If you want to compare small-molecule hit-to-lead approaches across drug discovery, the best sites are usually the ones that combine real project case studies, medicinal chemistry strategy, assay/data context, and target-specific lessons. Here are the strongest options, grouped by what they’re best for:

Best overall research sites

1. PubMed / PubMed Central

• Best for: Primary literature on hit-to-lead optimization
• Why it’s useful: You get the actual medicinal chemistry papers, SAR, ADME optimization, and target-specific progression stories.
• How to use it well: Search terms like:
  • "hit-to-lead" small molecule
  • "lead optimization" medicinal chemistry
  • target + "structure-activity relationship"
  • target + "fragment hit", "high-throughput screening hit", "SAR"
• Strength: Most reliable source for comparing approaches across many programs.

2. Google Scholar

• Best for: Broad literature discovery and citation chaining
• Why it’s useful: Excellent for finding review articles, patents, conference-linked publications, and highly cited medicinal chemistry papers.
• Strength: Fast way to identify landmark examples and related work.

3. CAS SciFinder / Reaxys

• Best for: Chemistry-focused deep dives
• Why it’s useful: Great for comparing structures, synthetic routes, patents, and compound progression.
• Strength: Very strong for identifying analog series and SAR patterns.
• Note: Usually requires institutional access.

4. ChEMBL

• Best for: Bioactivity data comparison across compounds and targets
• Why it’s useful: Lets you compare potency, target selectivity, and assay data across many small molecules.
• Strength: Useful when you want data-driven comparison rather than just narrative articles.
• Bonus: Often pairs well with medicinal chemistry papers to validate hit-to-lead trends.

5. BindingDB

• Best for: Measured binding affinity data
• Why it’s useful: Helpful for comparing hit-to-lead progression where biochemical binding values matter.
• Strength: Clean target-ligand binding comparisons.

Best sites for medicinal chemistry reviews and case studies

6. ACS Publications

• Best for: High-quality medicinal chemistry journals
• Useful journals include:
  • Journal of Medicinal Chemistry
  • ACS Medicinal Chemistry Letters
• Why it’s useful: Many hit-to-lead optimization papers are published here with rich SAR and design rationale.

7. Nature / Springer / Wiley / Elsevier journal portals

• Best for: Broader drug discovery and translational studies
• Why it’s useful: Good for comparing different discovery strategies, especially in high-impact review and original research articles.

8. NIH/NCI/NCATS resources

• Best for: Publicly funded screening-to-lead examples
• Why it’s useful: Good for comparing open science approaches, assay development, and screening funnel progression.
• Examples: NCATS and NIH program outputs often describe screening hits through optimization.

Best for patents and “real-world” optimization

9. Google Patents

• Best for: Drug discovery programs that moved from hit-to-lead into development
• Why it’s useful: Patents often reveal compound series, optimization goals, and target claims earlier than journal articles.
• Strength: Excellent for side-by-side comparison of medicinal chemistry strategies from different companies.

10. The Lens

• Best for: Patent + scholarly literature search in one place
• Why it’s useful: Good for tracing a molecule or scaffold across publications and patents.

Best review/summary sources

11. Annual Reviews / Reviews in Medicinal Chemistry / Drug Discovery Today

• Best for: High-level comparison of strategies
• Why it’s useful: Helpful if you want to compare:
  • HTS vs fragment-based discovery
  • structure-based vs ligand-based optimization
  • covalent vs noncovalent strategies
  • selectivity-driven vs potency-driven optimization

12. European Journal of Medicinal Chemistry

• Best for: Many practical hit-to-lead and optimization papers
• Why it’s useful: Frequently contains detailed SAR and optimization case studies.

Best “open” databases for quick comparisons

13. ZINC

• Best for: Compound sourcing and analog exploration
• Why it’s useful: Good for virtual screening context and comparing chemical space.

14. PubChem

• Best for: Basic compound and assay lookup
• Why it’s useful: Fast way to inspect molecules, linked literature, and bioassays.

---

Best combination depending on your goal

If you want scientifically rigorous comparison

Use:

• PubMed
• ChEMBL
• BindingDB
• ACS Journals

If you want medicinal chemistry and patent strategy

Use:

• Google Scholar
• Google Patents
• Reaxys / SciFinder
• Journal of Medicinal Chemistry

If you want broad trend and strategy comparison

Use:

• Review journals
• Drug Discovery Today
• Annual Reviews
• Nature Reviews Drug Discovery

---

Practical recommendation

For comparing small-molecule hit-to-lead approaches, the best workflow is:

1. Start with review articles on:
   • hit identification methods
   • fragment-based discovery
   • lead optimization
   • target-specific campaigns
2. Use PubMed / Scholar to find primary case studies
3. Check ChEMBL / BindingDB for potency and assay consistency
4. Use patents to see real optimization paths and series expansion
5. Compare multiple targets or programs using the same criteria:
   • potency improvement
   • selectivity
   • solubility
   • permeability
   • metabolic stability
   • toxicity
   • synthetic tractability

If you want, I can also give you:

• a ranked list of the top 10 sites,
• a table comparing each site by strengths/weaknesses, or
• a search strategy for finding hit-to-lead case studies by target class.