Senior Principal Scientist, Drug Substance

About Loyal Loyal is a clinical-stage veterinary medicine company developing longevity drugs for dogs. Our mission is to help dogs live longer, healthier lives. We're pioneering a new category of veterinary prescription drugs that proactively and preventatively target the underlying drivers of aging, delaying the onset of disease and preserving quality of life as dogs age. We've already made significant progress in our mission to develop the first FDA-approved drugs to extend canine lifespan: as of early 2026 we've completed two of three major FDA review sections for our lead program, LOY-002, and are targeting submission of the third and final section later this year. Loyal is a well-funded startup with teams of scientists, veterinarians, engineers, operators, and creatives. You'll help us continue on our path of earning FDA approval for the first lifespan extension medicine for any species — and change what's possible for the dogs we love. About the role Loyal is seeking a Senior Principal Scientist, Drug Substance to serve as the technical leader for drug substance process development and manufacturing from early development through commercialization. This high-impact, externally-facing role will drive drug substance process development and manufacturing, and deliver flawless execution across CDMO partners while serving as the internal subject matter expert informing cross-functional decision-making and long-term development strategy across Loyal's growing pipeline. You will be reporting to our VP of Manufacturing Your daily work will include Lead end-to-end drug substance process development and manufacturing for small molecule APIs from synthetic route assessment and impurity control through scale-up, technology transfer, and commercial manufacturing readiness at CDMOs. Serve as the primary technical interface with drug substance CDMOs spanning partner selection, day-to-day oversight, troubleshooting, PAI preparation and performance management; ensure drug substance supply continuity, including second source qualification and starting material supply risk strategy, in support of clinical and commercial manufacturing. Lead RSM designation, ICH Q11 assessments, impurity fate and purge strategies and ICH M7 mutagenic impurity risk assessments; establish CQAs, CPPs, and ICH Q6A-aligned control strategies. Lead drug substance process validation from PPQ protocol development through batch execution and CPP/CQA verification; align PPQ timelines and batch disposition with drug product process validation and registration batch campaigns. Author, review, and approve drug substance CMC sections for regulatory submissions (VMF, INAD/NADA); represent drug substance CMC in agency interactions and ensure a technically integrated and consistent regulatory package. Partner with drug product development to translate drug substance CQAs into formulation design, excipient selection, container closure strategy and final dosage form decisions. Partner with analytical development to define method development, qualification, and validation strategy for drug substance release and stability testing. Partner with Quality to align drug substance specifications, batch disposition, and GMP compliance across CDMOs, and to support inspection and regulatory submission readiness. Manage drug substance post-approval change control strategy for manufacturing changes at CDMOs. About you Ph.D. in Chemistry, Chemical Engineering, Biochemistry, or a related discipline. 12+ years of industry experience in drug substance process development and manufacturing, with demonstrated ownership from early development through regulatory submission and commercialization phase. Hands-on expertise in small molecule API process development, including synthetic process understanding, impurity profiling, ICH Q11 RSM assessment, and ICH M7 mutagenic impurity control. Proven experience selecting, managing, and technically overseeing CDMOs for small molecule drug substance develo…