Improved Procedure for the Preparation of cis‐2,4‐Dimethylglutaranhydride

Addition of 2.5 mol% DBU to a mixture of isomeric 2,4‐dimethylglutaric anhydrides in ethyl acetate promotes crystallization‐induced transformation, affording the pure cis‐2,4‐dimethylglutaric anhydride in 87% yield.     

Regio- and stereoselectivity of polar [2+3] cycloaddition reactions between (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone and selected (E)-2-substituted nitroethenes

[2+3] Cycloaddition reactions of the highly reactive (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone with (E)-2-R-nitroethenes proceed under mild conditions and yield mixtures of stereoisomeric 2-methyl-3-(3,4,5-trimethoxyphenyl)-4-nitro-5-R-isoxazolidines. The effect of regiospecificity of the cycloadditions may be accounted for by the theory of electrophilicity indexes. Stereoselectivity, however, is determined by a compilation of steric and secondary orbital effects.      

Enantioselective Synthesis of D-erythro-Sphingosine and of Ceramide

The enynol 2 was transformed into D -erythro-sphingosine 11 (7 steps, 46%) and into ceramide 1 (8 steps, 41% overall yield). The key steps were the mono-epoxidation of the enynol 5 (Ti(t-BuO)₄, (?)-D -diethyl tartrate, t-BuOOH) to 6 (86%, ≥ 98% ee), the regioselective intramolecular opening of the oxirane 6 via the benzylurethane 7 , and the reductive tranformation of the acetylene 9 into the oxazolidinone 10 (Li, EtNH₂, 88%).     

Synthesis, biological evaluation, and modeling of a C,D-seco-taxoid

A C,D-seco-paclitaxel derivative 12 was prepared and tested for biological activity. The key step in the synthesis was a free radical fragmentation of the bicyclic tertiary alcohol 7 under the conditions of the hypobromite reaction. The compound 12 showed no activity in the tubulin test.     

Does a fluorinated Lewis acid catalyst change the molecular mechanism of the decomposition process of nitroethyl carboxylates?

The molecular mechanism of the decomposition reaction of nitroethyl benzoates catalyzed by Lewis acids based on boron element—BH₃ and BF₃—was studied using density functional theory methods. These reactions take place much faster than the uncatalyzed process. However, the presence of fluorinated Lewis acids has a unique influence on the molecular mechanism. In the case of BF₃, a change from a one-step mechanism to a two-step one involving a zwitterionic intermediate is observed.     

ANALYSIS OF MULTIPLE PHOTORECEPTOR PIGMENTS FOR PHOTOTROPISM IN A MUTANT OF Arabidopsis thaliana

Abstract
The shape of the fluence-response relationship for the phototropic response of the JK224 strain of Arabidopsis thaliana depends on the fluence rate and wavelength of the actinic light. At low fluence rate (0.1 μmol m^-2s^-1), the response to 450-nm light is characterized by a single maximum at about 9 μmol m^-2. At higher fluence rate (0.4 μmol m^-2s^-1), the response shows two maxima, at 4.5 and 9 μmol m^-2. The response to 510-nm light shows a single maximum at 4.5 μmol m^-2. Unilateral preirradiation with high fluence rate (25 μmol m^-2s^-1) 510-nm light eliminates the maximum at 4.5 μmol m^-2 in the fluence response curve to a subsequent unilateral 450-nm irradiation, while the second maximum at 9 μmol m^-2 is unaffected. Based on these results, it is concluded that a single photoreceptor pigment has been altered in the JK224 strain of Arabidopsis thaliana.