Process Development Flashcards
Telescoping
Product from a chemical reaction is not isolated and purified –instead it is used directly in the next reaction.
Telescoping
Advantages and disadvantages
Avoids isolation of unstable or toxic compounds, or compounds with undesirable physical characteristics (oily, non-crystalline compounds)–Can only be used for reactions that generate minimal impurities, and reach completion (no unreacted starting materials)–Isolation and purification steps are often most difficult/time consuming steps –telescoping highly desirable where possible.
Linear routes
Advantages and disadvantages
Often utilised as the starting point for process development-gives option for late-stage diversification critical to medicinal chemistry.•Reduced overall yield -most importantly low yielding steps near the end of the route need to be identified (key focus early development is speed of delivery).•Simplified manufacturing process –no holds are required, BUT large margin needed in planning•Unanticipated low yield = lengthy resynthesis.
Convergent Routes
Advantages and disadvantages
Greater efficiency•Scheduling and stability may be problematic•Unanticipated low yield accommodated by short synthesis
Purification Techniques:
Crystallisation
Chromatography
Crystallisation
Main purification method used for intermediate or API purification –scalable•Crystalline target highly desirable due to manufacturing process and stability of product•Very high purities attainable (99.9%)•Potential to improve d.e. / e.e. of reactions•Polymorphism –needs to be considered
Chromatography
Requires large quantities of solvent, silica•Requires days on scale•Performance decreases with scale (non-plug flow, channeling)
Now, use of automated chromatography systems (plant scale) reduces the inefficiency of this technique•Enantiomericseparations by chromatography using chiral columns –extensively used in commercial production.
Green Chemistry define
Used to support and reinforce movement towards greener and sustainable chemistry
Green Chemistry metrics
1.Atom Economy2.Environmental Factor3.Reaction Mass Efficiency4.Process Mass Intensity
Atom economy Definition:
MWtof desired product /MWtof all products x 100%
Easy to calculate from reaction scheme-Does not take into account reaction yield, solvent usage or other reagents used in the work-up
E-factor:
environmental
defined as ratio of waste over product
Reaction mass efficiency
•Defined as:=
mass of desired product/ mass of all reactants percentage
Process Mass Intensity•Defined as:
Mass of all materials used to produce product/ Mass of product (x 100%)
Biocatalysis
Catalyst is an enzyme derived from renewable resources that is biodegradable.•
Biocatalysis
Advantages and disadvantages
Catalysis generally proceeds with high chemo-, regio-and stereoselectivity. Often a clean reaction•Avoids the need for protection and deprotectionsteps.•Reactions often carried out in water with mild conditions (temperature, pH and pressure).•Purification is simplified•Catalyst may be recycled•Very favourable for large-scale work.
Around 54% of APIs are chiral with two stereogeniccentres (on average) –of these around 50% are racemic mixtures
.•Enantiomers have ______physical and chemical properties in an achiral environment –biological systems are chiral, therefore each enantiomer can behave differently in vivo.
•Enantiomers of chiral drugs must considered as ______drugs with different properties UNLESS proven otherwise (move towards enantiopuredrugs).
identical
separate
Chirality installation
•Chirality is derived from purchased starting material for 55% of chiral APIs –desire to introduce chirality early into reaction schemes.
–Chiral pool approach ( Cheap, enantiopure•Similarity to drug?•Atom efficiency)
In-house generation of chirality (–resolution (62% of APIs): classical salt formations accounts for 2/3 of resolution technique other methods include dynamic kinetic, enzymatic and chromatographic resolutions–asymmetric synthesis (~20% of APIs) -catalytic in nature.)
Route design and selection
•Process chemistry involves investigation of multiple synthetic routes to a single API target
–All routes must be evaluated how? to find the most efficient process
the SELECTcriteria is routinely used for route evaluation: Safety, Environmental, Legal, Economics, Control and Throughput.
