Precise PEG® Products Acknowledged in RSC Chemical Biology (2026) Publication
Overview
A recent publication in RSC Chemical Biology [1] highlights an advanced strategy for the modular, site-selective synthesis of multi-payload antibody conjugates, representing a significant step forward in antibody–drug conjugate (ADC) design.
This work demonstrates how precise control over payload-to-antibody ratio (PAR) and the ability to attach multiple distinct payloads can help address key challenges in ADC development, including drug resistance and suboptimal efficacy.
Importantly, key linker building blocks used in this study are commercially available from suppliers including Precise PEG, underscoring our role in supporting and accelerating this cutting-edge ADC research.
Key Scientific Advances of DiBrPD
Maleimides are derived from the reaction of maleic anhydride with amine derivatives. They readily undergo nucleophilic Michael addition with thiol groups (-SH) to form stable thioether bonds. Maleimides react with thiols in the pH range of 6.5–7.5, and their reaction rate is about 1000 times faster than with amines, enabling complete conversion with minimal reagent usage. [2]
However, a major drawback of maleimide alkylation is the retro-Michael addition reaction of thiols, whose rate strongly depends on the pKa of the specific cysteine residue involved. This reverse reaction may lead to premature release of linker–drug conjugates in circulation and unwanted coupling with biomolecules such as albumin, resulting in off-target conjugation and toxicity. [3]
In 2011, Chudasama V. and et al. [4a] first reported a bromopyridazinedione-mediated bioconjugation method between cysteine-containing proteins and disulfide-containing peptides. The resulting conjugates can be cleaved in the presence of excess thiols as well as exhibit high hydrolytic stability. Subsequently, further work [4b–4c] demonstrated that bromopyridazinedione-mediated thiol bridging could be used to construct ADCs with higher stability, greater homogeneity and enhanced flexibility. This approach enables site-specific modification, excellent multifunctionality and retention of antibody binding and structure after modification. This represents a significant step toward next-generation antibody-based therapeutics [Figure 1].
Figure 1. Functional disulfide rebridging and subsequent dual-click strategy
In 2018, Boyle et al. [5] reported a method combining DiBrPD-based disulfide re-bridging and click chemistry to construct photosensitizer–antibody conjugates [Figure2]. The key highlights include:
· Site-specific and highly homogeneous conjugation
· More than 4 porphyrin molecules loaded onto intact IgG
· Optimal conjugate identified via photophysical evaluation
· Targeting HER2 with an average drug-to-antibody ratio (DAR) of 15.4:1
Figure 2. Construction Method of High-DAR Photosensitizer–Antibody Conjugates
In 2023, Chudasama and co-workers [6a–6b] reported a first-in-class method using DiBrPD re-bridging and click chemistry to generate Fc-containing IgG-like mono and bispecific antibodies. These constructs follow the FcZ-(FabX)-FabY format and contain two different Fab fragments and one Fc fragment. These fragments may originate from different antibodies and are covalently and homogeneously linked. These molecules were termed Synthetic Antibodies (SynAbs) [Figure 3].
Figure 3. Synthetic Strategy for Bispecific Synthetic Antibodies (SynAb)
DiBrPD represents a major innovation in disulfide re-bridging chemistry, especially for antibody modification. It has the following key advantages:
· Precisely controllable DAR
· Fast and mild reaction conditions
· Easy monitoring
· Overcomes limitations of traditional conjugation methods
Bioconjugates formed via DiBrPD exhibit high homogeneity and well-defined functional payload loading. The strategy enables excellent control over DAR values (e.g., 2, 4, 8, or 4+4). [7]
Precise PEG offers a selection of off-the-shelf dibromopyridazinedione (DiBrPD) linker building blocks designed to support rapid development of site-specific bioconjugates. Our ready-to-ship DiBrPD products are manufactured with high purity and consistency, enabling researchers to quickly access reliable DiBrPD reagents without long lead time. For example, we’ve developed mature chemistry for AAD-9328 (6,7-dibromo-5,8-dioxo-2,3,5,8-tetrahydro-1H-pyrazolo[1,2-a]pyridazine-2-carboxylic acid | 2924558-98-3 | Precise PEG – Precise PEG LLC), a hard-to-make key building block, and its direct derivatives. These building blocks are compatible with a wide range of payloads and functional handles, making them ideal for ADC, bispecific antibody, and broader bioconjugation applications. For selected products, scalable synthetic processes have already been established, supporting a smooth transition from early research to larger-scale development and manufacturing. Customized products based on such building blocks can also be made upon customer’s request. Below are several representative products from our catalog (Figure 4). For full collection of DiBrPD products, please visit our website, following the link: Bis-Sulfhydryl Reactive | Di-Thiol for dual Click and Cysteine Crosslinking – Precise PEG LLC.
Figure 4. Representative DiBrPD products from our catalog
References
[1] McMahon, C., Queval, C. J., Thanasi, I. A., Lau, D. H. W., Howell, M., Wang, N., Lee, M. T. W., Gaynord, J. S., Baker, J. R., Chudasama, V. Enabling the synthesis of multi-payload thio-antibody conjugates through the use of pyridazinediones, p-anisidine derivatives and various click chemistries. RSC Chem. Biol., 2026, Advance Article.
[2] (a) Shen, B.Q.; Xu, K.; Liu, L.; et al. Conjugation site modulates the in vivo stability and therapeutic activity of antibody-drug conjugates. Nat. Biotechnol. 2012, 30, 184-189; (b) Huang, W.; Wu, X.; Gao, X; et al. Maleimide-thiol adducts stabilized through stretching. Nat. Chem. 2019, 11, 310-319.
[3] Tsuchikama, K.; An, Z. Antibody-drug conjugates: recent advances in conjugation and linker chemistries. Protein Cell 2018, 9, 33-46.
[4] (a) Chudasama, V.; Smith, M. E. B.; Schumacher, F. F.; et al. Bromopyridazinedione-mediated protein and peptide bioconjugation. Chem. Commun. 2011, 47, 8781-8783; (b) Maruani, A.; Smith, M.; Miranda, E.; et al. A plug-and-play approach to antibody-based therapeutics via a chemoselective dual click strategy. Nat. Commun. 2015, 6, 6645-6653; (c) Bahou, C.; Richards, D. A.; Maruani, A.; et al. Highly homogeneous antibody modification through optimisation of the synthesis and conjugation of functionalised dibromopyridazinediones. Org. Biomol. Chem. 2018, 16, 1359-1366.
[5] Bryden, F.; Maruani, A.;Rodrigues, J. M. M.; et al. Assembly of High-Potency Photosensitizer-Antibody Conjugates through Application of Dendron Multiplier Technology. Bioconjugate Chem. 2018, 29, 176-181.
[6] (a) Thoreau, F.; Szijj, P. A.; Greene, M. K. et al. Modular Chemical Construction of IgG-like Mono- and Bispecific Synthetic Antibodies (SynAbs). ACS Cent. Sci. 2023, 9, 476-487; (b) Szijj, P. A.; Gray, M. A.; Ribi, M. K; et al. Chemical generation of checkpoint inhibitory T cell engagers for the treatment of cancer. Nat. Chem. 2023, 15, 1636-1647.
[7] Bahou, C.; Chudasama, V. The use of bromopyridazinedione derivatives in chemical biology. Org. Biomol. Chem. 2022, 20, 5879-5890.