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# ZINC Database API Reference
## Overview
Complete technical reference for programmatic access to the ZINC database, covering API endpoints, query syntax, parameters, response formats, and advanced usage patterns for ZINC22, ZINC20, and legacy versions.
## Base URLs
### ZINC22 (Current)
- **CartBlanche22 API**: `https://cartblanche22.docking.org/`
- **File Repository**: `https://files.docking.org/zinc22/`
- **Main Website**: `https://zinc.docking.org/`
### ZINC20 (Maintained)
- **API**: `https://zinc20.docking.org/`
- **File Repository**: `https://files.docking.org/zinc20/`
### Documentation
- **Wiki**: `https://wiki.docking.org/`
- **GitHub**: `https://github.com/docking-org/`
## API Endpoints
### 1. Substance Retrieval by ZINC ID
Retrieve compound information using ZINC identifiers.
**Endpoint**: `/substances.txt`
**Parameters**:
- `zinc_id` (required): Single ZINC ID or comma-separated list
- `output_fields` (optional): Comma-separated field names (default: all fields)
**URL Format**:
```
https://cartblanche22.docking.org/substances.txt:zinc_id={ZINC_ID}&output_fields={FIELDS}
```
**Examples**:
Single compound:
```bash
curl "https://cartblanche22.docking.org/[email protected]_fields=zinc_id,smiles,catalogs"
```
Multiple compounds:
```bash
curl "https://cartblanche22.docking.org/substances.txt:zinc_id=ZINC000000000001,ZINC000000000002,ZINC000000000003&output_fields=zinc_id,smiles,tranche"
```
Batch retrieval from file:
```bash
# Create file with ZINC IDs (one per line or comma-separated)
curl -X POST "https://cartblanche22.docking.org/substances.txt?output_fields=zinc_id,smiles" \
-F "zinc_id=@zinc_ids.txt"
```
**Response Format** (TSV):
```
zinc_id smiles catalogs
ZINC000000000001 CC(C)O [vendor1,vendor2]
ZINC000000000002 c1ccccc1 [vendor3]
```
### 2. Structure Search by SMILES
Search for compounds by chemical structure with optional similarity thresholds.
**Endpoint**: `/smiles.txt`
**Parameters**:
- `smiles` (required): Query SMILES string (URL-encode if necessary)
- `dist` (optional): Tanimoto distance threshold (0-10, default: 0 = exact)
- `adist` (optional): Alternative distance metric (0-10, default: 0)
- `output_fields` (optional): Comma-separated field names
**URL Format**:
```
https://cartblanche22.docking.org/smiles.txt:smiles={SMILES}&dist={DIST}&adist={ADIST}&output_fields={FIELDS}
```
**Examples**:
Exact structure match:
```bash
curl "https://cartblanche22.docking.org/smiles.txt:smiles=c1ccccc1&output_fields=zinc_id,smiles"
```
Similarity search (Tanimoto distance = 3):
```bash
curl "https://cartblanche22.docking.org/smiles.txt:smiles=CC(C)Cc1ccc(cc1)C(C)C(=O)O&dist=3&output_fields=zinc_id,smiles,catalogs"
```
Broad similarity search:
```bash
curl "https://cartblanche22.docking.org/smiles.txt:smiles=c1ccccc1&dist=5&adist=5&output_fields=zinc_id,smiles,tranche"
```
URL-encoded SMILES (for special characters):
```bash
# Original: CC(=O)Oc1ccccc1C(=O)O
# Encoded: CC%28%3DO%29Oc1ccccc1C%28%3DO%29O
curl "https://cartblanche22.docking.org/smiles.txt:smiles=CC%28%3DO%29Oc1ccccc1C%28%3DO%29O&dist=2"
```
**Distance Parameters Interpretation**:
- `dist=0`: Exact match
- `dist=1-3`: Close analogs (high similarity)
- `dist=4-6`: Moderate analogs
- `dist=7-10`: Diverse chemical space
### 3. Supplier Code Search
Query compounds by vendor catalog numbers.
**Endpoint**: `/catitems.txt`
**Parameters**:
- `catitem_id` (required): Supplier catalog code
- `output_fields` (optional): Comma-separated field names
**URL Format**:
```
https://cartblanche22.docking.org/catitems.txt:catitem_id={SUPPLIER_CODE}&output_fields={FIELDS}
```
**Example**:
```bash
curl "https://cartblanche22.docking.org/catitems.txt:catitem_id=SUPPLIER-12345&output_fields=zinc_id,smiles,supplier_code,catalogs"
```
### 4. Random Compound Sampling
Generate random compound sets with optional filtering by chemical properties.
**Endpoint**: `/substance/random.txt`
**Parameters**:
- `count` (optional): Number of compounds to retrieve (default: 100, max: depends on server)
- `subset` (optional): Filter by predefined subset (e.g., 'lead-like', 'drug-like', 'fragment')
- `output_fields` (optional): Comma-separated field names
**URL Format**:
```
https://cartblanche22.docking.org/substance/random.txt:count={COUNT}&subset={SUBSET}&output_fields={FIELDS}
```
**Examples**:
Random 100 compounds (default):
```bash
curl "https://cartblanche22.docking.org/substance/random.txt"
```
Random lead-like molecules:
```bash
curl "https://cartblanche22.docking.org/substance/random.txt:count=1000&subset=lead-like&output_fields=zinc_id,smiles,tranche"
```
Random drug-like molecules:
```bash
curl "https://cartblanche22.docking.org/substance/random.txt:count=5000&subset=drug-like&output_fields=zinc_id,smiles"
```
Random fragments:
```bash
curl "https://cartblanche22.docking.org/substance/random.txt:count=500&subset=fragment&output_fields=zinc_id,smiles,tranche"
```
**Subset Definitions**:
- `fragment`: MW < 250, suitable for fragment-based drug discovery
- `lead-like`: MW 250-350, LogP ≤ 3.5, rotatable bonds ≤ 7
- `drug-like`: MW 350-500, follows Lipinski's Rule of Five
- `lugs`: Large, unusually good subset (highly curated)
## Output Fields
### Available Fields
Customize API responses using the `output_fields` parameter:
| Field | Description | Example |
|-------|-------------|---------|
| `zinc_id` | ZINC identifier | ZINC000000000001 |
| `smiles` | Canonical SMILES string | CC(C)O |
| `sub_id` | Internal substance ID | 123456 |
| `supplier_code` | Vendor catalog number | AB-1234567 |
| `catalogs` | List of suppliers | [emolecules, mcule, mcule-ultimate] |
| `tranche` | Encoded molecular properties | H02P025M300-0 |
| `mwt` | Molecular weight | 325.45 |
| `logp` | LogP (partition coefficient) | 2.5 |
| `hba` | H-bond acceptors | 4 |
| `hbd` | H-bond donors | 2 |
| `rotatable_bonds` | Rotatable bonds count | 5 |
**Note**: Not all fields are available for all endpoints. Field availability depends on the database version and endpoint.
### Default Fields
If `output_fields` is not specified, endpoints return all available fields in TSV format.
### Custom Field Selection
Request specific fields only:
```bash
curl "https://cartblanche22.docking.org/[email protected]_fields=zinc_id,smiles"
```
Request multiple fields:
```bash
curl "https://cartblanche22.docking.org/[email protected]_fields=zinc_id,smiles,tranche,catalogs"
```
## Tranche System
ZINC organizes compounds into tranches based on molecular properties for efficient filtering and organization.
### Tranche Code Format
**Pattern**: `H##P###M###-phase`
| Component | Description | Range |
|-----------|-------------|-------|
| H## | Hydrogen bond donors | 00-99 |
| P### | LogP × 10 | 000-999 (e.g., P035 = LogP 3.5) |
| M### | Molecular weight | 000-999 Da |
| phase | Reactivity classification | 0-9 |
### Examples
| Tranche Code | Interpretation |
|--------------|----------------|
| `H00P010M250-0` | 0 H-donors, LogP=1.0, MW=250 Da, phase 0 |
| `H05P035M400-0` | 5 H-donors, LogP=3.5, MW=400 Da, phase 0 |
| `H02P-005M180-0` | 2 H-donors, LogP=-0.5, MW=180 Da, phase 0 |
### Reactivity Phases
| Phase | Description |
|-------|-------------|
| 0 | Unreactive (preferred for screening) |
| 1-9 | Increasing reactivity (PAINS, reactive groups) |
### Parsing Tranches in Python
```python
import re
def parse_tranche(tranche_str):
"""
Parse ZINC tranche code.
Args:
tranche_str: Tranche code (e.g., "H05P035M400-0")
Returns:
dict with h_donors, logp, mw, phase
"""
pattern = r'H(\d+)P(-?\d+)M(\d+)-(\d+)'
match = re.match(pattern, tranche_str)
if not match:
return None
return {
'h_donors': int(match.group(1)),
'logp': int(match.group(2)) / 10.0,
'mw': int(match.group(3)),
'phase': int(match.group(4))
}
# Example usage
tranche = "H05P035M400-0"
props = parse_tranche(tranche)
print(props) # {'h_donors': 5, 'logp': 3.5, 'mw': 400, 'phase': 0}
```
### Filtering by Tranches
Download specific tranches from file repositories:
```bash
# Download all compounds in a specific tranche
wget https://files.docking.org/zinc22/H05/H05P035M400-0.db2.gz
```
## File Repository Access
### Directory Structure
ZINC22 3D structures are organized hierarchically by H-bond donors:
```
https://files.docking.org/zinc22/
├── H00/
│ ├── H00P010M200-0.db2.gz
│ ├── H00P020M250-0.db2.gz
│ └── ...
├── H01/
├── H02/
└── ...
```
### File Formats
| Extension | Format | Description |
|-----------|--------|-------------|
| `.db2.gz` | DOCK database | Compressed multi-conformer DB for DOCK |
| `.mol2.gz` | MOL2 | Multi-molecule format with 3D coordinates |
| `.sdf.gz` | SDF | Structure-Data File format |
| `.smi` | SMILES | Plain text SMILES with ZINC IDs |
### Downloading 3D Structures
**Single tranche**:
```bash
wget https://files.docking.org/zinc22/H05/H05P035M400-0.db2.gz
```
**Multiple tranches** (parallel download with aria2c):
```bash
# Create URL list
cat > tranche_urls.txt <<EOF
https://files.docking.org/zinc22/H05/H05P035M400-0.db2.gz
https://files.docking.org/zinc22/H05/H05P035M400-0.db2.gz
https://files.docking.org/zinc22/H05/H05P040M400-0.db2.gz
EOF
# Download in parallel
aria2c -i tranche_urls.txt -x 8 -j 4
```
**Recursive download** (use with caution - large data):
```bash
wget -r -np -nH --cut-dirs=1 -A "*.db2.gz" \
https://files.docking.org/zinc22/H05/
```
### Extracting Structures
```bash
# Decompress
gunzip H05P035M400-0.db2.gz
# Convert to other formats using OpenBabel
obabel H05P035M400-0.db2 -O output.sdf
obabel H05P035M400-0.db2 -O output.mol2
```
## Advanced Query Patterns
### Combining Multiple Search Criteria
**Python wrapper for complex queries**:
```python
import subprocess
import pandas as pd
from io import StringIO
def advanced_zinc_search(smiles=None, zinc_ids=None, dist=0,
subset=None, count=None, output_fields=None):
"""
Flexible ZINC search with multiple criteria.
Args:
smiles: SMILES string for structure search
zinc_ids: List of ZINC IDs for batch retrieval
dist: Distance parameter for similarity (0-10)
subset: Subset filter (lead-like, drug-like, fragment)
count: Number of random compounds
output_fields: List of fields to return
Returns:
pandas DataFrame with results
"""
if output_fields is None:
output_fields = ['zinc_id', 'smiles', 'tranche', 'catalogs']
fields_str = ','.join(output_fields)
# Structure search
if smiles:
url = f"https://cartblanche22.docking.org/smiles.txt:smiles={smiles}&dist={dist}&output_fields={fields_str}"
# Batch retrieval
elif zinc_ids:
zinc_ids_str = ','.join(zinc_ids)
url = f"https://cartblanche22.docking.org/substances.txt:zinc_id={zinc_ids_str}&output_fields={fields_str}"
# Random sampling
elif count:
url = f"https://cartblanche22.docking.org/substance/random.txt:count={count}&output_fields={fields_str}"
if subset:
url += f"&subset={subset}"
else:
raise ValueError("Must specify smiles, zinc_ids, or count")
# Execute query
result = subprocess.run(['curl', '-s', url],
capture_output=True, text=True)
# Parse to DataFrame
df = pd.read_csv(StringIO(result.stdout), sep='\t')
return df
```
**Usage examples**:
```python
# Find similar compounds
df = advanced_zinc_search(
smiles="CC(C)Cc1ccc(cc1)C(C)C(=O)O",
dist=3,
output_fields=['zinc_id', 'smiles', 'catalogs']
)
# Batch retrieval
zinc_ids = ["ZINC000000000001", "ZINC000000000002"]
df = advanced_zinc_search(zinc_ids=zinc_ids)
# Random drug-like set
df = advanced_zinc_search(
count=1000,
subset='drug-like',
output_fields=['zinc_id', 'smiles', 'tranche']
)
```
### Property-Based Filtering
Filter compounds by molecular properties using tranche data:
```python
def filter_by_properties(df, mw_range=None, logp_range=None,
max_hbd=None, phase=0):
"""
Filter DataFrame by molecular properties.
Args:
df: DataFrame with 'tranche' column
mw_range: Tuple (min_mw, max_mw)
logp_range: Tuple (min_logp, max_logp)
max_hbd: Maximum H-bond donors
phase: Reactivity phase (0 = unreactive)
Returns:
Filtered DataFrame
"""
# Parse tranches
df['tranche_props'] = df['tranche'].apply(parse_tranche)
df['mw'] = df['tranche_props'].apply(lambda x: x['mw'] if x else None)
df['logp'] = df['tranche_props'].apply(lambda x: x['logp'] if x else None)
df['hbd'] = df['tranche_props'].apply(lambda x: x['h_donors'] if x else None)
df['phase'] = df['tranche_props'].apply(lambda x: x['phase'] if x else None)
# Apply filters
mask = pd.Series([True] * len(df))
if mw_range:
mask &= (df['mw'] >= mw_range[0]) & (df['mw'] <= mw_range[1])
if logp_range:
mask &= (df['logp'] >= logp_range[0]) & (df['logp'] <= logp_range[1])
if max_hbd is not None:
mask &= df['hbd'] <= max_hbd
if phase is not None:
mask &= df['phase'] == phase
return df[mask]
# Example: Get drug-like compounds with specific properties
df = advanced_zinc_search(count=10000, subset='drug-like')
filtered = filter_by_properties(
df,
mw_range=(300, 450),
logp_range=(1.0, 4.0),
max_hbd=3,
phase=0
)
```
## Rate Limiting and Best Practices
### Rate Limiting
ZINC does not publish explicit rate limits, but users should:
- **Avoid rapid-fire requests**: Space out queries by at least 1 second
- **Use batch operations**: Query multiple ZINC IDs in single request
- **Cache results**: Store frequently accessed data locally
- **Off-peak usage**: Perform large downloads during off-peak hours (UTC nights/weekends)
### Etiquette
```python
import time
def polite_zinc_query(query_func, *args, delay=1.0, **kwargs):
"""Wrapper to add delay between queries."""
result = query_func(*args, **kwargs)
time.sleep(delay)
return result
```
### Error Handling
```python
def robust_zinc_query(url, max_retries=3, timeout=30):
"""
Query ZINC with retry logic.
Args:
url: Full ZINC API URL
max_retries: Maximum retry attempts
timeout: Request timeout in seconds
Returns:
Query results or None on failure
"""
import subprocess
import time
for attempt in range(max_retries):
try:
result = subprocess.run(
['curl', '-s', '--max-time', str(timeout), url],
capture_output=True,
text=True,
check=True
)
# Check for empty or error responses
if not result.stdout or 'error' in result.stdout.lower():
raise ValueError("Invalid response")
return result.stdout
except (subprocess.CalledProcessError, ValueError) as e:
if attempt < max_retries - 1:
wait_time = 2 ** attempt # Exponential backoff
print(f"Retry {attempt + 1}/{max_retries} after {wait_time}s...")
time.sleep(wait_time)
else:
print(f"Failed after {max_retries} attempts")
return None
```
## Integration with Molecular Docking
### Preparing DOCK6 Libraries
```bash
# 1. Download tranche files
wget https://files.docking.org/zinc22/H05/H05P035M400-0.db2.gz
# 2. Decompress
gunzip H05P035M400-0.db2.gz
# 3. Use directly with DOCK6
dock6 -i dock.in -o dock.out -l H05P035M400-0.db2
```
### AutoDock Vina Integration
```bash
# 1. Download MOL2 format
wget https://files.docking.org/zinc22/H05/H05P035M400-0.mol2.gz
gunzip H05P035M400-0.mol2.gz
# 2. Convert to PDBQT using prepare_ligand script
prepare_ligand4.py -l H05P035M400-0.mol2 -o ligands.pdbqt -A hydrogens
# 3. Run Vina
vina --receptor protein.pdbqt --ligand ligands.pdbqt \
--center_x 25.0 --center_y 25.0 --center_z 25.0 \
--size_x 20.0 --size_y 20.0 --size_z 20.0
```
### RDKit Integration
```python
from rdkit import Chem
from rdkit.Chem import AllChem, Descriptors
import pandas as pd
def process_zinc_results(zinc_df):
"""
Process ZINC results with RDKit.
Args:
zinc_df: DataFrame with SMILES column
Returns:
DataFrame with calculated properties
"""
# Convert SMILES to molecules
zinc_df['mol'] = zinc_df['smiles'].apply(Chem.MolFromSmiles)
# Calculate properties
zinc_df['mw'] = zinc_df['mol'].apply(Descriptors.MolWt)
zinc_df['logp'] = zinc_df['mol'].apply(Descriptors.MolLogP)
zinc_df['hbd'] = zinc_df['mol'].apply(Descriptors.NumHDonors)
zinc_df['hba'] = zinc_df['mol'].apply(Descriptors.NumHAcceptors)
zinc_df['tpsa'] = zinc_df['mol'].apply(Descriptors.TPSA)
zinc_df['rotatable'] = zinc_df['mol'].apply(Descriptors.NumRotatableBonds)
# Generate 3D conformers
for mol in zinc_df['mol']:
if mol:
AllChem.EmbedMolecule(mol, randomSeed=42)
AllChem.MMFFOptimizeMolecule(mol)
return zinc_df
# Save to SDF for docking
def save_to_sdf(zinc_df, output_file):
"""Save molecules to SDF file."""
writer = Chem.SDWriter(output_file)
for idx, row in zinc_df.iterrows():
if row['mol']:
row['mol'].SetProp('ZINC_ID', row['zinc_id'])
writer.write(row['mol'])
writer.close()
```
## Troubleshooting
### Common Issues
**Issue**: Empty or no results
- **Solution**: Check SMILES syntax, verify ZINC IDs exist, try broader similarity search
**Issue**: Timeout errors
- **Solution**: Reduce result count, use batch queries, try during off-peak hours
**Issue**: Invalid SMILES encoding
- **Solution**: URL-encode special characters (use `urllib.parse.quote()` in Python)
**Issue**: Tranche files not found
- **Solution**: Verify tranche code format, check file repository structure
### Debug Mode
```python
def debug_zinc_query(url):
"""Print query details for debugging."""
print(f"Query URL: {url}")
result = subprocess.run(['curl', '-v', url],
capture_output=True, text=True)
print(f"Status: {result.returncode}")
print(f"Stderr: {result.stderr}")
print(f"Stdout length: {len(result.stdout)}")
print(f"First 500 chars:\n{result.stdout[:500]}")
return result.stdout
```
## Version Differences
### ZINC22 vs ZINC20 vs ZINC15
| Feature | ZINC22 | ZINC20 | ZINC15 |
|---------|--------|--------|--------|
| Compounds | 230M+ purchasable | Focused on leads | ~750M total |
| API | CartBlanche22 | Similar | REST-like |
| Tranches | Yes | Yes | Yes |
| 3D Structures | Yes | Yes | Yes |
| Status | Current, growing | Maintained | Legacy |
### API Compatibility
Most query patterns work across versions, but URLs differ:
- ZINC22: `cartblanche22.docking.org`
- ZINC20: `zinc20.docking.org`
- ZINC15: `zinc15.docking.org`
## Additional Resources
- **ZINC Wiki**: https://wiki.docking.org/
- **ZINC22 Documentation**: https://wiki.docking.org/index.php/Category:ZINC22
- **ZINC API Guide**: https://wiki.docking.org/index.php/ZINC_api
- **File Access Guide**: https://wiki.docking.org/index.php/ZINC22:Getting_started
- **Publications**:
- ZINC22: J. Chem. Inf. Model. 2023
- ZINC15: J. Chem. Inf. Model. 2020, 60, 6065-6073
- **Support**: Contact via ZINC website or GitHub issues