Nodulisporic acid side-chain modifications: access to the 2", 3", 4", and 6" registers

Biosynthesis of Nodulisporic Acids: A Multifunctional Monooxygenase Delivers a Complex and Highly Branched Array

Nodulisporic acids (NAs) are structurally complex potent antiinsectan indole diterpenes. We previously reported the biosynthetic gene cluster for these metabolites in Hypoxylon pulicicidum and functionally characterised the first five steps of the biosynthetic pathway. Here we reveal a highly complex biosynthetic array, furnishing multiple end products through expression of cluster components in Penicillium paxilli. We show that seven additional cluster-encoded gene products comprise the biosynthetic machinery that elaborate precursor NAF in this highly branched pathway. The combined action of these enzymes delivers 37 NA congeners including four major end products, NAA, NAA₁ , NAA₂ and NAA₄ . The plethora of intermediates arises due to modification of the carboxylated prenyl tail by a single promiscuous P450 monooxygenase, NodJ, a pivotal branchpoint enzyme which produces four distinct biosynthetic products giving rise to the complex metabolic grid that characterises NA biosynthesis.

Total Synthesis of (-)-Nodulisporic Acids D, C, and B: Evolution of a Unified Synthetic Strategy

A unified synthetic strategy leading to the total synthesis of (-)-nodulisporic acids D, C, and B is described. Key synthetic transformations include a nickel-chromium-mediated cyclization, an aromatic ring functionalization employing a novel copper-promoted alkylation, a palladium-catalyzed cross-coupling cascade/indole ring construction, and a palladium-mediated regio- and diastereoselective allylic substitution/cyclization reaction, the latter to construct ring D.

Indole diterpene synthetic studies. Total synthesis of (+)-nodulisporic acid F and construction of the heptacyclic cores of (+)-nodulisporic acids A and B and (-)-nodulisporic acid D

A first-generation strategy for construction of (+)-nodulisporic acids A (1) and B (2) is described. The strategy entails union of the eastern and western hemisphere subtargets via the indole synthesis protocol developed in our laboratory. Subsequent elaboration of rings E and F, however, revealed the considerable acid instability of the C(24) hydroxyl, thereby preventing further advancement. Nonetheless, preparation of the heptacyclic core of (+)-nodulisporic acids A and B, the total synthesis of (+)-nodulisporic acid F, the simplest member of the nodulisporic acid family, and elaboration of the heptacyclic core of (-)-nodulisporic acid D were achieved.

A New Modular Indole Synthesis. Construction of the Highly Strained CDEF Parent Tetracycle of Nodulisporic Acids A and B

[reaction: see text] Construction of the highly strained CDEF parent tetracycle, a structural motif found only in the potent ectoparasiticidal agents (+)-nodulisporic acids A and B and related congeners, has been achieved via a new modular indole synthesis, exploiting a sequential Stille cross-coupling/Buchwald-Hartwig union/cyclization tactic. The new indole synthesis holds the promise of rapid assembly of diverse, highly substituted indoles possessing uncommon substitution patterns.

Indole Diterpenoid Synthetic Studies. The Total Synthesis of (+)-Nodulisporic Acid F

[structure: see text] A stereocontrolled total synthesis of (+)-nodulisporic acid F, the simplest member of a family of novel ectoparasiticidal agents, has been achieved. Highlights of the effective modular synthetic strategy include anionic union of a tricyclic lactone with o-toluidine via our 2-substituted indole synthetic protocol, an optimized C-ring construction protocol, and a late-stage installation of the alpha,beta-unsaturated carboxylic acid side chain via the B-alkyl Suzuki-Miyaura cross-coupling tactic.

Nodulisporic acids D-F: structure, biological activities, and biogenetic relationships

Nodulisporic acids D, E, and F are the newest members of a family of nontremorogenic indole-diterpenoids that are potent, orally bioavailable, antiflea agents derived from a fungus belonging to the genus Nodulisporium. The four members of the D series are each devoid of an isoprene residue that is present at C-26 in the three nodulisporic acids described originally (the A series). Nodulisporic acid E (11a) has a simpler structure, which lacks not only the isoprene residue at C-26 but also two that form the A/B rings. Nodulisporic acid F is the simplest of all nodulisporic acids and is devoid of all three isoprene residues of the indole unit; as such, it represents the earliest biosynthetic intermediate in this series. A biogenetic grid based on mutation studies is proposed that encompasses all the known nodulisporic acids. Structure-activity relationships of the known natural nodulisporic acids have been elucidated. Within a series the most active compound possesses a dienoic acid chain, and overall, the end product of the biogenetic grid, i.e., nodulisporic acid A, exhibits the most potent antiflea activity. Additionally, the stereochemistries of C-3' ' and C-4' ' of nodulisporic acid D(2) and therefore of nodulisporic acids A(2), B(2), and C(2) have been assigned.