---
language:
- en
tags:
- retrosynthesis
- chemistry
- smi
- molecular-generation
- transformer
- drug-discovery
datasets:
- uspto
metrics:
- accuracy
license: mpl-2.0
---

# RetroGPT

**RetroGPT** is a transformer-based model for single-step retrosynthetic prediction. Given a target product molecule in SMILES format, the model predicts the required reactant molecules through sequence-to-sequence generation.

## Model Details

### Model Description
RetroGPT is a lightweight transformer architecture specifically designed for chemical reaction prediction. The model learns to "reverse" chemical reactions by predicting precursor reactants from product molecules.

- **Developed by**: kssrikar4
- **Model type**: Transformer-based Sequence-to-Sequence
- **Language**: SMILES (Simplified Molecular Input Line Entry System)
- **License**: MIT

### Model Sources

- **Architecture**: Custom transformer with RMSNorm, SwiGLU activation, and multi-head attention
- **Code**: Training code available upon request

## Uses

### Direct Use
The model is intended for retrosynthetic analysis in drug discovery and organic chemistry:
- Predicting reactant molecules for a given target product
- Assisting chemists in planning synthetic routes
- Educational purposes for teaching retrosynthetic thinking
- High-throughput virtual synthesis planning

### Out-of-Scope Use
- Multi-step synthesis planning (requires integration with search algorithms)
- Predicting reaction conditions or yields
- Stereochemistry-specific predictions without additional fine-tuning

## How to Get Started with the Model

```python
import torch, sys
from transformers import AutoModelForCausalLM
from rdkit.Chem import AllChem, Draw
from IPython.display import display

def get_reaction(product, model_id="kssrikar4/RetroGPT"):
    model = AutoModelForCausalLM.from_pretrained(model_id, trust_remote_code=True).eval()
    tok = getattr(sys.modules[model.__class__.__module__], "RetroGPTTokenizer").from_pretrained(model_id)
    ids = torch.tensor([tok.convert_tokens_to_ids(tok.tokenize(f"<s>{product}<sep>"))])
    
    out = model.generate(
        input_ids=ids, 
        attention_mask=torch.ones_like(ids),
        max_length=256, 
        num_beams=5, 
        num_return_sequences=1
    )

    reac = tok.decode(out[0].tolist(), skip_special_tokens=True).split("<sep>")[-1].replace(" ", "")
    rxn = AllChem.ReactionFromSmarts(f"{reac}>>{product}", useSmiles=True)
    
    if rxn:
        AllChem.Compute2DCoordsForReaction(rxn)
        display(Draw.ReactionToImage(rxn, subImgSize=(350, 350)))

get_reaction("your smiles")
```

## Training

### Training Data
The model was trained on the **USPTO dataset** (`uspto.csv`), which contains patent-derived chemical reactions extracted from US patents. The dataset includes:
- Single-product, multi-reactant reactions
- Canonicalized SMILES representations
- Reactions spanning multiple decades (1976-present)

**Dataset Statistics**:
- Training split: ~99% of data
- Validation split: ~1% of data
- Maximum sequence length: 256 tokens

### Training Procedure

**Architecture**:
- Transformer layers: 6
- Hidden dimension (d_model): 512
- Attention heads: 8
- Vocabulary size: ~150 chemical tokens
- Positional encoding: Learned embeddings

**Hyperparameters**:
- Batch size: 64 (effective batch: 128 with gradient accumulation)
- Learning rate: 3e-4 with AdamW optimizer
- Weight decay: 0.01
- Dropout: 0.1
- Training epochs: 80
- Gradient accumulation steps: 2
- Learning rate scheduler: Cosine annealing

**Optimization**:
- Mixed precision training (AMP)
- Gradient clipping
- Distributed training support (DDP)

### Training Hyperparameters

| Hyperparameter | Value |
|----------------|-------|
| Transformer Layers | 6 |
| Hidden Size | 512 |
| Attention Heads | 8 |
| Max Sequence Length | 256 |
| Batch Size | 64 |
| Learning Rate | 3e-4 |
| Weight Decay | 0.01 |
| Dropout | 0.1 |
| Epochs | 80 |
| Optimizer | AdamW |

## Evaluation

### Evaluation Metrics
The model is evaluated using **Top-k Accuracy** based on exact canonical SMILES matching:
- **Top-1 Accuracy**: The exact correct reactant mixture is the model's first prediction
- **Top-3 Accuracy**: The correct answer appears in the top 3 beam search candidates
- **Top-5 Accuracy**: The correct answer appears in the top 5 candidates

### Test Results

![Top-k Accuracy](top_k_accuracy.png)

**Performance on Validation Set**:
- **Top-1 Accuracy**: 59.2%
- **Top-3 Accuracy**: 73.0%
- **Top-5 Accuracy**: 76.4%

### Temporal Performance

![Accuracy by Patent Year](class_accuracy.png)

The model maintains consistent performance across different patent years, demonstrating robust generalization to reactions from different time periods.

### Token-Level Analysis

![Token Confusion Matrix](token_confusion_matrix.png)

The confusion matrix reveals:
- **Strong diagonal dominance**: The model correctly predicts chemical tokens with high accuracy
- **Aromatic vs. Aliphatic**: Minor confusion between aromatic (`c`) and aliphatic (`C`) carbons
- **Ring closures**: Some challenges with numeric ring closure markers (1, 2, etc.)
- **Branching syntax**: Occasional misplacement of parentheses for molecular branches

### Qualitative Examples

![Reaction Examples](reaction_examples_grid.png)

**Disclaimer**: This model is intended for research and educational purposes. Always verify predictions with chemical expertise and experimental validation before laboratory use.