Enzyme-induced degradation of natural and artificial linear polyanions.

Synthetic and natural polymers are widely used for constructing drug delivery systems. Biocompatibility, water solubility and non-toxicity make polymers a convenient matrix for encapsulation, delivery and release of bioactive compounds. Coupling of a drug with a biodegraded polymer matrix is a promising way for a controlled drug delivery.

[3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-][1,2]oxazine Derivatives.

A rhodium(II)-catalyzed reaction of cyclic nitronates (5,6-dihydro-4-1,2-oxazine -oxides) with vinyl diazoacetates proceeds as a [3+3]-annulation producing bicyclic unsaturated nitroso acetals (4a,5,6,7-tetrahydro-2-[1,2]oxazino[2,3-][1,2]oxazines). Optimization of reaction conditions revealed the use of Rh(II) octanoate as the preferred catalyst in THF at room temperature, which allows the preparation of target products in good yields and excellent diastereoselectivity. Under basic conditions, namely, the combined action of DBU and alcohol, these nitroso acetals undergo ring contraction of an unsaturated oxazine ring into the corresponding pyrrole.

Tandem double acylation/[3,3]-rearrangement of aliphatic nitro compounds: a route to α-oxygenated oxime derivatives.

A new tandem double acylation/rearrangement reaction of nitro compounds is described. It has a broad substrate scope allowing the mild and efficient synthesis of α-acyloxy oxime esters in high yields and regioselectivity. According to the obtained data, the mechanism for transformation was proposed.

Acylation of Nitronates: [3,3]-Sigmatropic Rearrangement of in Situ Generated N-Acyloxy, N-oxyenamines.

Acylation of nitronates affords α-acyloxyoxime derivatives via an umpolung functionalization of the α-position. This transformation involves generation of hitherto unknown N-acyloxy, N-oxyenamines and their fast [3,3]-sigmatropic rearrangement driven by the cleavage of the weak N-O bond. The reaction has a broad scope, and it is regioselective in the case of nitronates possessing nonsymmetrically substituted α-positions.