Molecular amplifiers: synthesis and functionalization of a poly(aminopropyl)dextran bearing a uniquely reactive terminus for univalent attachment to biomolecules

Abstract

The synthesis and characterization of the versatile dextran-based molecular amplifier 6 is described. Dextran (Mr = 40,200) was selectively monofunctionalized in high yield at its reducing terminus via reductive amination with 2-(4-nitrophenyl)ethylamine to give 1. The nitro group in 1 serves as a masked amino group which is eventually converted into a reactive isothiocyanato group used for monovalent attachment of the completed assembly to a target molecule. Cyanoethylation of 1 gave the terminally nitrophenylated poly(cyanoethyl)dextran 5 which was selectively reduced to the corresponding poly(aminopropyl) derivative 6 with BH3.THF, a reagent which preserved the end nitro group. Conjugation of amplifier 6 with the isothiocyanate-derivatized Gd(III) chelate 7 gave conjugate 9 containing about 22 mol of chelate/mol of amplifier. The T1 relaxivity per Gd(III) ion of 9 in H2O was 15.0 mM-1 s-1, about 3-fold higher than that of free Gd(III)DTPA in H2O. The nitro group of 9 was then selectively reduced to the corresponding amine 10, which was converted into isothiocyanate 11. The reactivity of the single isothiocyanate group in 11 was demonstrated by coupling to 5-aminoeosin, giving conjugate 12. Amplifier 6 was also conjugated with the acid-labile N-cis-aconityl derivative 8 of the potent anticancer agent daunomycin. The nitro group of the resulting conjugate 13 was then reduced and the resulting amine 14 was converted into mono isothiocyanate 15. Compound 15 reacted with a water-insoluble amine-containing solid support to give 16. Free daunomycin was released from 16 by exposure to citrate-phosphate buffer at pH 4.0.

Degradation of acetalated dextran can be broadly tuned based on cyclic acetal coverage and molecular weight

“…Optical density assay was used for all degradation measurements in this study because it provided more reliable readings across different pH levels and could be used for polymers of different MWs. In the BCA assay, a copper ion reacts with only the reducing end group of the dextran molecule (Mann et al, 1992). Because polymers of higher dextran MW have larger units and fewer terminal groups, BCA was less reactive to Ace-DEX polymers with a MW larger than 10 kDa.…”

Release from polymeric prodrugs: Linkages and their degradation

“…This linkage was stable at physiological pH and could be cleaved easily at the acidic pH encountered in endosomes and lysosomes. Since then, several other polymeric prodrugs employing the cis ‐aconityl amide linkage like poly(aminopropyl)dextran‐daunorobicin,118 alginate‐daunomycin,119 chitosan–adriamycin,120 mPEG–PLLA–doxorubicin,86 and HPMA–doxorubicin82 have been synthesized. Release from a polymeric prodrug containing a cis ‐aconityl amide bond is represented in Scheme .…”

Alkynyl Ethers of Glucans: Substituent Distribution in Propargyl‐, Pentynyl‐ and Hexynyldextrans and ‐amyloses and Support for Silver Nanoparticle Formation

“…[4] Mann et al prepared termini-labelled aminopropyldextrans for targeted drug release. [5] Amphiphilic dextrans [6,7] have also been applied for nanoparticle coating, and as drug carrier systems in emulsion polymerisation [8] or direct nanoparticle formation. [9] Heinze and coworkers have prepared a wide range of ester derivatives, which form nanoparticles by dialysis from dimethylacetamide à (DMAc) solution against water.…”