Development of solvent-free protocols for obtaining highly substituted maleates of hyaluronic acid and other glycosaminoglycans.

Solvent-free protocols using microwave-assisted heating (i) or conventional heating without additives (ii) or adding K2CO3 (iii), or triturating at room temperature in the presence of K2CO3 (iv) were first used to esterify glycosaminoglycans (GAG) with maleic anhydride. High and low molecular weight hyaluronic acid (HMW and LMW HA), dermatan sulfate (Ds), heparin (HEP) and C6-oxidized HA (carboxy-HA) were used as substrates for maleation. Protocols (i)-(iii) were most effective for obtaining maleates with high DS (1.39-2.47), but had a strong degrading effect on GAG. Protocol (iv) did not have destructive effect, but was suitable for obtaining only HMW HA maleate (DS 0.71-1.15). Primary hydroxyl groups of HA and Ds showed a higher reactivity compared to the secondary ones. A specific feature of the HEP maleation was substitution of N-sulfate groups for N-maleate groups. To demonstrate the potential of the obtained maleates for thiol-ene click-chemical strategies, the reaction with l-cysteine was performed.

Three (-)-cytisine derivatives and 1-hydroxyquinopimaric acid as acetylcholinesterase inhibitors.

In vitro acetylcholinesterase (AChE) inhibition was studied using novel derivatives of (-)-cytisine derivatives N-allylcytisine-12-carbamide (A-63), cytisine-12-carbamide (A-36), N-1-adamantylcytisine-12-thiocarbamide (U-12), and 1-hydroxyquinopimaric acid (U-201). Inhibition of acetylcholinesterase with compound A-63 was described as mixed inhibition. Substances (A-36) and (U-201) acted as competitive inhibitors with Ki equal to 6.71 mM and 3.89 mM, respectively, while (U-12) behaved as an uncompetitive inhibitor with Ki at 0.07 mM. The IC50 values were estimated at 1.47, 13.73, 3.39, and 7.81 mM, respectively. According to toxicity assessment, compound A-63 was non-toxic; it did not affect A. salina viability at a concentration less than 1000 ppm, while at 1000 ppm, only 3% mortality was observed. Mortality of A. salina was less than 50% in the same concentration range for the other three compounds that allow classifying them as moderately toxic. Although tested compounds have the characteristics of weak inhibitors, they could be useful as protectors against potent organophosphates. The present research may be fundamental to the design of new substances for acetylcholinesterase inhibition.