Tubulysins are among the most recent antimitotic compounds to enter into antibody/peptide‐drug conjugate (ADC/PDC) development. Thus far, the design of the most promising tubulysin payloads relied on simplifying their structures, e.g., by using small tertiary amide N‐substituents (Me, Et, Pr) on tubuvaline residue. Cumbersome solution‐phase approaches are typically used for both syntheses and functionalization with cleavable linkers. p‐Aminobenzyl quaternary ammonium (PABQ) linkers were a remarkable advancement for targeted delivery, but the procedures to incorporate them into tubulysins are only of moderate efficiency. Here we describe a novel all‐on‐resin strategy permitting a loss‐free resin linkage and an improved access to super potent tubulysin analogs showing close resemblance to the natural compounds. For the first time, a protocol enables the integration of on‐resin tubulysin derivatization with, e.g., a maleimido‐Val‐Cit‐PABQ linker, which is a notable progress for the payload‐PABQ‐linker technology. The strategy also allows tubulysin diversification of the internal amide N‐substituent, thus enabling to screen a tubulysin library for the discovery of new potent analogs. This work provides ADC/PDC developers with new tools for both rapid access to new derivatives and easier linker‐attachment and functionalization.

Salinity poses a serious threat to global agriculture and human food security. A better understanding of plant adaptation to salt stress is, therefore, mandatory. In the non-photosynthetic cells of the root, salinity perturbs oxidative balance in mitochondria, leading to cell death. In parallel, plastids accumulate the jasmonate precursor cis (+)12-Oxo-Phyto-Dienoic Acid (OPDA) that is then translocated to peroxisomes and has been identified as promoting factor for salt-induced cell death as well. In the current study, we probed for a potential interaction between these three organelles that are primarily dealing with oxidative metabolism. We made use of two tools: (i) Rice OPDA Reductase 7 (OsOPR7), an enzyme localised in peroxisomes converting OPDA into the precursors of the stress hormone JA-Ile. (ii) A Trojan Peptoid, Plant PeptoQ, which can specifically target to mitochondria and scavenge excessive superoxide accumulating in response to salt stress. We show that overexpression of OsOPR7 as GFP fusion in tobacco (Nicotiana tabacum L. cv. Bright Yellow 2, BY-2) cells, as well as a pretreatment with Plant PeptoQ can mitigate salt stress with respect to numerous aspects including proliferation, expansion, ionic balance, redox homeostasis, and mortality. This mitigation correlates with a more robust oxidative balance, evident from a higher activity of superoxide dismutase (SOD), lower levels of superoxide and lipid peroxidation damage, and a conspicuous and specific upregulation of mitochondrial SOD transcripts. Although both, Plant PeptoQ and ectopic OsOPR7, were acting in parallel and mostly additive, there are two specific differences: (i) OsOPR7 is strictly localised to the peroxisomes, while Plant PeptoQ found in mitochondria. (ii) Plant PeptoQ activates transcripts of NAC, a factor involved in retrograde signalling from mitochondria to the nucleus, while these transcripts are suppressed significantly in the cells overexpressing OsOPR7. The fact that overexpression of a peroxisomal enzyme shifting the jasmonate pathway from the cell-death signal OPDA towards JA-Ile, a hormone linked with salt adaptation, is accompanied by more robust redox homeostasis in a different organelle, the mitochondrion, indicates that cross-talk between peroxisome and mitochondrion is a crucial factor for efficient adaptation to salt stress.

Mannan is a class of cell wall polysaccharides widespread in the plant kingdom. Mannan structure and properties vary according to species and organ. The cell walls of cereal grains have been extensively studied due to their role in cereal processing and to their beneficial effect on human health as dietary fiber. Recently, we showed that mannan in wheat (Triticum aestivum) grain endosperm has a linear structure of β-1,4-linked mannose residues. The aim of this work was to study the biosynthesis and function of wheat grain mannan. We showed that mannan is deposited in the endosperm early during grain development, and we identified candidate mannan biosynthetic genes expressed in the endosperm. The functional study in wheat was unsuccessful therefore our best candidate genes were expressed in heterologous systems. The endosperm-specificTaCslA12 gene expressed in Pichia pastoris and in an Arabidopsis thaliana mutant depleted in glucomannan led to the production of wheat-like linear mannan lacking glucose residues and with moderate acetylation. Therefore, this gene encodes a mannan synthase and is likely responsible for the synthesis of wheat endosperm mannan.

Aetokthonotoxin has recently been identified as the cyanobacterial neurotoxin causing Vacuolar Myelinopathy, a fatal neurologic disease, spreading through a trophic cascade and affecting birds of prey such as the bald eagle in the USA. Here, we describe the total synthesis of this specialized metabolite. The complex, highly brominated 1,2’-biindole could be synthesized via a Somei-type Michael reaction as key step. The optimised sequence yielded the natural product in five steps with an overall yield of 29 %.

The multicomponent backbone N‐modification of peptides on solid‐phase is presented as a powerful and general method to enable peptide stapling at the backbone instead of the side chains. This work shows that a variety of functionalized N‐substituents suitable for backbone stapling can be readily introduced by means of on‐resin Ugi multicomponent reactions conducted during solid‐phase peptide synthesis. Diverse macrocyclization chemistries were implemented with such backbone N‐substituents, including the ring‐closing metathesis, lactamization, and thiol alkylation. The backbone N‐modification method was also applied to the synthesis of α‐helical peptides by linking N‐substituents to the peptide N‐terminus, thus featuring hydrogen‐bond surrogate structures. Overall, the strategy proves useful for peptide backbone macrocyclization approaches that show promise in peptide drug discovery.

Aiming at providing an efficient and versatile method for the diversity‐oriented decoration and ligation of fullerenes, we report the first C60 derivatization strategy based on isocyanide‐multicomponent reactions (I‐MCRs). The approach comprises the use of Passerini and Ugi reactions for assembling pseudo‐peptidic scaffolds (i.e., N‐alkylated and depsipeptides, peptoids) on carboxylic acid‐functionalized fullerenes. The method showed wide substrate scope for the oxo and isocyanide components, albeit the Ugi reaction proved efficient only for aromatic amines. The approach was successfully employed for the ligation of oligopeptides and polyethyleneglycol chains (PEG) to C60, as well as for the construction of bis‐antennary as well as PEG‐tethered dimeric fullerenes. The quantum yields for the formation of 1O2 was remarkable for the selected compounds analyzed.

Boron's unusual properties inspired major advances in chemistry. In nature, the existence and importance of boron has been fairly explored (e.g. bacterial signaling, plant development) but its role as biological catalyst was never reported. Here, we show that boric acid [B(OH)3] can restore chloroperoxidase activity of Curvularia inaequalis recombinant apo‐haloperoxidase's (HPO) in the presence of hydrogen peroxide and chloride ions. Molecular modeling and semi‐empirical PM7 calculations support a thermodynamically highly favored (bio)catalytic mechanism similarly to vanadium haloperoxidases (V‐HPO) in which [B(OH)3] is assumedly located in apo‐HPO's active site and a monoperoxyborate [B(OH)3(OOH)−] intermediate is formed and stabilized by interaction with specific active site amino acids leading ultimately to the formation of HOCl. Thus, B(OH)3−HPO provides the first evidence towards the future exploitation of boron′s role in biological systems.

The contribution of carbon assimilation and allocation and of invertases to the stimulation of adventitious root formation in response to a dark pre-exposure of petunia cuttings was investigated, considering the rooting zone (stem base) and the shoot apex as competing sinks. Dark exposure had no effect on photosynthesis and dark respiration during the subsequent light period, but promoted dry matter partitioning to the roots. Under darkness, higher activities of cytosolic and vacuolar invertases were maintained in both tissues when compared to cuttings under light. This was partially associated with higher RNA levels of respective genes. However, activity of cell wall invertases and transcript levels of one cell wall invertase isogene increased specifically in the stem base during the first two days after cutting excision under both light and darkness. During five days after excision, RNA accumulation of four invertase genes indicated preferential expression in the stem base compared to the apex. Darkness shifted the balance of expression of one cytosolic and two vacuolar invertase genes towards the stem base. The results indicate that dark exposure before planting enhances the carbon sink competitiveness of the rooting zone and that expression and activity of invertases contribute to the shift in carbon allocation.

Various cleavage products of C40 carotenoid substrates are formed preferentially or exclusively in roots. Such apocarotenoid signaling or regulatory compounds differentially induced in roots during environmental stress responses including root colonization by arbuscular mycorrhizal fungi include ABA, strigolactones and C13 α-ionol/C14 mycorradicin derivatives. The low carotenoid levels in roots raise the question of whether there is a regulated precursor supply channeled into apocarotenoid formation distinct from default carotenoid pathways. This review describes root-specific isogene components of carotenoid pathways toward apocarotenoid formation, highlighting a new PSY3 class of phytoene synthase genes in dicots. It is clearly distinct from the monocot PSY3 class co-regulated with ABA formation. At least two members of the exclusive dicot PSY3s are regulated by nutrient stress and mycorrhization. This newly recognized dicot PSY3 (dPSY3 vs. mPSY3 from monocots) class probably represents an ancestral branch in the evolution of the plant phytoene synthase family. The evolutionary history of PSY genes is compared with the evolution of MEP pathway isogenes encoding 1-deoxy-d-xylulose 5-phosphate synthases (DXS), particularly DXS2, which is co-regulated with dPSY3s in mycorrhizal roots. Such stress-inducible isoforms for rate-limiting steps in root carotenogenesis might be components of multi-enzyme complexes committed to apocarotenoid rather than to carotenoid formation.

Constraining small peptides into specific secondary structures has been a major challenge in peptide ligand design. So far, the major solution for decreasing the conformational flexibility in small peptides has been cyclization. An alternative is the use of topological templates, which are able to induce and/or stabilize peptide secondary structures by means of covalent attachment to the peptide. Herein a multicomponent strategy and structural analysis of a new type of peptidosteroid architecture having the steroid as N‐substituent of an internal amide bond is reported. The approach comprises the one‐pot conjugation of two peptide chains (or amino acid derivatives) to aminosteroids by means of the Ugi reaction to give a unique family of N‐steroidal peptides. The conjugation efficiency of a variety of peptide sequences and steroidal amines, as well as their consecutive head‐to‐tail cyclization to produce chimeric cyclopeptide–steroid conjugates, that is, macrocyclic lipopeptides, was assessed. Determination of the three‐dimensional structure of an acyclic N‐steroidal peptide in solution proved that the bulky, rigid steroidal template is capable of both increasing significantly the conformational rigidity, even in a peptide sequence as short as five amino acid residues, and inducing a β‐turn secondary structure even in the all‐s‐trans isomer. This report provides the first evidence of the steroid skeleton as β‐turn inducer in linear peptide sequences.