Synthesis Of HIV-1 Protease Inhibitors Research Articles

Synthesis of HIV-1 Protease Inhibitors

Key words HIV-1 protease inhibitors - Pauson–Khand reaction - kinetic resolution - lipase

Synthesis of HIV-1 Protease Inhibitors

Synthesis of HIV-1 Protease Inhibitors

Synthesis of novel HIV-1 protease inhibitors via diastereoselective Henry reaction with nitrocyclopropane

Novel reaction and work-up conditions were developed for the unprecedented Henry reaction using nitrocyclopropane in the key step towards the synthesis of HIV-1 protease inhibitors. This procedure may find application in the preparation of diverse compounds of potential biological interest.

Enantiomeric resolution, stereochemical assignment and toxicity evaluation of TPA enantiomers.

Tetrahydro-α-(1-methylethyl)-2-oxo-1(2H)-pyrimidineacetic acid (TPA) is a critical intermediate in the synthesis of HIV protease inhibitors. A simple and efficient method for the separation and determination of TPA enantiomers was developed. The TPA was separated into its enantiomers with an enantiomeric purity of 99% using an HPLC system equipped with a Chiralpak OD-H column. Semi-preparative HPLC enantioseparations were carried out for further enrichment of the enantiomers. The validity of this method was evaluated on the basis of its precision, accuracy, linearity and recovery. The method was observed to be suitable for the rapid separation and semi-preparation of TPA isomers. The separated enantiomers were identified by optical rotation and high-resolution electrospray ionization mass spectrometry. Furthermore, the stereochemical structures of the TPA enantiomers were definitively confirmed using a combination of experimental and calculated electronic circular dichroism spectra. The toxicity of the separated pure enantiomers against Oryzias melastigma was evaluated using the median lethal concentration (LC50 ) values. The results indicated that (S)-(-)-TPA is ~2.5 times more toxic than its enantiomorphism.

ChemInform Abstract: A Concise One‐Pot Organo‐ and Biocatalyzed Preparation of Enantiopure Hexahydrofuro[2,3‐b]furan‐3‐ol: An Approach to the Synthesis of HIV Protease Inhibitors.

AbstractThe one‐pot synthesis of the title species (IV) involves condensation of dihydrofuran with glycolaldehyde dimer (II) followed by lipase‐catalyzed kinetic resolution.

A Concise One‐Pot Organo‐ and Biocatalyzed Preparation of Enantiopure Hexahydrofuro[2,3‐b]furan‐3‐ol: An Approach to the Synthesis of HIV Protease Inhibitors

AbstractA simple and efficient one‐pot synthesis of enantiopure hexahydrofuro[2,3‐b]furan‐3‐ol, a crucial component of HIV‐1 protease inhibitors, was developed. The one‐pot process involves an organocatalytic condensation followed by an enzymatic optical resolution. The condensation of 1,2‐dihydrofuran and glycolaldehyde was achieved using Schreiner's thiourea catalyst (1 mol‐%). A subsequent lipase‐catalyzed kinetic resolution gave the target alcohol with >99 % ee. To demonstrate the practicality of this method, Darunavir, an HIV‐1 protease inhibitor used to treat multi‐drug‐resistant HIV, was synthesized.

Continuous Flow Synthesis of α-Halo Ketones: Essential Building Blocks of Antiretroviral Agents

The development of a continuous flow process for the multistep synthesis of α-halo ketones starting from N-protected amino acids is described. The obtained α-halo ketones are chiral building blocks for the synthesis of HIV protease inhibitors, such as atazanavir and darunavir. The synthesis starts with the formation of a mixed anhydride in a first tubular reactor. The anhydride is subsequently combined with anhydrous diazomethane in a tube-in-tube reactor. The tube-in-tube reactor consists of an inner tube, made from a gas-permeable, hydrophobic material, enclosed in a thick-walled, impermeable outer tube. Diazomethane is generated in the inner tube in an aqueous medium, and anhydrous diazomethane subsequently diffuses through the permeable membrane into the outer chamber. The α-diazo ketone is produced from the mixed anhydride and diazomethane in the outer chamber, and the resulting diazo ketone is finally converted to the halo ketone with anhydrous ethereal hydrogen halide. This method eliminates the need to store, transport, or handle diazomethane and produces α-halo ketone building blocks in a multistep system without racemization in excellent yields. A fully continuous process allowed the synthesis of 1.84 g of α-chloro ketone from the respective N-protected amino acid within ~4.5 h (87% yield).

Design and synthesis of HIV-1 protease inhibitors for a long-acting injectable drug application

The design and synthesis of novel HIV-1 protease inhibitors (PIs) (1–22), which display high potency against HIV-1 wild-type and multi-PI-resistant HIV-mutant clinical isolates, is described. Lead optimization was initiated from compound 1, a Phe–Phe hydroxyethylene peptidomimetic PI, and was directed towards the discovery of new PIs suitable for a long-acting (LA) injectable drug application. Introducing a heterocyclic 6-methoxy-3-pyridinyl or a 6-(dimethylamino)-3-pyridinyl moiety (R3) at the para-position of the P1′ benzyl fragment generated compounds with antiviral potency in the low single digit nanomolar range. Halogenation or alkylation of the metabolic hot spots on the various aromatic rings resulted in PIs with high stability against degradation in human liver microsomes and low plasma clearance in rats. Replacing the chromanolamine moiety (R1) in the P2 protease binding site by a cyclopentanolamine or a cyclohexanolamine derivative provided a series of high clearance PIs (16–22) with EC50s on wild-type HIV-1 in the range of 0.8–1.8nM. PIs 18 and 22, formulated as nanosuspensions, showed gradual but sustained and complete release from the injection site over two months in rats, and were therefore identified as interesting candidates for a LA injectable drug application for treating HIV/AIDS.

A General Approach to Chiral Building Blocks via Direct Amino Acid-Catalyzed Cascade Three-Component Reductive Alkylations: Formal Total Synthesis of HIV-1 Protease Inhibitors, Antibiotic Agglomerins, Brefeldin A, and (R)-γ-Hexanolide

Multicatalysis cascade (MCC) process for the synthesis of highly substituted chiral building blocks (2-alkyl-CH-acids, 2-alkylcyclohexane-1,3-diones, 2-alkylcyclopentane-1,3-diones, and H-P ketone analogues) is presented based on the cascade three-component reductive alkylation's (TCRA) platform. Herein, we developed the high-yielding alkylation of a variety of CH-acids with (R)-glyceraldehyde acetonide/(S)-Garner aldehyde and Hantzsch ester through amino acid-catalyzed TCRA reaction without racemization at the alpha-position to carbonyl. Direct sequential combination of the L-proline-catalyzed TCRA reaction with other reactions like cascade alkylation/ketenization/esterification (A/K/E), alkylation/ketenization/esterification/alkylation (A/K/E/A), Brønsted acid-catalyzed cascade hydrolysis/lactonization/esterification (H/L/E), hydrolysis/esterification (H/E), hydrolysis/oxy-Michael/dehydration (H/OM/DH), and Robinson annulation (RA) of CH-acids, chiral aldehydes, Hantzsch ester, diazomethane, methyl vinyl ketone, various active olefins, and acetylenes furnished the highly functionalized chiral building blocks in good to high yields with excellent diastereoselectivities. In this context, many of the pharmaceutically applicable chiral building blocks were prepared via MCC reactions.

Design and synthesis of HIV-1 protease inhibitors incorporating oxazolidinones as P2/P2' ligands in pseudosymmetric dipeptide isosteres.

A series of novel HIV-1 protease inhibitors based on two pseudosymmetric dipeptide isosteres have been synthesized and evaluated. The inhibitors were designed by incorporating N-phenyloxazolidinone-5-carboxamides into the hydroxyethylene and (hydroxyethyl)hydrazine dipeptide isosteres as P2 and P2' ligands. Compounds with (S)-phenyloxazolidinones attached at a position proximal to the central hydroxyl group showed low nM inhibitory activities against wild-type HIV-1 protease. Selected compounds were further evaluated for their inhibitory activities against a panel of multidrug-resistant protease variants and for their antiviral potencies in MT-4 cells. The crystal structures of lopinavir (LPV) and two new inhibitors containing phenyloxazolidinone-based ligands in complex with wild-type HIV-1 protease have been determined. A comparison of the inhibitor-protease structures with the LPV-protease structure provides valuable insight into the binding mode of the new inhibitors to the protease enzyme. Based on the crystal structures and knowledge of structure-activity relationships, new inhibitors can be designed with enhanced enzyme inhibitory and antiviral potencies.

Enantioseparation of phenylglycinol in chiral‐modified zeolite HY: A molecular simulation study

A mechanism has been proposed for the separation of valinol enantiomers using a chiral-modified zeolite HY (i.e., zeolite HY containing (+)-(1R;2R)-hydrobenzoin) Molecular modeling of chiral-modified zeolite HY employed in enantioselective separation. Jirapongphan SS, Warzywoda J, Budil DE, Sacco A Jr. Chirality 2007; in press, which accurately predicted the experimentally measured enantioseparation. This methodology has been applied to predict the separation of an enantiomeric pair of phenylglycinol molecules (a precursor in the synthesis of HIV-1 protease inhibitors) using the modified zeolite HY as a CSP. Phenylglycinol and valinol molecules are similar in terms of the presence of polar (i.e., amine and hydroxyl) groups. These functional groups are important in the proposed chiral discrimination. Supercage-based docking simulations yielded an enantioselectivity of 1.3 with (+)-(S)-phenylglycinol molecule better retained in the zeolite. Also, the simulations predicted two binding modes that were the same as those in the valinol system. This suggests that specific structural features (i.e., number and type of polar groups), which generate the hypothesized binding modes, are required in an enantioseparation utilizing the chiral-modified zeolite HY.

Efficient Enzymatic Process for the Production of (2S)-4,4-Difluoro-3,3-dimethyl-N-Boc-proline, a Key Intermediate in the Synthesis of HIV Protease Inhibitors

(2S)-4,4-Difluoro-3,3-dimethyl-N-Boc-proline (3) is a key intermediate for the synthesis of HIV protease inhibitors. Here, several approaches for the preparation of enantiopure 3 and its analogues are disclosed. Among these methods, one strategy relies on resolving the racemic methyl ester of 3 through a protease-catalyzed enantioselective hydrolysis. Despite the fact that this resolution was applied to prepare kilogram quantities of optically pure acid 3 for clinical trials, this process suffered from low efficiency, high cost and difficulties in improvement by medium engineering. An alternative much more efficient and cost-effective enzymatic process was therefore developed by switching the protective group of the proline esters from a Boc to a benzyl moiety. This new process has a much higher throughput (6.3 mmol/h/L vs 0.11 mmol/h/L), and the cost of the process was also dramatically reduced to only 5% of the protease resolution process.

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.

Design and synthesis of HIV-1 protease inhibitors. Novel tetrahydrofuran P2/P2′-groups interacting with Asp29/30 of the HIV-1 protease. Determination of binding from X-ray crystal structure of inhibitor protease complex

A series of HIV-1 protease inhibitors having new tetrahydrofuran P2/P2′ groups have been synthesised and tested for protease inhibition and antiviral activity. Six novel 4-aminotetrahydrofuran derivatives were prepared starting from commercially available isopropylidene-α- d-xylofuranose yielding six symmetrical and six unsymmetrical inhibitors. Promising sub nanomolar HIV-1 protease inhibitory activities were obtained. The X-ray crystal structure of the most potent inhibitor ( 23, K i 0.25 nM) co-crystallised with HIV-1 protease is discussed and the binding compared with inhibitors 1a and 1b.

ChemInform Abstract: Stereocontrol of the Horner—Wadsworth—Emmons Reaction: Application to the Synthesis of HIV‐1 Protease Inhibitors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Structure-based design and synthesis of HIV-1 protease inhibitors employing β- d-mannopyranoside scaffolds

A preliminary account on the structure-based design, synthesis and evaluation of peptidomimetic inhibitors of HIV-1 protease containing β- d-mannopyranoside scaffolds is given. The compounds prepared had IC 50 values in the micromolar range. The results provide a platform for the development of more potent carbohydrate-based inhibitors of HIV-1 and other aspartic proteases.

Design and synthesis of a conformationally restricted trans peptide isostere based on the bioactive conformations of saquinavir and nelfinavir.

The design and synthesis of a new peptide isostere which contains a trans alkene core is described. The key step involves a Wadsworth-Emmons reaction between chiral aldehyde (2S)-9a and chiral phosphonate 7 under base-sensitive conditions to give a chiral enone (2R)-24a which was reduced to afford the desired trans alkene isosteres (2R,5R)-6a and (2R,5S)-6b (Scheme 6). A potential application of this isostere in the synthesis of HIV protease inhibitors is also discussed.

Stereocontrol of the Horner-Wadsworth-Emmons Reaction: Application to the Synthesis of HIV-1 Protease Inhibitors

A systematic study on the Horner–Wadsworth–Emmons (HWE) reaction has shown that ethyl diphenylphosphonoacetate and methyl diphenylphosphonoacetate give a high excess of (Z)-alkenes. These reaction conditions were then used to prepare (Z)-ethyl-5-phenylpent-2-enoate, the corresponding (E)-isomer being prepared by standard Wittig chemistry. Reduction of each allylic ester, with diisobutylaluminium hydride (DIBAL), gave the allylic alcohols (15) and (19), respectively. Epoxidation of (15) and (19), under Sharpless conditions, gave separate samples of all four stereoisomers of 2,3-epoxy-5-phenylpentan-1-ol. Esterification of each isomer with Cbz-valine, under Mitsunobu conditions, provided (9)–(12) which were assayed against HIV protease. The cis series (9)–(10) proved to be significantly more potent than the trans (11)–(12) and, within each of these series, the isomers derived from L-diisopropyltartrate [(9) and (11)] were the most active.

Solid phase assisted synthesis of HIV-1 protease inhibitors. Expedient entry to unsymmetrical substitution of aC2symmetric template

A solid phase synthesis has been developed leading up to unsymmetrical HIV-1 protease inhibitors that are not readily available by conventional solution phase chemistry (18a–g). To prepare these compounds the hydroxyl group of (1S,2R)-(–)-cis-1-phthalimido-2-indanol (3) was coupled to a Merrifield resin via a dihydropyrane linker. Cleavage of the phthalimido protecting group and reaction of the liberated amine with the bis-activated symmetrical diacid 15 resulted in the resin bound amide 16. Coupling of 16 with amino acids and amines followed by hydrolysis produced the desired unsymmetrical products 18a–g from which potent HIV-1 protease inhibitors were identified, e.g., 18e (ki= 0.1 nM), 18a (ki= 0.2 nM) and 18c (ki= 2 nM).Key words: HIV, inhibitor, protease, solid phase.

ChemInform Abstract: A Convenient Synthesis of 1‐(S)‐(1′‐(S)‐(t‐Butyloxycarbonylamino)‐2′‐ phenylethyl)oxirane. A Useful Building Block in the Synthesis of HIV Protease Inhibitors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.