72719-00-7Relevant articles and documents
One-handed helical screw direction of homopeptide foldamer exclusively induced by cyclic α-amino acid side-chain chiral centers
Demizu, Yosuke,Doi, Mitsunobu,Kurihara, Masaaki,Maruyama, Tokumi,Suemune, Hiroshi,Tanaka, Masakazu
scheme or table, p. 2430 - 2439 (2012/03/27)
Chiral cyclic α,α-disubstituted amino acids, (3S,4S)- and (3R,4R)-1-amino-3,4-(dialkoxy)cyclopentanecarboxylic acids ((S,S)- and (R,R)-Ac5cdOR; R: methyl, methoxymethyl), were synthesized from dimethyl L-(+)- or D-(-)-tartrate, and their homochiral homoligomers were prepared by solution-phase methods. The preferred secondary structure of the (S,S)-Ac5cdOMe hexapeptide was a left-handed (M) 3 10 helix, whereas those of the (S,S)-Ac5cdOMe octa- and decapeptides were left-handed (M) α helices, both in solution and in the crystal state. The octa- and decapeptides can be well dissolved in pure water and are more α helical in water than in 2,2,2-trifluoroethanol solution. The left-handed (M) helices of the (S,S)-Ac5c dOMe homochiral homopeptides were exclusively controlled by the side-chain chiral centers, because the cyclic amino acid (S,S)-Ac 5cdOMe does not have an α-carbon chiral center but has side-chain γ-carbon chiral centers. Copyright
The stereoselective synthesis of novel 4-octulose derivatives
Izquierdo Cubero, Isidoro,Plaza Lopez-Espinosa, Maria T.,Rodriguezalonso, Miguel,Asenjo Asenjo, Rafael,Ramirez Fernandez, Antonio
, p. 217 - 221 (2007/10/03)
Dihydroxylation of methyl (E)-2,3-dideoxy-4,5:6,8-di-O-isopropylidene- L-xylo-oct-2-ene-4-ulofuranosonate (1) with osmium tetraoxide took place with high diastereoselectivity to give a 7:1 mixture of methyl 4,5:6,8-di-O- isopropylidene-α-L-glycero-D-galacto- (2) and -D-ido-oct-4-ulofuranosonate (3). When 1 was dihydroxylated in the presence of dihydroquinine and dihydroquinidine p-chlorobenzoate, an appreciable increase and decrease, respectively, in the 2/3 ratio was observed. Compound 2 was transformed into its 2,3-di-O-methyl derivative 4 which was deisopropylidenated to methyl 2,3- di-O-methyl-α-L-glycero-D-galacto-oct-4-ulopyranosonate (5) and subsequently degraded to dimethyl 2,3-di-O-methyl-(+)-L-tartrate (6). On the other hand, compounds 2 and 3, separately, were isopropylidenated to the corresponding 2,3:4,5:6,8-tri-O-isopropylidene derivatives 7 and 8, which were reduced with LiAlH4 to the related 2,3:4,5:6,8-tri-Oisopropylidene-α-L-glycero-D- galacto- (9) and -D-ido-oct-4-ulofuranose (10). Finally, compounds 9 and 10 were deisopropylidenated to the corresponding L-glycero-D-galacto- (11) and L-glycero-Dido-oct-4-ulose (12).
Absolute Rates for Dimerization of Capto-dative Substituted Methyl Radicals in Solution: Absence of Kinetic Stabilization
Korth, Hans-Gert,Sustmann, Reiner,Merenyi, Robert,Viehe, Heinz Guenther
, p. 67 - 74 (2007/10/02)
For three capto-dative substituted methyl radicals, t-butoxy(cyano)methyl radical (1), t-butylthio(cyano)methyl radical (2), and methoxy(methoxycarbonyl)methyl radical (3), absolute rates for dimerization have been measured by e.s.r. spectroscopy and substantiated by product analysis.Values for the rate constants of 1.0E8 - 1.5E9 l mol-1s-1 in the temperature range -60 to +60 deg C support the diffusion-controlled nature of the dimerization.The comparison of Arrhenius activation parameters for dimerization with those for the bulk viscosity of the solutions does not provide evidence for noticeable intrinsic barriers to recombination, indicating the absence of kinetic stabilization for capto-dative substituted methyl radicals.
