Bovine serum albumin-mediated enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylate

Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxyalate (AC) was performed at 25 degrees C in aqueous buffer solution (pH 7) in the presence of bovine-serum albumin (BSA) to afford four [4 + 4] cyclodimers, i.e., anti- and syn-head-to-tail (HT) (1 and 2) and anti- and syn-head-to-head (HH) dimers (3 and 4), of which only 2 and 3 are chiral. We found that (1) BSA possesses four sets of binding sites for AC of different affinities, stoichiometries, and chiral environment for photoreaction, which bind 1, 3, 2, and 3 AC molecules with binding constants of 5.3 x 107, 1.3 x 105, 1.4 x 104, and 3.0 x 103 M-1, respectively, (2) the regioselectivity of photodimerization is switched from HT to HH by adding BSA (the HH/HT ratio varies from 0.28 to 4.3), (3) BSA-mediated photodimerization of AC affords optically active products 2 and 3 of up to 29% and 41% ee, respectively. It is emphasized that the selective excitation of bound substrate, utilizing the spectral shift upon complexation with BSA, is not a prerequisite for efficient photochirogenesis using biomolecules.     

Efficient Organocatalytic Construction of C4‐Alkyl Substituted Piperidines and Their Application to the Synthesis of (+)‐α‐Skytanthine

Chiral piperidines which contain an alkyl group at C4 positions are one of the important architectures because it is appeared in several natural products. An efficient protocol for the preparation of C4‐alkyl substituted chiral piperidines using secondary amine catalyzed formal aza [3+3] cycloaddition reaction with aliphatic α,β‐unsaturated aldehydes and thiomalonamate derivatives is reported. In our reaction system, thiomalonamate is an excellent nucleophile and the addition of suitable acid and its amount is an important factor for the acceleration effect in organocatalytic reaction. Furthermore, water and MeOH also have an acceleration effect. These efforts lead to only 0.1 mol % catalyst loading in multigram scale synthesis for suitable reaction time. In addition, the efficient enantioselective total synthesis of (+)‐α‐skytanthine by using our developed reaction as key step was achieved in total 15 % yield. All carbon and nitrogen units were introduced by one step with high enantioselectivity.     

A truncated palytoxin analogue,palytoxin carboxylic acid,isolated as an insecticidal compound from the red alga, Chondria armata

Palytoxin (PTX) has been widely studied owing to its outstanding toxic properties and complex structural features. It is a great challenge to identify and isolate analogues of PTX from various organisms and reveal their physiological activities. We previously reported the isolation of PTX as an insecticidal compound from the red alga, Chondria armata. In this study, we investigate another active compound from C. armata, which has similar toxicity and chromatographic behavior as PTX. Our detailed structural analysis reveals that this compound is palytoxin carboxylic acid. We characterized its physicochemical properties and conducted extensive NMR studies. This analogue has a structure devoid of the terminus of PTX, such that its presence in the alga implies the role of symbiotic microorganisms in marine ecosystems.     

Immobilization of Photosynthetic Pigments into Silica-Surfactant Nanocomposite Films

Highly transparent silica-surfactant nanocomposite films containing photosynthetic pigments have been successfully formed through the solubilization of chlorophyll a (Chl a) into surfactant micelles. The UV-vis absorption spectra indicated that a large amount of Chl a were transformed into pheophytin a in the films. These photosynthetic pigments were well dispersed in the surfactant assemblies and their chlorin rings were exposed to the surface of silica layers. Even under an air atmosphere, the photostability of immobilized pigments was largely improved in comparison with that in a homogeneous Chl a solution. Because both Chl a and pheophytin a molecules are effective for the photosensitive charge separation, the present film system is very suitable for heterogeneous immobilizing media for photosynthetic pigments from the viewpoint of in vitro biomimetic devices for solar energy conversion.     

Control of Hydrolysis and Condensation Reactions of Titanium tert-butoxide by Chemical Modification with Catechol

Titanium tert-butoxide (Ti(OC(CH₃)₃)₄; Ti(O ^t Bu)₄) was chemically modified with catechol (C₆H₄(OH)₂) and hydrolysis and condensation behavior of a resultant modified alkoxide was studied. Spectroscopic results revealed that the reaction between titanium tert-butoxide and catechol resulted in the formation of catecholate groups (C₆H₄O₂ ^2–) bound to titanium and corresponding release of tert-butanol. The mass spectrometry and cryoscopy indicated that main species was a dimer [(C₆H₄O₂)₂Ti₂(O ^t Bu)₄]. The hydrolysis of the modified alkoxide in the system with Ti:tetrahydrofuran (THF):H₂O = 1:10:x (x = 0.5–10) resulted in the partial hydrolysis, and all the hydrolyzed products after the drying under reduced pressure were soluble in THF and chloroform.     

Crab-Eating Monkey Acidic Chitinase (CHIA) Efficiently Degrades Chitin and Chitosan under Acidic and High-Temperature Conditions

Chitooligosaccharides, the degradation products of chitin and chitosan, possess anti-bacterial, anti-tumor, and anti-inflammatory activities. The enzymatic production of chitooligosaccharides may increase the interest in their potential biomedical or agricultural usability in terms of the safety and simplicity of the manufacturing process. Crab-eating monkey acidic chitinase (CHIA) is an enzyme with robust activity in various environments. Here, we report the efficient degradation of chitin and chitosan by monkey CHIA under acidic and high-temperature conditions. Monkey CHIA hydrolyzed α-chitin at 50 °C, producing N-acetyl-d-glucosamine (GlcNAc) dimers more efficiently than at 37 °C. Moreover, the degradation rate increased with a longer incubation time (up to 72 h) without the inactivation of the enzyme. Five substrates (α-chitin, colloidal chitin, P-chitin, block-type, and random-type chitosan substrates) were exposed to monkey CHIS at pH 2.0 or pH 5.0 at 50 °C. P-chitin and random-type chitosan appeared to be the best sources of GlcNAc dimers and broad-scale chitooligosaccharides, respectively. In addition, the pattern of the products from the block-type chitosan was different between pH conditions (pH 2.0 and pH 5.0). Thus, monkey CHIA can degrade chitin and chitosan efficiently without inactivation under high-temperature or low pH conditions. Our results show that certain chitooligosaccharides are enriched by using different substrates under different conditions. Therefore, the reaction conditions can be adjusted to obtain desired oligomers. Crab-eating monkey CHIA can potentially become an efficient tool in producing chitooligosaccharide sets for agricultural and biomedical purposes.     

Laser-Induced Hydrogen Radical Removal in UV MALDI-MS Allows for the Differentiation of Flavonoid Monoglycoside Isomers

Negative-ion matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra and tandem mass spectra of flavonoid mono-O-glycosides showed the irregular signals that were 1 and/or 2 Da smaller than the parent deprotonated molecules ([M – H]^–) and the sugar-unit lost fragment ions ([M – Sugar – H]^–). The 1 and/or 2 Da mass shifts are generated with the removing of a neutral hydrogen radical (H*), and/or with the homolytic cleavage of the glycosidic bond, such as [M – H* – H]^–, [M – Sugar – H* – H]^–, and [M – Sugar – 2H* – H]^–. It was revealed that the hydrogen radical removes from the phenolic hydroxy groups on the flavonoids, not from the sugar moiety, because the flavonoid backbones themselves absorb the laser. The glycosyl positions depend on the extent of the hydrogen radical removals and that of the homolytic cleavage of the glycosidic bonds. Flavonoid mono-glycoside isomers were distinguished according to their TOF MS and tandem mass spectra.