Development of a targeted polymorph screening approach for a complex polymorphic and highly solvating API

Elucidation of the most stable form of an active pharmaceutical ingredient (API) is a critical step in the development process. Polymorph screening for an API with a complex polymorphic profile can present a significant challenge. The presented case illustrates an extensively polymorphic compound with an additional propensity for forming stable solvates. In all, 5 anhydrous forms and 66 solvated forms have been discovered. After early polymorph screening using common techniques yielded mostly solvates and failed to uncover several key anhydrous forms, it became necessary to devise new approaches based on an advanced understanding of crystal structure and conformational relationships between forms. With the aid of this analysis, two screening approaches were devised which targeted high-temperature desolvation as a means to increase conformational populations and enhance overall probability of anhydrous form production. Application of these targeted approaches, comprising over 100 experiments, produced only the known anhydrous forms, without appearance of any new forms. The development of these screens was a critical and alternative approach to circumvent solvation issues associated with more conventional screening methods. The results provided confidence that the current development form was the most stable polymorph, with a low likelihood for the existence of a more-stable anhydrous form.

Pyrazolinone-piperidine dipeptide growth hormone secretagogues (GHSs). Discovery of capromorelin

Novel pyrazolinone-piperidine dipeptide derivatives were synthesized and evaluated as growth hormone secretagogues (GHSs). Two analogues, capromorelin (5, CP-424391-18, hGHS-R1a K(i)=7 nM, rat pituicyte EC(50)=3 nM) and the des-methyl analogue 5c (hGHS-R1a K(i)=17 nM, rat pituicyte EC(50)=3 nM), increased plasma GH levels in an anesthesized rat model, with ED(50) values less than 0.05 mg/kg iv. Capromorelin showed enhanced intestinal absorption in rodent models and exhibited superior pharmacokinetic properties, including high bioavailabilities in two animal species [F(rat)=65%, F(dog)=44%]. This short-duration GHS was orally active in canine models and was selected as a development candidate for the treatment of musculoskeletal frailty in elderly adults.

Discovery of the hemifumarate and (alpha-L-alanyloxy)methyl ether as prodrugs of an antirheumatic oxindole: prodrugs for the enolic OH group

Ether, ester, and carbonate derivatives of the antirheumatic oxindole 1 were prepared and screened as potential prodrugs of 1. This effort led to the discovery of the (alpha-L-alanyloxy)-methyl ether and hemifumarate derivatives of 1 which deliver the drug efficiently into the circulation of test animals, are stable in the solid state, and possess good stability in solution at low pH as required to ensure gastric stability. Success in achieving acceptable bioavailabilities of 1 across species (rats, dogs, and monkeys) followed the inclusion of ionizable functionality within the promoiety to compensate for masking the polar enolic OH group of the free drug. However, the introduction of ionizable functionality was often associated with decreased stability, as demonstrated by the hemisuccinate, hemiadipate, hemisuberate, and alpha-amino ester derivatives of 1 which could not be isolated. A clear exception was the hemifumarate derivative of 1 which was not only isolable but actually more stable at neutral pH than the nonionizable ester analogues. The solution and solid state stability of the hemifumarate, together with its activity as a prodrug of 1, suggests that hemifumarate be considered as an alternative to hemisuccinate as a prodrug derivative for alcohols, particularly in situations where solution state stability is an issue.