Syntheses of aminoalcohol-derived macrocycles leading to a small-molecule binder to and inhibitor of Sonic Hedgehog

Abstract

We report the synthesis and biological activity of a library of aminoalcohol-derived macrocycles from which robotnikinin (17), a binder to and inhibitor of Sonic Hedgehog, was derived. Using an asymmetric alkylation to set a key stereocenter and an RCM reaction to close the macrocycle, we were able to synthesize compounds for testing. High-throughput screening via small-molecule microarray (SMM) technology led to the discovery of a compound capable of binding ShhN. Followup chemistry led to a library of macrocycles with enhanced biological activity relative to the original hit compounds. Differences in ring size and stereochemistry, leading to alterations in the mode of binding, may account for differences in the degree of biological activity. These compounds are the first ones reported that inhibit Shh signaling at the ShhN level.Polyketide synthase-derived macrolactones are rich in structural diversity and biological activity. Examples include pikromycin 1 and erythromycin 2 (inhibitors of bacterial protein synthesis), enterobactin (inhibitor of bacterial iron transport), 3 epothilones A, B, D (stabilizer of microtubules), 4 and FK506 (inhibitor of PP2B phosphatase via its FKBP12 complex). 5,6,7 We report here a synthesis of macrolactones that has yielded a powerful new small-molecule probe of the Hedgehog signaling pathway, which plays key roles in development and oncogenesis.Our synthesis exploits 1,2-aminoalcohols as simple templates upon which 12-, 13-and 14-membered macrocycles are built (Scheme 1). The pathway extends previous work, reported by D. Lee et al., which also derived macrocyclic scaffolds from aminoalcohol templates, and yields macrocycles that can be optimized with great facility when they are identified as hits in © 2009 Elsevier Ltd. All rights reserved. *Corresponding Author: lpeng@partners.org. ** These authors contributed equally *** Senior Author *** This article is dedicated to the memory of Brian L. Gray.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. small-molecule screens. 8 We report herein a new asymmetric alkylation sequence to the pathway, a modification that installs a stereogenic center bearing an amide side-chain on the macrocycle scaffold and that resulted in a new scientific discovery. Starting from commercially available γ-unsaturated pentenoyl chloride, the Evans oxazolidinone, 9 and readily available chiral 1,2-aminoalcohols, the target macrolactones were synthesized in nine steps. Following an asymmetric alkylation with α-bromo-tert-butyl acetate, which proceeded with over 19:1 diastereoselectivity, the tert-butyl ester w...

Modulators of the hedgehog signaling pathway

“…Robotnikin is a moderately active hh inhibitor at the level of Shh and shows no cytotoxicity at relevant inhibitory concentrations. 75,76 An approach using antibodies to inactivate the Shh ligand has been successfully conducted with the Shh monoclonal antibody 5E1. 77 Statins are a class of drugs that reduce serum cholesterol by HMG-CoA reductase inhibition.…”

Small molecule inhibitors of Smoothened ciliary localization and ciliogenesis

“…Robotnikinin is an inhibitor of Sonic hedgehog (Shh) activity, and GANT61, JK184 and HPI4 inhibit Gli transcription factors (18)(19)(20)(21), but the majority of identified Hh pathway antagonists inhibit Smo. These include cyclopamine (a natural steroidal alkaloid), Cur61414, Vismodegib/ GDC-0449, and LDE225 (22)(23)(24)(25).…”

Macrocyclic Inhibitors of GPCR's, Integrins and Protein–Protein Interactions

“…Binding of Shh to Ptc1 reverses its inhibitory effect on Smo (Smoothened), which activates transcription of target genes such as Gli1 and Pct1. By small-molecule microarray screening of a macrocyclic library generated by diversity-oriented synthesis (DOS), 227 an initial hit (100, Figure 8.40) inhibiting the interaction of ShhN and Pct1 was found (K D ¼ 9 mM, determined by SPR). 228 As part of a medicinal chemistry program to explore macrocycles with improved activity, compound 101 (robotnikinin, Figure 8.40) was identified.…”