Design, synthesis, and QSAR studies of novel lysine derives as amino-peptidase N/CD13 inhibitors Qiang Wang, a Maoying Chen, a Huawei Zhu, a Jie Zhang, a Hao Fang, a Binghe Wang b and Wenfang Xu a, * a Department of Medicinal Chemistry, School of Pharmacy, Shandong University, Ji’nan, Shandong 250012, PR China b Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA Received 30 January 2008; revised 6 April 2008; accepted 8 April 2008 Available online 11 April 2008 Abstract—A series of novel L-lysine derivatives were designed, synthesized, and assayed for their inhibitory activities on amino-pepti- dase N (APN)/CD13 and matrix metalloproteinase-2 (MMP-2). The preliminary biological test showed that most of the compounds displayed a high inhibitory activity against MMP-2 and a low activity against APN except compound B6 which exhibited good potency (IC 50 = 13.2 lM) similar with APN inhibitor Bestatin (IC 50 =15.5 lM), and could be used as lead compound in the future. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction As a zinc-dependent endopeptidase, amino-peptidase N (APN) is also known as CD13. Scientific research has been found that APN is over-expressed on tumor cells and play an important role in extracellular matrix degra- dation and invasion of tumor cells. Therefore, APN has been a target for anticancer agents design. Since 1976, a great amount of natural inhibitors have been found to bind APN with high affinity (Fig. 1), including Bestatin (1), 1 probestin (2), 2 amastatin (3), 3 actinonin (4), 4 phebestin ( 5), 5 lapstatin (6), 6 AHPA-Val (7), 7 leuhistin (8), 8 curcumin (9) 9 , and pasmmaplin A (10). 10 Our group has synthesized a series of 3-galloylamido- N 0 -substituted 2,6-piperidinedione-N-acetamide pepti- domimetics and found that the two target compounds displayed a similar inhibitory activity compared with Bestatin. 11 In our on-going work, the strategy of computer-aided molecular design has been used for developing new peptidomimetics as APN inhibitors and the docking studies have been done with natural APN inhibitors listed in Figure 1. The results suggested that the APN inhibitors can be divided into three parts. Part A: hydrophobic fragment; Part B: zinc binding group (ZBG); and Part C: heterocyclic rings or hydro- phobic groups (Fig. 2). According to the literature, ZBG (part 2) could be car- boxylic acid and hydroxymate. Then, the next step we need to do should be not only the determination of the hydrophobic fragment or heterocycle as part A and part C, but also the choosing of a linker to connect the three parts. In our preliminary studies, L-lysine was selected as a linker due to its structure containing two amino groups and one carboxylic acid which can be used as ZBG. Therefore, a series of L-lysine derivatives could be designed with different a-amino substitution and N 6 -amino substitution. In this study, we reported the preparation and in vitro APN inhibition studies of N 6 -Cbz substituted L-lysine derivatives. 2. Chemistry The synthesis of target compounds is shown in Scheme 1. The N 6 -amino of L-lysine was selectively protected by Cbz (carbobenzoxy) and then esterificated with HCl in methanol to generate methyl 2-amino-6-(benzyloxy- carbonylamino)hexanoate hydrochloride. Then, 10 dif- ferent aromatic acids were converted to acyl chloride and reacted with 2-amino group of L-lysine. Finally, the ester functional group was hydrolyzed with NaOH/ H 2 O in methanol or treated with NH 2 OK in methanol to get hydroxymic acid. 0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2008.04.012 Keywords: Lysine derivatives; Synthesis; APN/CD13; Inhibitor; QSAR. * Corresponding author. Tel./fax: +86 531 88382264; e-mail: xuwenf@sdu.edu.cn Available online at www.sciencedirect.com Bioorganic & Medicinal Chemistry 16 (2008) 5473–5481