Critical condition of inner cylinder radius for sustaining rotating detonation waves in rotating detonation engine thruster

We describe the critical condition necessary for the inner cylinder radius of a rotating detonation engine (RDE) used for in-space rocket propulsion to sustain adequate thruster performance. Using gaseous C₂H₄ and O₂ as the propellant, we measured thrust and impulse of the RDE experimentally, varying in the inner cylinder radius r_i from 31 mm (typical annular configuration) to 0 (no-inner-cylinder configuration), while keeping the outer cylinder radius (r_o = 39 mm) and propellant injector position (r_inj = 35 mm) constant. In the experiments, we also performed high-speed imaging of self-luminescence in the combustion chamber and engine plume. In the case of relatively large inner cylinder radii (r_i = 23 and 31 mm), rotating detonation waves in the combustion chamber attached to the inner cylinder surface, whereas for relatively small inner cylinder radii (r_i = 0, 9, and 15 mm), rotating detonation waves were observed to detach from the inner cylinder surface. In these small inner radii cases, strong chemical luminescence was observed in the plume, probably due to the existence of soot. On the other hand, for cases where r_i = 15, 23, and 31 mm, the specific impulses were greater than 80% of the ideal value at correct expansion. Meanwhile, for cases r_i = 0 and 9 mm, the specific impulses were below 80% of the ideal expansion value. This was considered to be due to the imperfect detonation combustion (deflagration combustion) observed in small inner cylinder radius cases. Our results suggest that in our experimental conditions, r_i = 15 mm was close to the critical condition for sustaining rotating detonation in a suitable state for efficient thrust generation. This condition in the inner cylinder radius corresponds to a condition in the reduced unburned layer height of 4.5–6.5.     

"Click peptide" based on the "o-acyl isopeptide method": control of A beta1-42 production from a photo-triggered A beta1-42 analogue

A clear understanding of the dynamic events of amyloid beta peptide (Abeta) 1-42, such as the folding, self-assembly, and aggregation processes, would be of great significance in Alzheimer's disease (AD) research. However, elucidation of these Abeta1-42 dynamic events is a difficult issue due to uncontrolled polymerization, which also poses a significant obstacle for establishing an experimental system that clarifies the pathological function of Abeta1-42. On the basis of the O-acyl isopeptide method, we herein developed a novel photo-triggered "click peptide" of Abeta1-42, for example, 26-N-Nvoc-26-AIAbeta42, in which the photocleavable 6-nitroveratryloxycarbonyl (Nvoc) group was introduced at the alpha-amino group of Ser26 in 26-O-acyl isoAbeta1-42 (26-AIAbeta42). From the results, (1) the click peptide did not exhibit the self-assembling nature under physiological conditions due to one single modified ester; (2) photoirradiation of the click peptide and subsequent O-N intramolecular acyl migration afforded the intact Abeta1-42 with a quick and one-way conversion reaction (so-called "click"), while the click peptide was stable under nonphotolytic or storage conditions. In addition, it is advantageous that no additional fibril inhibitory auxiliaries were released during conversion to Abeta1-42. This method provides a novel system useful for investigating the dynamic biological functions of Abeta1-42 in AD by inducible activation of Abeta1-42 self-assembly.     

Poly-oxygenated tricyclobutabenzenes via repeated [2 + 2] cycloaddition of benzyne and ketene silyl acetal

Described herein is a synthesis of highly functionalized tricyclobutabenzenes, a class of molecules of structural and theoretical interest. The preparation is based on the repeated [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where two types of regioselectivity enable discrimination of the functionalities on the four-membered rings. By these steps, we were able to prepare poly-oxygenated octamethoxytricyclobutabenzene and its hydrolyzed tetra-oxo derivatives. Structural study on the latter compound showed the interesting properties related to the strained four-membered ring.     

Total synthesis of ciguatoxin and 51-hydroxyCTX3C

Ciguatoxins, the principal causative toxins of ciguatera seafood poisoning, are large ladder-like polycyclic ethers with the 13 ether rings ranging from five- to nine-membered. In this paper, we describe the total synthesis of the two most toxic members of the ciguatoxin family, ciguatoxin 1 and 51-hydroxyCTX3C 2, based on a unified synthetic strategy. The key features in our syntheses were (i) direct construction of the O,S-acetal from the corresponding left and right wing fragments (3, 4, 14); (ii) stereo- and chemoselective radical reaction of the alpha-oxyradical with pentafluorophenyl acrylate to achieve cyclization of the seven-membered G-ring; (iii) ring-closing metathesis reaction to build the nine-membered F-ring; and (iv) an efficient protective group strategy using the oxidatively removable 2-naphthylmethyl groups.     

Regio- and stereoselective nickel-catalyzed homoallylation of aldehydes with 1,3-dienes

Ni(acac)(2) catalyzes homoallylation of aldehydes with 1,3-dienes in the presence of triethylborane. Triethylborane serves as a reducing agent delivering a formal hydride to the C2 position of 1,3-dienes, thus generating a formal homoallyl anion species and enabling the novel homoallylation of aldehydes. The reaction proceeds smoothly at room temperature in the absence of any phosphane or nitrogen ligands and is highly regioselective and stereoselective for a wide variety combination of aldehydes and 1,3-dienes: e.g., isoprene and benzaldehyde combine to give a mixture of anti- and syn-1-phenyl-3-methyl-4-penten-1-ol (2.2) in a ratio of 15:1 in 90% yield. Under the conditions, sterically congested aliphatic aldehydes and ketones show low yields. In such cases, diethylzinc serves as a substitute for triethylborane and yields the expected products in good yields with similarly high regio- and stereoselectivity. 1,3-Cyclohexadiene is one exception among 24 kinds of dienes examined and undergoes allylation (not homoallylation) selectively.     

Catalytic four-component assembly based on allenylboronate platform: new access to privileged allylic amine structures

We developed a novel palladium-catalyzed four-component assembly based on allenylboronate platform, by which privileged allylic amine structures can be constructed in a regioselective, stereoselective, and diversity-oriented manner. The boryl group acts not only as a useful group that can be transformed to various functional groups afterward but also as a stereochemical controller in the generation of key (pi-allyl)palladium intermediates. A short synthesis of rolipram (selective phosphodiesterase-4 inhibitor) is also demonstrated.     

Antiproliferative constituents from umbelliferae plants. IX. New triterpenoid glycosides from the fruits of Bupleurum rotundifolium

The MeOH extract of the fruits of Bupleurum rotundifolium showed inhibitory activity against human gastric adenocarcinoma (MK-1) cell growth. Bioactivity-guided fractionation of the MeOH extract led to the isolation of four new triglycosides of 13beta,28-epoxy oleanane-type triterpenes, named rotundiosides O, Q, S and T; 12 new glycosides of oleanane-type triterpenes, named rotundiosides J-N, P, R, U-Y, and others; echinocystic acid 3-O-sulfate; and three known oleanane-type triterpene glycosides, rotundiosides A, F and G. The structures of the new isolates were determined based on chemical and spectroscopic evidence. The GI(50) of isolates against MK-1, HeLa and B16F10 cell lines are reported.     

Effects of interaction between the chelate rings and π‐conjugated systems in fused salphen complexes on UV‐Vis‐NIR spectra

Dinuclear (Zn₂, Ni₂, and NiZn) complexes of fused salphen with acene‐type annelation were synthesized from 3,7‐diformyl‐2,6‐dihydroxynaphthalene. The spectroscopic properties of these complexes were compared with those of their constitutional isomers with phene‐type annelation. The acene‐type complexes exhibited a characteristic absorption band in the near‐infrared region that showed a noticeable solvent effect. Time‐dependent density functional theory calculations suggested that the absorption arose from a π → π* transition localized at the naphthalene ring, which was perturbed by the adjoining chelate rings. Effects of the connection topology in the fused salphen complexes are discussed by comparison with those of polycyclic aromatic hydrocarbons.     

Synthesis of isoquinoline derivatives using ROM-RCM of cyclobutene-yne

Isoquinoline derivatives were synthesized from cyclobutenylmethylamine derivatives having an alkyne moiety in a tether using a second-generation ruthenium carbene complex under ethylene gas in good yields.     

Nickel-catalyzed four-component connection of oraganoaluminium (organozinc), isoprene, aldehydes and amines: stereo- and regioselective synthesis of trisubstituted (E)-homoallylamines

Ni(acac)2 catalyzes the four-component connection reaction of trimethylaluminium (or diphenylzinc), isoprene, aromatic aldehydes and p-anisidine in this order and provides (E)-1-aryl-1-(p-methoxyphenyl)amino-3-methyl-3-hexenes (or (E)-1-aryl-1-(p-methoxyphenyl)amino-3-methyl-5-phenyl-3-pentenes) selectively in good yield.