Green chemistry guides the sustainable
drug synthesis. Classical
metrics (AE, E-factor, and process-mass-intensity) cover only 2 of
the 12 green chemistry principles (GCPs) (prevention and AE). Other
important GCPs are grossly ignored (benign solvents, reagents, and
catalysis). Recently newer metrics green aspiration level (GAL) and
improved (iGAL) were proposed. These metrics consider the E-factor
but miss other important principles, such as the use of benign solvents,
reagents, and catalysis. The recently proposed principle-specific
score also requires proprietary data. Thus, a simple and novel metric/score
that includes additional GCPs for objective assessment of environmental
impacts, safety, and greenness of the synthesis routes is urgently
required. This article proposes novel metrics, principle-specific,
and average green chemistry principle scores (AGCPx and AGCP) and
a cumulative green chemistry principle score (CGCP score) that considers
four GCPs (x = 2, 3, 5, and 9) to allow objective
and quantitative assessments of the different routes for an API. CGCP
score has been quantitatively benchmarked against the classical metrics
for sildenafil which is known for its green synthesis procedures.
Additionally, the AGCP and CGCP scores have been validated by using
the US-EPA and ACS-GCI awarded green chemistry routes for a chemically
and therapeutically diverse set of drugs. Although the process-chemistry
green synthesis routes tend to have an average CGCP score of 0.59,
a synthesis route with the AGCP score of ∼0.53 can be considered
green (e.g., discovery route for carbimazole). We also demonstrate
the utility of CGCP score for the discovery (medchem) and process-chemistry
routes for four FDA-approved PARP-1 drugs. CGCP score allows the objective
comparison and assessment of synthesis schemes for a given drug and
between multiple drugs. CGCP correctly identifies the greenness (or
lack thereof) of known synthesis routes (talazoparib and niraparib,
respectively) and offers novel green chemistry insights for further
improvements. CGCP score is a useful synthesis design tool and valuable
addition to the armory of discovery and process chemists.