Improving API Synthesis - Pharmaceutical Technology

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Improving API Synthesis
O-arylation and O-alkylation, a one-pot protein synthesis, a combined approach in continued and chemocatalysis, and green-chemistry applications are the target of some recent advances in API synthesis.


Pharmaceutical Technology
Volume 35, Issue 8, pp. 52-56


IMAGE: STOCKBYTE / GETTY IMAGES
Organic chemists face the ongoing challenge of developing and optimizing a synthesis for active pharmaceutical ingredients (APIs). These challenges involve a multitude of issues designed to improve yield, purity, stereoselectivity, process conditions (i.e., temperature and pressure), scalability, and production economics. A recent literature review reveals insight into some of these challenges as they relate to organic chemical production overall and pharmaceutical chemical development in particular.

O-arylation and O-alkylation


Patricia Van Arnum
Researchers at Merck & Co. recently reported on a large-scale synthesis of a potent glucokinase inhibitor, MK-0941, through selective O-arylation and O-alkylation. Glucokinase inhibitors are under clinical development for treating Type II diabetes. MK-0941 is a glucokinase inhibitor that has a differentially substituted 3,5-dihydroxybenzamide structure, and an efficient synthesis that would be suitable for large-scale preparation was required. The researchers reported on several drawbacks of the early-stage synthesis, including multiple recrystallizations to improve enantomeric purity, yield variability, and batch-to-batch variability in the impurity profile of the desired compound. Several factors were key to improving the synthesis: a highly selective mono-O-arylation of methyl 3,5-dihydroxybenzoate with 2-ethanesulfonyl-5-chloropyridine and the selection of a proper protective group for the SN2 O-alkylation (1).

One-pot protein synthesis

Researchers at the University of Chicago recently developed a one-pot protein synthesis involving a 204-residue covalent-dimer vascular endothelial growth factor (VEGF). VEGF is a protein involved in vasculogenesis and angiogenesis and is studied in reference to pharmaceutical compounds, particularly anticancer compounds. The researchers reported that they prepared a 204-residue covalent dimmer VEGF with full mitogenic activity from three unprotected peptide segments by one-pot native chemical ligations. The covalent structure of the synthetic VEGF was confirmed through mass measurements, and the three-dimensional structure of the synthetic protein was determined by high-resolution X-ray crystallography (2, 3).

Chemical protein synthesis is one research area of University of Chicago professor Stephen B.H. Kent, a co-author of the recently published research on the VEGF synthesis. One area of focus is the preparation of long polypeptide chains of protein molecules by the chemoselective reaction (i.e. chemical ligation) of unprotected protein segments containing mutually reactive functional groups. An example of these ligation chemistries is thioester-mediated, amide-forming ligation or native ligation. The resulting polypeptide chains are folded with good efficiency to produce high-purity synthetic proteins. The covalent structure of the molecule is confirmed by mass spectrometry, and the three-dimensional fold structure of the synthetic protein is determined by X-ray crystallography. Another area of research focus is kinetically controlled ligation, a chemistry used for the full convergent synthesis of large protein molecules. The research group is examining insertion reactions for creating molecular diversity in preformed molecular scaffolds and the use of polymer-supported ligation.


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