Rauter, Amélia PilarCachatra, Vasco2025-03-192025-01-102024-07-31http://hdl.handle.net/10400.5/99495This PhD thesis focused on the synthesis and development of new synthetic strategies towards carbohydrate-based compounds with potential relevance for biological applications. Firstly, the development of a new synthetic methodology to prepare bicyclic sugar moieties bearing a fused furan ring was achieved. This strategy relies on a key Wittig reaction to afford the branched chain at position 3 of the sugar moiety with the required stereochemistry. The regio- and stereo-control was possible through optimization of the reaction conditions, as well as careful construction of the substrate. The presence of a bulky 2-O-pivaloyl group and the use of chloroform as solvent, led to the required (3E)-alkene by reaction of the 3-ulose with [(ethoxycarbonyl)methylene]triphenylphosphorane, while a 2-O-benzoyl protection afforded the corresponding (3Z)-alkene. When using acetonitrile as the reaction solvent, a (2Z)-alkene was formed regardless of the protecting group chosen. This domino reaction occurs through a keto-enol tautomerization, followed by an intramolecular migration of the acyl group at position 2 to position 3, and formation of the corresponding 2-ulose, which finally reacts with the phosphorane to afford the corresponding (2Z)-alkene. These results were significant towards the construction of bicyclic sugar moieties bearing a fused furan ring, present in several biological important compounds, such as the miharamycins sugar moiety as well as a selective butyrylcholinesterase inhibitor. A library of purine nucleosides derived from a previously known selective butyrylcholinesterase inhibitor, the α-anomer of a fully benzylated sugar moiety N7 linked to a 2-acetamidopurine, was also investigated. Although this compound was a strong candidate for drug development, it presented a few pharmacokinetic problems, such as its water solubility and a high molecular weight, due to the high number of benzyl protection groups in the sugar moiety. With the goal of reducing the overall molecular weight, different patterns of protection of the sugar moiety were devised to access the significant positions for the displayed activity. Since an ether protection was necessary as previous studies showed no activity for ester protected sugar moieties, the smaller methyl group was chosen. A strategy was devised to regioselectively protect the different positions of the gluco sugar core by decreasing the number of benzyl groups present in the final compound, until a per-methylated glycosyl donor was synthesized. The presence of a benzyl group at positions 2 and 3 led to a slight decrease of the βN7 yield when compared to the fully benzylated purine nucleoside. When these positions were protected with a methyl group, selectivity towards the βN9 isomer was observed as no αN7 was detected and the βN7 yield was significantly decreased from ≈ 25 % to ≈ 9 %. Biological assays from the synthesized nucleosides, with both acetylcholinesterase and butyrylcholinesterase, showed a significant decrease in the activity of these compounds when compared to the fully benzylated derivative, and the most active compound was 2,3-di-O-benzyl-4,6-di-O-methyl αN7 purine nucleoside, although it showed no selectivity towards butyrylcholinesterase (Kia = 12 μM for AChE, Kia = 83 μM for BuChE). As displayed by these and the previous results, the αN7 isomer seems to favor activity towards cholinesterases. Although this isomer gives the best results, the reaction conditions did not favor the formation of this compound as it was obtained in yields lower than 10 %. The next step was to investigate reaction conditions to improve the αN7 yield. For this, changing the starting material with different leaving groups at the anomeric position as well as different Lewis acid activation in the N-glycosylation were tested. These changes did not present significant improvements, so the reaction was tested at different temperatures, where an increase in the αN7 yield was observed when the reaction was carried out at room temperature when compared to the previously reported temperature of 65 °C. A new analogue of the lead compound was synthesized to perform biodistribution in vivo studies. A 6-bromo purine nucleoside was obtained to undergo a SN2 reaction with a radioiodinated reagent to afford a radioactive labelled compound. This compound was then injected into healthy CD1 mice and results were measured at 2- and 60- min post-injection. The low brain uptake (0.36 % and 0.10 % at 2- and 60- min respectively) suggests that only a low fraction of the radioiodinated compound crosses the BBB. These results encouraged the docking studies of the active site of BuChE with the lead compound. Key interactions were identified with the acetamido group of the purine and the benzyl group from position 2. Since different protecting groups showed lower activity, deoxygenation was attempted at selected positions of the sugar moiety. A regioselective synthetic strategy was then developed towards 4 different deoxygenated sugar moieties. Results showed that removing the benzyloxy group at position 6 or using the corresponding lyxo-pentopyranoside still maintained selective inhibition of butyrylcholinesterase. The most active compounds were also tested for their cytotoxicity and showed low cytotoxicity at the active concentrations.engStereoselectivityRegioselectivityPurine nucleosidesWittig reactionDomino reactionEstereoselectividadeRegioselectividadeNucleósidos de purinasReação de WittigReação dominodoctoral thesis101474016