The Synthetic Routes of (3S,4R)-benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo

(3S,4R)-benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo[2,1-b]pyridine-2-yl)amide, also known as GDC-0980, is a synthetic drug that is used in the treatment of various types of cancer, including melanoma, gastric, colorectal, and non-small cell lung cancer.
The synthesis of GDC-0980 involves several steps, which can be broadly classified into two categories: synthetic routes that involve the synthesis of the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold and synthetic routes that involve the synthesis of the benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo[2,1-b]pyridine-2-yl)amide side chain.

The synthesis of the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold typically involves the condensation of two aromatic aldehydes in the presence of a Lewis acid catalyst, followed by a series of hydrogenation and dehydrogenation steps to install the desired functional groups.
One of the most popular synthetic routes involves the synthesis of the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold using a modified version of the Ullmann condensation reaction.
This route involves the condensation of 2-aminomethyl-4,5,6,7-tetrahydrobenzothiazole with 2-bromo-1,3-benzenedicarboxylate in the presence of triphenylphosphine as a catalyst, followed by hydrogenation of the resulting intermediate to install the desired functional groups.

Once the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold has been synthesized, the synthesis of the benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo[2,1-b]pyridine-2-yl)amide side chain typically involves the synthesis of a suitably functionalized benzyl alcohol, followed by the condensation of this benzyl alcohol with the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold in the presence of a condensation agent, such as dicyclohexylcarbodiimide (DCC) or hydrochloric acid.

One of the most convenient synthetic routes for the synthesis of the benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo[2,1-b]pyridine-2-yl)amide side chain involves the synthesis of a benzyl alcohol derivative that contains a terminal alkyne group.
This benzyl alcohol derivative can then be condensed with the imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold in the presence of DCC, followed by hydrogenation of the resulting intermediate to install the desired functional groups.

Alternatively, the benzyl 3-ethyl-4-(3H-imidazo[1,2-a]pyrrolo[2,1-b]pyridine-2-yl)amide side chain can also be synthesized using a modified version of the Suzuki reaction.
This route involves the synthesis of a boronic acid derivative of the desired benzyl alcohol, followed by the condensation of this boronic acid derivative with a suitably functionalized imidazo[1,2-a]pyrrolo[2,1-b]pyridine scaffold in the presence of a palladium catalyst, such as palladium(II) acetate.

Overall, the synthesis of (3S,4R)-ben