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.     

Design and synthesis of a new bicyclic dipeptide isostere

The synthesis of a new Gly-Pro turn mimetic and the computational study of its ability to induce beta-turn is reported.     

Diastereoselective synthesis of the Leu-Pro type phosphinyl dipeptide isostere

A diastereoselective synthesis of the Leu-Pro type phosphinyl dipeptide isostere in its protected form was achieved from stereodefined α-amino-H-phosphinate. The methodology involved a cross-coupling reaction with alkenyl triflate and subsequent diastereoselective hydrogenation of the alkene moiety, which capitalized on the phosphorus chirality.     

An efficient synthetic method for Z-fluoroalkene dipeptide isosteres: Application to the synthesis of the dipeptide isostere of Sta-Ala

Reaction of γ,γ-difluoro-α,β-enoates having a δ-hydroxyl group with trialkylaluminum (R₃Al) was found to be promoted by CuI·2LiCl and to proceed in SN2′ manner giving rise to the α-alkylated (Z)-γ-fluoro-β,γ-enoates, while reductive defluorination of γ,γ-difluoro-α,β-enoates with Me₂CuLi followed by reaction with alkyl halides provided the corresponding (Z)-α-alkylated products in high yields. The latter reaction was applied to the preparation of the dipeptide (Z)-fluoroalkene isostere of Sta-Ala, which is the central dipeptide unit in Pepstatin, a natural inhibitor of aspartate proteases.     

3-Methoxalylchromone--a novel versatile reagent for the regioselective purine isostere synthesis

The first synthesis of 3-methoxalylchromone was described. The reaction of the latter with electron-rich aminoheterocycles afforded a set of heteroannelated pyridines bearing a CO(2)Me substituent located at the α-position of the pyridine core.     

A simple and versatile route to ketomethylene dipeptide analogs

A facile and versatile procedure for the synthesis of ketomethylene dipeptides by using N^α-Z-amino acid halomethyl ketones and dimethyl malonate as starting materials is reported. By application of this method, alanyl and phenylalanyl derivatives containing C-terminal Gly, Ala, Asp, Phe and Trp residues have been prepared.     

Synthesis of a Gln-Phe hydroxy-ethylene dipeptide isostere

[structure: see text] The protected Gln-Phe hydroxyethylene dipeptide isostere 1 was synthesized as a precursor for preparation of potential inhibitors of Botulinum neurotoxin B metalloprotease. The method allows for the synthesis of additional hydroxyethylene dipeptide isosteres such as 2 with functionalized P1 side chains. The isosteres prepared were coupled with a dipeptide to produce protected pseudotetrapeptide derivatives.     

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.     

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).     

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.     

Synthesis of a Val-Pro diaminodiol dipeptide isostere by epoxyamine cyclization

[reaction: see text] The stereoselective synthesis of a novel proline-containing dipeptide isostere is described. Starting from l-valine, three new contiguous stereocenters are generated by asymmetric induction and epoxide chemistry, while the pyrrolidine ring of proline is introduced in the final step via intramolecular ring opening of the amino acid derived epoxyamine. Proline-containing peptidomimetics are potentially attractive as selective inhibitors of proline-specific enzymes, such as PPIases and retroviral proteases, and as analogues of bioactive peptides.     

A simple and efficient synthesis of an Asp-Gly dipeptide mimetic

Alkylation of N^α-Boc protected aspartic acid with allyl bromide in the presence of lithium bis(trimethylsilyl)amide (LHMDS) and hexamethylphosphoramide (HMPA) afforded chiral β-allyl substituted aspartic acid in good yields. After deprotection of the N^α-Boc group and reprotection as a trifluoroacetamide, the terminal alkene was oxidized to an aldehyde. The aldehyde was then coupled with l-cysteine through a cascade three-bond formation process to afford aspartic acid-glycine bicyclic dipeptide mimetics.     

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.     

Short and efficient diastereoselective synthesis of pyrrolidinone-containing dipeptide analogues

The pyrrolidine-2,4-diones have been identified as a convenient starting point for the synthesis of peptide analogues. Herein we describe an optimized two-step reductive amination procedure, which provides a small library of pyrrolidinone-containing dipeptide analogues in high yield and excellent diastereoselectivity.     

A versatile solid-phase synthesis of 3-aryl-1,2,4-oxadiazolones and analogues

We report here the first method to load acidic heterocyclic compounds (1,2,4-oxadiazol-5-one, 1,2,4-oxadiazol-5-thione and 1,2,3,5-oxathiadazol-2-oxide) on a polymer. Using Mitsunobu conditions, these heterocycles were anchored on a 4-hydroxymethyl-3-methoxyphenoxybutyric acid benzhydrylamine (HMPB-BHA) resin. After diversification, compounds can be recovered by a simple treatment in diluted TFA. To illustrate the utility of this procedure, iodophenyl derivatives were anchored on the same resin. A HRMAS-NMR analysis shed light on the reactivity of these heterocycles in Mitsunobu conditions. A subsequent diversification using a Sonogashira coupling produced a small array of novel (arylethynyl)-phenyl-1,2,4-oxadiazol-5-ones.     

Synthesis of the pro-gly dipeptide alkene isostere using olefin cross-metathesis

An approach to the synthesis of dipeptide olefin isosteres using intermolecular olefin cross-metathesis is presented. In particular, a synthesis of the Pro-Gly isostere (1) is reported. Conversion of N-BOC-proline into the corresponding vinyl-substituted carbamate provides the N-terminal cross-metathesis partner (2). Methyl 3-butenoate (3) is employed as the C-terminal component. Treatment of the two partners in an optimized molar ratio affords the cross product 1 (83% yield). Three other examples are demonstrated to evaluate the potential of the approach.     

A versatile synthesis of tricyclic analogues of quinolone antibacterial agents: Use of a novel reformatsky reaction

A simple synthesis of tricyclic analogues of the quinolone antibiotics bearing a diverse range of substituents on the aromatic ring is described. The key steps involve unprecedented Reformatsky reaction between diethyl bromomalonate and N-arylpyrrolidine-2-thiones 8, followed by cyclisation of the resulting enaminone intermediates 9 in polyphosphoric acid.