from transformers import AutoTokenizer, AutoModelForSeq2SeqLM

tokenizer = AutoTokenizer.from_pretrained("sagawa/ReactionT5v2-retrosynthesis", return_tensors="pt")
model = AutoModelForSeq2SeqLM.from_pretrained("sagawa/ReactionT5v2-retrosynthesis")

inp = tokenizer('CCN(CC)CCNC(=S)NC1CCCc2cc(C)cnc21', return_tensors='pt')
output = model.generate(**inp, num_beams=1, num_return_sequences=1, return_dict_in_generate=True, output_scores=True)
output = tokenizer.decode(output['sequences'][0], skip_special_tokens=True).replace(' ', '').rstrip('.')
output # 'CCN(CC)CCN=C=S.Cc1cnc2c(c1)CCCC2N'

Training Details

Training Procedure

We used the Open Reaction Database (ORD) dataset for model training. In addition, we used USPTO_50k dataset's test split to prevent data leakage. The command used for training is the following. For more information about data preprocessing and training, please refer to the paper and GitHub repository.

python

cd task_retrosynthesis
python train.py \
    --output_dir='t5' \
    --epochs=80 \
    --lr=2e-4 \
    --batch_size=32 \
    --input_max_len=100 \
    --target_max_len=150 \
    --weight_decay=0.01 \
    --evaluation_strategy='epoch' \
    --save_strategy='epoch' \
    --logging_strategy='epoch' \
    --train_data_path='../data/preprocessed_ord_train.csv' \
    --valid_data_path='../data/preprocessed_ord_valid.csv' \
    --test_data_path='../data/preprocessed_ord_test.csv' \
    --USPTO_test_data_path='../data/USPTO_50k/test.csv' \
    --pretrained_model_name_or_path='sagawa/CompoundT5'

Results

Model	Training set	Test set	Top-1 [% acc.]	Top-2 [% acc.]	Top-3 [% acc.]	Top-5 [% acc.]
Sequence-to-sequence	USPTO_50k	USPTO_50k	37.4	-	52.4	57.0
Molecular Transformer	USPTO_50k	USPTO_50k	43.5	-	60.5	-
SCROP	USPTO_50k	USPTO_50k	43.7	-	60.0	65.2
T5Chem	USPTO_50k	USPTO_50k	46.5	-	64.4	70.5
CompoundT5	USPTO_50k	USPTO_50k	44,2	55.2	61.4	67.3
ReactionT5 (This model)	-	USPTO_50k	13.8	18.6	21.4	26.2
ReactionT5	USPTO_50k	USPTO_50k	71.2	81.4	84.9	88.2

Performance comparison of Compound T5, ReactionT5, and other models in product prediction.

Citation

@article{Sagawa2025,
  title   = {ReactionT5: a pre-trained transformer model for accurate chemical reaction prediction with limited data},
  author  = {Sagawa, Tatsuya and Kojima, Ryosuke},
  journal = {Journal of Cheminformatics},
  year    = {2025},
  volume  = {17},
  number  = {1},
  pages   = {126},
  doi     = {10.1186/s13321-025-01075-4},
  url     = {https://doi.org/10.1186/s13321-025-01075-4}
}