The screening of natural products in the search for new lead compounds against Alzheimers disease has unveiled several plant polyphenols that are capable of inhibiting the formation of toxic b-amyloid fibrils.G allic acid based gallotannins are among these polyphenols,but their antifibrillogenic activity has thus far been examined using "tannic acid", ac ommercial mixture of gallotannins and other galloylated glucopyranoses.T he first total syntheses of two true gallotannins,ahexagalloylglucopyranose and ad ecagalloylated compound whose structure is commonly used to depict "tannic acid", are nowd escribed. These depsidic gallotannins and simpler galloylated glucose derivatives all inhibit amyloid b-peptide (Ab)a ggregation in vitro,a nd monogalloylated a-glucogallin and an atural b-hexagalloylglucose are shown to be the strongest inhibitors.Abnormal amyloid b-peptide (Ab)accumulation and aggregation into toxic fibrils is one of the major processes occurring during the progression of Alzheimers disease (AD), which today affects approximately 36 million people worldwide. [1a, 2] Although the etiology of this severe neurodegenerative disorder,w hich causes dementia in the elderly,r emains unknown, [1b,2] ag lobal effort was initiated in the early 1990s to search for neuroprotective therapeutic agents with antifibrillogenic activity. [1c,d] In this context, natural-product screening programs were implemented with the aim of identifying molecules that are capable of preventing the aggregation and/or promoting the clearance of Ab. [1c,e] Afew recent investigations have focused on plant polyphenols, which are known for their antioxidant activity and their metal-chelation and protein-binding abilities,aset of properties that makes them potentially good candidates as multifunctional drugs for the treatment of AD and other fibrillogenic neurodegenerative disorders,s uch as Parkinsons and Huntingtons diseases. [1c,e,3] Curcuminoids,s uch as curcumin itself,stilbenoids,s uch as resveratrol, and flavonoids,s uch as myricetin and epigallocatechin gallate (EGCg), all belong to aselect group of plant polyphenols that have been identified as inhibitors of Ab aggregation, mainly in vitro. [1c, 4] Gallic acid based polyphenols,s uch as the gallotannins and ellagitannins (Scheme 1), [3a, 5, 6a,b] have surprisingly been mostly left aside in these investigations,likely because of the difficulties associated with accessing them in pure form.Concerning the gallotannins,tothe best of our knowledge, investigations have been limited to the evaluation of 1) their ultimate precursor,1 ,2,3,4,6-penta-O-galloyl-b-d-glucopyranose (b-PGG, b-3;Scheme 1), which was shown to inhibit Ab fibril formation and to destabilize pre-formed Ab fibrils in vitro and in vivo, [7a] and 2) commercial tannic acid (TA), which was reported to destabilize Ab fibrils in vitro. [7b] TA is the sole available standard that is commonly but inappropriately used to assess the (biological) properties of gallotannins. [8,9a] It is usually depicted as the meta-deps...