Mónica Söllhuber

Flavonoid glycosides from Eugenia jambos.

Two flavonol diglycosides isolated from the leaves of Eugenia jambos were characterized as quercetin and myricetin 3-O-beta-D-xylopyranosyl(1-->2) alpha-L-rhamnopyranosides by means of spectral analyses applying 2D NMR techniques and NOE experiments.

1-Alkyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones as glycine templates. Synthesis of Fiscalin B

Abstract An excess of base allows the regio- and diastereoselective alkylation at C(4) of the glycine templates 1-methyl(isopropyl)-2,4-dihydro-1 H -pyrazino[2,1- b ]quinazoline-3,6-diones 9a and 9b without the need for N (2)-protecting groups. While the alkylation of 9a gave exclusively the 1,4- anti -isomers, the isopropyl derivative 9b required much longer reaction times and occurred with lower diastereoselectivity. Fiscalin B 3 was obtained by alkylation of 9b with N -Boc-3-indolylmethyl bromide followed by indole deprotection.

New findings in the alkylation and N-deprotection of (4S)-4-methyl-2-benzyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones

Abstract Alkyl halides behave differently to benzyl halides in C-1 alkylation of the title compounds. The syn and anti 1,4-disubstituted diastereomers thus obtained show different regioselectivity by further alkylation leading to the 1,4,4- and 1,1,4-trisubstituted compounds, respectively. Alkylation is always directed anti with respect to the bulkier substituent at C-1 or C-4. Debenzylation attempts on 2-benzyl-derivatives 1b by treatment with HCOOH and C/Pd or H 2 /C–Pd/MeOH/H + led to C-1 oxidised or 7,8,9,10-tetrahydro-derivatives. Deprotection of 2- p -methoxybenzyl- and 2-(2,4-dimethoxybenzyl)-derivatives with CAN and with TFA/anisole, respectively, was successful, but in the latter case epimerization at C-1 occurred.

The application of ultrasound to the strecker synthesis on 9,10-dimethoxy-1,3,4,6,7,11b-hexahydrobenzo[a]quinolizin-2-one

Abstract Irradiation with ultrasound in acetic acid solution was found to facilitate the aminocyanation of 9,10-dimethoxy-1,3,4,6,7, 11b-hexahydrobenzo[a] quinolizin-2-one.

Asymmetrically induced alkylation of 2-benzyl-4-isopropyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-dione

Abstract The substitution of the 4-methyl group by a 4-isopropyl group in the 2-benzyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-dione system allows a notable improvement in the stereoselective alkylation at C-1. The configuration of the newly introduced stereogenic centre has been assigned on the basis of 1H NMR data and NOE measurements.

Stereochemical course of acylation and aldol condensation in (4S)-4-methyl-2-benzyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones

Abstract Acylation of 1 leads to the syn derivatives 2 . Traces of the anti isomers equilibrate to the syn isomers when stored in CHCl 3 . Aldol condensation showed great diastereoselectivity, but racemization could not be avoided. The configuration of the new introduced stereogenic centres has been assigned on the basis of 1 H-NMR data and NOE measurements.

A short synthesis of de-‘prenyl’-ardeemin

A four-step synthesis of the ardeemin framework by starting from N-2-aminobenzoyl-α-amino esters is described. In the last step, the acid promoted cyclization of the 1,4-anti-4-alkyl-1-(3-indolylmethyl)-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones occurs irreversible and stereocontrolled.

Synthesis and reactivity of Michael adducts of lithiated 2,5-dimethoxy-N-pivaloylanilines and arylidenemalonates

Abstract Michael addition of lithiated 2,5-dimethoxypivaloylaniline to diisopropyl arylidenmalonates, followed by acid cyclization, affords 5,8-dimethoxy-4-aryl-3,4-dihydro-2(1 H )quinolinones ( 5 ). These compounds are very inert to the 3,4-dehydrogenation, but were easily transformed to 4-aryl-3,4-dihydro-(1 H )quinoline-2,5,8-triones ( 10 ) which, through Diels-Alder heterocyclization, gave 4-aryl-3,4-dihydro-1,8-diazaanthracene-2,9,10-triones ( 16 ).

Isoscutellarein 7-glucosyl(1 → 2)xyloside from sixteen species of Sideritis

A new flavone diglycoside isolated from the aerial parts of Sideritis lutoela was characterized as isoscutellarein 7-O-beta-D-glucopyranosyl(1-->2) beta-D-xylopyranoside by means of spectral analyses, applying 2D NMR techniques and NOE experiments. Its presence in 15 other species of Sideritis is described.

Reactivity as glycine templates of 1,2-dialkyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones

The 1-methyl(iso-propyl)-2-benzyl-2,4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-diones 8 and 9 could be regio- and diastereoselectively alkylated at C(4) with retention of configuration at both stereocentres.