D-3,5-Difluorophenylalanine

We report on the design of benzodiazepinones as peptidomimetics at the carboxy terminus of hydroxyamides. Structure-activity relationships of diazepinones were investigated and orally active gamma-secretase inhibitors were synthesized. Active metabolites contributing to Abeta reduction were identified by analysis of plasma samples from Tg2576 mice. In particular, (S)-2-((S)-2-(3,5-difluorophenyl)-2-hydroxyacetamido)-N-((S,Z)-3-methyl-4-oxo-4,5-dihydro-3H-benzo[d][1,2]diazepin-5-yl)propanamide (BMS-433796) was identified with an acceptable pharmacodynamic and pharmacokinetic profile. Chronic dosing of BMS-433796 in Tg2576 mice suggested a narrow therapeutic window and Notch-mediated toxicity at higher doses.

A previous study by us suggests the utility of cerebrospinal fluid (CSF) and plasma Abeta as biomarkers of beta- or gamma-secretase inhibition. The present study characterized further Abeta pharmacodynamics in these tissues from Tg2576 mice and examined their correlation with brain Abeta after acute treatment with a potent gamma-secretase inhibitor, N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-l-alaninamide (LY-411575). A single dose of LY-411575 dose-dependently (0.1-10 mg/kg p.o.) reduced Abeta(1-40) and Abeta(1-42) in the CSF and the brain. In contrast, plasma Abeta levels were increased by 0.1 mg/kg LY-411575 and were followed by a dose-dependent reduction at higher doses. The time courses of Abeta reduction and recovery were distinct for the three tissues: maximal declines in Abeta levels were evident by 3 h in the CSF and plasma but not until 9 h in the brain.

The efficacy of gamma-secretase inhibitors in vivo has, to date, been generally assessed in transgenic mouse models expressing increased levels of amyloid-beta (Abeta) peptide thereby allowing the detection of changes in Abeta production. However, it is not clear whether the in vivo potency of gamma-secretase inhibitors is independent of the level of amyloid precursor protein expression. In other words, does a gamma-secretase inhibitor have the same effect in nontransgenic physiological animals versus transgenic overexpressing animals? In the present study, an immunoassay has been developed which can detect Abeta(40) in the rat brain, where concentrations are much lower than those seen in transgenic mice such as Tg2576 (c. 0.7 and 25 nM, respectively) and in cerebrospinal fluid (CSF, c. 0.3 nM). Using this immunoassay, the effects of the gamma-secretase inhibitor LY-411575 [N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide] were assessed and robust dose-dependent reductions in rat brain and CSF Abeta(40) levels were observed with ID(50) values of 1.

Accumulation of amyloid beta-peptide (Abeta) is considered a key step in the etiology of Alzheimer's disease. Abeta is produced by sequential cleavage of the amyloid precursor protein by beta- and gamma-secretase enzymes. Consequently, inhibition of gamma-secretase provides a promising therapeutic approach to treat Alzheimer's disease. Preclinically, several gamma-secretase inhibitors have been shown to reduce plasma and brain Abeta, although they also produce mechanism-based side effects, including thymus atrophy and intestinal goblet cell hyperplasia. The present studies sought to establish an efficient screen for determining the therapeutic window of gamma-secretase inhibitors and to test various means of maximizing this window. Six-day oral administration of the gamma-secretase inhibitor N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-l-alaninamide (LY411,575) reduced cortical Abeta(40) in young (preplaque) transgenic CRND8 mice (ED(50) approximately 0.