42293-86-7

The structure of the glycopeptide antibiotic OA-7653 is assigned as 2.Elucidation of the structure is based primarily on two-dimensional NMR experiments, analogies with other glycopeptide antibiotics of the vancomycin series, and selective degradation studies.Antibiotic OA-7653 contains a heptapeptide aglycon core in which the amino acids N,N-dimethylalanine and glutamine are encountered as a G and F components of this unit.Mild acid hydrolysis of the antibiotic effects the conversion of the δ-carboxamide of the glutamine residue to yield the carboxylic acid 3 in a reaction that is shown to proceed without rearrangement.This latter conversion to 3 proceeds without effecting cleavage of the β-glycosidic link between the aglycon and glucose.The 1H spectra of OA-7653 and its derivatives in DMSO at pH 4.0 are shown to represent major and minor conformers that are exchanging at rates comparable to the NMR time scale.

Simple amino acid-derived esters have been identified as promising chiral sources for the ytterbium-catalyzed aldol-Tishchenko reaction of aromatic aldehydes with aliphatic ketones. The 1,3-anti-diols with three stereogenic centers were isolated in excellent yields, complete anti-diastereocontrol and enantioselectivities of up to 50% ee.

The stereochemistry of the indium-promoted reaction of allyl bromide with α-thia (PhS and MeS), disubstituted α-amino (Bn2N, Me2N, isoindolyl), and protected α-amino aldehydes (Ac and Boc) in water has been evaluated. The reactions involving the sulfur derivatives are minimally diastereoselective, indicating that the allylindium reagent is not thiophilic. Chelation is not observed and π-facial discrimination is achieved via Felkin - Ahn transition states under the steric control of the substituents. The Garner aldehyde is also anti-diastereoselective. Interestingly, N-acetylmannosamine is appreciably responsive to chelation control and is capable of generating 90% of the syn β-amino alcohol when reacted in a 0.5 M NH4Cl solution. While the α-dibenzylamino substituent is too bulky to enter into complexation, the α-dimethylamino group is not and can lead to high levels (99%) of syn diastereomer. The size of other neighboring substituents does have an impact on π-facial discrimination in these systems and can erode the stereoselectivity accordingly.