Combinatorial diversification of indinavir: in vivo mixture dosing of an HIV protease inhibitor library

doi:10.1016/S0960-894X(00)00276-6

Bioorganic & Medicinal Chemistry Letters

Volume 10, Issue 14, 17 July 2000, Pages 1527-1530

https://doi.org/10.1016/S0960-894X(00)00276-6 Get rights and content

Abstract

An efficient combination solution-phase/solid-phase route enabling the diversification of the P₁′, P₂′, and P₃ subsites of indinavir has been established. The synthetic sequence can facilitate the rapid generation of HIV protease inhibitors possessing more favorable pharmacokinetic properties as well as enhanced potencies. Multiple compound dosing in vivo may also accelerate the identification of potential drug candidates.

Introduction

The human immunodeficiency virus type 1 (HIV-1) is the etiologic agent of acquired immunodeficiency syndrome (AIDS). The discovery of clinically effective HIV protease inhibitors¹ in the recent past has significantly improved the lifestyle of many individuals afflicted with the virus. Never-the-less, current protease inhibitors suffer to some extent from issues not limited to first-pass metabolism, toxicities and food restrictions which often times contribute to patient non-compliance. More recently, the emergence of multi-drug resistant viral variants has been confirmed,² further compromising the effectiveness of current PI therapy. Indinavir, a potent and specific orally bioavailable HIV protease inhibitor, is metabolized by P450 isoforms in the CYP3A subfamily.³ In order to further address the pharmacokinetic properties as well as in vivo potencies of indinavir, we have initiated an investigation directed toward the examination of its metabolically labile sites via generation of an ‘indinavir-based’ combinatorial library.⁴ Depicted in Figure 1 are the major sites of metabolism of indinavir.³ We postulated that diversification of these sites would lead to a second generation HIV protease inhibitor possessing improved pharmacokinetic and potency profiles.

Section snippets

Chemistry

Our synthetic endeavor began with lactone 1 (Scheme 1) as previously prepared by Dorsey et al.⁵ Hydrolysis of 1 employing aqueous LiOH in DME followed by removal of the water and subsequent exposure to allyl bromide provided hydroxyethylene isostere 2 (containing the ‘X’ dimension of the library). Tethering the secondary alcohol of 2 to the resin was determined to provide the greatest synthetic flexibility. Accordingly, esterification of Rapp TentaGel S CO₂H resin⁶ employing 2 as the

Results

The biological activities of the 3 pools are displayed in Table 1. The compounds were tested for their ability to prevent cleavage of a substrate by the protease enzyme (IC₅₀) and to inhibit the spread of viral infection in MT4 human T-lymphoid cells infected with the IIIb isolate (CIC₉₅).¹⁴ The results in Table 1 indicate that mixtures had no deleterious effects on our assays. As anticipated, the pool containing the Z₁ ligand (present in indinavir) displayed the highest affinity for the HIV

Pharmacokinetics

The next challenge we faced was the multiple component in vivo dosing of our library (0.5 mpk/compound; 20 compounds per dog [n=2], 0.05 M citric acid solution). We postulated that individual compounds possessing optimal pharmacokinetic properties would be readily discernible within the mixture.¹⁵ This strategy would accelerate the identification of those compounds using only 2 dogs rather than the 40 dogs required to dose 20 individual compounds. However, if accurate pharmacokinetic data were

Conclusion

In summary, we have established a flexible solid-phase synthesis enabling the diversification of the P₁′, P₂′, and P₃ subsites of indinavir. The synthetic route can be utilized in the generation of an ‘indinavir-based’ library or libraries directed toward identification of a second generation HIV protease inhibitor possessing improved metabolic and potency profiles. We have also demonstrated that in vitro potency can be measured accurately on mixtures obtained from libraries. Furthermore,

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