Abstract: The deposition of Amyloid beta peptides (Aβ) in the formation of amyloid fibrils is believed to be causally linked to Alzheimer's disease. A short Aβ fragment (KLVFF; Aβ_16-20) can bind full-length Aβ. The Aβ recognition peptide including KLVFF was attached with hydrophilic groups, and then the product altered the Aβ aggregation pathways and inhibited Aβ toxicity (Tjernberg, L. O. et al. J. Biol. Chem. 1996, 271, 8545-8548. ). Since flavins is widely known as biological oxidation reagents, the flavin-linked KLVFF is likely to directly hydroxylate aggregated Aβ fibrils and then disrupt the aggregated Aβ fibril. 2-Aminoethanethiol derivatives, such as cysteine, is reacted with　aldehydes, and five-membered heterocyclic ring is formed via formation of imine. Since formylmethylflavin (FMF) contains aldehyde group, FMF is likely to bind cysteine. Then, the peptides containing Aβ recognition region and cysteine, such as CKLVFF, also can be attached with FMF to form the flavin-linked KLVFF. The preliminary experiment of this reaction, the reaction between FMF and cysteine, was investigated. FMF (2.84 mg, 10 μmol) was suspended in phosphate buffer (pH 7, 10 ml), and cysteine (2.42 mg, 20 μmol) was added. The suspension was stirred at 65ºC for 1h. As a result, FMF was completely reacted, and flavin-linked cystein were detected using HPLC and ESI-MS.