- Organocatalytic ?±-addition of isocyanides to aldehydes
-
?±-Hydroxyamide is an important chemical component widely observed in biologically active natural products. One of the most direct methods to access a ?±-hydroxyamide is the Passerini-type reaction. However, this catalytic process was limited. Herein, we
- Yamada, Takeshi,Hirose, Tomoyasu,O??mura, Satoshi,Sunazuka, Toshiaki
-
supporting information
p. 296 - 301
(2015/03/04)
-
- Enzymatic approach to both enantiomers of N-Boc hydrophobic amino acids
-
Protease catalysed hydrolysis of N-Boc-amino acid esters allows us to obtain N-Boc l-acids and d-esters of amino butanoic acid, nor-leucine, nor-valine, leucine and t-leucine in excellent ee. The reaction occurs in short reaction times and high concentrations. When a biphasic system (buffer-MTBE) is employed, a strong solvent effect is observed. This method could be of significance for the preparation of d-t-leucine, for which a practical method is currently unavailable.
- Agosta, Eleonora,Caligiuri, Antonio,D'Arrigo, Paola,Servi, Stefano,Tessaro, Davide,Canevotti, Renato
-
p. 1995 - 1999
(2007/10/03)
-
- Nucleophilic acyl substitutions of anhydrides with protic nucleophiles catalyzed by amphoteric, oxomolybdenum species
-
(Chemical Equation Presented) Among six different group VIb oxometallic species examined, dioxomolybdenum dichloride and oxomolybdenum tetrachloride were the most efficient catalysts to facilitate nucleophilic acyl substitution (NAS) of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. In contrast to the well-recognized redox chemical behaviors associated with oxomolybdenum(VI) species, the catalytic NAS was unprecedented and tolerates virtually all kinds of functional groups. By using benzoic anhydride as a mediator for in situ generation of an incipient mixed anhydride-MoO2Cl2 adduct with a given functional alkanoic acid, one can achieve oleate, dipeptide, diphenylmethyl, N-Fmoc-α-amino, pyruvic, and tert-butylthio ester, N-tert-butylamide, and trityl methacrylate syntheses with appropriate protic nucleophiles. The amphoteric character of the Mo=O unit in oxomolybdenum chlorides was found to be responsible for the catalytic NAS profile as supported by a control NAS reaction of using an authentic adduct-MoOCl2(O2-CBu t)2 between pivalic anhydride and MoO2Cl 2 as the catalyst.
- Chen, Chien-Tien,Kuo, Jen-Huang,Pawar, Vijay D.,Munot, Yogesh S.,Weng, Shieu-Shien,Ku, Cheng-Hsiu,Liu, Cheng-Yuan
-
p. 1188 - 1197
(2007/10/03)
-
- Versatile synthons for optically pure alpha-amino aldehydes and alpha-amino acids: (+)- and (-)-4,5-dialkoxy-2-oxazolidinones.
-
Both enantiomers of trans-5-benzyloxy-4-methoxy- (BMOx) and trans-4,5-dimethoxy-2-oxazolidinones (DMOx), which are readily accessible from simple 2-oxazolone heterocycles, represent good candidates for a new class of chiral synthons for use in the preparation of optically pure alpha-amino aldehydes and alpha-amino acids, respectively.
- Morita,Nagasawa,Yahiro,Matsunaga,Kunieda
-
p. 897 - 899
(2007/10/03)
-
- Asymmetric syntheses of (R)- and (S)-2-aminobutanesulfonic acid and their 3,3-dimethylderivatives
-
(R)- and (S)-2-aminobutanesulfonic acid, 3a and 3b, and (R)- and (S)-2-amino-3,3-dimethylbutanesulfonic acid, 4a and 4b, were synthesized from the corresponding N-Boc protected β-amino alcohols in good yields and high enantiomeric purities (> 99% ee).
- Braghiroli, Daniela,Di Bella, Maria
-
p. 2145 - 2150
(2007/10/03)
-
- On the Preparation of β-Amino Acids from α-Amino Acids Using the Arndt-Eistert Reaction: Scope, Limitations and Stereoselectivity. Application to Carbohydrate Peptidation. Stereoselective α-Alkylations of Some β-Amino Acids
-
The Arndt-Eistert homologation of α-amino acids was studied to determine the stereoselectivity in this reaction by chromatographic up-to-date analytical methods.While carbamate-protected phenylglycine was transformed to the corresponding β-amino acid methyl ester with a stereoselectivity of only 9:1, all other tested amino acid derivatives (Ala, Phe, Ser, Orn, tert-Leu and perhydro-azepine-2-carboxylic acid, suitably protected) were homologated with full retention of configuration (products 9-17).The intermediate diazo ketones 1-8 were purified and characterized by their NMR spectra.When nucleophiles derived from partially protected sugars were present during decomposition of the diazo ketones (derived from amino acids or dipeptides), a strong dependence of the yield (products 21-24) on the degree of steric hindrance of the nucleophilic OH group was observed.Two of the β-amino acids obtained from the homologation reaction were transformed to α-substituted (25-27, 31, 32) and α,α-disubstituted β-amino acid derivatives (28, 29) with excellent selctivities (in most cases, a single diastereoisomer was obtained). - Key Words: β-Amino acids, α-branched/Glycopeptides
- Podlech, Joachim,Seebach, Dieter
-
p. 1217 - 1228
(2007/10/02)
-