Synthesis of polyglycerol, porphyrin-cored dendrimers using click chemistry

Polyglycerol, porphyrin-cored dendrimers were synthesized by the click reaction of azide-cored polyglycerol dendrons and octa-alkynylporphyrin 19. The dendrons were synthesized divergently starting with TBDPS-protected allyl alcohol 2. Two, three and four cycles of dihydroxylation-allyl etherification gave dendrons [G-2.5] 6, [G-3.5] 8, [G-4.5] 11, with four, eight, and sixteen alkene groups, respectively. Dendron 11 was readily prepared on large scale with an overall yield of 45%. Dendron 8 was deprotected and converted into the corresponding alkyne - and azide-cored dendron 13 and 15 in 89% and 75% yield, respectively. Dendron 11 was deprotected and converted into the corresponding alkyne - and azide-cored dendron 16 and 18 in 68% and 24% yield, respectively. Both the [G-3.5]-azide 15 and [G-4.5]-azide 18 were separately "clicked" to polyalkyne core 19 via the Huisgen 1,3-dipolar cycloaddition to afford 20 and 21 in 65% and 66% yield, respectively. Dendrimer 21 has a MW of ca. 16000 and 128 peripheral alkene groups.