20-ISO-20-Deethylaspidospermidine

The two-step process of hydrogenation of l-alkyl-3-acylpyridinium salts and cyclization of the resultant 1, 4, 5, 6-tetrahydropyridines has been the foundation of a general scheme of alkaloid synthesis.¹ Its application in the indole alkaloid field has yielded ready access to tetrahydro-β-carboline systems, e.g. 1a → 2 → eburnamonine.² Since acid treatment of N_b -acyl derivatives of substances related to la has been shown to lead to products of indole β-cyclization³, it became of interest to test the cyclization behavior of the vinylogous imide lb, prepared by the dicyclohexylcarbodiimide-induced acylation of 3-acetyl-1, 4, 5, 6-tetrahydropyridine⁴ with indoleacetic acid. Treatment of lb with boron trifluoride gave a 62 yield of ketolactam 3a. Thus a two-step entry into the pentacyclic Aspidosperma alkaloid skeleton is on hand.     

B20N20团簇的结构与稳定性

B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of ten B20N20 clusters. It was found that two new proposed isomers with two octagons, twelve hexagons, eight squares in Cab and C2 symmetry were more stable than the isomer with sixteen hexagons and six squares in C2 symmetry which was previously deemed to the most stable by 79.5 and 13.8 kJ/mol respectively. The isomer with two decagons in S10 symmetry is much higher in energy than the most stable structure in C4h symmetry by 637.2 kJ/mol.     

Crystalline transition behaviors of nylons 12 20 and 10 20

The crystalline transition behaviors under different crystalline conditions of newly synthesized long alkane nylon 12 20 and nylon 10 20 are studied by wide-angle X-ray diffraction (WAXD) and real time Fourier transform infrared spectroscopy (FT-IR). The results show that their crystalline transition behaviors under WAXD were, to a large extend, related to the condition under which the crystals were prepared. The dilute solution-grown lamellar crystals of nylons 12 20 and 10 20 did not show distinct Brill transition behaviors before melting. Unlike the lamellar crystals of many other even-even nylons which display two crystal signals until melting temperature (T_M), they presented a broad amorphous-like signal when the temperature increased to around 10 °C below T_M. However, the post-annealing samples of nylons 12 20 and 10 20 displayed Brill transition at 155 and 157 °C, respectively, and the solution casting samples of nylons 12 20 and 10 20 at 110 and 135 °C, respectively. Furthermore, the IR spectra of nylons 12 20 and 10 20 displayed an interesting phenomenon: the intensity of the peak at 942 cm⁻¹ declined on heating and finally disappeared around Brill temperature (T_B), instead of T_M as is in usual nylons. This suggests that the long alkane segments, introduced by 18-octadecanedicarboxylic acid, may undergo a local melting at T_B.     

Total synthesis of 20-hydroxy- and 20-carboxy-leukotrienes B4

The total synthesis of 20-hydroxy- and 20-carboxy-leukotrienes B₄ (1 and 2) from key intermediates 13, 14 and 15 is described.     

Synthesis of 20-deoxoluteone

20-Deoxoluteone has been synthesized from sclareol. Sclareol was brominated with phosphorus tribromide to form a mixture of primary allyl bromides, from which, by the malonic synthesis, a mixture of bicyclogeranylgeranylacetic acids was obtained which was cyclized with fluorosulfonic acid to form a mixture of two diastereomeric -lactones. The predominating lactone was converted by successive reduction with lithium tetrahydroaluminate, oxidation with oxalyl chloride in dimethyl sulfoxide, reaction with methylmagnesium iodide, and oxidation by the chromium trioxide/pyridine complex into 20-deoxyluteone.Institute of Chemistry, Moldavian SSR Academy of Science, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 346–353, May–June, 1990.     

Synthesis of 20-deoxoluteone

20-Deoxoluteone has been synthesized from sclareol. Sclareol was brominated with phosphorus tribromide to form a mixture of primary allyl bromides, from which, by the malonic synthesis, a mixture of bicyclogeranylgeranylacetic acids was obtained which was cyclized with fluorosulfonic acid to form a mixture of two diastereomeric δ-lactones. The predominating lactone was converted by successive reduction with lithium tetrahydroaluminate, oxidation with oxalyl chloride in dimethyl sulfoxide, reaction with methylmagnesium iodide, and oxidation by the chromium trioxide/pyridine complex into 20-deoxyluteone. Institute of Chemistry, Moldavian SSR Academy of Science, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 346–353, May–June, 1990.     

First Example of Trifluoromethylation in the Ecdysteroid Series. Synthesis of (20RS)-20-O-Hydro-20-trifluoromethylpoststerone

The title compound was synthesized by trifluoromethylation of poststerone derivatives with trimethyl(trifluoromethyl)silane in the presence of tetrabutylammonium fluoride.     

Circular dichroism and stereochemistry of the C-20 and C-22 asymmetric centers of 17-isoxazolinyl- and 20-hydroxy-20-isoxazolinylsteroids

The CD spectra of a number stereoisomeric isoxazolinylsteroids have been investigated. Starting from established rules, it has been shown that this method can be used to determine the configurations of the C-20 and C-22 centers of the 17- and 20-isoxazolinylsteroids studied.     

Circular dichroism and stereochemistry of the C-20 and C-22 asymmetric centers of 17-isoxazolinyl- and 20-hydroxy-20-isoxazolinylsteroids

The CD spectra of a number stereoisomeric isoxazolinylsteroids have been investigated. Starting from established rules, it has been shown that this method can be used to determine the configurations of the C-20 and C-22 centers of the 17- and 20-isoxazolinylsteroids studied.The numbering of the atoms of the isoxazoline ring corresponds to the numbering of the side-chain of cholesterol.Institute of Bioorganic Chemistry, Belarus Academy of Sciences, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 391–397, May–June, 1994.