Sarpogrelate hydrochloride synthesis Introduction Lysophosph

Introduction Lysophosphatidic Sarpogrelate hydrochloride synthesis (LPA) is a key, serum-borne phospholipid, regulating a number of cellular processes such as proliferation, migration and differentiation through its interaction with G-protein coupled receptors. LPA receptor signaling has been implicated in several disease states including fibrosis, cholestatic pruritus and tumour metastasis. There are a number of forms of LPA, varying in length and unsaturation levels of the lipid sidechain, as well as at least six known receptors, whose roles are not all clearly understood. Autotaxin (ATX), also known as ectonucleotide pyrophosphatase/phosphodiesterase 2 (eNPP2), is thought to be the predominant enzyme responsible for production of the various LPAs. Autotaxin exhibits lysophospholipase D activity, which cleaves lysophosphatidylcholines (LPC) to the respective LPAs (Fig. 1). Receptor mediated LPA signaling has been shown to be an important mechanism in lung fibrosis and Bristol-Myers Squibb have been developing the selective LPA1 antagonist, BMS-986020, for treatment of idiopathic pulmonary fibrosis (IPF). Another approach for blockade of this signaling pathway is inhibition of ATX, preventing formation of LPA. Galapagos are currently testing this approach with the autotaxin inhibitor GLPG-1690. This paper is the first of two describing our discovery of autotaxin inhibitors for potential treatment of IPF. PF-8380 (Fig. 2), characterised by Pfizer, is a high affinity ATX inhibitor that has been shown by crystallization studies to occupy a similar binding pocket to LPA (Fig. 3). The benzyl carbamate occupies a hydrophobic pocket, similarly to the lipophilic chain of LPC, whilst the benzoxazolone is bound by the catalytic zinc. Initially, library work was carried out using the fragment 1 (Scheme 1). In an attempt to improve solubility, a number of alternative alcohols (ROH) were used to reduce the number of aromatic rings via saturation. Whilst 2b and 2c maintained the activity (Table 1) when compared with unsubstituted compound 2a, none of these changes resulted in an improvement in thermodynamic solubility, which remained unmeasurable at physiological pH. Replacement of the dichlorophenyl moiety of PF-8380 with heterocycles such as pyridine led to a significant loss of activity (data not shown). The linker region of PF-8380 was then modified, in an attempt to gain solubility via change in geometry or incorporation of heteroatoms, as shown in Scheme 2, to give a series of amide carbamates (6). Several potent compounds were identified (Table 2), but again, thermodynamic solubility remained unmeasurable at physiological pH. It became apparent at this time, that all compounds explored contained the benzoxazolone, and that all showed high crystallinity. We hypothesized that the crystallinity was due to the benzoxazolone, and that high crystal lattice energy was leading to poor dissolution, and hence poor solubility. In an attempt to reduce the crystal lattice energy, the benzoxazolone was truncated to the oxazolinone (8). Intermediates (7) were prepared analogously to 5, then coupled to 2-oxo-2,3-dihydrooxazole-5-carboxylic acid (Scheme 3). We were pleased to find that this led to an improvement in solubility, despite a reduction in activity. Some activity could be recovered by replacing the piperazine with a piperidine to give compound 8b. Within the series, it had been noted that hydrogen bond donor (HBD) count greatly affected permeability, as measured in artificial membrane experiments (PAMPA). This was reflected in the permeability data (Table 3) for compounds 8a and 8b containing two HBDs. Methylation of 8b to give 8c improved this permeability, as well as leading to another small improvement in activity. Compound 8c showed high intrinsic clearance in rat microsomes, but was highly bound to plasma protein (Fig. 4). When compound 8c was dosed in vivo, it showed reasonable exposure, due to lower clearance and a moderate volume of distribution. This suggested that the compound distributed into tissues, as well as being highly bound to plasma proteins. However, further profiling of 8c showed that despite being inactive in a dofetilide radioligand binding assay, it had significant activity in a hERG automated patch clamp assay. Finally, when tested for chemical stability, compound 8c was unstable in acid. As all compounds synthesized at this point had contained the carbamate moiety and had shown no signs of instability, the acid degradation was attributed to the oxazolinone head group.