The novel C(2)-symmetric bis(imidazolidine)pyridine (PyBidine) ligand was easily synthesized in a single condensation of 2,6-pyridyl aldehyde and optically active (S,S)-diphenylethylenediamine. In the C(2)-symmetric PyBidine-Cu(OTf)(2) complex, imidazolidine rings act as "chiral fences" to shield the first and third quadrants. Use of the PyBidine-Cu(OTf)(2) complex as a catalyst enabled the highly endo-selective reaction of imino esters and nitroalkenes to give the adducts in up to 99% ee.
A chitosanase was concentrated from the culture broth of Bacillus circulans MH-K 1 and was purified to homogeneity by CM-cellulose and gel permeation chromatography. The enzyme has a molecular weight of about 30,000, its Km is 0.63 mg chitosan/ml and its pus 9.2. The maximum velocity of chitosan degradation by the enzyme was obtained at 50°C when pH was maintained at 6.5. The enzyme was stable within the range of 0-40°C and pH 4.0-9.0. p-Chloromercuribenzoate and the metal ions of Cue +, Hg2 +, Nit +, and Zn2 + inhibited the enzyme activity. The enzyme degraded chitosan, glycolchitosan and CM-chitosan, but f-1,4-glucans such as chitin or its derivatives and CM-cellulose were not susceptible to the enzyme. The degree of deacetylation of chitosan significantly affected its susceptibility to the enzyme action. The most susceptible substrate was 80 deacetylated chitosan, and the substrates with less than 40% deacetylation were not affected by the enzyme. It is suggested that the presence of Nacetylglucosamine residues in the molecule of chitosan play an important role in the recognition of the substrate by the enzyme. The enzyme showed an endo-splitting type of activity, and the end product of chitosan degradation contained a mixture of the dimer and trimer of glucosamine. The smallest of the substrates was a tetramer of glucosamine.Chitosan is a polymer with 18-1,4-linked glucosamine residues. It is usually obtained by artificial deacetylation of chitin, a polymer of N-acetyl;/3-Dglucosamine, with a concentrated NaOH solution. Recently, as the medical uses of chitosan, its derivatives or its partially degraded oligosaccharides have been developed, the demands are growing for chitosanases, needed for mild degradation of chitosan (1).
Condensation of chiral diamines and aldehydes gave a series of chiral imidazolidine-pyridine compounds with high diastereoselectivities. The ability of these compounds to act as chiral ligands was examined in the catalytic Henry reaction.The synthesis of chiral molecules in a catalytic asymmetric manner is essential for supplying fundamentally valuable organic compounds. 1 Because the creation of a wellorganized reaction sphere using highly functionalized chiral ligands is the key to controlling stereoselective metal catalysis, the design and development of new chiral ligands is at the forefront of research on catalytic asymmetric synthesis. In this communication, the quick and efficient stereoselective synthesis of imidazolidine compounds is reported, and their ability to act as chiral ligands is examined in the Cu(OAc) 2 -catalyzed Henry reaction. 2,3As part of our research program for exploring efficient asymmetric catalysts, we have succeeded in developing imidazoline-containing chiral ligands for metal-catalyzed reactions. 4,5 For example, imidazoline-aminophenol (L0)-Cu complexes have been realized as efficient catalysts for the Henry reaction, 4d the Friedel-Crafts reaction, 4d,e and the tandem Friedel-Crafts-Henry reaction. 4fAlthough the unique asymmetric reaction sphere produced by the imidazoline-aminophenol (L0)-metal complex has potential for successful application to other various asymmetric reactions, the simple imidazolinepyridine analogues (L1) were not effective for the Cu(OAc) 2 -catalyzed Henry reaction (Table 1, entries 2-5). We assumed that the relatively flat structure around the Cu center in the square-planar L1-Cu(II) complex was not sufficient to promote the stereoselective reactions [see Figure 1, L1 and Figure 4, L1b-Cu(OAc) 2 ]. To produce more stereochemical complexity, we focused on the imidazolidine ring, in which the sp 2 -carbon of the imidazoline ring is replaced by a sp 3 -carbon [Figure 1, L2 and Figure 4, L2a-Cu(OAc) 2 ].Relatives of the imidazolidines, chiral imidazolidinones are widely employed as organocatalysts for asymmetric reactions, as pioneered by MacMillan. 6 Furthermore, Uozumi reported elegant work on the stereoselective synthesis of an imidazoindole ligand for asymmetric palladium catalyses. 7 Despite the prevailing applications as organocatalysts, 8 however, the challenges on the ligand for the metal catalysts are rather limited. 9,10 Figure 1 Structurally simplified analogues (L1 and L2) of L0Although the newly formed sp 3 -carbon is a stereogenic center, we envisioned that the configuration of the product would be controlled by the steric repulsion relayed from the substituents of the chiral diamine. A DFT calculation at the level of B3LYP/6-31G* suggested that L2 depicted in Figure 2 is more stable than the epimer at the newly formed asymmetric sp 3 -carbon by 5.7 kcal/mol.The synthesis of imidazolidine-pyridine ligands was readily achieved by a simple condensation of monoalkyl chiral diamines and aldehydes using acetic acid Table 1 Henry Reaction Catalyzed b...
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