Shu-Hui Chen

Synthesis and evaluation of tripeptidyl α-Ketoamides as human rhinovirus 3C protease inhibitors

Abstract We describe herein the synthesis and biological evaluation of a series of tripeptidyl α-ketoamides as human rhinovirus (HRV) 3C protease inhibitors. The most potent inhibitor discussed in this manuscript, 4I, exhibited impressive enzyme inhibitory activity as well as antiviral activity against HRV-14.

Syntheses and antifungal activities of novel 3-amido bearing pseudomycin analogues.

As a result of our core SAR effort, we discovered a large number of 3-amido pseudomycin B (PSB) analogues (e.g., 4e LY448212 and 5b LY448731) that retain good in vitro and in vivo (IP) activities against Candida and Cryptococcus without inherent tail vein irritation. Several dimethylamino termini bearing 3-amides (e.g., 5b) also exhibited improved potency against Aspergillus in vitro. When evaluated in a two-week rat toxicology study, it was found that all animals receiving 4e (up to 75 mg/kg) were found to be normal. On the basis of these observations, we are convinced that it is possible to broaden the antifungal spectrum and improve the safety profile of pseudomycin analogues at the same time.

Biochemical and kinetic characterization of BACE1: investigation into the putative species-specificity for β- and β′-cleavage sites by human and murine BACE1

β‐amyloid peptides (Aβ) are produced by a sequential cleavage of amyloid precursor protein (APP) by β‐ and γ‐secretases. The lack of Aβ production in beta‐APP cleaving enzyme (BACE1)–/– mice suggests that BACE1 is the principal β‐secretase in mammalian neurons. Transfection of human APP and BACE1 into neurons derived from wild‐type and BACE1–/– mice supports cleavage of APP at the canonical β‐secretase site. However, these studies also revealed an alternative BACE1 cleavage site in APP, designated as β′, resulting in Aβ peptides starting at Glu11. The apparent inability of human BACE1 to make this β′‐cleavage in murine APP, and vice versa, led to the hypothesis that this alternative cleavage was species‐specific. In contrast, the results from human BACE1 transgenic mice demonstrated that the human BACE1 is able to cleave the endogenous murine APP at the β′‐cleavage site. To address this discrepancy, we designed fluorescent resonance energy transfer peptide substrates containing the β‐ and β′‐cleavage sites within human and murine APP to compare: (i) the enzymatic efficiency; (ii) binding kinetics of a BACE1 active site inhibitor LY2039911; and (iii) the pharmacological profiles for human and murine recombinant BACE1. Both BACE1 orthologs were able to cleave APP at the β‐ and β′‐sites, although with different efficiencies. Moreover, the inhibitory potency of LY2039911 toward recombinant human and native BACE1 from mouse or guinea pig was indistinguishable. In summary, we have demonstrated, for the first time, that recombinant BACE1 can recognize and cleave APP peptide substrates at the postulated β′‐cleavage site. It does not appear to be a significant species specificity to this cleavage.

Prodrugs of 3-amido bearing pseudomycin analogues: novel antifungal agents

With the aim of identifying safer pseudomycin derivatives, we synthesized and evaluated a number of N-acyloxymethyl carbamate linked prodrugs of 3-amido pseudomycin analogues. To our satisfaction, all of the prodrug-amide combinations prepared exhibited good in vivo efficacy against murine Candidiasis. When evaluated in a dose elevation study, all of the newly synthesized combinations (e.g., 4A, 6A, 8A, and 8B) demonstrated improved toxicity profiles in comparison to their corresponding 3-amides as well as the parent pseudomycin B.

8-amido-bearing pseudomycin B (PSB) analogue: novel antifungal agents

During the course of a structure-activity relationship (SAR) study on novel depsinonapeptide pseudomycin B, we synthesized a total of 12 8-amidopseudomycin analogues via standard two-step sequence from either ZPSB 2 or AllocPSB 3. A number of these amides exhibited good in vitro antifungal activities.

Syntheses and antifungal activity of pseudomycin side-chain analogues. Part 1.

We have described herein the syntheses of three novel series of aromatic ring containing pseudomycin side-chain analogues. Preliminary biological evaluations of these analogues clearly indicate that it is possible to synthesize rigid pseudomycin side-chain analogues without compromising in vitro antifungal activity.

Synthesis and evaluation of novel pseudomycin side-chain analogues. Part 3.

To increase the therapeutic utility of C-18 side-chain bearing pseudomycin analogue 2, we prepared additional analogues and prodrugs of 2 containing further modifications at various positions within its core structure. Each of the newly synthesized derivatives (10-15) exhibited reduced tail vein toxicity relative to the parent compound. Some of the new pseudomycin derivatives (e.g., 14) also showed improved in vivo antifungal activity relative to its corresponding parent compound.

Serendipitous synthesis of novel dehydro- and dechloro-pseudomycin B (PSB) derivatives

The syntheses and preliminary investigation of antifungal activities of two dehydro PSB derivatives 8 and 10 as well as one 3-imido-9-dechloro PSB analogue 13 are described.

Syntheses and biological evaluation of novel pseudomycin side-chain analogues. Part 2.

A series of aliphatic side-chain analogues of pseudomycin was synthesized and evaluated during the course of our side-chain SAR effort. We found that several of the pseudomycin side-chain analogues (e.g., 10) exhibited good in vitro activity against all three major fungi responsible for systemic fungal infections.

Preorganization of the Hydroxyethylene Dipeptide Isostere: The Preferred Conformation in Solution Resembles the Conformation Bound to BACE

Conformational analysis in solution of beta-secretase inhibitors 1 and 2 by NMR spectroscopy reveals that the hydroxyethylene isostere, an apparently flexible fragment widely used as a scissile bond replacement in aspartic protease inhibitors, exists in one predominant conformation in solution. This preferred conformation is similar to that adopted by the hydroxyethylene core of 1 in complex with beta-secretase and that adopted by hydroxyethylene cores of related compounds when bound to aspartic proteases, indicating that this structural unit is preorganized in solution.