Indinavir

Aziridine Ring-Opening Approach

The most efficient route to Fragment A begins with (S)-tert-butyl-N-p-tosylaziridine-2-carboxamide. Regioselective ring opening at the C-3 position using 3-picolylamine under phase-transfer catalysis yields a secondary amine intermediate. Subsequent N,N′-bisalkylation with diphenyl vinyl sulfonium triflate forms the piperazine core. Final N-detosylation with HBr/acetic acid affords the target fragment in 20% overall yield across three steps. This method avoids chromatographic purification, enhancing scalability (Table 1).

Table 1: Optimization of Fragment A Synthesis

Alternative Resolution Methods

Early routes employed enzymatic kinetic resolution of racemic piperazine-2-carboxamide using L-leucine aminopeptidase, achieving 38% yield for the (S)-enantiomer. However, this method required specialized biocatalysts and produced stoichiometric waste, limiting industrial viability.

Construction of the Hydroxyethylamine Isostere (Fragment B)

Stereoselective Aldol Condensation

Fragment B is synthesized via Evans’ oxazolidinone-mediated aldol reaction. (R)-4-Phenyl-2-oxazolidinone directs the stereochemistry during condensation of benzyloxyacetaldehyde with a protected amino acid derivative. Reductive cleavage of the chiral auxiliary with LiBH₄ yields the desired (1S,2R)-diol configuration critical for protease binding.

Industrial-Scale Modifications

Merck’s manufacturing process replaces oxazolidinones with cheaper tert-butyl carbamates, employing Sharpless asymmetric dihydroxylation to install stereocenters. This adjustment reduced production costs by 40% while maintaining enantiomeric excess >99%.

Convergent Coupling and Final Assembly

The penultimate stage couples Fragment A and B using HATU (Hexafluorophosphate Azabenzotriazole Tetramethyl Uronium) activation in dimethylacetamide at −20°C. Final global deprotection under acidic conditions (HCl/dioxane) yields this compound free base, which is converted to the sulfate salt for pharmaceutical use.

Critical Process Parameters:

• Temperature control during coupling (−20°C ± 2°C) prevents epimerization
• Strict anhydrous conditions maintain reagent activity (H₂O < 0.1%)
• Purification via crystallization from ethyl acetate/heptane achieves >99.5% purity

Industrial Production and Scale-Up Challenges

Merck’s patented route (US 5,413,999) produces this compound sulfate in 11 linear steps with an overall yield of 8–12%. Key innovations include:

• Continuous flow hydrogenation for aziridine synthesis
• Membrane-based chiral separation replacing chromatographic methods
• Reactive crystallization to control polymorph formation

Batch records indicate a typical production cycle of 14 days for 500 kg batches, with critical quality attributes monitored via in-line PAT (Process Analytical Technology).

Recent Methodological Advances

Biocatalytic Approaches

Immobilized Candida antarctica lipase B enables kinetic resolution of piperazine intermediates with E-values >200, reducing catalyst loading by 80% compared to traditional methods.

Flow Chemistry Implementations

Microreactor systems have been demonstrated for the high-pressure (50 bar) hydrogenolysis step, decreasing reaction time from 48 hours to 90 minutes while improving safety profile.

Analytical Characterization

Quality control protocols employ:

• Chiral HPLC (Chiralpak AD-H column, 95:5 hexane/ethanol) to verify enantiopurity
• ¹H-NMR (500 MHz, DMSO-d₆) for structural confirmation (δ 8.54 ppm, pyridinyl H; δ 5.32 ppm, hydroxyethylamine CH)
• XRPD to identify polymorphic forms (Form II preferred for tablet formulation)

Environmental and Cost Considerations

Life-cycle assessments reveal that 73% of the process’s carbon footprint originates from solvent use (DMF, CH₂Cl₂). Recent solvent substitution initiatives replaced dichloromethane with cyclopentyl methyl ether, reducing VOC emissions by 65%.

Structural and Functional Comparison with Similar Compounds

Structural Analogs and Ligand-Based Similarity

Ligand-based screening identified compounds with structural similarity to indinavir (Table 1). Approved drugs like quinapril (ACE inhibitor) and sirolimus (mTOR inhibitor) showed lower similarity, indicating divergent therapeutic applications despite structural parallels .

Pharmacokinetic and Metabolic Distinctions

• Species Variability : this compound’s bioavailability ranges from 19% in monkeys to 72% in dogs due to hepatic first-pass metabolism differences .
• Pregnancy : Reduced exposure during pregnancy correlates with CYP3A4 induction, necessitating dose adjustments .
• Drug-Drug Interactions : Co-administration with Sophora flavescens or St. John’s wort decreases this compound exposure via CYP3A4 induction .

Clinical Considerations

• Dosage Optimization : this compound/ritonavir (800/100 mg vs. 400/100 mg bid) showed comparable efficacy in ART-naive patients, but higher doses correlated with increased nephrotoxicity .
• Pediatric Use : Children required 50 mg/kg doses to achieve therapeutic AUC levels, highlighting age-dependent pharmacokinetics .

Q. How can computational methods elucidate Indinavir’s binding mechanism to HIV-1 protease?

Methodological Answer: Use umbrella sampling molecular dynamics (UMD) simulations to characterize binding pathways. Focus on flap regions (e.g., Trp98, Phe67) and catalytic residues (Asp32) critical for interaction energies. Perform 360 replicas over 4+ microseconds to map ligand entry into the protease pocket . Validate findings with AutoDockTools for ligand-receptor docking, incorporating United Atom models and grid map calculations for energy minimization .

Q. What methodologies are recommended to assess this compound’s efficacy in the central nervous system (CNS)?

Methodological Answer: Measure CSF and plasma concentrations via HPLC with UV detection. Use pharmacokinetic modeling to assess active transport out of the CNS (e.g., compare passive vs. active transport models). Correlate CSF this compound levels (>210 nmol/L) with viral load reductions and normalization of CSF cell counts/IgG-index in longitudinal cohorts .

Q. How to analyze crystalluria and urinary complications in patients receiving this compound?

Methodological Answer: Perform microscopic urinalysis with polarized filters to identify this compound crystals. Confirm composition via HPLC (reverse-phase C-18 column) and mass spectrometry (fast atom bombardment). Track asymptomatic crystalluria frequency (67% incidence) and correlate with urinary pH ≤5.5 and high specific gravity (≥1.025) in longitudinal studies .

Q. What experimental designs are suitable for studying this compound’s pharmacokinetic interactions with herbal supplements (e.g., Hypoxis hemerocallidea)?

Methodological Answer: Use Caco-2 cell monolayers to measure apical-to-basolateral transport (Papp values) with this compound (200 µM) ± test compounds (500 µg/mL). Apply ANOVA with Tukey’s post hoc tests for AUC comparisons. Include verapamil (P-gp inhibitor) as a positive control .

Q. How to design a crossover pharmacokinetic study for this compound-drug interactions (e.g., omeprazole)?

Methodological Answer: Use a non-compartmental analysis to calculate Cmax, tmax, and AUC0-24. Apply linear mixed-effect models to compare geometric mean AUCs. Power studies to detect ≥50% AUC reduction (90% power). Include ritonavir-boosted arms to offset pH-dependent exposure changes .

Advanced Research Questions

Q. How to resolve contradictions in this compound’s metabolic pathway inhibition (CYP3A vs. glucuronidation)?

Methodological Answer: Conduct in vitro hepatocyte assays with midazolam as a probe. Quantify N-glucuronide/19-hydroxymidazolam ratios via LC-MS. Compare IC50 values for CYP3A inhibition (e.g., this compound IC50 = 0.24 mM vs. ketoconazole IC50 = 0.05 mM). Validate in human trials by measuring urinary metabolite shifts (8-fold N-glucuronide increase) .

Q. What statistical approaches address virologic failure despite sustained this compound therapy?

Methodological Answer: Perform genotypic (protease/reverse transcriptase sequencing) and phenotypic resistance assays on rebound isolates. Use mixed-effects models to impute missing data from treatment discontinuations. Analyze minority HIV subpopulations in semen via clonal sequencing to detect resistance mutations (e.g., V77I, M46L) .

Q. How to optimize this compound-ritonavir dosing regimens using pharmacokinetic data?

Methodological Answer: Model steady-state exposures with ritonavir boosting (100–200 mg BID). Calculate fold-increases in Cmax (1.6–1.8×) and AUC0-24 (2.7–3.6×) vs. This compound monotherapy. Use cohort surveys to compare efficacy (77% undetectable viral load) and toxicity (22% nausea) in 800/100 mg vs. 400/400 mg BID regimens .

Q. How to evaluate pharmacogenomic factors affecting this compound clearance in diverse populations?

Methodological Answer: Genotype CYP3A5 (e.g., CYP3A51/1 vs. CYP3A53), MRP2 (e.g., T4131G), and UGT1A1 polymorphisms. Use multivariable regression to adjust for race/sex. Corporate findings into mechanistic models (e.g., 44% faster clearance in CYP3A5 expressors) .

Q. What strategies mitigate this compound-induced renal toxicity in long-term studies?

Methodological Answer: Monitor urinary casts/leukocytes via weekly urinalysis. Implement hydration protocols (≥1.5 L/day) and alkalinization (pH >6.0). Use renal scintigraphy to detect parenchymal defects in symptomatic patients. Analyze plasma protein binding variability (54–70%) to adjust unbound drug exposure .