Stilbene-bridged tert-butylcalix[4]arene as photoswitchable molecular receptors

Using a designed control of conformations of tert-butylcalix[4]arene between cone and pinched cone, a highly selective receptor for small electron-deficient molecules with photoswitching binding ability was attained. [reaction: see text]     

A practical synthesis of optically active arylglycines via catalytic asymmetric Strecker reaction

A practical procedure for catalytic asymmetric synthesis of optically active arylglycine derivatives via optically active α-aminonitriles has been developed. The N-benzhydryl α-arylaminonitrile intermediates were prepared in excellent yield (89–99%) and enantiomeric purity (96 to >98% ee) by enantioselective cyanation of aldimines with TMSCN/ⁱPrOH in the presence of 2.5 mol % of an easily prepared Ti/chiral amino alcohol complex at 0 °C, without requiring slow addition of the cyanating agent. The easily racemized α-aminonitrile intermediates were efficiently hydrolyzed by an aqueous HCl/TFA mixture to give the arylglycine derivatives in good yield (60–92%) and moderate to excellent enantiomeric purity (85–98% ee).     

Sanguinamide B analogs: identification of active macrocyclic structures

We report the synthesis of three new sanguinamide B (San B) analogs. We substituted in amino acids along the San B backbone with an N-Me, glycine, or an aromatic moiety (Phe or d-Phe) generating twelve derivatives in total. Testing in HCT-116 colon cancer cell lines resulted in establishing a structure–activity relationship. Our data show that the substitution of l- or d-Phe adjacent to the thiazole in the San B backbone locks the macrocycle into a single conformer, but only d-Phe analogs are cytotoxic. We demonstrate that the conformation of the macrocycle is extremely sensitive to stereochemistry and amino acid placement.     

Synthesis of alkyl glycosides from cyclodextrin using cyclodextrin glycosyltransferase from Paenibacillus sp. RB01

Alkyl glycosides have potential use as biodegradable detergents due to their high surface activity with low toxicity. Recent progress in the application of enzymes to the preparation of these surface-active compounds demonstrates the advantages to the chemical synthesis. In this work, alkyl glycosides were, for the first time, synthesized from cyclodextrin (CD) and various soluble alcohols by transglycosylation reaction using cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01. Several alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol) as glycosyl-acceptor substrates were evaluated. It was found that the reaction products which were analyzed by TLC were maximum for 30% methanol, 20?C30% ethanol, 10?C20% 1-propanol, 10% 2-propanol, 8% 1-butanol and 5?C10% 2-butanol. In addition, the increase in the yield of alkyl glycoside formation was achieved by using methanol as an acceptor. Optimal reaction conditions for methyl glycoside synthesis from CD were to incubate 1.2% (w/v) ??-CD and 240 U/mL of CGTase in a water/methanol system containing 30% (v/v) methanol, pH 6.0 and a temperature of 40???C. At least three main methyl glycoside products were formed having 1?C3 monosaccharide units attached to methanol which were in accordance with the results of MS analysis.     

The photo-Arbuzov rearrangement of dimethyl 9-anthrylmethyl phosphite and the photodimerization of the corresponding phosphonate

Upon irradiation, 9-anthrylmethyl phosphite ( 2 ) undergoes the photo-Arbuzov rearrangement to give the corresponding phosphonate 3 . Prolonged irradiation led to the clean formation of the centrosymmetric, head to tail, [4 + 4] photocycloaddition product 4 as indicated by X-ray crystallographic analysis. The same photodimer results on irradiation of phosphonate 3 itself in solution or in the solid phase. Phosphite 2 does not undergo photodimerization to 6 . © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:155–160, 1998     

Effect of amino substituents on the stereochemical outcome of the photo-Arbuzov rearrangements of 1-arylethyl phosphorodiamidites

The essentially stereochemically pure 1-arylethyl phosphorodiamidites 8 and 9 were irradiated by UV light in acetonitrile, benzene, and cyclohexane (Tables 1-4). Reaction via singlet free-radical pairs, formed by carbon-oxygen bond scission (Scheme 1), which are somewhat longer lived than those from the analogous phosphites 5 and 6, is proposed. Tetramethyl 1-phenylethylphosphorodiamidite (8) gives the photo-Arbuzov rearrangement product 10 in 59% +/- 2% GC yield, based on percent 8 consumed (Tables 1 and 4), along with the free radical dimerization product 2,3-diphenylbutane, 12a, in in amounts corresponding to ca. 19% of the potentially formed 1-phenylethyl radicals. Similarly, from 9, the photorearrangement product 11 is generated in 64 +/- 4% yield (Tables 2 and 4) along with a 18 +/- 2% accountability of the 1-naphthylethyl radicals as 12b. The photorearrangement of stereochemically enriched 8 (R/S = 99:1) gives 10 in which an apparent 67 +/- 2% (100y, eq 3, Table 4) of the initial radical pairs [3,14] recombine with retention of configuration at the stereogenic carbon (34 +/- 3% net retention, eq 5). With TEMPO present, 70% (100y, eq 3) of the initial 1-phenylethyl radicals, 14, from 8 combine with radicals 3 in the solvent cage with retained configuration at carbon (40% percent net retention, eq 5). The yield of product 10 is reduced to 54%, and 12a is absent. Similarly, the five-membered ring naphthylethyl analogue, phosphorodiamidite 9 (R/S = 98:2), affords largely (R)-11 with apparent 34 +/- 3% net retention. The degree of stereorandomization observed in these systems is higher than was reported previously for phosphites 5 and 6. The neglect of reconversion of pro-S 14 to pro-R 14 on the results of these studies is addressed. Estimated maximum values (eq 4) of kcomb/krot (2.3) for the proximate radical pairs [3,14] from 8 with TEMPO present appear to be at least 6-fold smaller than those of the analogous phosphite (R)-5 (average kcomb/krot = 13 with TEMPO present). Possible origins for this effect are proposed.     

Antioxidant and Anticholinesterase Activities of Extracts and Phytochemicals of Syzygium antisepticum Leaves

Bioassay-guided separation of young leaves extracts of Syzygium antisepticum (Blume) Merr. & L.M. Perry led to the isolation of four triterpenoids (betulinic acid, ursolic acid, jacoumaric acid, corosolic acid) and one sterol glucoside (daucosterol) from the ethyl acetate extract, and three polyphenols (gallic acid, myricitrin, and quercitrin) from the methanol (MeOH) extract. The MeOH extract of S. antisepticum and some isolated compounds, ursolic acid and gallic acid potentially exhibited acetylcholinesterase activity evaluated by Ellman’s method. The MeOH extract and its isolated compounds, gallic acid, myricitrin, and quercitrin, also strongly elicited DPPH radical scavenging activity. In HEK-293 cells, the MeOH extract possessed cellular antioxidant effects by attenuating hydrogen peroxide (H₂O₂)-induced ROS production and increasing catalase, glutathione peroxidase-1 (GPx-1), and glutathione reductase (GRe). Furthermore, myricitrin and quercitrin also suppressed ROS production induced by H₂O₂ and induced GPx-1 and catalase production in HEK-293 cells. These results indicated that the young leaves of S. antisepticum are the potential sources of antioxidant and anticholinesterase agents. Consequently, S. antisepticum leaves are one of indigenous vegetables which advantage to promote the health and prevent diseases related to oxidative stress.