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The practice of deploying and teaching retrosynthesis is on the cusp of considerable change, which in turn forces practitioners and educators to contemplate whether this impending change will advance or erode the efficiency and elegance of organic synthesis in the future. A short treatise is presented herein that covers the concept of retrosynthesis, along with exemplified methods and theories, and an attempt to comprehend the impact of artificial intelligence in an era when freely and commercially available retrosynthetic and forward synthesis planning programs are increasingly prevalent. Will the computer ever compete with human retrosynthetic design and the art of organic synthesis? Will the computer ever compete with human retrosynthetic design and the art of organic synthesis? [ABSTRACT FROM AUTHOR]

The bulky, but symmetrically beautiful, adamantane ring system is now pervasive throughout physical, medicinal and synthetic chemistry, since it was first discovered in 1924 and coined 'dekaterpene'. This fascinating name lived up to its natural product roots when adamantane was isolated from crude oil in 1933, but it was not until 1957 in a landmark contribution by Paul von Ragué Schleyer that adamantane was made readily accessible through synthesis. Beyond the legacy to physical and medicinal chemistry, the adamantane moiety has been quintessential in the development of some of the most important catalysts to date. Considering adamantane's impact on catalyst development past, present and future, this subject is for the first time reviewed herein. [ABSTRACT FROM AUTHOR]

Numerous variations on structural motifs exist within pharmaceutical compounds that have entered the clinic. These variations have amounted over many decades based on years of drug development associated with screening natural products and de novo synthetic systems. Caged (or bridged) bicyclic structural elements offer a variety of diverse features, encompassing three-dimensional shape, and assorted pharmacokinetic properties. This review highlights approximately 20 all carbon cage containing pharmaceuticals, ranging in structure from bicyclo[2.2.1] through to adamantane, including some in the top-selling pharmaceutical bracket. Although, a wide variety of human diseases, illnesses and conditions are treated with drugs containing the bicyclic motif, a common feature is that many of these lipophilic systems display CNS and/or neurological activity. In addition, to an extensive overview of the history and biology associated with each drug, a survey of synthetic methods used to construct these entities is presented. An analysis section compares natural products to synthetics in drug discovery, and entertains the classical caged hydrocarbon systems potentially missing from the clinic. Lastly, this unprecedented review is highly pertinent at a time when big pharma is desperately trying to escape flatland drugs. [ABSTRACT FROM AUTHOR]

Bredt's rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry-the field in which the rule was originally formulated-is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into 'isolable', 'observable', and 'unstable' classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be 'isolable'. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the 'observable' or 'unstable' ranges is a red flag for error. [ABSTRACT FROM AUTHOR]

Bredt's rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry-the field in which the rule was originally formulated-is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into 'isolable', 'observable', and 'unstable' classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be 'isolable'. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the 'observable' or 'unstable' ranges is a red flag for error. [ABSTRACT FROM AUTHOR]

The article offers information on the 7th Heron Island Conference on Reactive Intermediates and Unusual Molecules – Synthesis and Mechanism held from July 9-15, 2016 at the Heron Island Resort on the Great Barrier Reef. Topics discussed include the chemistry topics discussed at the conference including physical, spectroscopic and mechanistic chemistry, Professors John Gladysz and Paul Chirik from "Organometallics" who attended the meeting, and several papers discussed at the conference.

A 2-azabicyclo[4.2.0]octa-4,7-diene derivative was unexpectedly isolated from the photochemical irradiation of 2-vinyl-1,2-dihydropyridine. A cascading 6π–8π–4π electrocyclic rearrangement has been proposed as a possible mechanistic pathway. Herein disclosed is the isolation of the 2-azabicyclo[4.2.0]octa-4,7-diene skeleton derived from the photochemical irradiation of 2-vinyl-1,2-dihydropyridine. A cascading 6π–8π–4π electrocyclic rearrangement is proposed as the mechanistic rationale. This is the first observation of this ring system. [ABSTRACT FROM AUTHOR]

Homocubane, a highly strained cage hydrocarbon, contains two very different positions for the introduction of a nitrogen atom into the skeleton, e. g. a position 1 exchange results in a tertiary amine whereas position 9 yields a secondary amine. Herein reported is the synthesis of 9‐azahomocubane along with associated structural characterization, physical property analysis and chemical reactivity. Not only is 9‐azahomocubane readily synthesized, and found to be stable as predicted, the basicity of the secondary amine was observed to be significantly lower than the structurally related azabicyclo[2.2.1]heptane, although similar to 1‐azahomocubane. [ABSTRACT FROM AUTHOR]

Using computational methods and chemical intuition, the proposed structure of janthinolide A is shown to be incorrect. It is further shown that the material described as janthinolide A is highly likely to be janthinolide C. [ABSTRACT FROM AUTHOR]

With the burgeoning interest in cage motifs for bioactive molecule discovery, and the recent disclosure of 1,4‐cubane‐dicarboxylic acid impact sensitivity, more research into the safety profiles of cage scaffolds is required. Therefore, the impact sensitivity and thermal decomposition behavior of judiciously selected starting materials and synthetic intermediates of cubane, bicyclo[1.1.1]pentane (BCP), and bicyclo[2.2.2]octane (BCO) were evaluated via hammer test and sealed cell differential scanning calorimetry, respectively. Iodo‐substituted systems were found to be more impact sensitive, whereas hydroxymethyl substitution led to more rapid thermodecomposition. Cubane was more likely to be impact sensitive with these substituents, followed by BCP, whereas all BCOs were unresponsive. The majority of derivatives were placed substantially above Yoshida thresholds—a computational indicator of sensitivity. [ABSTRACT FROM AUTHOR]

Painful diabetic neuropathy (PDN) is a type of peripheral neuropathic pain that develops as a consequence of prolonged hyperglycaemia‐induced injury to the long nerves. Apart from pain, PDN is also characterized by morphine hyposensitivity. Intriguingly, in streptozotocin (STZ)‐induced diabetic rats exhibiting marked morphine hyposensitivity, dietary administration of the nitric oxide (NO) precursor, L‐arginine at 1 g/d, progressively rescued morphine efficacy and potency over an 8‐week treatment period. In earlier work, single bolus doses of the furoxan nitric oxide (NO) donor, PRG150 (3‐methylfuroxan‐4‐carbaldehyde), evoked dose‐dependent pain relief in STZ‐diabetic rats but the efficacious doses were 3‐4 orders of magnitude higher in advanced diabetes than that required in early STZ diabetes. Together, these findings suggested a role for NO in the modulation of μ‐opioid (MOP) receptor signalling. Therefore, the present study was designed to assess a role for NO released from PRG150, in modulating MOP receptor function in vitro. Here, we show an absolute requirement for the MOP receptor, but not the δ‐opioid (DOP) or the κ‐opioid (KOP) receptor, to transduce the cellular effects of PRG150 on forskolin‐stimulated cAMP responses in vitro. PRG150 did not interact with the classical naloxone‐sensitive binding site of the MOP receptor, and its effects on cAMP responses in HEK‐MOP cells were also naloxone‐insensitive. Nevertheless, the inhibitory effects of PRG150 on forskolin‐stimulated cAMP responses in HEK‐MOP cells were dependent upon pertussis toxin (PTX)‐sensitive Gi/o proteins as well as membrane lipid rafts and src kinase. Together, our findings implicate a role for NO in modulating MOP receptor function in vivo. [ABSTRACT FROM AUTHOR]

Structural misassignments of natural products are prevalent in the literature. Developing methods and theoretical concepts to assist those undertaking structural elucidation is therefore of paramount importance, such that biologists and synthetic chemists avoid pursuing phantom chemical entities. Herein described is a strategy for predicting the isolabilities of oxygen‐substituted bridgehead natural products based on calculations of olefin strain energies, NMR chemical shifts and coupling constants (DU8+). This approach provides corroborating evidence for the structures of certain bridgehead alkene natural products while leading to the reassignment of several other structures. [ABSTRACT FROM AUTHOR]

Structural misassignments of natural products are prevalent in the literature. Developing methods and theoretical concepts to assist those undertaking structural elucidation is therefore of paramount importance, such that biologists and synthetic chemists avoid pursuing phantom chemical entities. Herein described is a strategy for predicting the isolabilities of oxygen‐substituted bridgehead natural products based on calculations of olefin strain energies, NMR chemical shifts and coupling constants (DU8+). This approach provides corroborating evidence for the structures of certain bridgehead alkene natural products while leading to the reassignment of several other structures. [ABSTRACT FROM AUTHOR]

Review: [143 refs. [ABSTRACT FROM AUTHOR]

Review: [117 refs. [ABSTRACT FROM AUTHOR]

The front cover image, provided by Kylie Agnew ‐ Francis and Craig Williams, illustrates diverse examples of catalytic systems that contain the sterically bulky adamantane moiety. This ‘big guy’ molecule has become well regarded in the literature for its powerful electron ‐ donating properties in addition to its size, and has thus marked its place in the organic chemist’s toolbox as an excellent (and often superior) addition to catalyst and ligand design. Details can be found in the review on pages 675 – 700 (K. A. Agnew ‐ Francis, C. M. Williams, Adv. Synth. Catal.­ 2016, 358, 675 – 700; DOI:10.1002/adsc.201500949). [ABSTRACT FROM AUTHOR]

Review: 376 refs. [ABSTRACT FROM AUTHOR]

Bredt's rule for bridgehead alkenes is important for physical organic chemists, but has been rarely applied to natural products. In their Communication on page 10608 ff., C. M. Williams and E. H. Krenske show that calculations of the olefin strain energy, first introduced by Schleyer, predict the stability of complex natural products containing bridgehead alkenes. This method can be used to determine the viability of the structures of newly identified natural products proposed to contain a bridgehead alkene. [ABSTRACT FROM AUTHOR]

Die Bredt ‐ Regel für Brückenkopfalkene ist für physikalisch ‐ organische Chemiker von großem Interesse, wurde jedoch selten auf Naturstoffe angewendet. In der Zuschrift auf S. 10754 ff. zeigen C. M. Williams und E.H. Krenske, wie Berechnungen der Olefinspannungsenergie, eingeführt von Schleyer, die Stabilität komplexer Naturstoffe mit Brückenkopfalkenen vorhersagen. Dies hilft, die Plausibilität der Struktur neu identifizierter Naturstoffe, bei denen eine Brückenkopfalkeneinheit vermutet wird, zu prüfen. [ABSTRACT FROM AUTHOR]

The redox and ligand exchange reactions of oxido-ruthenium complexes are central to the function of the Sharpless and Griffith–Ley one-step alcohol oxidation protocols. However, their mechanisms have not been elucidated. Cyclic voltammetry and UV-vis spectroelectrochemical analysis of [RuO4]− has provided new insight into the key ruthenium oxidation states involved in catalysis. Furthermore, the oxidation states sensitive to the presence of the N-oxide co-oxidant N-methylmorpholine N-oxide (NMO), and its role in catalysis, have been determined. [ABSTRACT FROM AUTHOR]

Natural products continue to be reported at an astonishing rate from a wide range of multidisciplinary research activities in the pursuit of understanding the chemistry of biodiversity. However, the elucidation of chemical structure in the modern era is heavily reliant on the analysis and interpretation of multiple spectroscopic outputs, and in most cases this activity is by no means trivial. Structural errors continue to be described given the inherent complexity of natural products. Computer‐Assisted Structure Elucidation (CASE) continues to provide improved resolving power in this regard, but for enhanced accuracy quantum chemical spectrum prediction methodology is paramount. Reported herein are a range of counterfactual natural products, identified through chemical principal screening, which have been reassigned using a combination of chemical intuition, chemical synthesis, CASE and DU8+ spectrum prediction. [ABSTRACT FROM AUTHOR]

Acetohydroxyacid synthase (AHAS) inhibitors are highly successful commercial herbicides. New kinetic data show that the binding of these compounds leads to reversible accumulative inhibition of AHAS. Crystallographic data (to a resolution of 2.17 Å) for an AHAS-herbicide complex shows that closure of the active site occurs when the herbicidal inhibitor binds, thus preventing exchange with solvent. This feature combined with new kinetic data shows that molecular oxygen promotes an accumulative inhibition leading to the conclusion that the exceptional potency of these herbicides is augmented by subversion of an inherent oxygenase side reaction. The reactive oxygen species produced by this reaction are trapped in the active site, triggering oxidation reactions that ultimately lead to the alteration of the redox state of the cofactor flavin adenine dinucleotide (FAD), a feature that accounts for the observed reversible accumulative inhibition. [ABSTRACT FROM AUTHOR]

Acetohydroxyacid synthase (AHAS) inhibitors are highly successful commercial herbicides. New kinetic data show that the binding of these compounds leads to reversible accumulative inhibition of AHAS. Crystallographic data (to a resolution of 2.17 Å) for an AHAS-herbicide complex shows that closure of the active site occurs when the herbicidal inhibitor binds, thus preventing exchange with solvent. This feature combined with new kinetic data shows that molecular oxygen promotes an accumulative inhibition leading to the conclusion that the exceptional potency of these herbicides is augmented by subversion of an inherent oxygenase side reaction. The reactive oxygen species produced by this reaction are trapped in the active site, triggering oxidation reactions that ultimately lead to the alteration of the redox state of the cofactor flavin adenine dinucleotide (FAD), a feature that accounts for the observed reversible accumulative inhibition. [ABSTRACT FROM AUTHOR]

Painful diabetic neuropathy ( PDN) is a type of peripheral neuropathic pain that is often intractable. Elevated nitric oxide ( NO) from neuronal and non-neuronal sources in the somatosensory system is implicated in the pathobiology of peripheral neuropathic pain. However, in diabetes, nitrergic nerve degeneration to deplete NO bioactivity appears causal in the pathogenesis of irreversible autonomic neuropathy, another long term complication of diabetes. Hence, this study hypothesized that progressive NO depletion may underpin the pathobiology of PDN and that NO donors may alleviate PDN. Diabetes was induced in rats with intravenous streptozotocin ( STZ) at 70 mg/kg and confirmed if blood glucose levels ( BGLs) on day 10 post- STZ were ≥15 mmol/L. Analgesic efficacy of subcutaneous (s.c.) bolus doses of the furoxan NO donor, PRG150 was assessed in the STZ-diabetic rat model of PDN at 10-, 14- and 24-weeks post- STZ relative to the sydnominine NO donor, SIN-1 and its prodrug, molsidomine. PRG150 produced dose-dependent analgesia in STZ-diabetic rats whereas SIN-1 and molsidomine evoked neuro-excitatory side-effects, but not analgesia. The 1000-fold larger doses of PRG150 needed to produce analgesia at 14- and 24-weeks (800 pmol/kg) c.f. 10-weeks (8 fmol/kg) post- STZ in rats, suggest that progressive NO depletion is also causal in PDN. Importantly, doses of PRG150 up to 10 000 fold higher than the analgesic dose did not produce hypotension in rats. The 50-fold greater release of NO by SIN-1 c.f. PRG150 in vitro, may underpin the neuro-excitatory rather than analgesic effects of SIN-1/molsidomine. PRG150 is worthy of further investigation as a potential novel analgesic for PDN. [ABSTRACT FROM AUTHOR]

N,N,N′,N′-Tetramethylethylenediamine dioxide (TMEDAO2) was explored as a more atom economical co-oxidant for the Ley–Griffith oxidation of alcohols to aldehydes. TMEDAO2 was found to selectivity oxidise benzylic and allylic alcohols in comparable yields to that of the standard Ley–Griffith co-oxidant (NMO). Importantly TMEDAO2 facilitated tandem Ley–Griffith-Wittig reactions with stabilised ylides, in good to excellent yields, without the requirement of anhydrous conditions. [ABSTRACT FROM AUTHOR]

Unusual polyenols that defied chemical principles were reassigned as the nucleosides, adenosine and uridine, using a combination of chemical intuition underpinned by Computer Assisted Structure Elucidation (CASE) and DFT methods. [ABSTRACT FROM AUTHOR]

UbiA prenyltransferase domain‐containing protein‐1 (UBIAD1) is responsible for the biosynthesis of menaquinone‐4 (MK‐4), a cofactor for extrahepatic carboxylation of vitamin K‐dependent (VKD) proteins. Genetic variations of UBIAD1 are mainly associated with Schnyder corneal dystrophy (SCD), a disease characterized by abnormal accumulation of cholesterol in the cornea. Results from in vitro studies demonstrate that SCD‐associated UBIAD1 mutations are defective in MK‐4 biosynthesis. However, SCD patients do not exhibit typical phenotypes associated with defects of MK‐4 or VKD carboxylation. Here, we coupled UBIAD1's biosynthetic activity of MK‐4 with VKD carboxylation in HEK293 cells that stably express a chimeric VKD reporter protein. The endogenous Ubiad1 gene in these cells was knocked out by CRISPR‐Cas9‐mediated genome editing. The effect of UBIAD1 mutations on MK‐4 biosynthesis and VKD carboxylation was evaluated in Ubiad1‐deficient reporter cells by determining the production of MK‐4 or by measuring the efficiency of reporter‐protein carboxylation. Our results show that the hot‐spot mutation N102S has a moderate impact on MK‐4 biosynthesis (retained ˜ 82% activity) but does not affect VKD carboxylation. However, the G186R mutation significantly affected both MK‐4 biosynthesis and VKD carboxylation. Other mutations exhibit varying degrees of effects on MK‐4 biosynthesis and VKD carboxylation. These results are consistent with in vivo results obtained from gene knock‐in mice and SCD patients. Our findings suggest that UBIAD1's MK‐4 biosynthetic activity does not directly correlate with the phenotypes of SCD patients. The established cell‐based assays in this study provide a powerful tool for the functional studies of UBIAD1 in a cellular milieu. [ABSTRACT FROM AUTHOR]

A non-hygroscopic tetraphenylborate salt of N-methylmorpholine- N-oxide (NMO) is reported (NMO ⋅TPB), which modulates the standard Ley-Griffith oxidation such that benzylic and allylic alcohols are oxidised selectively. An attractive feature of this new protocol is that anhydrous conditions are not required for this selective tetra- n-propylammonium perruthenate (TPAP) oxidation, superseding the requirement of molecular sieves. [ABSTRACT FROM AUTHOR]

Well over a hundred years ago, Professor Julius Bredt embarked on a career pursuing and critiquing bridged bicyclic systems that contained ring strain induced by the presence of a bridgehead olefin. These endeavors founded what we now know as Bredt's rule (Bredtsche Regel). Physical, theoretical, and synthetic organic chemists have intensely studied this premise, pushing the boundaries of such systems to arrive at a better understood physical phenomenon. Mother nature has also seen fit to construct molecules containing bridgehead double bonds that encompass Bredt's rule. For the first time, this topic is reviewed in a natural product context. [ABSTRACT FROM AUTHOR]

Vor über hundert Jahren begann Professor Julius Bredt seine Forschungskarriere auf dem Gebiet der verbrückten bicyclischen Systeme, die durch ein Brückenkopf-Alken unter Ringspannung stehen. Seine kritischen Betrachtungen mündeten in der Formulierung dessen, was wir heute als die Bredtsche Regel kennen. Seitdem versuchen Physikochemiker, Theoretiker und Synthesechemiker gleichermaßen, die Grenzen dieses physikalische Phänomens auszuloten, um es besser kennenzulernen. Der Bauplan der Natur sieht durchaus Brückenkopf-Doppelbindungen nach der Bredtschen Regel vor. In diesem Aufsatz wird erstmals die Anwendung der Bredtschen Regel auf Naturstoffe umfassend erörtert. [ABSTRACT FROM AUTHOR]

Nonstabilised azomethine ylids (NAYs) are useful 1,3-dipoles, but their synthetic applications are restricted by the high temperatures often needed for their generation, and by an incomplete understanding of the effect of heteroatoms in cyclic systems. We have examined the behaviour of N-methylmorpholine N-oxide (NMO) as a NAY precursor in the Roussi reaction (low-temperature reaction of an N-oxide with strong base). The choice of base is critical to achieving cycloadduct formation. We report synthetic and computational (density functional theory) investigations of the products obtained with different bases and their mechanisms of formation. [ABSTRACT FROM AUTHOR]

Tandem oxidative-dehydrogenation of primary alcohols to give α,β-unsaturated aldehydes in one pot are rare transformations in organic synthesis, with only two methods currently available. Reported herein is a novel method using the bench-stable salt methyltriphenylphosphonium perruthenate (MTP3), and a new co-oxidant NEMO·PF6 (NEMO = N -ethyl- N -hydroxymorpholinium) which provides unsaturated aldehydes in low to moderate yields. The Ley-Griffith oxidation of (hetero)arylated primary alcohols with N -oxide co-oxidants NMO (NMO = N -methylmorpholine N -oxide)/NEMO, is expanded by addition of the N -oxide salt NEMO·PF6 to convert the intermediate saturated aldehyde into its unsaturated counterpart. The discovery, method development, reaction scope, and associated challenges of this method are highlighted. The conceptual value of late-stage dehydrogenation in natural product synthesis is demonstrated via the synthesis of a polyene scaffold related to auxarconjugatin B. A novel method is described, using perruthenate salts, for performing the rarely reported dehydrogenation of primary alcohols to afford unsaturated aldehydes in low to moderate yields. The discovery, method development, reaction scope, and associated challenges of this method are presented in detail. [ABSTRACT FROM AUTHOR]

Cubane, a hexahedral hydrocarbon, can be converted into an asymmetric molecule with a minimum of three substituents. The resulting chiral cubane can be used as a pharmacophore or a chiral ligand. Starting from the cubane carboxamide, the 1,2,3‐substituted compound was synthesized by sequential ortho‐metalation. The 1,3,5‐substituted compound was synthesized by combining site‐selective halogenation and halogen‐metal exchange and the resulting racemate was subjected to enantiomeric resolution by HPLC. [ABSTRACT FROM AUTHOR]

Tyrosinase (TYR) is a key enzyme that catalyzes the synthesis of melanin in plants, microorganisms and mammalian cells. Kojic acid (KA) is a well-known TYR inhibitor widely used as a popular cosmetic skin-lightening ingredient. However, KA is reported to have poor inhibitory activity against pigmentation within intact melanocytes or in clinical assays. In this study, a series of dihydropyrano[3,2-b] chromenedione (DHPC) (1a, 2a, 3a, 4a, 5a, 6a and 7a) and 1,8-dioxooctahydroxanthene (DOHX) (1b, 2b, 3b and 4b) derivatives were evaluated using a DPPH radical-scavenging assay. These results showed that 7a exhibited the most potent radical-scavenging activity. Compound 7a was characterised by X-ray crystallographic studies. Molecular docking was carried out to shed light on the mode of action and types of interaction between the compounds and the target. A metal-binding study suggested that these synthetic heterocyclic compounds may behave as competitive inhibitors for the L-DOPA binding site of the TYR. Finally, molecular modeling provided important insight into the mechanism of binding interactions with the TYR copper active site. [ABSTRACT FROM AUTHOR]

The long-standing perception of Protein Kinase C (PKC) as a family of oncoproteins has increasingly been challenged by evidence that some PKC isoforms may act as tumor suppressors. To explore the hypothesis that activation, rather than inhibition, of these isoforms is critical for anticancer activity, we isolated and characterized a family of 16 novel phorboids closely-related to tigilanol tiglate (EBC-46), a PKC-activating epoxytigliane showing promising clinical safety and efficacy for intratumoral treatment of cancers. While alkyl branching features of the C12-ester influenced potency, the 6,7-epoxide structural motif and position was critical to PKC activation in vitro. A subset of the 6,7-epoxytiglianes were efficacious against established tumors in mice; which generally correlated with in vitro activation of PKC. Importantly, epoxytiglianes without evidence of PKC activation showed limited antitumor efficacy. Taken together, these findings provide a strong rationale to reassess the role of PKC isoforms in cancer, and suggest in some situations their activation can be a promising strategy for anticancer drug discovery. [ABSTRACT FROM AUTHOR]

the proposed structure of arneroma B has been revised from a cyclopentadienone to a 2,4-disubstituted furan. The reassignment has been confirmed by total synthesis of the revised structure. [Display omitted] • Molecular formula reassigned by MS. • Structure reassignment by NMR. • Confirmed by synthesis. [ABSTRACT FROM AUTHOR]

The tigliane ring system, which encompasses iconic members such as phorbol and TPA, is widely renowned due to numerous observations of displaying potent biological activity, and subsequent use as mainstream biochemical tools. Traditionally, naturally occurring phorboids are regarded as tumor promotors through PKC activation, although in recent times more highly oxidized natural derivatives have been identified as anti‐tumor agents. In the view that only limited synthetic investigations toward skeletal stereochemical modification have been undertaken, non‐natural systems could be useful for a better understanding of the tigliane pharmacophore via interrogation of cellular sensitivity. In this context the concise construction of a number of highly functionalized non‐natural D‐ring inverted phorbol esters were synthesized, via a rhodium‐catalyzed [4+3] cycloaddition, and biologically evaluated using a range of cancer cell lines. The biological results highlight the notion that subtle changes in structure have dramatic effects on potency. Furthermore, although the non‐natural derivatives did not outcompete the natural systems in the PKC‐activation sensitive MCF7 cancer cell line, they outperformed in other cancer cell lines (MM96L and CAL27). This observation strongly suggested an alternate mode of action not involving activation of PKC, but instead involves thiol addition as indicated by glutathione addition and NF‐κB reporter activity. [ABSTRACT FROM AUTHOR]

Structurally unique halimanes EBC‐232 and EBC‐323, isolated from the Australian rainforest plant Croton insularis, proved considerably difficult to elucidate. The two diastereomers, which consist an unusual oxo‐6,7‐spiro ring system fused to a dihydrofuran, were solved by unification and consultation of five in silico NMR elucidation and prediction methods [i.e. ACDLabs, olefin strain energy (OSE), DP4, DU8+ and TD DFT CD]. Structure elucidation challenges of this nature are prime test case examples for empowering future AI learning in structure elucidation. [ABSTRACT FROM AUTHOR]

The Australian rainforest plant, Croton insularis, has provided a further casbane diterpene family member in the form of EBC‐342, which contains a novel tetrahydrofuran ring. A combination of DP4 and TD‐DFT CD methods were required to confirm both structure and absolute stereochemistry. [ABSTRACT FROM AUTHOR]

Dysphania is an abundant genus of plants, many of which are endemic to the Australian continent, occurring primarily in arid and temperate zones. Despite their prevalence, very few investigations into the phytochemistry of native Dysphania have been undertaken. Described herein, is the isolation and elucidation of two enantiomeric diastereomers of humulene diepoxide C from D. kalpari and D. rhadinostachya, of which unassigned diastereomers of humulene diepoxide C have been previously reported as components in beer brewed from aged hops. In addition, two (+)‐humulene diepoxiols (humulene diepoxiol C‐I and C‐II) were isolated from D. rhadinostachya. Analysis of Chinook hops oil confirmed the presence of both humulene diepoxide C‐I and C‐II as trace components, and in turn enabled GC‐MS peak assignment to the relative stereochemistry. Anticancer assays did not reveal any significant activity for the (+)‐humulene diepoxides. Antifungal assays showed good activity against a drug‐resistant strain of C. auris, with MIC50 values of 8.53 and 4.91 μm obtained for (+)‐humulene diepoxide C‐I and C‐II, respectively. [ABSTRACT FROM AUTHOR]

Marine derived cyclic peptides have inspired chemists for decades as the cavitand architecture can be compared with macrocyclic ligands, and hence easily conceived as mediators of metal-ion transport. Lissoclinamide 5 and ascidiacyclamide are two such cyclic peptides that have received much attention both for their metal ion complexation properties and biological activity; the metal ion binding properties of mimics of these two systems have been reported. Reported herein is a computational study aimed at evaluating the stability, and potential for copper(ii) ion binding by lissoclinamide 5 mimics that substitute the naturally occurring 4-carboxy-1,3-thiazole units for novel valine- and phenylalanine-derived 1,2,4-thiadiazole units. Our results suggest that one lissoclinamide 5 mimic, 1,2,4-thiadiazole (TDA)-lissoclinamide 9 , may be capable of forming a complex with one CuII ion, [Cu(9 -H)(H2O)]+. A complex with two CuII ions, [Cu2(9 -H)(μ-OH)]2+, was also considered. These results set the stage for synthetic and experimental metal binding studies. 1,2,4-Thiadiazole-lissoclinamide 9 , a next generation mimic design, was evaluated in silico for metal binding aptitude towards CuII ions. DFT calculations suggest that TDA-lissoclinamide may be capable of forming a complex with one CuII ion, [Cu(9 -H)(H2O)]+. These results underpin future synthetic and experimental metal binding studies. [ABSTRACT FROM AUTHOR]

Common oxidants used in chemical synthesis, including newly developed perruthenates, were evaluated in the context of understanding (and better appreciating) the sensitiveness and associated potential hazards of these reagents. Analysis using sealed cell differential scanning calorimetry (scDSC) facilitated Yoshida correlations, which were compared to impact sensitiveness and electrostatic discharge experiments (ESD), that enabled sensitiveness ranking. Methyltriphenylphoshonium perruthenate (MTP3, 8), isoamyltriphenylphosphonium perruthenate (ATP3, 7) and tetraphenylphosphonium perruthenate (TP3, 9) were found to be the most sensitive followed by 2‐iodoxybenzoic acid (IBX, 2) and benzoyl peroxide (BPO, 10), whereas the most benign were observed to be Oxone (12), manganese dioxide (MnO2, 13), and N‐bromosuccinimide (NBS, 17). [ABSTRACT FROM AUTHOR]

As infrared seeking technology evolves, threats are better able to distinguish defensive infrared (IR) flares from true targets. Spectrally matched flares, which generally employ carbon‐based fuels, are better able to decoy some advanced missiles by more closely mimicking the IR emission of the target. Cubane is a high‐energy carbon‐based scaffold which may be suitable for use as a fuel in spectrally matched flares. The enthalpy of formation and strain energy of a series of cubanes was predicted in silico, and their thermal and impact stability examined. All were found to undergo highly exothermic decomposition in sealed cell differential scanning calorimetry, and two cubanes subsequently underwent quantitative sensitiveness testing. Despite their F of I values being in the secondary explosive range, cubane‐1,4‐dicarboxylic acid (F of I=70) and 4‐carbamoylcubane‐1‐carboxylic acid (F of I=90) were identified as potentially useful fuels for pyrotechnic infrared countermeasure flare formulations. [ABSTRACT FROM AUTHOR]

Stachyonic acid A, arising from the first in‐depth phytochemical investigation of the herb Basilicum polystachyon, was found to display potent inhibitory activity against dengue virus, with limited cytotoxicity. Andrographolide, a known dengue virus inhibitor and closely related labdane‐type diterpene, is structurally more complex but displayed poor antiviral activity in the PRNT assay, and increased cytotoxicity in comparison. Furthermore, a Diels–Alder reaction with PTAD identified the active pharmacophore of stachyonic acid to be the conjugated diene. [ABSTRACT FROM AUTHOR]

The scope and limitations of Eaton's rhodium(I)‐catalyzed valence isomerization of cubane to cyclooctatetraene (COT) were investigated in the context of functional group tolerability, multiple substitution modes and the ability of cubane‐alcohols to undergo one‐pot tandem Ley–Griffith Wittig reactions in the absence of a transition metal catalyst. Releasing the strain! This work aims to take Eaton's rhodium(I)‐catalyzed valence isomerization of cubane to cyclooctatetraene (COT) to the next level. Functional group tolerability, scope, and limitations of this reaction were investigated in the context of developing deployable methodology for the increasing number of applications involving the COT ring system. [ABSTRACT FROM AUTHOR]

D‐Ring‐seco‐limonoids (tetranortriterpenoids), such as gedunin and xylogranin B display anti‐cancer activity, acting via inhibition of Hsp90 and/or associated chaperon machinery (e.g. p23). Despite this, these natural products have received relatively little attention, both in terms of an enabling synthetic approach (which would allow access to derivatives), and as a consequence their structure–activity relationship (SAR). Disclosed herein is a generally applicable synthetic route to the BCD ring system of the seco‐D‐ring double bond containing limonoids. Furthermore, cell based assays revealed the first skeletal fragment that exhibited inhibition of the p23 enzyme at a level which was equipotent to that of gedunin, despite being much less structurally complex. The first synthetic route to the BCD ring system of the seco‐D‐ring limonoids has been devised. A synthetic intermediate displayed an equipotent p23 enzyme inhibitory effect to that of the more complex gedunin. [ABSTRACT FROM AUTHOR]

Investigation of the Australian rainforest plant Croton insularis revealed seven new cis‐, two new trans‐cyclopropane casbanes, and the first trans‐cyclopropane seco‐casbane. The relative configuration of the cyclopropane moiety for all compounds (EBC‐182, 217, 218, 220, 343, 357, 358, 361, 365, 373; EBC=EcoBiotics Compound) was assigned using 13C NMR data. Comparison of the experimental electronic circular dichroism (ECD) spectra with the theoretical curves, calculated by TD‐DFT at the B3LYP/6‐31+G**//B3LYP/6‐31+G** level, in conjunction with NOE data afforded the absolute configuration. EBC‐180, 181 and 220 displayed potent activity against cervical carcinoma (HeLa cells). Ask for casbanes andCrotongiveth: The Australian rainforest plant Croton Insularis revealed new cis‐ and trans‐casbanes, along with the first trans‐seco‐casbane. Absolute configuration of all 10 casbanes was determined by ECD and one derivative displayed potent activity against HeLa cells. [ABSTRACT FROM AUTHOR]

The Ley–Griffith oxidation, which is catalyzed by tetra‐n‐propylammonium perruthenate (TPAP, nPr4N[RuO4]), is a popular method for not only controlled oxidation of primary alcohols to aldehydes, but also a host of other synthetically useful transformations. While the fundamental reaction mechanism has recently been elucidated, several key hydrogen‐bonding interactions between the reagents were implicated but not investigated. Herein the prevalence of H‐bonding between the co‐oxidant N‐methylmorpholine N‐oxide (NMO), the alcohol substrate, water and the perruthenate catalyst is established. These observations help to rationalize the importance of drying the reagents and lead to several practical suggestions. Further exploration of the Ley–Griffith (TPAP) oxidation has unveiled a better understanding of the role N‐methylmorpholine N‐oxide (NMO) plays, not just as a co‐oxidant, but also a hydrogen bonding partner to the alcohol substrate and water. These additional attributes impact reaction performance, with important implications for the practicing synthetic chemist. [ABSTRACT FROM AUTHOR]