Augusto Rivera

A Novel Manich Type Reaction Using Aminals in Alkaline Medium

Abstract A one-step synthesis of 1,3-bis[2′ -hydroxy-5, - substituted-benzyl] imidazolidines (3a-d) using a mannich type reaction in basic media is described.

Chromenes from Ageratum conyzoides

Abstract-Analysis of the aerial part of Ayeratum conyzoides afforded 11 chromenes, sitosterol, (+)-sesamin and caryophyllene oxide. One chromene is new and eight of the others were obtained for the first time from this species. The ‘C NMR spectral data for four of the chromenes have not been published before. INTRODUCIION Over the last two or three decades, great attention has been focused on the biological activity of natural com- pounds of plant origin for their potential as natural pesticides against phytophagous insects. In Colombia, plants have been used for centuries for their insecticidal. repellent or antifeedant properties in the protection of crops from insect attack [I]. Ageratum conyzoides, a widespread weed in Colombia and elsewhere, known to contain precocene I and precocene II [2,3], has been used both in folk medicine and as an insecticide. A study of the insecticidal activity of various fractions of an n-hexane extract of

Methoxyflavones from Ageratum conyzoides

Abstract Nine methoxyflavones were obtained from aerial parts of Ageratum conyzoides , two of which are new: 5,6,8,3′,4′,5′-hexamethoxyflavone and 8-hydroxy-5,6,7,3′,4′,5′-hexamethoxyflavone.

Sesquiterpene lactones from Salvia palaefolia

Abstract The aerial part of Salvia palaefolia yielded (−)-glechomafuran, 1β,10α;4α,5β-diepoxy-8β-hydroxyglechoman-8α,12-olide and the new eudesmanolides: 1α-acetoxy-8α-hydroxy-2-oxo-eudesman-3,7(11)-dien-8,12-olide and 1α,8α-dihydroxy-2-oxo-eudesman-3,7(11)-dien-8,12-olide. The structure of the former new compound was determined from its spectral data and chemical behaviour and its absolute configuration by CD experiments. The absolute configuration of 1β,10α;4α,5β-diepoxy-8β-hydroxyglechoman-8α,12-olide was established by X-ray diffraction analysis.

Nitrosation of Aminals : Preparation and Characterization of 1,3-Dinitrosoimidazolidine

Abstract Reaction of the polycyclic aminal 1,3,6,8-tetraazatricyclo [4.4.1.1.3,8]dodecane 1 with nitrous acid affords 1,3-dinitrosoimidazolidine 2 as a mixture of three stereoisomers.

AN EFFICIENT APPROACH TO 1,3,5-TRIS-ARYLHEXAHYDRO-1,3,5-TRIAZINES

ABSTRACT In this paper we report a facile and efficient procedure for the synthesis of 1,3,5-tris-arylhexahydro-1,3,5-triazines (3) by reaction of anilines 1 with 1,3,6,8-tetrazatricyclo[4.4.1.1[3], [8a], [8b]- dodecane (TATD) (2). The diequatorial chair conformational preference of 3b (Ar = p-tolyl) in the solid state was established by X-ray crystallography and agrees well with molecular mechanics calculations.

NUCLEOPHILIC SUBSTITUTION AT THE AMINALIC CARBON OF SOME MACROCYCLIC POLYAMINALS

I N T R O D U C T I O N Benzotriazole (1) is a synthetic aid which has become very useful in obtaining several organic compounds due to the properties it confers on its derivatives. Benzotriazole derivatives can be obtained by displacing a halogen in alkyl or acyl halides, a hydroxyl group in alcohols and an alkoxyl group in acetals or ketals. Other important routes involve adding benzotriazole to aldehydes (and their conjugate analogues), to imines, to iminium salts, and to enamines. Katrytzky et al (1,2) reported that benzotriazol derivatives 4a and 5a were obtained by ethane1,2-diamine and propane-1,3-diamine reaction, respectively, with benzotriazole and formaldehyde in water at 20°C. Katritzky et al (3,4) has also reported synthesising l,3-bis(benzotriazol-yl-methyl)-2,3-dihydrobenzilimidazol 6a by reacting benzotriazole with formaldehyde and o-phenylenediamine. However, it is well known (5,6) that diamines, such as ethane-1,2diamine, propane-1,3-diamine and o-phenylenediamine, react easily with formaldehyde in aqueous medium to produce macrocyclic polyaminals l ,3,6,8-tetraazatricyclo[4.4.1.1 ]dodecane 1; 1:3,7:9,13:15,19:21-tetramethyleneperhydropyrimidine 2, and 6 H , I 3 H 5:12,7:14-dimethanedibenzo[d,i] [ l ,3,6,8]tetrazecine 3, respectively.

A new ceramide from Suillus luteus and its cytotoxic activity against human melanoma cells.

A new phytosphingosine‐type ceramide, suillumide (1), was isolated from the EtOH extract of the basidiomycete Suillus luteus (L.) S. F. Gray, along with ten known compounds: ergosta‐4,6,8(14),22‐tetraen‐3‐one, ergosterol, ergosterol peroxide, suillin, (E)‐3,4,5‐trimethoxycinnamic alcohol, 5α,6α‐epoxyergosta‐8,22‐diene‐3β,7β‐diol, (R)‐1‐palmitoylglycerol, ergosta‐7,9(11),22‐triene‐3β,5α,6β‐triol, cerevisterol, and 4‐hydroxybenzoic acid. The structure of 1 was determined on the basis of spectroscopic and mass‐spectrometric analyses, as well as by chemical methods. Compound 1 and its synthetic diacetyl derivative 2 were tested for their cytotoxic activities against the human melanoma cell line SK‐MEL‐1. Both drugs showed IC50 values of ca. 10 μM after 72 h of exposure.

1,3-bis(2'-Hydroxybenzyl)imidazolidines as Novel Precursors of 3,3′-Ethylene-bis(3,4-dihydro-2H-1,3-benzoxazine)

Abstract A one-step synthesis of 3,3′-ethylene-bis(3,4-dihydro-6-substituted-2H-1,3-benzoxazines) (2a-e) from 1,3-bis(2′-hydroxy-5′-substituted-benzyl)imidazolidines (1a-e) and formaldehyde is reported.

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.