norstatine side chain

New taxanes 15 and 18, containing the unsaturated and saturated baccatin[14,1-d]furan-2-one nucleus, respectively, were prepared starting from the readily available 13-oxo-7-Tes-baccatin III (3). Sequential formation of the enolate of 3 and reaction with ethyl glyoxylate gave the 13-oxo-7-Tes-baccatin[14,1-d]-3,4-dehydrofuran-2-one 4. The reduction of 4 can result in the formation of a mixture of compounds corresponding to 13-hydroxy alcohol 5 and 13-enol derivative 6. Both 5 and 6 were transformed into 13-oxo-7-Tes-baccatin[14,1-d]furan-2-one 8 by treatment with a base. Further reduction of 8 gave 13-hydroxy compound 9. Esterification of 6 and 9 with N,O-protected norstatine 12, followed by deprotection, gave the new promising anticancer taxanes 15 and 18, respectively.     

Semisynthesis of new D-seco-C-nor-taxane derivatives containing a polyfunctionalized furanosyl or cyclopentenyl or cyclopentyl C-ring

The synthesis of new D-seco-C-nor-taxane derivatives in which the D-ring has been deleted and the C-ring has been transformed into a new pentatomic ring, i.e., the polyfunctionalized tetrahydrofuranosyl and cyclopentenyl or cyclopentyl ring, was performed starting from baccatin III derivatives. The synthetic strategy adopted took advantage of the oxetane ring opening and disconnection of the C4-C5 bond, followed by an intramolecular condensation. The formation of furanosyl or cyclopentyl rings is strictly dependent on the presence of unprotected or protected oxygen at C-7 in the starting material. The reactions proceeded with good diastereoselectivity with control of the stereochemistry of one or two stereocenters.     

An efficient route to all stereoisomeric enantiopure 6-amino-3-alkyl-3- azabicyclo[3.2.1]octane-6-carboxylic acids

A single-step synthesis on a gram scale of four pure stereoisomers of the 6-amino-3-azabicyclo[3.2.1]octane-6-carboxylic acid was carried out using (R)-1-phenylethylamine to confer chirality. The phenylethyl group, and the p-methoxy group linked to the N-atom, are easily removed by hydrogenolysis to afford the corresponding NH-3 derivatives. A series of N-3-alkyl compounds were prepared by way of a "one-pot" deprotection-alkylation procedure starting from the above key compounds. Their biological activity has been evaluated on the GABA receptor.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Diastereoselective protocols for the synthesis of 2,3-trans- and 2,3-cis-6-methoxy-morpholine-2-carboxylic acid derivatives

Two diastereoselective and straightforward protocols for the high-yielding synthesis of 2,3-trans- and 2,3-cis-6-methoxy-3-substituted morpholine-2-carboxylic esters were realized in few steps, through the condensation between 5,6-diethoxy-5,6-dimethyl-1,4-dioxan-2-one and an appropriate imine, which is the key reaction to control the C2-C3 relative stereochemistry, followed by a methanolysis/ring-closure tandem reaction sequence. In particular, 2,3-trans-morpholines derive from the R*,S*-product of the acid condensation of N-functionalized alkylimines with the silylketene acetal of the above lactone, whereas 2,3-cis-morpholines derive from the R*,R*-product of basic condensation of an N-tosylimines with the lactone.     

Unusual Chemoselective RhII‐Catalysed Transformations of α‐Diazocarbonyl Piperidine Cores

The reactivity of various α‐diazocarbonyl piperidine scaffolds, characterised by an increased molecular complexity, was tested with various Rh^II catalysts. The structure of the starting reagent is of relevance to the synthetic results. An unexpected dimerisation took place, starting from the simple piperidine scaffold, to give the hexahydrotetrazine ring system. Products derived from a nitrogen ylide intermediate or aromatic substitution (1,3,4,5‐tetrahydro‐2,5‐methanobenzo[c]azepine and 1,2,3,3a‐tetrahydrocyclopenta[de]isoquinolin‐4(5 H)‐one rings, respectively) were obtained from tetrahydroisoquinoline derivatives. The chemoselectivity of the reaction could be controlled by the choice of starting reagent, Rh^II catalyst and the reaction conditions. Finally, it was found that the azepino heterocycle could coordinate to the catalyst to give new Rh^II complexes.     

Alpha,gamma-diamino acids: asymmetric synthesis of new constrained 6-amino-3-azabicyclo[3.2.1]octane-6-carboxylic acids

The synthesis of two new diastereomeric 6-amino-3-azabicyclo[3.2.1]octane-6-carboxylic acids exo- and endo-8,9 is reported using exo- and endo-norbornene amino acids as chiral building blocks. This method provides a fast access to optically pure amino acids 8 and 9 which can be considered both alpha,gamma- and alpha,delta-diamino acids containing sterical constraints and characterized by alpha,alpha-disubstitution.