and were able to decrease oxidative metabolism significantly. These studies resulted in the discovery of once daily sGC stimulator vericiguat (BAY 1021189; MK‐1242) that we decided to develop for chronic HF (see Section 3.6).
Table 3.1 Hemodynamic changes and QoL at 16 weeks in patients with high vs low PVR at baseline.
| PVR ≤240 dyn·s/cm5 | PVR >240 dyn·s/cm5 | Inter‐ action p‐value | |||
|---|---|---|---|---|---|
| Parameter a | n b | LS mean diff. (95% CI)Riociguat 2 mg vs placebo | n b | LS mean diff. (95% CI)Riociguat 2 mg vs placebo | |
| SVR (dyn·s/cm5) | 21/25 | −276 (−459 to −93) | 32/31 | −210 (−386 to −34) | 0.6 |
| SBP (mmHg) | 21/25 | −0.96 (−9.5 to 7.6) | 32/31 | +1.4 (−5.2 to 7.9) | 0.7 |
| Cardiac index (l/min/m2) | 22/25 | +0.6 (0.3 to 0.9) | 32/31 | +0.2 (−0.02 to 0.4) | 0.03 |
| Stroke volume (ml) | 22/25 | +17 (7 to 28) | 32/31 | +7 (−1 to 14) | 0.07 |
| PCWP (mmHg) | 22/25 | −6.55 (−10.65 to −2.44) | 31/31 | +1.18 (−2.47 to 4.83) | 0.005 |
| mPAP (mmHg) | 22/25 | −8.8 (−13.3 to −4.3) | 32/31 | +1.1 (−3.4 to 5.6) | 0.002 |
| PAC (ml/mmHg) | 22/25 | +1.7 (0.9 to 2.6) | 32/30 | +0.4 (−0.2 to 1.0) | <0.005 |
| MLHF QoL total score | 27/30 | −12 (−21 to −3) | 40/39 | −6 (−12 to 0.2) | 0.3 |
a Per‐protocol population used for hemodynamics; ITT used for QoL. Estimates and CIs are based on an ANCOVA model with baseline value, treatment effect and region as fixed effects. p‐value is based on an ANCOVA model with baseline value, treatment effect, region and subgroup as fixed effects and interaction of subgroup and treatment (placebo and riociguat 2 mg).
b Riociguat 2 mg/placebo [27].
3.3 Medicinal Chemistry Program
Optimization strategy. The goal of this medicinal chemistry program resulting in vericiguat 2 was to identify an orally bioavailable sGC stimulator with a longer duration of action than riociguat 1. In order to support a profile allowing for once daily oral dosing, the strategy is to reduce oxidative metabolism which would also lower drug–drug interaction potentials. Riociguat is a very potent sGC stimulator in vitro and in vivo; however, it has a moderate half‐life in different animal species [28] and this pharmacokinetic profile translated into a three times daily dosing regimen in patients. N‐demethylation to compound 10 appears to be the main biotransformation pathway of riociguat as described by Gnoth et al. [29] in 2015. This step is mainly catalyzed by CYP1A1, but also by CYP3A4, CYP3A5, and CYP2J2 [29–35]. Our optimization strategy was aiming for further optimizing the metabolic stability of riociguat and hence reducing blood clearance in order to achieve a longer half‐life. We began by varying the substituents on the 5‐carbamoyl residue on the pyrimidine ring, aiming to achieve metabolically more stable derivatives while maintaining good potency. In a second optimization step, we later focused on variations of the central pyrazolopyridine scaffold.
SAR and DMPK optimization. First, the SAR of a series of novel N‐substituted methyl carbamates 1, 3–9 was explored using a cGMP formation assay with sGC‐overexpressing Chinese hamster ovary (CHO) cells [36]. In addition, the metabolic stability of the analogs was assessed in vitro by incubation with rat hepatocytes. Initially, different carbamate N‐substituents were synthesized with the aim of achieving higher metabolic stability than 1 while maintaining high potency (Table 3.2). Increasing steric bulk (e.g. ethyl 3) or the introduction of polarity (e.g. a hydroxyethyl functionality, as in 4) led to a significant loss of potency relative to 1, along with decreased metabolic stability. Also, the introduction of fluorine atoms at the terminal position of the N‐substituent, a common strategy to block metabolism, was not met by success. Interestingly, both the 2,2‐difluoroethyl and 2,2,2‐trifluoroethyl derivatives, 5 and 6, exhibited high potency in the cGMP assay but unfortunately had a 2‐ to 4.5‐fold higher clearance in rat hepatocytes. N‐fluorobenzyl substitution revealed that the ortho‐fluoro derivative 7 is significantly more potent (MEC = 0.1 μM) than the meta and para isomers, 8 and 9 (MEC = 0.2 and 0.7 μM, respectively). Nevertheless, all the benzylic derivatives were characterized by high clearance in rat hepatocytes. These results and the testing of many further derivatives (data not shown) suggested that improving the metabolic stability by altering the N‐substitution might be very difficult to achieve. As a consequence, optimization efforts were focused on the main metabolite of riociguat, the N‐desmethyl derivative 10. This compound is less potent than 1 but displayed a somewhat higher metabolic stability in the rat hepatocyte assay, with a clearance of 0.1 l/h/kg. When tested in rats (i.v. dosing), compound 10 had insufficient pharmacokinetic properties (moderate clearance of 1.2 l/h/kg and a short half‐life of only 1.2 hours).
Therefore, variations in the carbamate alkoxy group were examined next while leaving the N‐position unsubstituted, with the goal of improving DMPK properties relative to compound 10 (Table 3.3).
The introduction of steric bulk in the form of an isopropyl residue (compound 11) led to a strong decrease in potency as well as decreased metabolic stability. Interestingly, potency was slightly increased in cyclobutyl derivative 12; however, the analog was also unfavorable with respect to in vitro clearance. In some cases, the oxetanyl
