Inhibition of amyloid-b aggregation by coumarin analogs can be manipulated by functionalization of the aromatic center Deborah D. Soto-Ortega a , Brandon P. Murphy a,  , Francisco J. Gonzalez-Velasquez a , Kelly A. Wilson a , Fang Xie b , Qian Wang b,⇑ , Melissa A. Moss a,⇑ a Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208, USA b Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA article info Article history: Received 9 December 2010 Revised 26 February 2011 Accepted 6 March 2011 Available online 12 March 2011 Keywords: Alzheimer’s disease Amyloid-b protein Coumarin Amyloid aggregation Inhibitor abstract Aggregation of the amyloid-b protein (Ab) plays a pathogenic role in the progression of Alzheimer’s dis- ease, and small molecules that attenuate Ab aggregation have been identified toward a therapeutic strat- egy that targets the disease’s underlying cause. Compounds containing aromatic structures have been repeatedly reported as effective inhibitors of Ab aggregation, but the functional groups that influence inhibition by these aromatic centers have been less frequently explored. The current study identifies ana- logs of naturally occurring coumarin as novel inhibitors of Ab aggregation. Derivatization of the coumarin structure is shown to affect inhibitory capabilities and to influence the point at which an inhibitor inter- venes within the nucleation dependent Ab aggregation pathway. In particular, functional groups found within amyloid binding dyes, such as benzothiazole and triazole, can improve inhibition efficacy. Further- more, inhibitor intervention at early or late stages within the amyloid aggregation pathway is shown to correlate with the ability of these functional groups to recognize and bind amyloid species that appear either early or late within the aggregation pathway. These results demonstrate that functionalization of small aromatic molecules with recognition elements can be used in the rational design of Ab aggrega- tion inhibitors to not only enhance inhibition but to also manipulate the inhibition mechanism. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Current therapies for Alzheimer’s disease (AD) target disease symptoms by increasing neurotransmission between surviving neurons to enhance memory and learning and thus improve qual- ity of life. However, these therapies do not provide long-term ben- efits as they fail to treat the disease’s underlying cause. 1,2 Leading theories suggest that amyloid plaques, which accumulate in the hippocampus and cerebral cortex, are the primary abnormality in AD. The principal component of these plaques, the amyloid-b pro- tein (Ab), is a proteolytic product of the transmembrane amyloid precursor protein (APP) and exhibits amphiphilic character as a result of its position within APP. Driven primarily by hydrophobic interactions, Ab undergoes a nucleation dependent aggregation to produce ordered amyloid fibrils that deposit as plaques. This aggregation has been strongly implicated in disease progres- sion. 1,3,4 Thus, preventing aggregation of Ab represents a therapeu- tic strategy that directly targets AD pathogenesis. 1,5 Numerous small molecules have been reported to interfere with the process of Ab aggregation. 6–8 In particular, compounds contain- ing aromatic centers are capable of preventing the assembly of monomeric Ab into amyloid fibrils. 7,9,10 These compounds are hypothesized to interact with aromatic residues within the hydro- phobic core of Ab 11–15 and to inhibit aggregation by disrupting p- stacking of these aromatic residues, which is proposed to play a key role in amyloid aggregate formation and growth. 11 Less is known, however, about how the functionalization of aromatic cen- ters can influence inhibitory capabilities. Among the limited reports of substituents that enhance inhibition are flexible hydrophobic moieties for functionalization of bisphenols; 12 hydroxy substitu- tions of the D-ring of apomorphorine; 13 polar, hydrogen bonding groups as substituents of aromatic centers within curcumin ana- logs; 14 the positioning of carboxylic acid groups and the optimal length of the linker between aromatic centers for anthranilic acid analogs; 15 and conformational flexibility of linkers that separate aromatic centers within derivatives of anthracycline, tetracycline, and carbazole. 16 Expanding the knowledge of functional groups that 0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2011.03.010 Abbreviations: Ab, amyloid-b protein; AChE, actylcholinesterase; AD, Alzhei- mer’s disease; APP, amyloid precursor protein. ⇑ Corresponding authors. Addresses: Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC 29208, USA. Tel.: +1 803 777 8436; fax: +1 803 777 9521 (Q.W.); Department of Chemical Engineering, University of South Carolina, 2C02 Swearingen Engineering Center, Columbia, SC 29208, USA. tel.: +1 803 777 5604; fax: +1 803 777 0973 (M.A.M.). E-mail addresses: wang@mail.chem.sc.edu (Q. Wang), mossme@cec.sc.edu (M.A. Moss).   Present address: Marathon Petroleum Co LLC, Garyville, LA, USA. Bioorganic & Medicinal Chemistry 19 (2011) 2596–2602 Contents lists available at ScienceDirect Bioorganic & Medicinal Chemistry journal homepage: www.elsevier.com/locate/bmc