Amphipathic small molecules mimic the binding mode and function of endogenous transcription factors.

Small molecules that reconstitute the binding mode(s) of a protein and in doing so elicit a programmed functional response offer considerable advantages in the control of complex biological processes. The development challenges of such molecules are significant, however. Many protein-protein interactions require multiple points of contact over relatively large surface areas. More significantly, several binding modes can be superimposed upon a single sequence within a protein, and a true small molecule replacement must be preprogrammed for such multimodal binding. This is the case for the transcriptional activation domain or TAD of transcriptional activators as these motifs utilize a poorly characterized multipartner binding profile in order to stimulate gene expression. Here we describe a unique class of small molecules that exhibit both function and a binding profile analogous to natural transcriptional activation domains. Of particular note, the small molecules are the first reported to bind to the KIX domain within the CREB binding protein (CBP) at a site that is utilized by natural activators. Further, a comparison of functional and nonfunctional small molecules indicates that an interaction with CBP is a key contributor to transcriptional activity. Taken together, the evidence suggests that the small molecule TADs mimic both the function and mechanism of their natural counterparts and thus present a framework for the broader development of small molecule transcriptional switches.

Succinct synthesis of beta-amino acids via chiral isoxazolines.

beta-Amino acids are important synthetic targets due to their presence in a wide variety of natural products, pharmaceutical agents, and mimics of protein structural motifs. While beta-amino acids containing geminal substitution patterns have enormous potential for application in these contexts, synthetic challenges to the stereoselective preparation of this class of compound have thus far limited more complete studies. We present here a straightforward method employing chiral isoxazolines as key intermediates to access five different beta-amino acid structural types with excellent selectivity. Of particular note is the use of this approach to prepare highly substituted cis-beta-proline analogues. The ready access to these diversely substituted compounds is expected to facilitate future studies of the structure and function of this important class of molecules.

Stereochemical promiscuity in artificial transcriptional activators.

Small molecule replacements of transcriptional activation domains are highly desirable targets due to their utility as mechanistic tools and their long-term therapeutic potential for a variety of human diseases. Here, we examine the ability of amphipathic isoxazolidines differing only in the placement of constituent side chains to function as transcriptional activation domains. The results reveal that precise positioning of functional groups within a conformationally constrained small molecule scaffold is not required for transcription function; rather, the balance of polarity and hydrophobicity within the scaffold is the more important determinant of transcription function. This suggests that a number of different organic molecule scaffolds should function as transcriptional activator domains when appropriately functionalized, a hypothesis currently under investigation.

A concise approach to structurally diverse beta-amino acids.

We have demonstrated that the high yields and selectivities of 1,3-dipolar cycloadditions can be translated into facile stereoselective syntheses of a diverse array of beta-amino acids, key components of bioactive natural products, beta-lactams, and peptidomimetics. Simply by selecting different combinations of three readily available starting materials (an oxime, a chiral allylic alcohol, and a nucleophile), we used the reaction sequence to prepare four different beta-amino acid structural types with a variety of substitution patterns in good overall yield. Of particular note is the use of this approach to prepare highly substituted beta-amino acids not readily accessible by previously reported methodologies. This will pave the way for future studies of the structure and function of this important class of molecules.

A small molecule transcriptional activation domain.

Artificial transcriptional activators are excellent tools for studying the mechanistic details of transcriptional regulation. Furthermore, as the correlation between a wide range of human diseases and misregulated transcription becomes increasingly evident, such molecules may in the long run serve as the basis for transcription-based therapeutic agents. The greatest challenge in this arena has been the discovery of organic molecules that are functional mimics of transcriptional activation domains, sequences of natural proteins that participate in a variety of protein-protein interactions to control transcriptional levels. We describe the first examples of small molecules that function in this capacity, isoxazolidines containing an array of polar and hydrophobic functional groups. Despite their small size, the most potent of the structures functions nearly as well as a natural activation domain.

Targeting the transcriptional machinery with unique artificial transcriptional activators.

The link between a growing number of human diseases and misregulation of gene expression has spurred intense interest in artificial transcriptional activators that could be used to restore controlled expression of affected genes. To expand the repertoire of activation domains available for the construction of artificial transcriptional regulators, a selection strategy was used to identify two unique activation domain motifs. These activation domains bear little sequence homology to endogenous counterparts and bind to unique sites within the transcriptional machinery. A comparison with two well-characterized activation domains, VP2 and P201, demonstrated for the first time that functional potency is not solely dictated by binding affinity. Finally, the selection strategy described is readily applicable to the identification of small molecule activation domains.