An Unusual Ferryl Intermediate and Its Implications for the Mechanism of Oxacyclization by the Loline-Producing Iron(II)- and 2-Oxoglutarate-Dependent Oxygenase, LolO.

-Acetylnorloline synthase (LolO) is one of several iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenases that catalyze sequential reactions of different types in the biosynthesis of valuable natural products. LolO hydroxylates C2 of 1--acetamidopyrrolizidine before coupling the C2-bonded oxygen to C7 to form the tricyclic loline core. Each reaction requires cleavage of a C-H bond by an oxoiron(IV) (ferryl) intermediate; however, different carbons are targeted, and the carbon radicals have different fates.

Structure Revision of Type B Polycyclic Polyprenylated Acylphloroglucinols Fused to a Partly Reduced Furan Ring.

Four previous papers reported the isolation and structural determination of 10 polycyclic polyprenylated acylphloroglucinols (PPAPs), uraliones F, G, K, and O, attenuatumiones E and F, and scabrumiones A-D, from species. Their structures were identified as type B PPAPs that featured not only the characteristic acyl group at C-3 of the bicyclo[3.3.

A Conformationally Restricted Gold(III) Complex Elicits Antiproliferative Activity in Cancer Cells.

Diamine ligands are effective structural scaffolds for tuning the reactivity of transition-metal complexes for catalytic, materials, and phosphorescent applications and have been leveraged for biological use. In this work, we report the synthesis and characterization of a novel class of cyclometalated [C^N] Au(III) complexes bearing secondary diamines including a norbornane backbone, (2,3)-,-dibenzylbicyclo[2.2.

Total synthesis and structural reassignment of garcinielliptone FC, a polycyclic polyprenylated acylphloroglucinol with diverse bioactivity.

Garcinielliptone FC (GFC) was assigned to be a type A polycyclic polyprenylated acylphloroglucinol (PPAP) and was found to exhibit diverse biological activities. Now we revise the structure of GFC to xanthochymol, a type B PPAP, NMR and total synthesis methods. The total syntheses of (±)-xanthochymol and (±)-cycloxanthochymol were accomplished in 12 and 13 steps, respectively.

1,2-Diamination of Alkenes via 1,3-Dipolar Cycloaddition with Azidium Ions or Azides.

We describe two new methods for the 1,2-diamination of alkenes. First, either an azidium ion (ArN═N═NAr) undergoes 1,3-dipolar cycloaddition with an alkene to give a 1,2,3-triazolinium ion directly, or an intramolecular azide-alkene cycloaddition followed by N-benzylation provides the same. Second, hydrogenation of the 1,2,3-triazolinium ion over Raney Ni excises the central N atom and gives the 1,2-diamine.

Synthesis of 6,6- and 7,7-Difluoro-1-acetamidopyrrolizidines and Their Oxidation Catalyzed by the Nonheme Fe Oxygenase LolO.

LolO, a 2-oxoglutarate-dependent nonheme Fe oxygenase, catalyzes both the hydroxylation of 1-exo-acetamidopyrrolizidine (AcAP), a pathway intermediate in the biosynthesis of the loline alkaloids, and the cycloetherification of the resulting alcohol. We have prepared fluorinated AcAP analogues to aid in continued mechanistic investigation of the remarkable LolO-catalyzed cycloetherification step. LolO was able to hydroxylate 6,6-difluoro-AcAP (prepared from N,O-protected 4-oxoproline) and then cycloetherify the resulting alcohol, forming a difluorinated analogue of N-acetylnorloline and providing evidence for a cycloetherification mechanism involving a C(7) radical as opposed to a C(7) carbocation.

Structural Revision of Hyperibrin B and Hyperscabrones H and I by Biosynthetic Considerations, NMR Analysis, and Chemical Synthesis.

Previously, Gao et al. reported the isolation and structural determination of three natural products, hyperibrin B (HB), hyperscabrone H (HH), and hyperscabrone I (HI), from . HB and HH had different NMR spectroscopic data, but they were assigned identical structures.

Structural Revision of Garcinielliptin Oxide and Garcinielliptone E.

Previously, Lin et al. reported the isolation and structural determination of two triterpenoids, garcinielliptin oxide (GO) and garcinielliptone E (GE). Their unusual structural features, which remained unparalleled in subsequent decades despite the intervening discovery of hundreds of other polycyclic polyprenylated acylphloroglucinols (PPAPs), caused us to question the originally assigned structures, so GO was reisolated from , and its NMR spectra were reacquired.

An unusually short inter-molecular N-H⋯N hydrogen bond in crystals of the hemi-hydro-chloride salt of 1--acetamido-pyrrolizidine.

The title compound [systematic name: (1*, 8)-2-acetamidoocta-hydro-pyrrol-izin-4-ium chloride--[(1, 8)-hexa-hydro-1-pyrrolizin-2-yl)acetamide (1/1)], 2(CHNO)·HCl or CHNO·Cl·CHNO, arose as an unexpected product when 1--acetamido-pyrrolizidine (AcAP; CHNO) was dissolved in CHCl. Within the AcAP pyrrolizidine group, the unsubstituted five-membered ring is disordered over two orientations in a 0.897 (5):0.

Revision of the Structure of Hypatulone A by NMR, Computations, and Biosynthetic Considerations.

Recently, a paper in this journal reported the isolation and structure determination of hypatulone A. Several features of the proposed structure and biosynthesis induced us to reexamine the compound's NMR spectra. Now we propose a revised structure, confirm it with quantum computations, and suggest a reasonable radical-mediated biosynthetic pathway to the revised structure.

Evidence for Modulation of Oxygen Rebound Rate in Control of Outcome by Iron(II)- and 2-Oxoglutarate-Dependent Oxygenases.

Iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) oxygenases generate iron(IV)-oxo (ferryl) intermediates that can abstract hydrogen from aliphatic carbons (R-H). Hydroxylation proceeds by coupling of the resultant substrate radical (R•) and oxygen of the Fe(III)-OH complex ("oxygen rebound"). Nonhydroxylation outcomes result from different fates of the Fe(III)-OH/R• state; for example, halogenation results from R• coupling to a halogen ligand cis to the hydroxide.

Canvass: A Crowd-Sourced, Natural-Product Screening Library for Exploring Biological Space.

Natural products and their derivatives continue to be wellsprings of nascent therapeutic potential. However, many laboratories have limited resources for biological evaluation, leaving their previously isolated or synthesized compounds largely or completely untested. To address this issue, the Canvass library of natural products was assembled, in collaboration with academic and industry researchers, for quantitative high-throughput screening (qHTS) across a diverse set of cell-based and biochemical assays.

Installation of the Ether Bridge of Lolines by the Iron- and 2-Oxoglutarate-Dependent Oxygenase, LolO: Regio- and Stereochemistry of Sequential Hydroxylation and Oxacyclization Reactions.

The core of the loline family of insecticidal alkaloids is the bicyclic pyrrolizidine unit with an additional strained ether bridge between carbons 2 and 7. Previously reported genetic and in vivo biochemical analyses showed that the presumptive iron- and 2-oxoglutarate-dependent (Fe/2OG) oxygenase, LolO, is required for installation of the ether bridge upon the pathway intermediate, 1- exo-acetamidopyrrolizidine (AcAP). Here we show that LolO is, in fact, solely responsible for this biosynthetic four-electron oxidation.

Research Progress of Polycyclic Polyprenylated Acylphloroglucinols.

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of hybrid natural products sharing the mevalonate/methylerythritol phosphate and polyketide biosynthetic pathways and showing considerable structure and bioactivity diversity. This review discusses the progress of research into the chemistry and biological activity of 421 natural PPAPs in the past 11 years as well as in-depth studies of biological activities and total synthesis of some PPAPs isolated before 2006. We created an online database of all PPAPs known to date at http://www.

Enzymes from fungal and plant origin required for chemical diversification of insecticidal loline alkaloids in grass-Epichloë symbiota.

The lolines are a class of bioprotective alkaloids that are produced by Epichloë species, fungal endophytes of grasses. These alkaloids are saturated 1-aminopyrrolizidines with a C2 to C7 ether bridge, and are structurally differentiated by the various modifications of the 1-amino group: -NH2 (norloline), -NHCH3 (loline), -N(CH3)2 (N-methylloline), -N(CH3)Ac (N-acetylloline), -NHAc (N-acetylnorloline), and -N(CH3)CHO (N-formylloline). Other than the LolP cytochrome P450, which is required for conversion of N-methylloline to N-formylloline, the enzymatic steps for loline diversification have not yet been established.

Ether bridge formation in loline alkaloid biosynthesis.

Lolines are potent insecticidal agents produced by endophytic fungi of cool-season grasses. These alkaloids are composed of a pyrrolizidine ring system and an uncommon ether bridge linking carbons 2 and 7. Previous results indicated that 1-aminopyrrolizidine was a pathway intermediate.

Rare case of upper arm compartment syndrome following biceps tendon rupture.

We present a case of upper arm compartment syndrome following a biceps tendon rupture in a 77-year old man on warfarin sodium. Compartment syndrome is common in the forearm and leg, but rare in the upper arm with only a handful of cases reported in the literature. Our patient's anticoagulated state predisposed him to the development of compartment syndrome.

Role of the LolP cytochrome P450 monooxygenase in loline alkaloid biosynthesis.

The insecticidal loline alkaloids, produced by Neotyphodium uncinatum and related endophytes, are exo-1-aminopyrrolizidines with an ether bridge between C-2 and C-7. Loline alkaloids vary in methyl, acetyl, and formyl substituents on the 1-amine, which affect their biological activity. Enzymes for key loline biosynthesis steps are probably encoded by genes in the LOL cluster, which is duplicated in N.

Insights into the substrate specificity of plant peptide deformylase, an essential enzyme with potential for the development of novel biotechnology applications in agriculture.

The crystal structure of AtPDF1B [Arabidopsis thaliana PDF (peptide deformylase) 1B; EC 3.5.1.

Loline alkaloids: Currencies of mutualism.

Several species of Lolium and other cool-season grasses (Poaceae subfamily Pooideae) tend to harbor symbiotic, seed-transmitted, fungi that enhance their fitness by various means. These fungal endophytes--species of Neotyphodium or Epichloë (Clavicipitaceae)--are known for production of antiherbivore metabolites such as the bioprotective loline alkaloids. Lolines are saturated pyrrolizidines with an exo-1-amine and an ether bridge between C-2 and C-7.

On the sequence of bond formation in loline alkaloid biosynthesis.

Loline alkaloids are saturated pyrrolizidines with an oxygen bridge between carbon atoms C-2 and C-7 and an amino group on C-1. They are bioprotective alkaloids produced by Epichloë and Neotyphodium species, mutualistic fungal endophytes that are symbiotic with cool-season grasses. The sequence of bond formation in loline alkaloid biosynthesis was determined by synthesizing deuterated forms of potential intermediates and feeding them to cultures of the endophyte Neotyphodium uncinatum.

Biosynthetic precursors of fungal pyrrolizidines, the loline alkaloids.

Loline alkaloids are saturated pyrrolizidines with a substituted 1-amino group and an oxygen bridge between C2 and C7, and are insecticidal metabolites of plant-symbiotic fungi (endophytes). Cultures of the endophyte, Neotyphodium uncinatum, incorporated labeled L-proline and L-homoserine into the 1-aminopyrrolizidine, N-formylloline. The A-ring carbons C1-C3 and the N1 were derived from L-homoserine; the B-ring carbons C5-C8 and the ring nitrogen were derived from L-proline.

A new synthetic approach to the polycyclic polyprenylated acylphloroglucinols.

[reaction: see text] The three-carbon alpha,alpha'-annulation of a sterically hindered cyclic beta-keto ester can be achieved by alkynylation with 3,3-diethoxypropyne, syn reduction of the alkyne with Co(2)(CO)(8) and Et(3)SiH, and an intramolecular aldol reaction. The method is potentially useful for the synthesis of nemorosone, hyperforin, and other polycyclic polyprenylated acylphloroglucinols.