Volume 18, Issue 2

A novel 6/12-membered bicyclic taxane with a 13,17-ether bridge, named canataxpyran A, was isolated from the needles of Taxus canadensis . The structures were characterized as 7β,9,10β,20-tetracetoxy-13β,17-epoxy-3,8-secotaxa-3 E ,8 E ,11-triene-2α,5α-diol (designated as canataxpyran A, 1 ). This bicyclic taxane gradually decomposed in CDCl 3 to give the corresponding enones, 10β,20-diacetoxy-13β,17-epoxy-4α,5α-dihydroxy-3,8-secotaxa-2 E ,7 E ,11-trien-9-one (canataxpyran B, 2 ) and 5α,10β,20-triacetoxy-13β,17-epoxy-4α-hydroxy- 3,8-secotaxa-2 E ,7 E ,11-trien-9-one (canataxpyran C, 3 ). Compound 1 is the first example of a natural 3,8-secotaxane with 13,17-oxygen bridge.

The efficient total synthesis of (±) solenopsin A ( 9 ) was achieved in a series of eight steps starting from readily available N -Bn- N -Boc alanine derivative 1 .

A facile method for the synthesis of benzo[ f ]chromene derivatives is reported. The procedure involves a novel three-component reaction of 1-naphthol or 2-naphthol, acetophenone derivatives and triethyl orthobenzoate in the presence of silica supported ionic liquid [pmim]HSO 4 SiO2 [silica supported 1-methyl-3-(triethoxysilylpropyl)imidazolium hydrogensulfate] as an efficient catalyst.

New derivatives of substituted saturated γ-lactones were synthesized from 2-(2,2-dimethyl-5-oxotetrahydrofuran-3-yl)acetyl chloride. All new compounds were characterized by NMR and IR and elemental analysis.

Kinetic data for the reaction of dimethyldioxirane ( 1 ) with a series of acyclic, aliphatic conjugated dienes 2a–f are reported. Monoepoxidation is the preferred process and the monoepoxides are formed in high yield as long as the dienes are in excess. The results show that epoxidation of the dienes is less sensitive to structural effects than that for simple alkenes. Furthermore, these monoepoxidations show little sensitivity to cis / trans substitution in marked contrast to those of simple aliphatic alkenes. The relative reactivities were modeled using a density function approach. Consistent with previous calculations on alkene systems, a concerted process with a spiro transition state was obtained for diene epoxidation regardless of the initial orientation of the reactants. The relative reactivities for monoepoxidation of 2c–e were calculated based on the weighted average of the calculated differences between E calc for reaction of the s - cis and s - trans conformer of each diene with 1 . The predicted relative reactivities were in reasonable agreement with those from the kinetic data.

Covalently linked pyrrole (Py)- and imidazole (Im)-containing H-pin polyamides bind in the minor groove of specific DNA sequences with high affinity. The synthesis of 1,2,3-triazole-linked and heterodimeric H-pin polyamides 13a , b formed from the Huisgen reaction of an alkyne-containing f-PyPyPy ( 6 ) with an azide-containing f-ImPyIm ( 7 ) is reported. The reaction proceeded smoothly under thermal conditions to give an inseparable mixture of 1,4- and 1,5-isomers ( 13a and 13b , respectively) by column chromatography. When the reaction was conducted under ‘click’ or Cu(I)-catalyzed conditions or in the presence of the cognate DNA sequence, no desired product was observed. Preliminary results from DNA thermal denaturation and circular dichroism titration studies provided evidence of mixture 13a , b binding to the target DNA sequence 5′-TCTCAA-3′.

A three-component reaction among 2-alkynylquinoline-3-carbaldehydes, primary amines, and chloroform leading to novel 1-(trichloromethyl)-1,2-dihydrobenzo[ b ][1,6]naphthyridines was developed using microwave initiation in an absence of any catalysts. This method provides a facile approach to the title compounds with moderate to higher yields.

A novel ionic liquid with multi-SO 3 H groups has been found to be an efficient acid catalyst for the one-pot three-component synthesis of fused 3,4-dihydropyrimidin-2(1 H )-ones and thiones under solvent free conditions. Good yields, short reaction times, straight forward workup, reusability of the catalyst and green conditions are the most obvious advantages of this methodology.

An efficient procedure for the synthesis of 2-(3,5-diaryl-4,5-dihydropyrazol-1-yl)-1,3,4-thiadiazoles via one-pot three-component condensation of 1-(1,3,4-thiadiazol-2-yl)hydrazines, acetophenones, and aromatic aldehydes is described. This protocol has advantages of mild conditions, high yield, and simple workup procedure.

Base- and acid-mediated heterocyclization of 2-(3-alkyl-4-methyl-2-thioxo-2,3-dihydro-thiazole-5-carbonyl)-hydrazinecarbodithioic acid potassium salts 3 , 4 yielded the corresponding 3 H -[1,3,4]thiadiazole(oxadiazole)-2-thiones 5 – 8 . The reaction of these products with alkyl halides gave S -substituted derivatives 9 – 12 . Treatment of oxadiazoles 7 , 8 with secondary amines furnished a mixture of cyclic and acyclic derivatives 13 – 16 . The preliminary biological assay showed that the synthesized compounds could be of interest as growth stimulants.

No abstract available.