Methotrexate α-tert-butyl ester is a protected analog of the antineoplastic and immunosuppressive drug methotrexate (MTX), in which the β-carboxyl group of the L-glutamate moiety is esterified with a tert-butyl group. Methotrexate α-tert-butyl ester is primarily used in chemical synthesis and prodrug development studies.

MTX-PVG exhibits activity against HT1080 cells, the OtBu-MTX-PVG derivative(Methotrexate α-tert-butyl ester) is less active, indicating that protecting the α-carboxyl group of MTX Results in decreased in vitro activity.[1]

In HT1080 tumor-bearing mice, Methotrexate α-tert-butyl ester significantly inhibits tumor growth. This finding suggests that protecting the α-carboxyl group of methotrexate can enhance the circulatory half-life and minimize liver accumulation for similar dendrimer conjugates without compromising their in vivo antitumor efficacy.[1]