Owing to a faster rate of sublimation of the racemic form as compared to the optically pure form, optical purification occurred without any external action or special environmental condition. We believe that the phenomenon of optical self-purification reported here deserves further systematic study as possibly one of the mechanisms leading to the emergence and maintenance of prebiotic homochirality.

This work has demonstrated that a previously unexplored approach to separation of enantiomers via formation of diastereomeric derivatives with three stereogenic centers has obvious practical potential and deserves further systematic study. The design reported here is based on the unusual application of a configurationally unstable stereogenic nitrogen, which plays a key role in setting up the stereochemical match between the three stereogenic centers in the corresponding products.

A synthetically practical and operationally convenient method for preparing (S)-2-[N-(N'-benzylprolyl)amino]benzophenone (BPBP) and hitherto unknown (S)-2-[N-(N'-benzylprolyl)amino]-4-methylbenzophenone (4-Me-BPBP), (S)-2-[N-(N'-benzylprolyl)amino]-5-nitrobenzophenone (5-NO(2)-BPBP), and their corresponding Ni(II) complexes with glycine [GlyNi(II)BPBP], a widely used chiral equivalent of nucleophilic glycine, and new analogues [GlyNi(II)-4-Me-BPBP] and [GlyNi(II)-5- NO(2)-BPBP] is described. The key step of the method is the synthetically efficient amid bond formation between the corresponding o-aminobenzophenones, featuring significant steric shielding and low nucleophilicity of the amino functionality as well as sterically constrained (S)-N-benzylproline (BP).

A new generation of modular achiral glycine equivalents have been evaluated with respect to their synthetic utility for the production of tailor-made, sterically constrained alpha-amino acids, which proved to be the most efficient approach developed to date for the synthesis of symmetrical alpha,alpha-disubstituted-alpha-amino acids. Among the new series of achiral glycine equivalents, one was found to be a superior glycine derivative for the Michael additions with various (R)- or (S)-N-(E-enoyl)-4-phenyl-1,3-oxazolidin-2-ones representing a general and practical synthesis of sterically constrained beta-substituted pyroglutamic acids. In particular, the application of these complexes allowed for the preparation of several beta-substituted pyroglutamic acids which include electron-releasing and sterically demanding substituents in the structure thus increasing the synthetic efficiency and expanding the generality of these Michael addition reactions.

No abstract

The pressure recovery of a low-solidity circular cascade diffuser of a centrifugal blower was predicted by a simple method combining a theory of circular cascade diffusers and that of vaneless diffusers and it was compared with a series of experiments. Furthermore the stall limit of the diffuser was studied. In order to improve the performance further, a series of tandem-cascade diffusers were tested. In these diffusers, the front row of the cascade was designed for a small flow rate while the rear row of the cascade was designed for a large flow rate so that the tandem cascade would accomplish good pressure recovery in a wide range of flow rate. Experimental results showed that the operating range was as wide as that of a vaneless diffuser and the pressure recovery was excellent at a small flow rate while it was somewhat better than that in a vaneless diffuser at a large flow rate.

Here we report a general method for the preparation of unnatural (R)-α-amino acids via complexation of α-(phenyl)ethylamine derived chiral reagent (S)- with various (S)-α-amino acids. The reactions proceed with synthetically useful chemical yields and thermodynamically controlled diastereoselectivity. Chiral reagent (S)- can be conveniently recovered and reused without any loss of enantiomeric purity and reactivity.

The Merrifield solid-phase peptide synthesis technique has been adapted to the synthesis of homo- and heterometallic metal−organic complex arrays (MOCAs). A terpyridine-appended and Fmoc-protected L-tyrosine derivative was metalated with Pt(II), Rh(III), or Ru(II) ions in solution and sequentially coupled at the surface of functionalized polymeric resin to give a metal complex triad (Rh−Pt−Ru), tetrad (Ru−Rh−Pt−Pt), pentad (Rh−Pt−Ru−Pt−Rh), and hexad (Rh−Pt−Ru−Pt−Rh−Pt) with specific metal sequence arrangements. These were cleaved from the resin, and their character was confirmed by mass spectrometry.