Preparation of Oxazolidine-Containing Peptides: Unusual effects in RhIII-catalyzed acetalizations of aldehydes with urethane-protected serine and threonine esters and with dipeptides containing serine or threonine residues at the N-terminus

The cyclization reaction of aldehydes with Z- and Boc-protected β-hydroxyamino-acid esters (Tables 1 and 2), or of dipeptides containing serine or threonine at the N-terminus (Table 3), to give oxazolidine derivatives, occurs in the presence of isopropyl orthoformate and catalytic amounts of [Rh(MeCN)₃(triphos)](CF₃SO₃)₃. The reaction may be carried out under kinetic or under thermodynamic control, so that the ratio of the two possible epimeric products can be changed. The protecting group can be removed from the 3-position of the oxazolidine ring, and the resulting NH group can be coupled with another amino acid. Thus, a new method for the preparation of peptides containing β-hydroxy-amino acid-derived oxazolidines (‘pseudo-prolines’) is available. N-Neopentyl-substituted tripeptides are also described.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

The Coordination Chemistry of 1,2-Bis[(diphenylphosphino)methyl]benzene with Nickel(II), Palladium(II), Platinum(II), and Platinum(0) and the X-Ray Crystals Structure of [Pt{1,2-bis[(diphenylphospino)methyl]benzene}(C2H4)]

The preparation of complexes [MX₂( 1 )] (M = Ni, Pd, and Pi; X - Cl, Br, and I; 1 = 1,2-bis[(diphenylphosphino)methyl]benzene). [Pt(OSO₂CH₃)Et( 1 )], [Pt(alkene)( 1 )] (alkene - C₂H₂, and CH₂ = CHCN), and [( 1 )Pt-(μ-H)₂PtH( 1 )][BPh₄] is reported. Their ¹H- and ³¹P-NMR spectra were recorded and used lor structural assignments. The X-ray crystal structure of [Pt(C₂H₄)( 1 )] was determined. It is shown that the P? Pt? P bond angle in this complex differs significantly from those found in related compounds with monodentate phosphines, and that this difference is likely to be due to intramolecular contacts.     

Transition metal complexes with bidentate ligand 2, 11-Bis (diphenylphosphinomethyl)benzo[c]phenanthrene (1). X. Preparation and spectroscopic properties of cis-[PtCl2 (1)] trans- and cis-[PtH (PPh3) (1)] [BF4] and crystal and molecular structure of cis-[PtCl2 (1)] · CHCl3

It is shown that ligand 1 , designed to span trans-positions, under appropriate conditions also gives cis-mononuclear complexes of platinum (II). The structure of cis-[PtCl₂ (1) ] (2) has been determined by single-crystal X-ray diffraction. The major distortion from square planar coordination is the P-Pt-P angle of 104.8°. Values of valence angles within the bidentate ligand indicate that this part of the molecule is very strained. Two phenyl groups, one on each phosphorus, lie almost parallel to each other separated by ca. 3.2–3.3 Å. The ¹H-NMR. data for this compound show that the π-phenyl interactions observed in the solid state occur also in solution. The preparation and NMR.-spectroscopic properties of trans- and cis-[PtH(PPh₃) (1) ] [BF₄] are reported.     

Comments on the Interpretation of NMR. Parameters in some platinum-olefin complexes

¹³C and ¹⁹⁵Pt-NMR. parameters for the complexes trans-[PtCl₂(C₅H₁₀N)-(CH₃CH?CHCH₃)] are presented. It is suggested that conclusions, concerning metal olefin bond strengths, drawn from NMR. studies of nuclei not directly involved in the bonding can be misleading.