Catalyst-free and mild synthetic methods for the construction of hindered α-amino acid derivatives are presented herein. A wide range of hindered amino acid amides can be readily obtained from the reaction of α-halohydroxamates with a variety of amines, including anilines, primary amines, and secondary amines. Moreover, the aza/aza-[4+3] cycloaddition of in situ-generated aza-oxyallyl cations with 2-aminophenyl α,β-unsaturated carbonyls to furnish seven-membered benzodiazepin-3-ones is reported for the first time.

The first organocatalytic asymmetric [4 + 3]-cycloaddition of 2-aminophenyl α,β-unsaturated carbonyls with in situ generated azaoxyallyl cations was developed, and enantioenriched functionalized seven-membered 1,4-benzodiazepine-3ones were obtained in good yields and with excellent enantioselectivities. This approach was also extended to the first asymmetric [4 + 3]-cycloaddition of δ-hydroxy α,β-unsaturated carbonyls, affording 1,4-oxazepanes in one step under mild conditions. Several of the novel adducts demonstrated promising bioactivity in the prevention of peripheral nerve degeneration.

A metal‐free [4 + 3]‐annulation of α‐halohydroxamates with 2‐aminophenyl α,β‐unsaturated esters has been developed for the construction of seven‐membered 1,4‐benzodiazepine‐3‐one‐5‐acetates in moderate to good yields (up to 82% yield). The annulation involved the cascade reaction of an generation of azaoxyallyl cation, aza‐addition to this azaoxyallyl cation, and intramolecular aza‐Michael reaction to yield 1,4‐benzodiazepine‐3‐one‐5‐acetates.

No abstract

The purpose of this study is to figure out the effect of maintaining period of PTFE membrane used in GBR with autogeonous bone, heterogeneous bone and synthetic bone on bone formation on rabbits' cranial defect. Eight adult New Zealand white rabbits were used in this study. Four defects were surgically made in their calvaria. Using a trephine bur, 4 'through and through' defects were created and classified into 4 groups, which were consisted of control (no graft), experimental group 1 (autogeonous bone) and experimental group 2 (deproteinized bovine bone: OCS-B®; NIBEC, Korea), experimental group 3 (synthetic bone: MBCP; Biomatlante, France). The defects were covered with PTFE membrane (Cytoplast®, Innova, Canada). Membranes were removed after 1, 2, 4 and 8 weeks post-GBR in each 2 rabbits. And then, all rabbits were sacrificed; specimens were taken and observed histologically..: After removing the membranes after 1 week of the experiment, bone formation was not evident in a control group but the area was replaced with only loose fibrous connective tissue. In group 1(autogeonous bone), thin bone formation and infiltration of connective tissue on the superficial layer were observed. Initial bone formation and infiltration of fibrous connective tissue were evident in group 2(deprotenized bovine bone) and 3(synthetic bone). When the membranes were removed after 2 weeks of the experiment, bridge shaped bone formation was shown in control group but mostly connective tissue took place. More increased bone thickness was evident in group 1 and increased bone formation than first week was shown in group 2 and 3. When the membranes were removed after 4 weeks of the experiment, 2/3 of normal bone thickness was formed in control group still with infiltration of connective tissue. In group 1, regular bone formation with normal bone thickness was shown and in group 2 and 3, similar bone thickness to the normal was evident. After the removal of the membranes in 8 weeks, bone thickness formed in control group was more increased than 4th week, but could not reach normal bone thickness. In group 1, normal bone thickness was formed and similar bone thickness to that of the normal was observed in group 2 and 3. Within the limited study, when performing the GBR procedure, at least 4-week period of the membrane retention is required, and more retention time of the xenograft or synthetic bone is needed than that of autogenous bone for better bone regeneration.