Synthesis of potent beta-secretase inhibitors containing a hydroxyethylamine dipeptide isostere and their structure-activity relationship studies

Several beta-secretase inhibitors were designed based on hydroxyethylamine dipeptide isostere (HDI) structures and were synthesized by a methodology using the aza-Payne rearragement and O,N-acyl transfer reactions to study their structure-activity relationships. Among these pseudopeptides, effective compounds were developed as the first beta-secretase inhibitors containing the HDI transition state mimic with potent enzyme inhibitory activity (IC50 < 100 nM).     

Rational design and synthesis of a novel class of active site-targeted HIV protease inhibitors containing a hydroxymethylcarbonyl isostere. Use of phenylnorstatine or allophenylnorstatine as a transition-state mimic.

A novel class of HIV-1 protease inhibitors containing a hydroxymethylcarbonyl (HMC) isostere were designed from the substrate transition state and synthesized. Phenylnorstatine [Pns; (2R,3S)-3-amino-2-hydroxy-4-phenylbutyric acid] and the 2S diastereomer, (2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid, named allophenylnorstatine (Apns) were effective transition-state mimics, and incorporation of Pns-Pro or Apns-Pro at the P1-P1' site gave potent and specific HIV-1 protease inhibitors. In the inhibitory assays, the chemically synthesized [Ala67,95] HIV-1 protease was used.     

Solid-phase synthesis of HTLV-1 protease inhibitors containing hydroxyethylamine dipeptide isostere

An efficient method has been developed for the first solid-phase synthesis of HTLV-1 protease inhibitors that contain hydroxyethylamine isostere as a transition-state mimetic. The synthetic procedure was designed to allow the evaluation of stereostructure-activity relationships at the scissile site. All the possible configurations at the hydroxy- and side chain-bearing asymmetric centers of the isostere were constructed by an ester-derived asymmetric aldol reaction. Each inhibitor containing the isostere backbone was synthesized on solid support by using the newly developed succinate ester linker. The configuration at the hydroxy- and side chain-bearing asymmetric center showed remarkable effects on the inhibitory activity; the K(i) value changed with approximately 2 orders of magnitude. The described approach enables an efficient preparation of the inhibitors containing secondary alcohol as a transition-state mimetic.     

Kynostatin (KNI)-227 and -272, highly potent anti-HIV agents: conformationally constrained tripeptide inhibitors of HIV protease containing allophenylnorstatine.

Selective and potent HIV protease inhibitors containing allophenylnorstatine [Apns; (2S, 3S)-3-amino-2-hydroxy-4-phenylbutyric acid] as a transition-state mimic were designed and synthesized. Among them, conformationally constrained tripeptide derivatives, kynostatin (KNI)-227 and -272 (Fig. 1), exhibited highly potent antiviral activities against a wide spectrum of HIV isolates. Ready availability due to the simple synthetic procedure and the excellent antiviral properties indicate that KNI-227 and KNI-272 are promising candidates as selective anti-AIDS drugs.     

An efficient, stereoselective synthesis of the hydroxyethylene dipeptide isostere core for the HIV protease inhibitor A-792611

A stereoselective synthesis of the hydroxyethylene dipeptide isostere 1 is described. The route employs a substrate-directed kinetic protonation of an alpha/gamma-substituted lactone to afford the desired stereochemistry. A method for converting the diastereomerically enriched intermediate lactone to the ring-open form with retention of stereochemistry is demonstrated. A novel procedure for utilizing N,N-dibromo-5,5-dimethylhydantoin in Hofmann rearrangements is disclosed. This route was used to prepare amino alcohol 1, the core portion of the HIV protease inhibitor A-792611, in 46% yield from phenylalanine-derived epoxide 2.     

New approaches to the industrial synthesis of HIV protease inhibitors

Efficient and industrially applicable synthetic processes for precursors of HIV protease inhibitors (Amprenavir, Fosamprenavir) are described. These involve a novel and economical method for the preparation of a key intermediate, (3S)-hydroxytetrahydrofuran, from l-malic acid. Three new approaches to the assembly of Amprenavir are also discussed. Of these, a synthetic route in which an (S)-tetrahydrofuranyloxy carbonyl is attached to l-phenylalanine appears to be the most promising manufacturing process, in that it offers satisfactory stereoselectivity in fewer steps.     

KNI-272, a highly selective and potent peptidic HIV protease inhibitor

Kynostatin {KNI-272; systematic name: 3-[3-benzyl-2-hydroxy-9-(isoquinolin-5-yl­oxy)-6-methyl­sulfanyl­methyl-5,8-dioxo-4,7-di­aza­nonanoyl]-N-tert-butyl-1,3-thia­zolane-4-carbox­amide}, a highly selective and potent HIV protease inhibitor containing allo­phenyl­norstatin [(2S,3S)-3-amino-2-hydroxy-4-phenyl­butyric acid], has been crystallized as the hydrate, C₃₃H₄₁N₅O₆S₂·0.803H₂O, from aqueous hexyl­ene glycol. The observed disorder of the phenyl group in the structure is related to the mode of hydration. The backbone conformation of the mol­ecule is twisted and the overall conformation of the free inhibitor is similar to that observed in its complex with HIV protease.     

Rapid synthesis and in situ screening of potent HIV-1 protease dimerization inhibitors

A library of dimerization inhibitors of HIV-1 protease is described based on crosslinked interfacial peptides. The 54 component library was designed to contain two modifications to the starting structure, one each in the Northern and Southern fragments. A rapid synthesis and in situ screening method in microtiter plates was developed to facilitate the generation and evaluation of the library members. More than 90% of the doubly modified agents were more potent than their respective singly mutated parent compounds, and five of the most potent dimerization inhibitors of HIV-1 protease described to date were identified. The free energy of binding for the combined two modifications was generally found to be additive, demonstrating the predictive value of earlier libraries.     

High-speed synthesis of potent C2-symmetric HIV-1 protease inhibitors by in-situ aminocarbonylations

Two novel series of C2-symmetric HIV-1 protease inhibitors were synthesized by microwave-promoted, palladium-catalyzed aminocarbonylations of the o-iodo- and m-bromobenzyloxy P1/P1' substituted core structures. Molybdenum hexacarbonyl was used as a convenient solid source of carbon monoxide in these transformations. After the initial high-speed library generation, biological testing identified highly active HIV-1 protease inhibitors. Selected ortho- and meta-decorated inhibitors were subsequently resynthesized on a larger scale and retested for their affinity toward HIV-1 protease, showing micromolar to low nanomolar inhibition. The discovery of highly active inhibitors containing large phenyl amide ortho substituents in the P1/P1' positions indicates that larger groups than previously believed are tolerated in this part of the S1/S1' pocket.     

A concise synthesis of silanediol-based transition-state isostere inhibitors of proteases

[reaction: see text] An efficient synthesis of silanediol-based transition-state inhibitors of proteases is described. A new convergent synthesis has been optimized by using a two-step sequence of hydrosilylation followed by the addition of a silyllithio species to an imine. The method should be applicable to the synthesis of a wide variety of silanediol isosteres to probe the utility of this unique transition-state isostere.     

Structure-activity relationship studies of gymnocin-A

The structural elements required for cytotoxicity of gymnocin-A, a polycyclic ether isolated from the red tide-forming dinoflagellate, Karenia mikimotoi, were investigated by the total synthesis and evaluation of the structural analogues. The results of the structure-activity relationship studies indicated that the α,β-unsaturated aldehyde functionality of the side chain as well as the molecular length were needed for exhibiting the cytotoxicity of gymnocin-A.     

A quick diversity-oriented amide-forming reaction to optimize P-subsite residues of HIV protease inhibitors

We report a new simple method that allows rapid preparation in solution of a library of compounds for in situ high-throughput screening to identify new inhibitors of HIV-1 protease. The method is based on the amide-forming reaction of a C(2)-symmetrical diamino diol core with various carboxylic acids, followed by a direct assay of the inhibition activity without product isolation. Sixty-two compounds were made and screened in less than 1 hr. The utility of this method is demonstrated by the identification of new P3-P3' residues that convert a transition state analog core from a poor binding molecule (1, K(i) > 2 microM) to a potent inhibitor (AB1, K(i) = 2 nM) against the wild-type, and the inhibition activities against resistant mutants are better than those of two existing drugs. This method reduces the time required for synthesis and testing of a large number of characterized inhibitors and should find useful applications in other enzyme systems.     

Synthesis of a first thiophene containing analog of the HIV protease inhibitor nelfinavir

A stereoselective and efficient preparation of a thiophene containing intermediate 2 from ethyl 3-thienyl propenoate 4 as the core of new possible HIV protease inhibitors is described. The chiral intermediate has been successfully used for the preparation of the analog 1 of the potent HIV inhibitor nelfinavir.     

Synthesis of a tripeptide derivative containing the Phe-Arg hydroxyethylene dipeptide isostere

The protected hydroxyethylene dipeptide isostere of Phe-Arg and the tripeptide derivative 1 were synthesized as components of potential peptidase inhibitors. Key to the success of these syntheses is selective rhodium-catalyzed hydroboration in the presence of a readily reduced lactone. A convenient one-pot conversion of azides to diprotected guanidines was developed on the basis of the Staudinger reaction.     

Synthesis of a tripeptide derivative containing the gln-arg hydroxyethylene dipeptide isostere

[structure: see text] The protected hydroxyethylene dipeptide isostere of Gln-Arg and the tripeptide derivative 1 were synthesized as components of potential peptidase inhibitors.