Three new compounds, named fiscalins A, B, and C, were found in culture broth produced by a Neosartorya fischeri. These compounds inhibit the binding of radiolabeled substance P ligand to the human neurokinin (NK-1) receptor, with Ki values of 57, 174, and 68 |UM, respectively.Detailed spectroscopic and amino acid analyses led to the elucidation of structures for the three fiscalins. Thestructures contain an indolyl moiety linked to an athranilic acid derived tricyclic system. The absolute configuration of fiscalin A was determined by X-ray crystallography and chiral amino acid analysis. The presence of fiscalins was detected directly in crude cellular extracts using LC-MS methods. 545Substance P (SP) is an undecapeptide belonging to a family of related peptides called neurokinins, which act as neurotransmitters and neuromodulators. Cell surface receptors for the neurokinins have been classified into three subtypes, based upon affinities for selective ligands.1* SP is a potent agonist, and believed to be the endogenous ligand for the neurokinin-1 (NK-1) receptor subtype. SP induces a variety of physiological responses such as salivation, vasodilation, smooth muscle contraction, and is thought to be involved in pain transmission and inflammatory response.2) Therefore, selective antagonists of SP might prove to be novel analgesics or anti-inflammatory agents.In order to evaluate the pharmacologic activities of SP antagonists, bioavailable and metabolically stable compoundsare required. Earlier work on SP antagonists generally focused on modifications of the SP peptide, such as described in a recent review.3) More recently, several nonpeptide SP antagonists have been reported, from synthetic4~7) or microbial8) sources, and a microbial cyclic peptide.9'10) These compounds, which varied in structural features, potency and receptor specificities, exhibited activity in various cellular, tissue or in vivo systems, furthering our understanding of the therapeutic potential of SP antagonists.In our search for novel nonpeptide SP antagonists, we wanted to detect compounds active against a NK-1receptor of human origin. Wetherefore screened microbial broth extracts for the ability to inhibit radiolabeled SP binding to human astrocytoma U373M6intact cells, which are a convenient source of the NK-1 receptor subtype. One strain of the fungus, Neosartorya fischeri, produced three new compounds, fiscalins A, B, and C (Fig. 1), which exhibit moderate inhibition of SP binding (Aj=57, 174, and 68piM, respectively). X-ray crystallography, chiral amino acid analysis, and spectroscopy were used to determine the structure of fiscalin A. Structure determination of all three metabolites and their production and biochemical properties are presented herein.

The aqueous solution structure of protoxin II (ProTx II) indicated that the toxin comprises a well-defined inhibitor cystine knot (ICK) backbone region and a flexible C-terminal tail region, similar to previously described NaSpTx III tarantula toxins. In the present study we sought to explore the structure-activity relationship of the two regions of the ProTx II molecule. As a first step, chimeric toxins of ProTx II and PaTx I were synthesized and their biological activities on Nav1.7 and Nav1.2 channels were investigated. Other tail region modifications to this chimera explored the effects of tail length and tertiary structure on sodium channel activity. In addition, the activity of various C-terminal modifications of the native ProTx II was assayed and resulted in the identification of protoxin II-NHCH3, a molecule with greater potency against Nav1.7 channels (IC50=42 pM) than the original ProTx II.

In the course of screening natural products for antagonists of CD18-mediated cell adhesion, an extract with inhibitory activity was identified from the stem and leaves of Conobea scoparioides. Bioassay-guided fractionation led to a pure compound, identified by spectroscopy as cucurbitacin E [1]. Although many biological activities have been reported for the cucurbitacins, this is the first report of cell adhesion inhibition. Furthermore, closely related cucurbitacin analogues had different potencies, pointing to substructural features that are important for the activity.

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