Eszter Baitz-Gács

Absolute configuration and total synthesis of (−)-cabenegrin A-I

Abstract The total synthesis of (−)-cabenegrin A-I [(−)- 1 ] in five steps was achieved from (−)-6a R ,11a R -maackiain [(−)- 5 ], which in turn was prepared by the optical resolution of racemic (±)- 5 using S -(−)- α -methylbenzyl isocyanate as the the chiral auxiliary. The homochirality of (−)-maackiain [(−)- 5 ] and (−)-cabenegrin A-I [(−)- 1 ] was proved by CD measurements. Synthesis of (±)-maackiain [(±)- 5 ] is also presented, starting from the readily available phenol derivatives resorcinol and sesamol, which demonstrates the synthetic utility of the Heck-type oxyarylation process for obtaining pterocarpane derivatives on a multigram scale. A new ring-opening reaction of pterocarpanes (7 → 28) is described.

Kinetic resolution of 2-acylated-1,2-diols by lipase-catalyzed enantiomer selective acylation

Abstract Enantiomer selectivity of lipase catalyzed acylation of 2-acylated 1,2-diols was studied. First, acylation of 2-acetoxyheptan-1-ol rac-3b with vinyl acetate was investigated by varying the enzyme and the solvent, showing the highest enantiomer selectivity by using lipase from Pseudomonas fluorescens (PfL) in hexane-vinyl acetate (VA). We have found varying or even reversed enantiomer selectivity for different secondary acyl moieties in 2-acyloxyheptan-1-ols rac-3bA-F. Next, all six possible types of enantiomer selective biotransformations (hydrolysis of diacetate and the two kinds of monoacetetes; acylation of diol and the two kinds of monoacetates) were compared on two model diols rac-4b,d. Among the transformations investigated, acetylation of secondary monoacetates rac-3b,d showed the highest enantiomer selectivity. Finally, PfL catalyzed acetylations of several 2-acetylated 1,2-diols rac-3a-g were investigated under our optimum conditions.

Synthesis of vinca alkaloids and related compounds—XVI: New route to the stereoselective synthesis of (+)-vincamine, (-)-vincamone and (+)-apovincaminic acid esters

Abstract A stereoselective method has been elaborated for the synthesis of oxime esters, (-)-4a, b, from which, as common intermediates, (+)-apovincaminic acid esters (3a,b), (+)-vincamine (1) and (-)-vincamone (2) can be prepared.

Antifungal Flavonoids from Ballota glandulosissima

Abstract The flavonoids kumatakenin (1), pachypodol (2), 5-hydroxy-7,3′,4′-trimethoxyflavone (3), velutin (4), salvigenin (5), retusin (6) and corymbosin (7) have been isolated from the aerial parts of Ballota glandulosissima Hub.-Mor & Patzak. Among them, 2–4 and 7 have not been reported previously in the genus Ballota. The antibacterial and antifungal activities of 1–4 and 6 were tested against Bacillus subtilis, Staphylococcus aureus, Staphylococcus faecalis, Echerichia coli, Pseudomonas aeruginosa, Candida albicans, Candida krusei and Candida galabrata.

Antifungal Diterpenoids and Flavonoids from Ballota inaequidens

ABSTRACT Two diterpenoids (hispanolone 1, ballonigrine 2) and six flavonoids (5-hydroxy-3,7,4′-trimethoxyflavone 3, retusin 4, 5-hydroxy-7,4′-dimethoxyflavone 5, pachypodol 6, 5-hydroxy-3,6,7,4′-tetramethoxyflavone 7, 5-hydroxy-7,3′,4′-trimethoxyflavone 8) have been isolated from the aerial parts of Ballota inaequidens. Hub.-Mor. & Patzak. Among them, 7 has not been reported previously in the genus Ballota.. The antibacterial and antifungal activities of 1–4, 6, and 8 were tested against Bacillus subtilis., Staphylococcus aureus., Escherichia coli., Pseudomonas aeruginosa., Candida albicans., and Candida crusei..

Synthetic studies towards (−)-carba-3′-deoxy-3′-fluorothymidine.

Abstract Stereospecific synthesis of (−)-carba-3′-deoxy-3′-fluorothymidine (−)- 11 is reported from the protected (−)-carbocyclic 3′-epi-thymidine (−)- 7 using diethylaminosulfur trifluoride. Under the conditions used, extensive dehydration of the blocked precursor into 10 and formation of the 4′-fluoro analogue ( 9 ) were also observed. An attempted simplification of our methodology based on (+)-(1R, 5S)-2-oxabicyclo[3.3.0]oct-6-en-3-one failed, but a novel cyclopentane ( 2 ) ring expansion to tetrahydropyran ( 18 ) was discovered.

Synthesis of vinca alkaloids and related compounds XLII: Transformation of vincamone into vincamines via diazomethane assisted homologization. application of 1h-noe measurements for the configurational as

Abstract The α-oxo-acids 4 and 5 derived from vincamone ( 1 ) were transformed into vicamines 2 , 8 , 10 ,respectively by methylene insertion with diazomethane. Homologisation of 3 and 6 dioxo compounds led to oxirane derivatives 8 , 16 , 11 , 13 , 13 , 18 , respectively. Configuration of the oxiranes was determined by 1H-NOE measurements.

Oxidation of vanillins with thallium(III) nitrate. An exercise in NMR spectroscopy and photochemistry

Abstract Oxidation of isovanillin, vanillin and o -vanillin with TI(NO 3 ) 3 in MeOH gave the dimethyl acetals of 6,6-dimethoxy-2,4-cyclohexadien-1-one aldehydes ( 4–6 which dimerized spontaneously to give a single product each ( 7–9 ) the structure of which was elucidated by 1 H and 13 C NMR, photocyclization to the cage compounds 12–14 and of 7 and 9 by X-ray diffraction as well.

Prins reaction of 2-oxabicyclo[3.3.0]oct-6-en-3-one and related derivatives

Abstract Reaction of formaldehyde with the title olefinic lactone in acetic acid affords diacetate of 1,3-diol ( 2a ) as the main product in 50 – 60% yield via regioselective trans-addition. Less favourable results were obtained with related bicyclic derivatives.

Synthesis and circular dichroism of steroids with 2,3-dihydro-1-benzofuran and 4H-benzopyran chromophores; revision of the absolute configuration of some norneolignans from Krameria cystisoides

Starting from cholesterol the 2,3-dihydrobenzo[b]furans 12a, 12b, and the 4H-benzopyran derivative 14 with known absolute conformation were synthesized by a stereocontrolled sequence. The same helicity rule was found to be valid for both chromophores; the P/M helicity of the heteroring leads to a negative/positive CD within the α-band. On the basis of this rule the absolute configuration of norneolignans 24–26 isolated from Krameria cystisoides was also revised.