Custom Synthesis: Milligram to Multi-Ton Scale

The Custom Synthesis Spectrum: Four Distinct Scales

Custom chemical synthesis is not a single process — it is a continuum of increasingly complex operations, each governed by its own technical constraints, cost structures, and strategic considerations. A compound that takes two days to produce at milligram scale may require six months of process development before it can be manufactured at multi-ton volumes — a topic we explore in detail in our article on scale-up challenges in custom synthesis. Understanding these distinctions is essential for procurement teams tasked with sourcing custom molecules on time and within budget.

Milligram Scale (1 mg to 100 mg)

Milligram-scale synthesis is where every custom synthesis project begins. At this stage, the primary objective is feasibility: can the target molecule be synthesized, and does the resulting material match the expected identity and purity profile?

Typical use cases at milligram scale include:

• Analytical reference standards for method development and validation
• Initial compound screening in drug discovery programs
• Proof-of-concept studies to confirm a proposed synthetic route
• Structure-activity relationship (SAR) studies requiring small panels of related analogs

At milligram scale, a skilled synthetic chemist can typically complete the work in 1 to 3 weeks, depending on molecular complexity. The chemistry is performed in standard laboratory glassware — round-bottom flasks, Schlenk lines, and benchtop reactors. Yields may be modest, and that is acceptable. The goal is not efficiency but confirmation.

Analytical requirements at this stage are relatively straightforward: proton and carbon-13 NMR to confirm molecular structure, high-resolution mass spectrometry (HRMS) for molecular formula verification, and HPLC to establish initial purity. For a deeper look at these techniques, see our guide on analytical testing methods for pharma buyers. Costs typically range from $2,000 to $15,000 per compound, depending on the number of synthetic steps, the availability of starting materials, and whether specialized techniques such as air-free chemistry or chiral resolution are required.

Gram Scale (1 g to 100 g)

Gram-scale synthesis supports the transition from initial discovery to active development. At this stage, sufficient material is needed for biological testing, formulation development, toxicology studies, and early pharmacokinetic evaluation.

The shift from milligram to gram scale is more than a simple volumetric increase. Reactions that worked cleanly on 50-milligram scale may behave differently at 10 grams due to mixing efficiency, heat transfer limitations, or changes in reagent stoichiometry.

This is where route evaluation begins in earnest — chemists assess whether the milligram-scale route is practical for scale-up or whether alternative pathways offer better yields, fewer steps, or more accessible starting materials.

Key activities at gram scale include:

• Reproducing the synthetic route at 5x to 100x the original scale
• Identifying bottleneck steps that may limit further scale-up
• Developing preliminary analytical methods for in-process controls
• Establishing initial specifications for purity, residual solvents, and impurity profiles
• Generating material for stability studies and formulation compatibility testing

Timelines at gram scale typically run 3 to 8 weeks, with costs ranging from $10,000 to $75,000 depending on complexity. Projects requiring chiral synthesis, multiple chromatographic purifications, or hazardous reagent handling will fall toward the upper end of both ranges.

Kilogram Scale (1 kg to 100 kg)

Kilogram-scale synthesis represents the critical bridge between research and commercial manufacturing. This is where process chemistry — as distinct from synthetic chemistry — becomes the dominant discipline. The questions shift from “can we make it?” to “can we make it reproducibly, safely, and economically at this volume?”

At kilogram scale, reactions move from laboratory glassware into jacketed reactors, typically ranging from 20 to 500 liters. Heat transfer, mixing dynamics, and mass transfer become engineering challenges rather than assumptions. A reaction that generates modest heat at gram scale may become dangerously exothermic at 50 kilograms if thermal management is not properly designed.

Kilogram-scale synthesis typically supports:

• Phase I and Phase II clinical trial material supply
• Pilot production runs for commercial launch preparation
• Process validation batches required for regulatory filings
• Initial commercial orders where annual demand is moderate

Process optimization at this stage involves systematic evaluation of reaction parameters: temperature profiles, addition rates, solvent volumes, catalyst loadings, and workup procedures. The goal is to maximize yield, minimize waste, reduce cycle time, and establish robust process controls that ensure batch-to-batch consistency.

Analytical requirements expand significantly at kilogram scale. In addition to standard identity and purity testing, manufacturers must implement validated analytical methods, establish acceptance criteria for all specified impurities (including genotoxic impurities below ICH M7 thresholds), perform residual solvent analysis per ICH Q3C, and generate certificates of analysis that meet regulatory submission requirements.

Timelines for kilogram-scale projects typically range from 3 to 6 months, including process development, scale-up, and production. Costs vary widely — from $50,000 for a straightforward two-step synthesis to well over $500,000 for complex multi-step sequences requiring cGMP compliance.

Multi-Ton Scale (100+ kg)

Multi-ton synthesis is full commercial manufacturing. At this scale, every aspect of the process has been optimized: synthetic efficiency, solvent recovery, waste minimization, energy consumption, and throughput. The economics of multi-ton production are governed by raw material costs, equipment utilization rates, and process cycle times.

Manufacturing at this scale typically occurs in dedicated or multi-purpose production facilities equipped with reactors ranging from 1,000 to 10,000 liters. Process automation, continuous monitoring, and statistical process control are standard.

Batch records are comprehensive, and every parameter is documented to support regulatory compliance and product quality assurance.

Multi-ton synthesis supports:

• Commercial pharmaceutical API production
• Specialty chemical supply for industrial applications
• Agrochemical manufacturing at commercial volumes
• Electronic materials and advanced materials production

At this scale, the relationship between the buyer and the manufacturer becomes a long-term partnership. Supply agreements typically span multiple years and include provisions for capacity reservation, demand forecasting, quality agreements, and change control procedures.

Costs per kilogram decrease significantly compared to smaller scales — often by 60% to 80% — but total project investment is substantial, frequently exceeding $1 million for process development, validation, and initial production campaigns.

Route Scouting: The Foundation of Scalable Synthesis

Route scouting is arguably the most consequential phase of any custom synthesis project. The synthetic route selected at the outset determines the project’s cost trajectory, timeline, scalability potential, and regulatory pathway for years to come. Changing routes after kilogram-scale production has begun is extraordinarily expensive and can delay product launches by 12 to 18 months.

A thorough route scouting exercise evaluates multiple synthetic pathways against a defined set of criteria:

• Step count: Fewer steps generally mean higher overall yields, lower costs, and shorter cycle times. A route reduction from eight steps to five can cut manufacturing costs by 30% to 40%.
• Starting material availability: Routes that depend on a single-source starting material create supply chain risk. Preferred routes use commodity or near-commodity starting materials available from multiple suppliers.
• Reaction robustness: Reactions that tolerate minor variations in temperature, concentration, and reagent quality are strongly preferred for scale-up. Air-sensitive or moisture-sensitive reactions require specialized equipment that adds cost.
• Hazard profile: Routes that avoid highly toxic reagents, explosive intermediates, or large-volume high-pressure reactions are safer and less expensive to implement at scale.
• Intellectual property landscape: Freedom-to-operate analysis should be conducted early to ensure the selected route does not infringe existing patents.
• Regulatory considerations: For pharmaceutical applications, the route must be compatible with ICH Q11 requirements for starting material designation and process understanding.

Experienced synthesis partners typically evaluate three to five candidate routes before recommending a lead pathway, with the evaluation taking 2 to 4 weeks and costing $15,000 to $40,000 — an investment that can save hundreds of thousands of dollars during scale-up.

Analytical Requirements Across Scales

Analytical testing is not static — it evolves in scope and rigor as synthesis scales up. Procurement teams should understand what analytical deliverables to expect at each stage, because inadequate analytical support at early stages creates costly problems later.

Discovery and Early Development

• Structure confirmation by NMR (1H, 13C, and 2D experiments as needed)
• Molecular formula confirmation by HRMS
• Purity assessment by HPLC (typically a single gradient method)
• Melting point or DSC for solid-state characterization

Process Development and Pilot Scale

• Validated analytical methods for assay and related substances (per ICH Q2)
• Impurity identification and qualification (per ICH Q3A/Q3B)
• Residual solvent analysis by headspace GC (per ICH Q3C)
• Elemental impurity screening by ICP-MS or ICP-OES (per ICH Q3D)
• Polymorph screening and form characterization by XRPD
• Particle size distribution analysis
• Water content by Karl Fischer titration
• Stability-indicating method development

Commercial Manufacturing

• Full ICH stability studies (accelerated and long-term conditions)
• Complete impurity fate and purge analysis
• Ongoing stability monitoring of commercial batches
• Annual product quality reviews
• Comparability studies if process changes are implemented

The analytical investment required at commercial scale is substantial — often representing 15% to 25% of total project costs — but it is non-negotiable for regulated applications.

Process Safety: The Non-Negotiable Priority

Process safety considerations escalate dramatically with scale. A reaction that is mildly exothermic at gram scale can become a thermal runaway hazard at kilogram scale if heat removal capacity is insufficient. Process safety evaluation is not optional — it is a regulatory and ethical imperative.

Key process safety assessments include:

• Differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) to characterize thermal stability of intermediates and products
• Reaction calorimetry (RC1 or similar) to measure heat of reaction, adiabatic temperature rise, and heat generation rates under process conditions
• Thermal screening of all intermediates to identify decomposition temperatures and exothermic onset points
• Dust explosion testing for powdered intermediates and final products (minimum ignition energy, Kst values, and explosion severity)
• HAZOP (Hazard and Operability) studies before executing any new process at pilot or production scale

The cost of process safety testing typically ranges from $20,000 to $80,000, depending on the number of intermediates and the complexity of the process. This is a small fraction of the total project cost and is vastly less expensive than the consequences of an incident.

Regulatory Documentation Requirements

For pharmaceutical custom synthesis, regulatory documentation requirements increase substantially with each stage of development. Procurement teams must understand what documentation their synthesis partner will deliver and whether it meets the requirements of the target regulatory submission.

At the investigational stage (IND-enabling), minimum documentation includes:

• Detailed description of the manufacturing process
• Specifications and test methods for the drug substance
• Batch analysis data for representative batches
• Information on the control of critical process parameters

For commercial registration (NDA/ANDA/MAA), documentation requirements expand to include:

• Complete process description with proven acceptable ranges for all parameters
• Full impurity profile with identification, qualification, and control strategy
• Validation of the manufacturing process (minimum three consecutive conforming batches)
• Validated analytical methods with full method validation reports
• Stability data supporting the proposed retest period or shelf life
• Detailed information on starting materials, reagents, and solvents
• Environmental assessment data as required by jurisdiction

A synthesis partner that understands these requirements from the outset can build the appropriate data packages progressively, avoiding the costly retroactive documentation campaigns that delay regulatory submissions. Contact ChemContract to discuss your regulatory documentation needs.

Cost Drivers at Every Scale

Understanding what drives costs in custom synthesis helps procurement teams negotiate effectively and set realistic budgets. The primary cost drivers shift as scale increases:

At milligram and gram scale, costs are dominated by chemist labor time (typically 60% to 70% of total cost), followed by analytical testing (15% to 25%) and materials (10% to 15%). The cost per gram at these scales is extremely high — often $500 to $5,000 per gram — but total project costs are manageable.

At kilogram scale, the cost structure shifts. Process development labor becomes the largest component (40% to 50%), followed by raw materials (20% to 30%), analytical testing and quality assurance (15% to 20%), and facility overhead (10% to 15%). Cost per gram drops to $5 to $100 depending on complexity.

At multi-ton scale, raw materials become the dominant cost driver (40% to 60%), followed by facility and equipment utilization (20% to 30%), labor (10% to 15%), and quality/analytical (5% to 10%). Cost per gram can drop below $1 for straightforward syntheses.

Understanding these dynamics helps procurement teams identify where negotiation leverage exists. At small scales, labor efficiency is the lever. At large scales, raw material sourcing and process yield optimization drive the economics.

How to Evaluate a Custom Synthesis Partner

Selecting the right custom synthesis partner is one of the most consequential decisions a procurement team makes. The wrong choice can result in months of delays, hundreds of thousands of dollars in wasted investment, and missed market windows. A rigorous evaluation should examine:

• Track record at the required scale: A partner with deep experience at milligram scale may lack the engineering capabilities for kilogram or multi-ton production. Ask for specific examples of projects completed at the scale you need. For a complete evaluation framework, see how to choose a custom synthesis partner.
• Analytical capabilities: In-house analytical capability is strongly preferred over outsourced testing, which adds time and creates communication gaps. Evaluate whether the partner has the specific instruments and validated methods relevant to your compound.
• Quality systems: For pharmaceutical applications, verify cGMP compliance through facility audits, review quality agreements, and examine their CAPA (corrective and preventive action) history.
• Project management maturity: Regular communication, milestone tracking, and proactive risk identification distinguish excellent partners from adequate ones. Ask about their project management methodology and reporting cadence.
• IP protection: Review confidentiality agreements carefully. Understand how the partner controls access to proprietary information, segregates projects, and protects your intellectual property.
• Scalability pathway: The ideal partner can support your project from discovery through commercial production, eliminating the costly and time-consuming technology transfer between different organizations at each scale transition.
• Geographic proximity: Domestic partners offer faster shipping, easier facility audits, real-time communication in the same time zone, and simplified regulatory compliance under a single jurisdiction.

Frequently Asked Questions

How much does custom chemical synthesis cost?

Custom synthesis costs vary enormously by scale and complexity. At milligram scale, expect $2,000 to $15,000 per compound. Gram-scale projects typically cost $10,000 to $75,000, while kilogram-scale manufacturing ranges from $50,000 to over $500,000. At multi-ton commercial scale, total project investment frequently exceeds $1 million, though the cost per kilogram drops significantly — often by 60% to 80% compared to smaller scales.

How long does a custom synthesis project take?

Timelines depend on scale and complexity. Milligram-scale feasibility studies take 1 to 3 weeks. Gram-scale synthesis runs 3 to 8 weeks. Kilogram-scale projects require 3 to 6 months including process development. Multi-ton commercial production adds another 3 to 6 months for validation and initial campaigns. Route scouting, which should be completed before scale-up begins, typically takes 2 to 4 weeks.

What is route scouting and why is it important?

Route scouting is the systematic evaluation of multiple synthetic pathways to identify the best route for your target molecule. It considers step count, starting material availability, reaction robustness, safety profile, and intellectual property landscape. Investing $15,000 to $40,000 in thorough route scouting can save hundreds of thousands of dollars during scale-up by avoiding routes that fail at larger volumes.

What analytical testing is required at each synthesis scale?

Discovery-stage projects need basic structure confirmation (NMR, HRMS) and purity assessment (HPLC). Process development requires validated analytical methods, full impurity profiling per ICH guidelines, residual solvent analysis, and elemental impurity screening. Commercial manufacturing adds ICH stability studies, ongoing batch monitoring, and comparability studies for any process changes. Analytical costs typically represent 15% to 25% of total project costs at commercial scale.

Should I use a domestic or offshore custom synthesis provider?

Domestic providers offer faster shipping, easier facility audits, same-timezone communication, and simplified regulatory compliance under a single jurisdiction. Offshore providers may offer lower per-project costs but introduce risks including tariff exposure, customs delays, longer lead times, and potentially weaker IP protection. The best choice depends on your specific priorities regarding cost, speed, IP sensitivity, and regulatory requirements.

Why ChemContract for Custom Synthesis

ChemContract provides custom synthesis services across the full scale spectrum — from initial milligram feasibility studies through multi-ton commercial production — within a single, integrated U.S.-based organization.

• Experienced synthetic chemists with expertise spanning complex heterocyclic chemistry, asymmetric synthesis, organometallic catalysis, and process chemistry
• Comprehensive in-house analytical capabilities including HPLC, GC-MS, NMR, ICP-OES, XRPD, and thermal analysis
• Scalable facilities supporting seamless progression from bench-scale through kilo lab, pilot plant, and full production
• Full regulatory documentation support including cGMP compliance for pharmaceutical applications
• Dedicated project managers providing weekly updates, milestone tracking, and transparent communication at every stage
• Domestic operations eliminating tariff exposure, customs delays, and IP protection concerns associated with offshore synthesis

For procurement teams managing custom synthesis projects, the path from molecule to material is complex but navigable with the right partner and the right planning. The investment in thorough route scouting, rigorous process development, and comprehensive analytical characterization pays dividends throughout the product lifecycle.