Water-soluble prodrugs of cyclosporine A with tailored conversion rates

Dipeptide Prodrugs of the Glutamate Modulator Riluzole

We have previously reported a prodrug strategy based on the marketed drug riluzole (2-amino-6-trifluoromethoxybenzothiazole), associated with the benefits of lower patient to patient variability of exposure and potentially once daily oral dosing, as opposed to the large variance and twice daily dosing, which is currently observed with the parent drug. Riluzole is a glutamate modulator that is currently approved by the US FDA to treat amyotrophic lateral sclerosis (ALS). Riluzole also strongly suppresses the growth of melanoma cells that express the type 1 metabotropic glutamate receptor (GRM1, mGluR1). Riluzole is a substrate for the variably expressed liver isozyme CYP1A2, which has been shown to contribute to the variance in exposure of riluzole in humans upon oral administration. In addition, an elevated C_max following oral administration is a probable cause of increased liver enzyme levels in some patients. In order to mitigate these issues, a series of natural and unnatural dipeptide prodrugs of riluzole were prepared as products that bear lower first-pass hepatic clearance. The prodrugs were evaluated for their ability to produce riluzole in serum while remaining intact prior to absorption from the GI tract, characteristic of a type IIB prodrug. Here, we describe dipeptide conjugates of riluzole and report that the t-Bu-Gly-Sar-riluzole analog FC-3423 (6) is absorbed well and converts to riluzole in rats and mice in a regular and well-defined manner. FC-3423 strongly suppress tumor cell growth in mouse xenograft models of melanoma at a molar dose 10-fold less than that of riluzole itself.

Semi-synthesis of cyclosporins

BACKGROUND

Since its isolation in 1970, and discovery of its potent inhibitory activity on T-cell proliferation, cyclosporin A (CsA) has been shown to play a significant role in diverse fields of biology. Furthermore, chemical modification of CsA has led to analogs with distinct biological activities associated with its protein receptor family, cyclophilins.

SCOPE OF REVIEW

This review systematically collates the synthetic chemistry performed at each of the eleven amino acids, and provides examples of the utility of such transformations. The various modifications of CsA are traced from early, modest chemistry performed at the unique Bmt residue, through the remarkable use of a polyanion enolate that can be stereoselectively manipulated, and onto application of more recently developed olefin metathesis chemistry to prepare new CsA derivatives with unexpected biological activity.

MAJOR CONCLUSIONS

The myriad biological activities of CsA and its synthetic derivatives have inspired the development of new approaches to modify the CsA ring. In turn, these new CsA derivatives have served as tools in the discovery of new roles for cyclophilins.

GENERAL SIGNIFICANCE

This review provides information on the types of cyclosporin derivatives that are available to the many biologists working in this field, and should be of value to the medicinal chemist trying to discover drugs based on CsA. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.

Synthesis and characterization of ester-based prodrugs of glucagon-like peptide 1

Peptides represent a rich natural source of potential medicines with one notable pharmaceutical limitation being their relatively short duration of action. A particularly good example of this phenomenon is glucagon-like peptide 1 (GLP), a hormone of appreciable interest for the treatment of type II diabetes. In the native form, GLP demonstrates an extremely short half-life in plasma and a relatively narrow therapeutic index with gastrointestinal adverse pharmacology. We envisioned a prodrug of GLP as a means to extend the duration of action and broaden the therapeutic index of this peptide hormone. We designed, synthesized, and characterized ester-based prodrugs of GLP that differentially convert to the parent drug under physiological conditions driven by their inherent chemical instability. In a set of dipeptide extended GLP-analogs we explored the rate of diketopiperazine (DKP) and diketomorpholine (DMP) formation, and the release of the active peptide. The rate of cleavage was observed to be a function of the conformation of the dipeptide promoiety and the strength of the cyclization nucleophile. Through the careful selection of chemical functionality, a set of GLP ester prodrugs of variable half-lives has been identified.