Convenient and Controllable Synthesis of Poly(2-oxazoline)-Conjugated Doxorubicin for Regulating Anti-Tumor Selectivity

Polyethylene glycol (PEG)-doxorubicin (DOX) conjugation is an important strategy to improve toxicity and enhance clinically therapeutic efficacy. However, with the frequent use of PEG-modified drugs, the accumulation of anti-PEG antibodies has become a tough issue, which limits the application of PEG-drug conjugation. As an alternative solution, poly(2-oxazoline) (POX)-DOX conjugation has shown great potential in the anti-tumor field, but the reported conjugation process of POX with DOX has drawbacks such as complex synthetic steps and purification. Herein, we propose a convenient and controllable strategy for the synthesis of POX-DOX conjugation with different chain lengths and narrow dispersity by N-boc-2-bromoacetohydrazide-initiated 2-ethyl-oxazoline polymerization and the subsequent deprotection of the N-Boc group and direct reaction with DOX. The DOX-PEtOx conjugates were firstly purified, and the successful conjugations were confirmed through various characterization methods. The synthetic DOX-PEtOx_n conjugates reduce the toxicity of DOX and increase the selectivity to tumor cells, reflecting the promising application of this POX-DOX conjugation strategy in drug modification and development.

Thermal and crystalline properties of poly(2-oxazoline)s

The review gathers together data concerning the influence of poly(2-substituted-2-oxazoline)s structure on their thermal and crystalline properties, and how this relationship can be adjusted in controlled manner.

Bioinspired Polymer-Bound Organocatalysts for Direct Asymmetric Aldol Reaction: Experimental and Computational Studies

A series of poly(2-oxazoline) (POX) derivatives bearing prolinamide pendants were designed as organocatalysts and evaluated in the direct asymmetric aldol reaction between aromatic aldehydes and cyclic ketones. The structural variation of the alkyl spacer connecting the polymer backbone with the catalytic unit was applied so as to deduce structure–performance relationships combined with comparable experiments from model catalysts. Results showed that the POX-bound prolinamides can promote the aldol reaction more effectively as compared to their small-molecular and non-POX-bound analogs. The catalyst P3 containing the pyrrolidine moiety closer to the tertiary amide backbone exhibited the overall best catalytic efficiency, affording anti-products in 84% yield with 89% ee in the representative aldol addition of cyclohexanone to 4-nitrobenzaldehyde at a 10 mol.% catalyst loading. Furthermore, the influence of trifluoroacetic acid as an additive on the asymmetric transformation was investigated. Theoretical calculations revealed that the protonation of the aldehyde carbonyl group switched the activation mode of the aldol acceptor through hydrogen bond interactions, thereby changing the relative energy barrier of the enamine/aldehyde reaction transition states, which accounted well for the significant improvement in the enantioselectivity of the acidic additives observed experimentally.

A Pseudopeptide Polymer Micelle Used for Asymmetric Catalysis of the Aldol Reaction in Water

Micelles assembled from amphiphilic molecules have proved to be ideal scaffolds to construct artificial catalysts mimicking enzymatic catalytic behavior. In this paper, we describe the synthesis of amphiphilic poly(2-oxazoline) derivatives with l-prolinamide units in the side chain and their application in asymmetric aldol reactions. Upon dissolution in water, the pseudopeptide polymers self-assembled into particles with different sizes, relying on the copolymer composition and distribution of hydrophilic/hydrophobic segments in the polymer chain. A preliminary study has demonstrated that the catalytic activity of these polymeric organocatalysts are strongly dependent on the aggregated architecture. The micelle-type assemblies can act as nanoreactors to efficiently promote the direct aldolisation of cyclohexanone with aromatic aldehydes in aqueous media, affording anti-aldol products in excellent yields (88⁻99%) and higher stereoselectivities (90/10 dr, 86% ee) compared to their nonmicellar systems under identical conditions.

Synthesis and evaluation of pseudopeptide chiral stationary phases for enantioselective resolution

Poly(2-oxazoline)s are regarded as bioinspired polymers due to their structural relation to polypeptides. In this work, a new kind of poly(2-oxazoline)s containing dipeptide segments in the side chains was synthesized through a bottom-up protocol, which involves ring-opening copolymerization of 2-(N-Boc-l-2-pyrrolidinyl)-2-oxazoline (PyOX_Boc) with 2-(3-butenyl)-2-oxazoline (BuOX) followed by deprotection and amide coupling with N-protected L-proline. The resulting vinyl-functionalized polymers were subsequently immobilized onto mercaptopropylated silica bead matrices by means of thio-click chemistry and their potential as the chiral stationary phase (CSP) for high-performance liquid chromatography was preliminarily evaluated with a series of structurally different racemates. The results showed that this class of pseudopeptide CSPs is particularly adapted to the enantiomeric separation of 1,1'-bi-2-naphthol and acyloin compounds (such as benzoin) under normal-phase conditions. Moreover, an increase in the length of polymer main chains is beneficial to the enhancement of both enantioselectivity and resolution ability. The chiral discrimination of analytes by the polymeric selectors stems primarily from hydrogen bonding and π-π interactions as well as steric hindrance.

Novel poly(2-oxazoline)s with pendant l-prolinamide moieties as efficient organocatalysts for direct asymmetric aldol reaction

Novel poly(2-oxazoline)-bound l-prolinamides have been developed as aldolase biomimetic systems for direct aldol reaction with high stereoselectivity.

Microwave-assisted cationic ring-opening polymerization of 2-oxazolines

Unlike any other polymer class, the (co-)poly(2-oxazoline)s have tremendously benefited from the introduction of microwave reactors into chemical laboratories. This review focuses on the research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and, correspondingly, summarizes the current-state-of the-art of the microwave-assisted synthesis of 2-oxazoline monomers and the microwave-assisted ring-opening (co-)polymerization of 2-oxazolines as well as prominent examples of post-polymerization modification of (co-)poly(2-oxazoline)s. Special attention is attributed to the kinetic analysis of the microwave-assisted polymerization of 2-oxazolines and the discussion of non-thermal microwave effects.