Synthesis and biological evaluation of novel 2,4-diaminoquinazoline derivatives as SMN2 promoter activators for the potential treatment of spinal muscular atrophy.

Proximal spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by death of motor neurons in the spinal cord that is caused by deletion and/or mutation of the survival motor neuron gene ( SMN1). Adjacent to SMN1 are a variable number of copies of the SMN2 gene. The two genes essentially differ by a single nucleotide, which causes the majority of the RNA transcripts from SMN2 to lack exon 7. Although both SMN1 and SMN2 encode the same Smn protein amino acid sequence, the loss of SMN1 and incorrect splicing of SMN2 have the consequence that Smn protein levels are insufficient for the survival of motor neurons. The therapeutic goal of our medicinal chemistry effort was to identify small-molecule activators of the SMN2 promoter that, by up-regulating gene transcription, would produce greater quantities of full-length Smn protein. Our initial medicinal chemistry effort explored a series of C5 substituted benzyl ether based 2,4-diaminoquinazoline derivatives that were found to be potent activators of the SMN2 promoter; however, inhibition of DHFR was shown to be an off-target activity that was linked to ATP depletion. We used a structure-guided approach to overcome DHFR inhibition while retaining SMN2 promoter activation. A lead compound 11a was identified as having high potency (EC50 = 4 nM) and 2.3-fold induction of the SMN2 promoter. Compound 11a possessed desirable pharmaceutical properties, including excellent brain exposure and long brain half-life following oral dosing to mice. The piperidine compound 11a up-regulated expression of the mouse SMN gene in NSC-34 cells, a mouse motor neuron hybrid cell line. In type 1 SMA patient fibroblasts, compound 11a induced Smn in a dose-dependent manner when analyzed by immunoblotting and increased the number of intranuclear particles called gems. The compound restored gems numbers in type I SMA patient fibroblasts to levels near unaffected genetic carriers of SMA.

The intramolecular asymmetric Pauson-Khand cyclization as a novel and general stereoselective route to benzindene prostacyclins: synthesis of UT-15 (treprostinil).

A general and novel solution to the synthesis of biologically important stable analogues of prostacyclin PGI(2), namely benzindene prostacyclins, has been achieved via the stereoselective intramolecular Pauson-Khand cyclization (PKC). This work illustrates for the first time the synthetic utility and reliability of the asymmetric PKC route for synthesis and subsequent manufacture of a complex drug substance on a multikilogram scale. The synthetic route surmounts issues of individual step stereoselectivity and scalability. The key step in the synthesis involves efficient stereoselection effected in the PKC of a benzoenyne under the agency of the benzylic OTBDMS group, which serves as a temporary stereodirecting group that is conveniently removed via benzylic hydrogenolysis concomitantly with the catalytic hydrogenation of the enone PKC product. Thus the benzylic chiral center dictates the subsequent stereochemistry of the stereogenic centers at three carbon atoms (C(3a), C(9a), and C(1)).