Miguel Díaz

Dual-band low-profile corrugated feeder antenna

A dual-operating-band planar horn antenna having very low profile is presented in this paper. By opening a subwavelength aperture into a corrugated conducting plate, good return losses and a narrow radiated beam in each of the two desired operating frequency bands can be measured. This behavior is very similar to that observed in optical wavelengths where enhanced transmission was measured through apertures etched in metallic corrugated plates. Here, the double-corrugated structure has been scaled into the microwave frequency range and the excitation has been done by a conventional closed metallic waveguide placed in the rear part of the structure. In this way, a new concept of a very low profile feeder is proposed with potential wireless applications.

Stereoselective Synthesis of 4,5-Dihydroxy-D-erythro- and 4,5-Dihydroxy-D-threo-L-norvaline from D-Ribonolactone

Abstract Nitrogen functions have been introduced stereoselectively at the C-2 position in D-ribonolactone derivatives in order to prepare the title unnatural amino acids. The synthetic strategies lie in the inversion of configuration in SN2-type substitution reactions and stereospecific hydrogenation of conveniently substituted butenolides. The threo -isomer is the key precursor in the synthesis of the antibiotic clavalanine.

Stereocontrolled synthetic entries to homochiral hydroxylated norbornene derivatives. Formal synthesis of some carbocyclic nucleosides.

Abstract Several homochiral hydroxylated norbornene derivatives have been synthesized from D-mannitol. Stereocontrolled Diels-Alder cycloadditions and stereospecific hydroxylations are key processes for the creation of the stereogenic centers in the target molecules. These compounds are real or potential precursors in the synthesis of carbocyclic nucleosides and related products.

Enantioselective synthesis of novel, highly conformationally constrained peptide surrogates

Abstract Two new enantiomeric peptide surrogates as well as a tripeptide, all of them having highly conformationally constrained structures, have been synthesized. (Z)-cyclo-Aspartic acid and convenient α-substituted isoserine derivatives, in both antipodal forms, as well as methyl ( R )-2-phenylglycinate, have been used as the monomeric units.

Enantioselective synthesis of novel homochiral α-substituted (S)-isoserine derivatives. Incorporation of this amino acid in a highly conformationally constrained dipeptide surrogate

Abstract Optically pure isoserine derivatives with a chiral polyfunctional bicyclo[3.1.0]hexyl substituent at the α-carboxyl position were synthesized from a common cyclopentene precursor bearing an α-epoxy ester function in a side-chain. Cyclopropanation of the double bond and nucleophilic oxirane-ring opening by using a homochiral amine were the key steps. One of the synthesized derivatives was condensed with Cbz-cyclo-Asp-OMe affording a highly conformationally constrained dipeptide surrogate.

A novel and efficient synthetic approach to polyfunctional bicyclo[3.1.0]hexane derivatives

Abstract 1,3-Dipolar cycloaddition of diazomethane and nucleophilic oxirane-ring opening are the key steps in the synthesis of chiral and highly functionalized title compounds all of them bearing two quaternary carbons and three other stereocenters. Hydroxy esters and hydroxy amino esters have been prepared in good yields as representative instances of the versatility of the method described.

ENANTIOSELECTIVE SYNTHESIS OF CHIRAL POLYFUNCTIONAL CYCLOPENTANE DERIVATIVES : EPOXY ESTERS, HYDROXY ESTERS, AND HYDROXY AMINO ESTERS

Abstract Enantiomeric epoxides have been synthetized in efficient and diastereoselective manner through the respective cycloadditions of diazomethane to the carbonyl group of antipodal cyclopentyl ketones. These epoxy derivatives are potent synthetic building blocks which have been used as versatile precursors to several enantiopure title compounds, these being molecules with a high functional density that bear, at least, four stereogenic centers in the cyclopentane ring and a quaternary stereocenter in the side-chain.

Stereoselective synthesis of new homochiral polyfunctional side-chain cyclopentane derivatives

Abstract A new homochiral polyfunctional cyclopentane derivative, containing an oxirane ring in a side-chain, has been synthesized stereoselectively . This compound is an useful intermediate in the synthesis of products such as hydroxyesters, polyols or aminoalcohols.

A SYNTHETIC APPROACH TO A NOVEL CLASS OF ENANTIOPURE CYCLOPENTYL CARBOCYCLIC NUCLEOSIDES AND RELATED COMPOUNDS

Abstract A synthetic entry to a novel class of cyclopentyl carbocyclic nucleosides and other functional derivatives, in enantiopure form, is presented. As a structural feature of these compounds, the base-moiety is separated from the carbocyclic ring by a C2-chain containing a quaternary stereogenic center and additional chemical functions.