## 3 Results and Discussion
### Functionalization of the Hydrophilic Block: MeO-PEG2000-PBA  
The MeO-PEG\({}_{2000}\) was directly esterified with 4-(Carboxymethyl)phenylboronic acid pinacol ester to obtain MeO-PEG\({}_{2000}\)-PBAPin through Steglich esterification [9], involving DCC and DMAP as catalyst. The pinacol moiety served as a protection and was successively  
Figure 1: Representation of MeO-PEG\({}_{2000}\)-PBGal-PLA based nanosystems and the controls, represented by conventional PEG-PLA and PLA nanoparticles. cleaved to give the phenylboronic acid-terminated PEG, MeO-PEG\({}_{2000}\)-PBA. The synthesis was settled up starting from a procedure previously described by [PERSON] et al. [5] for the functionalization of PEG. It is worth noting that we found that when the esterification with PBAPin was carried out in CH\({}_{2}\)Cl\({}_{2}\) and without the elimination of oxygen from the mixture, the \({}^{1}\)H NMR of the purified product in DMSO-\(d_{6}\) showed no signal of the methyl protons of the pinacol group. The \({}^{1}\)H NMR spectrum gave evidence of singlet signal at around 9 ppm instead. The peak had a 1:4 ratio with the protons of the aromatic group of PBA. This observation is compatible with the formation of a phenol derivative of PEG coming from oxidative cleavage of the boronic acid (Scheme 2). Only when the solvent was switched to anhydrous CHCl\({}_{3}\) and the MeO-PEG\({}_{2000}\) solution was bubbled with nitrogen before the addition of reagents (previously dried under vacuum over P\({}_{2}\)O\({}_{5}\)) was the product MeO-PEG\({}_{2000}\)-PBAPin obtained. By comparing the signal due to the methylene group of the esterified end of the isolated product at 4.1 ppm, with the signal of the methoxy group in the \({}^{1}\)H NMR spectrum, it was determined that PBAPin was installed in the 53.2 \(\pm\) 9.1% of the chains. Three different deprotection methods for the removal of cyclic boronate esters were attempted: (1) TFA-mediated acidic hydrolysis; (2) sodium periodate (NaAlO\({}_{4}\))-mediated cleavage; and (3) cationic-resin-mediated hydrolysis. Method 1 led to a product where the pinacolyl group was still present in at least 50% of the chains. This was ascertained by \({}^{1}\)H NMR by dividing the signal at about 1.3 ppm of the methyl protons of pinacolic group with the signals of aromatic protons of phenylboronic moiety. The second transformation tested, mediated by sodium periodate in water/THF and subsequent addition of diluted HCl [10], was more advantageous than the previous one, both in terms of timing and conditions as well as in terms of the percentage of deprotection obtained. In this case, the \({}^{1}\)H NMR spectrum showed the signal at around 1.3 ppm of the pinacol methyl protons only in traces. By analysis of the \({}^{1}\)H NMR spectrum and the calculation of pinacol still esterified, it was observed that only a residue of 6% of the phenylboronic groups was still protected, and that PBA was installed in about 60% of the chains in the final product. Although the method was effective, the product was unstable and suffered from oxidative cleavage, probably due to residual traces of NaAlO\({}_{4}\). The third method (previously explored by [PERSON] and [PERSON] [11] but in acetone at 50 \({}^{\circ}\)C) led to a deprotection rate up to 75%, resulting in the most advantageous approach in terms of workup and stability of the obtained product. The \({}^{1}\)H NMR spectrum of the MeO-PEG\({}_{2000}\)-PBA product with signal attribution to the structure and the detail of the characteristic peaks are shown in Figure 2. It was calculated that, on average, the free PBA content was 16.76 \(\times\) 10\({}^{-3}\) mmol/mg%. Interestingly, aromatic proton peak shift was observed after transformation of the tetrahedral anionic protected species to the neutral trigonal free PBA specie (Figure 2B), indicating the effective deprotection of PBA. Signals of deprotected PBA are already visible in the spectrum of MeO-PEG\({}_{2000}\)PBAPin, indicating that traces of MeO-PEG\({}_{2000}\)PBA were present in the sample.