Rodolfo Quevedo

Efficient tetrahydrosalen synthesis from mannich-type bases

Abstract Synthesizing a variety of tetrahydrosalens from hydrolyzing 1,3‐bis(2′‐hydroxy‐5′‐substituted‐benzyl)imidazolidines with hydrochloric acid is described. Further reaction of such tetrahydrosalens with aldehydes yielded 2‐substituted‐1,3‐bis(2′‐hydroxy‐5′‐substituted‐benzyl)imidazolidines.

Role of hydroxyl groups on the aromatic ring in the reactivity and selectivity of the reaction of β-phenylethylamines with non-enolizable aldehydes

The influence of hydroxyl groups on the β-phenylethylamine aromatic ring was studied during its reaction with non-enolizable aldehydes. Computational calculations established that the degree of hydroxylation generates differences in the activation patterns of the ring (different reaction pathways) and in the nucleophilicity of the nitrogen atoms (different reaction yields). Cyclic aminals, benzoxazinephanes, or tetrahydroisoquinolines were obtained in the reaction with formaldehyde, and Schiff’s bases or tetrahydroisoquinolines were produced in the reaction with other non-enolizable aldehydes. The product obtained depends on the degree of hydroxylation of the ring of the starting phenylethylamine.

A rare head–head binding pattern in bisbenzylisoquinoline alkaloids

Bioassay-guided fractionation of Berberis tabiensis against Culex quinquefasciatus third instar larvae afforded a new bisbenzyltetrahydroisoquinoline alkaloid having an unusual head–head binding pattern. This new alkaloid (tabienine B) is the first member of this family found to possess a diphenyl ether bridge in C-6 and C-7′.

1-Phenylisoquinoline larvicidal activity against Culex quinquefasciatus

The larvicidal potential of several dopamine 1-phenylisoquinoline derivatives against Culex quinquefasciatus third instar larvae was investigated in a rational search for insecticides. The results showed that these isoquinolines presented moderate larvicidal activity, that the presence of a substituent is needed on carbon 1 for such activity to be presented and that it may be possible to develop novel insecticidal compounds having potential use in controlling insects by appropriate structural modification of 1-phenylisoquinolines. This article presents a possible structure–larvicidal activity relationship for isoquinolinic compounds.

Heterogeneous Catalysts in Pictet-Spengler-Type Reactions

Several solid catalysts were evaluated as an alternative for 1,2,3,4-tetrahydroisoquinoline synthesis by means of the Pictet-Spengler reaction. The reaction catalysed by a mixed oxide (Mg and Al) led to the best yield and good regioselectivity; using an Al-pillared bentonite led to good yields and total regioselectivity. The results revealed no direct relationship between catalyst acidity and yield.

Larvicidal activity of single and macrocyclic tyrosine derivatives against three important vector mosquitoes

The larvicidal activity of several phenylethylamines derived from l-tyrosine against larvae of the mosquito species Anopheles albimanus, Aedes aegypti, and Culex quinquefasciatus was studied. The results showed that the phenylethylamine nucleus present in different organic compounds with larvicidal activity has moderate larvicidal activity in itself, that the phenolic hydroxyl group is not decisive in larvicidal activity, that macrocyclic amino acids have activity comparable to or less than that observed for simple phenylethylamines, that the hydrocarbon chain on the carboxyl group affects the larvicidal activity, and that intermolecular interactions are crucial to the larvicidal activity of phenylethylamines, which is a new aspect to consider in the design of alternative, environmentally friendly insecticides for vector control with importance for public health. This paper presents a possible structure–larvicidal activity relationship for phenylethylamines with potential to guide the rational search for new nitrogen compounds useful for control of diseases borne by mosquito vectors.

l-Tyrosine isopropyl ester

The title compound, C12H17NO3, adopts a folded conformation with a C—C(NH2)—C(=O)—O torsion angle of −95.9 (2)°. In the crystal, molecules are linked by an O—H⋯N hydrogen bond, forming helical chains along the b-axis direction. Weak N—H⋯O and C—H⋯O hydrogen bonds are observed between the chains.

1H-NMR spectroscopic and thermogravimetric research regarding alcohol interaction with tyrosine-derived azacyclophanes

This article describes the spectroscopic (1H-NMR) and thermogravimetric analysis of tyrosine-derived azacyclophanes. The results showed that these macrocycles could retain alcohol molecules through interactions involving hydrogen bonds between an alcohol and macrocycle heteroatoms and that alcohol release temperature depended on the structure of the macrocycle.

CONTRIBUCION AL ESTUDIO QUÍMICO Y DE BIOACTIVIDAD DE DOS ESPECIES NATIVAS : (Croton bogotanus.Cuatr. y Croton funckianus.Cuatr.) EUPHORBIACEAE

The ethanolic extracts from stay-green and senescent leaves of Croton bogotanus and Croton funckianus (Euphorbiaceae) were tested by brine shrimp toxicity assay and Culex quinquefasciatus larvicide bioassay. The extract from C. funckianus senescent leaves showed a significant activity. The preliminary chemical study provide evidence for the existence of flavonoids and diterpenic derivatives as major constituents of the active fraction.