Lyngbyacyclamides A and B, novel cytotoxic peptides from marine cyanobacteria Lyngbya sp.

Lyngbyacyclamides A (1) and B (2), novel cyclic peptides, were isolated from marine cyanobacteria Lyngbya sp. collected in Okinawa, Japan. Their structures were determined by spectroscopic analyses and degradation studies. They moderately inhibited the growth of B16 mouse melanoma cells.     

Theoretical study of TBD-catalyzed carboxylation of propylene glycol with CO2

The mechanisms for the reaction of propylene glycol (PG) with CO₂ catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were theoretically investigated by density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. Through analyzing the optimized structures and energy profiles along the reaction paths, the PG-activated route was identified as the most probable reaction path, in which the rate-determining step was the nucleophilic attack of one of the O atoms in CO₂ on the hydroxyl linked C atom in PG with energy barrier 56.96 kcal/mol. The catalytic role of TBD could be considered as a proton bridge activated by the synergistic action of its N atoms.     

C2-symmetric bicyclo[3.3.1]nonadiene as a chiral ligand for rhodium-catalyzed asymmetric arylation of N-(4-nitrobenzenesulfonyl)arylimines

[Reaction: see text] Asymmetric synthesis of diarylmethylamines with high enantioselectivity (95-99% ee) was realized by use of a new C2-symmetric diene ligand, (1R,5R)-2,6-diphenylbicyclo[3.3.1]nona-2,6-diene (Ph-bnd), for the rhodium-catalyzed asymmetric arylation of N-(4-nitrobenzenesulfonyl)arylimines with arylboroxines.     

Stereoselective total synthesis of the proposed structure of 2-epibotcinolide

[Structure: see text] The total synthesis of pseudo 2-epibotcinolide (1b) through several featured synthetic approaches has been attained. First, the chiral linear precursors of the nine-membered ring compound is stereoselectively constructed by the asymmetric aldol reaction for producing beta-hydroxy ester units. Second, the key cyclization reaction to form the nine-membered lactone moiety is efficiently achieved by the extremely facile and powerful mixed-anhydride method promoted by 2-methyl-6-nitrobenzoic anhydride (MNBA) with basic promoters.     

Access to Indole-Fused Benzannulated Medium-Sized Rings through a Gold(I)-Catalyzed Cascade Cyclization of Azido-Alkynes

Because benzannulated and indole-fused medium-sized rings are found in many bioactive compounds, combining these fragments might lead to unexplored areas of biologically relevant and uncovered chemical space. Herein is shown that α-imino gold carbene chemistry can play an important role in solving the difficulty in the formation of medium-sized rings. Namely, phenylene-tethered azido-alkynes undergo arylative cyclization through the formation of a gold carbene intermediate to afford benzannulated indole-fused medium-sized tetracycles. The reactions allow a range of different aryl substitution patterns and efficient access to these otherwise difficult-to-obtain medium-sized rings. This study also demonstrates the feasibility of the semihollow-shaped C-dtbm ligand for the construction of a nine-membered ring.     

Isomerization polymerization of 2-vinyl-1,3-dioxolane by α,α′-azobisisobutyronitrile or by γ-ray irradiation

2-Vinyl-1,3-dioxolane was polymerized by use of α,α′-azobisisobutyronitrile (AIBN) or by γ-ray irradiation. The polymer obtained was white amorphous powder which melted at ca. 70°C. and was soluble in chloroform, acetone, and p-dioxane. The infrared spectrum of the polymer indicated peaks at 1735 cm.^?1 characteristic of the carbonyl group, and at 1200–1000 cm.^?1 characteristic of the acetal group, while no absorption at 990 and 3100 cm.^?1 due to the vinyl group was observed. The spectra of the polymers obtained by AIBN and by γ-ray irradiation were essentially identical. The saponified product of the polymer was white powder and its reduced viscosity was a little larger than that of the original polymer. These results indicate that the polymer has no ester unit in the main chain. The results of gas chromatographic analysis of the saponified product of the polymer, indicate the presence of a small amount of ethyl alcohol. The results of the saponification showed that the ester content in the polymer varied from 7 to 25% depending upon the polymerization temperature. These results indicate that 2-vinyl-1,3-dioxolane polymerized by AIBN or by γ-irradiation with two modes of vinyl and hydrogen migration, yielding a copolymer having the unit structures      

Living polymerization of propylene and 1-hexene using bis-Cp type metallocene catalysts

To check the possibility of living polymerization with a biscyclopentadienyl metallocene, propylene polymerization was conducted by Cp₂ZrMe₂ at –78°C or Cp₂HfMe₂ at –50°C using B(C₆F₅)₃ and AlOct₃ as a cocatalyst. The polymer yield increased linearly with polymerization time. The polypropylene obtained showed narrow molecular weight distribution (M_w/M_n 1.04–1.15). In addition, the number-average molecular weight increased in proportion to the polymerization time. It was, thus, found that living polymerization of propylene proceeds with the catalyst systems at a very low temperature. Isospecific living polymerization of 1-hexene also proceeded with the rac-(et)Ind₂ZrMe₂ catalyst at –78°C.