Modified cyclodextrins solubilize elemental sulfur in water and enable biological sulfane sulfur delivery

An important form of biological sulfur is sulfane sulfur, or S⁰, which is found in polysulfide and persulfide compounds as well as in elemental sulfur. Sulfane sulfur, often in the form of S₈, functions as a key energy source in the metabolic processes of thermophilic Archaean organisms found in sulfur-rich environments and can be metabolized both aerobically and anaerobically by different archaeons. Despite this importance, S₈ has a low solubility in water (∼19 nM), raising questions of how it can be made chemically accessible in complex environments. Motivated by prior crystallographic data showing S₈ binding to hydrophobic motifs in filamentous glycoproteins from the sulfur reducing Staphylothermus marinus anaerobe, we demonstrate that simple macrocyclic hydrophobic motifs, such as 2-hydroxypropyl β-cyclodextrin (2HPβ), are sufficient to solubilize S₈ at concentrations up to 2.0 ± 0.2 mM in aqueous solution. We demonstrate that the solubilized S₈ can be reduced with the common reductant tris(2-carboxyethyl)phosphine (TCEP) and reacts with thiols to generate H₂S. The thiol-mediated conversion of 2HPβ/S₈ to H₂S ranges from 80% to quantitative efficiency for Cys and glutathione (GSH). Moreover, we demonstrate that 2HPβ can catalyze the Cys-mediated reduction of S₈ to H₂S in water. Adding to the biological relevance of the developed systems, we demonstrate that treatment of Raw 264.7 macrophage cells with the 2HPβ/S₈ complex prior to LPS stimulation decreases NO₂⁻ levels, which is consistent with known activities of bioavailable H₂S and sulfane sulfur. Taken together, these investigations provide a new strategy for delivering H₂S and sulfane sulfur in complex systems and more importantly provide new insights into the chemical accessibility and storage of S⁰ and S₈ in biological environments.

Sulfane sulfur, or S⁰, is found in polysulfide and persulfide compounds in biology. We demonstrate that modified cyclodextrins can solubilize S₈ in water, increase its reactivity with biological nucleophiles, and enable delivery to live cells.     

Cross-Talks Between Sulfane Sulfur and Thiol at a Zinc(II) Site

Transformations of sulfane sulfur compounds (e. g. organic polysulfides (R−S_n−R, n>2) and elemental sulfur (S₈)) play pivotal roles in the biochemical landscape of sulfur, and thus supports signaling activities of H₂S. Although a number of previous reports illustrate amine mediated reactions of S₈ and thiol (RSH) yielding R−S_n−R, this report illustrates that a tripodal [Zn^II] complex [( Bn₃Tren )Zn^II−OH₂](ClO₄)₂ ( 1 ) facilitates the reactions of sulfane sulfur and thiol (RSH), thereby offering an amine-free biologically relevant complementary route. UV-vis monitoring of the reactions and a set of control experiments underline the definitive role of [Zn^II] coordination motif in the reactions of sulfane sulfur (e. g. S₈ and R−S_n−R) with RSH. Detailed investigations (UV-vis, NMR, ESI-MS, intermediate trapping, and TEMPO radical interference experiments) disclose the key differences in the [Zn^II] versus previously known amine mediated routes. Moreover, the persulfide (RSS⁻) trapping experiments using 1-fluoro-2,4-dinitrobenzene (F-DNB) reveal the intermediacy of RSS⁻ species in the [Zn^II] mediated reactions of sulfane sulfur and thiol, thereby demonstrating [Zn^II] assisted persulfidation of thiol in the presence of sulfane sulfur species. Of broader impact, this study underscores the feasible influence of biologically relevant [Zn^II] coordination motifs (e. g. carbonic anhydrase) on the sulfane sulfur chemistry in biology.     

Alleviating Cellular Oxidative Stress through Treatment with Superoxide‐Triggered Persulfide Prodrugs

Overproduction of superoxide anion (O₂^.?), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O₂^.? to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H₂S). Termed SOPD‐NAC , this persulfide donor reacts specifically with O₂^.?, decomposing to generate N‐acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self‐assembling peptide (Bz‐CFFE‐NH₂) to make a superoxide‐responsive, persulfide‐donating peptide ( SOPD‐Pep ). Both SOPD‐NAC and SOPD‐Pep delivered persulfides/H₂S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD‐Pep mitigated toxicity induced by phorbol 12‐myristate 13‐acetate (PMA) more effectively than SOPD‐NAC and several control compounds, including common H₂S donors.     

Alleviating Cellular Oxidative Stress through Treatment with Superoxide-Triggered Persulfide Prodrugs

Overproduction of superoxide anion (O₂^.−), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O₂^.− to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H₂S). Termed SOPD-NAC , this persulfide donor reacts specifically with O₂^.−, decomposing to generate N-acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self-assembling peptide (Bz-CFFE-NH₂) to make a superoxide-responsive, persulfide-donating peptide ( SOPD-Pep ). Both SOPD-NAC and SOPD-Pep delivered persulfides/H₂S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD-Pep mitigated toxicity induced by phorbol 12-myristate 13-acetate (PMA) more effectively than SOPD-NAC and several control compounds, including common H₂S donors.     

A Persulfide Donor Responsive to Reactive Oxygen Species: Insights into Reactivity and Therapeutic Potential

Persulfides (RSSH) have been hypothesized as critical components in sulfur‐mediated redox cycles and as potential signaling compounds, similar to hydrogen sulfide (H₂S). Hindering the study of persulfides is a lack of persulfide‐donor compounds with selective triggers that release discrete persulfide species. Reported here is the synthesis and characterization of a ROS‐responsive (ROS=reactive oxygen species), self‐immolative persulfide donor. The donor, termed BDP‐NAC, showed selectivity towards H₂O₂ over other potential oxidative or nucleophilic triggers, resulting in the sustained release of the persulfide of N‐acetyl cysteine (NAC) over the course of 2 h, as measured by LCMS. Exposure of H9C2 cardiomyocytes to H₂O₂ revealed that BDP‐NAC mitigated the effects of a highly oxidative environment in a dose‐dependent manner over relevant controls and to a greater degree than common H₂S donors sodium sulfide (Na₂S) and GYY4137. BDP‐NAC also rescued cells more effectively than a non‐persulfide‐releasing control compound in concert with common H₂S donors and thiols.     

A paradigm for biological sulfur transfers via persulfide groups: a persulfide-disulfide-thiol cycle in 4-thiouridine biosynthesis

In support of the key features of sulfur transfer in the proposed mechanisms of 4-thiouridine generation, the enzyme ThiI can turn over only once in the absence of reductants of disulfide bonds, and Cys-456 of ThiI receives the sulfur transferred from the persulfide group of the sulfurtransferase IscS.     

Double design of host and guest synergistically reinforces the Na-ion storage of sulfur cathodes

Development of room-temperature sodium–sulfur batteries is significantly hampered by the shuttle effect of soluble intermediates and intrinsically sluggish conversion kinetics. In this work, a double design host and guest strategy (i.e., implantation of a polar V₂O₃ adsorbent into a carbon substrate and selenium doping of a sulfur guest) is proposed to synergistically reinforce the electrochemical properties of sulfur electrodes in sodium ion storage. The V₂O₃ adsorbent efficiently immobilizes sulfur species via strong polar–polar interactions, while the selenium dopant improves the electronic conductivity of sulfur cathodes and accelerates the redox conversion of sulfur cathodes. The synergistic effect between the V₂O₃ adsorbent and selenium dopant is shown to inhibit the shuttle effect and improve the redox kinetics, thus realizing greatly enhanced Na-ion storage properties of sulfur cathodes. The as-designed sulfur cathode delivers a superior rate capability of 663 mA h g⁻¹ at 2.0 A g⁻¹ and demonstrates excellent cyclability of 405 mA h g⁻¹ over 700 cycles at 1.0 A g⁻¹.

Development of room-temperature sodium–sulfur batteries is significantly hampered by the shuttle effect of soluble intermediates and intrinsically sluggish conversion kinetics.     

An Innovative Hydrogen Peroxide-Sensing Scaffold and Insight Towards its Potential as an ROS-Activated Persulfide Donor

Reactive sulfur species, such as hydrogen sulfide, persulfides, and polysulfides, have recently emerged as key signaling molecules and important physiological mediators within mammalian systems. To better assess the therapeutic potential of their exogenous administration, we report on the development of a unique hydrogen peroxide (H₂O₂)-sensing motif and its capacity for providing cellular protection against oxidative stress while serving as a reactive oxygen species (ROS)-activated persulfide donor. With the strategic implementation of a gem-dimethyl group to promote both stability and cyclization, we found the initial rate of payload release from this newly derived scaffold to be directly proportional to the concentration of H₂O₂ and to proceed via an unprecedented pathway that avoids the production of electrophilic byproducts, a severe limitation that has plagued the physiological application of previous designs.     

Sulfur(iv) reagents for the SuFEx-based synthesis of substituted sulfamate esters

Sulfur(vi) fluoride exchange chemistry has been reported to be effective at synthesizing valuable sulfur(vi) functionalities through sequential nucleophilic additions, yet oxygen-based nucleophiles are limited in this approach to phenolic derivatives. Herein, we report a new sulfur(iv) fluoride exchange strategy to access synthetically challenging substituted sulfamate esters from alkyl alcohols and amines. We also report the development of a non-gaseous, sulfur(iv) fluoride exchange reagent, N-methylimidazolium sulfinyl fluoride hexafluorophosphate (MISF). By leveraging the reactivity of the sulfur(iv) center of this novel reagent, the sequential addition of alcohols and amines to MISF followed by oxidation afforded the desired substituted sulfamates in 40–83% yields after two steps. This new strategy expands the scope of SuFEx chemistry by increasing the accessibility of underdeveloped –S(O)F intermediates for future explorations.

N-Methylimidazolium sulfinyl fluoride hexafluorophosphate (MISF) was developed as a solution-stable sulfur(iv) reagent to access substituted sulfamate esters using a sulfur(iv) fluoride exchange strategy.

Sulfur fluoride exchange (SuFEx) reagents have powerful applications in pharmaceuticals, chemical biology, and materials science.¹ The most commonly utilized reagents are sulfur(vi) compounds, such as sulfuryl fluoride (SO₂F₂) and its derivatives, that can be used to efficiently synthesize a wide range of functionalities through sequential nucleophilic additions (Fig. 1a).² Sulfamate esters are targets of particular interest as they display potential as anticancer agents and as a new class of antibiotics,³ as well as versatility as synthetic intermediates.⁴ Oxygen-based nucleophiles are limited to phenolic derivatives with sulfur(vi) SuFEx reagents, restricting their use in sulfamate ester syntheses. The reaction of aliphatic alcohols with SO₂F₂ leads to aliphatic fluorosulfate intermediates that are very unstable, and results in rapid substitution at the fluorosulfate alpha-position (Fig. 1b).^5,6O-Alkyl sulfamate esters (ROSO₂NH₂) are readily synthesized with alternatives to SuFEx-based methods,⁷ but the substituted analogues require harsh conditions, multiple steps, and long reaction times.⁸ For example, sulfur(vi) chloride reagents have been utilized in the syntheses of sulfur(vi) moieties, yet are limited due to their inherent instability and prevalent side reactions.^9,10 A fast, mild, and SuFEx-based approach to the syntheses of substituted alkyl sulfur(vi) motifs is, therefore, desired.Open in a separate windowFig. 1SuFEx chemistry for the syntheses of S(vi) functionalities. (a) Reported sulfur(vi) SuFEx approach to linking nucleophiles. (b) Limitations of sulfur(vi) reagents in accessing fluorosulfate intermediates. (c) This work. Use of novel sulfur(iv) SuFEx reagent followed by oxidation to access synthetically challenging sulfur(vi) motifs that are inaccessible with sulfur(vi) reagents.The aforementioned limitations of sulfur(vi) SuFEx reactions may be overcome by utilizing a novel approach involving sulfur(iv) fluoride reagents (Fig. 1d). The addition of an alkyl alcohol to a sulfur(iv) fluoride exchange reagent should readily form the corresponding fluorosulfite intermediate. In contrast to fluorosulfates, fluorosulfites 2 may be more reactive at the sulfur center than the alpha-position.¹¹ Therefore, the addition of a heteroatom nucleophile to the sulfur(iv) center of a fluorosulfite should be faster and more selective than the sulfur(vi) analogue. A subsequent oxidation of the sulfur(iv) center would then afford the desired sulfur(vi) motif. While the oxidation step limits the substrate scope, this strategy provides a route to substrates that were previously inaccessible.Thionyl fluoride (SOF₂), the sulfur(iv) analogue of SO₂F₂, has displayed versatile reactivity despite the relatively few studies on its use.^11,12 The initial addition of a heteroatomic nucleophile to thionyl fluoride has been reported to be an efficient protocol for achieving amino sulfinyl fluorides and fluorosulfites,¹³ yet further reactivity of these intermediates has not been reported. There are also several major drawbacks to its use, including safety hazards associated with handling the gaseous reagent.¹⁴ There is no literature precedence for non-gaseous sulfur(iv) derivatives of thionyl fluoride. Therefore, a non-gaseous derivative that maintains the fundamental reactivity of SOF₂ is essential for the broad adoption of this class of sulfur(iv) reagents.     

Activation of MoS2 monolayer electrocatalysts via reduction and phase control in molten sodium for selective hydrogenation of nitrogen to ammonia

Electrochemical nitrogen fixation under ambient conditions is promising for sustainable ammonia production but is hampered by high reaction barrier and strong competition from hydrogen evolution, leading to low specificity and faradaic efficiency with existing catalysts. Here we describe the activation of MoS₂ in molten sodium that leads to simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer via reduction and phase transformation. The resultant catalyst exhibits intrinsic activities for electrocatalytic N₂-to-NH₃ conversion, delivering a faradaic efficiency of 20.5% and an average NH₃ rate of 93.2 μg h⁻¹ mg_cat⁻¹. The interfacial heterojunctions with sulfur vacancies function synergistically to increase electron localization for locking up nitrogen and suppressing proton recombination. The 1T phase facilitates H–OH dissociation, with S serving as H-shuttling sites and to stabilize . The subsequently couple with nearby N₂ and NH_x intermediates bound at Mo sites, thus greatly promoting the activity of the catalyst. First-principles calculations revealed that the heterojunction with sulfur vacancies effectively lowered the energy barrier in the potential-determining step for nitrogen reduction, and, in combination with operando spectroscopic analysis, validated the associative electrochemical nitrogen reduction pathway. This work provides new insights on manipulating chalcogenide vacancies and phase junctions for preparing monolayered MoS₂ with unique catalytic properties.

We describe the activation of MoS₂ in molten sodium that leads to the simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer electrocatalyst via reduction and phase transformation.     

Amide-bridged conjugated organic polymers: efficient metal-free catalysts for visible-light-driven CO2 reduction with H2O to CO

The visible-light-driven photoreduction of CO₂ to value-added chemicals over metal-free photocatalysts without sacrificial reagents is very interesting, but challenging. Herein, we present amide-bridged conjugated organic polymers (amide-COPs) prepared via self-condensation of amino nitriles in combination with hydrolysis, for the photoreduction of CO₂ with H₂O without any photosensitizers or sacrificial reagents under visible light irradiation. These catalysts can afford CO as the sole carbonaceous product without H₂ generation. Especially, amide-DAMN derived from diaminomaleonitrile exhibited the highest activity for the photoreduction of CO₂ to CO with a generation rate of 20.6 μmol g⁻¹ h⁻¹. Experiments and DFT calculations confirmed cyano/amide groups as active sites for CO₂ reduction and second amine groups for H₂O oxidation, and suggested that superior selectivity towards CO may be attributed to the adjacent redox sites. This work presents a new insight into designing photocatalysts for artificial photosynthesis.

Amino nitrile-derived conjugated organic polymers can realize the photoreduction of CO₂ with water to CO without H₂ generation efficiently.     

An unexpected all-metal aromatic tetranuclear silver cluster in human copper chaperone Atox1

Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins. Herein we report the formation and crystal structure of a planar square tetranuclear silver cluster when silver ions were mixed with human copper chaperone Atox1. Quantum chemical studies reveal that two Ag 5s¹ electrons in the tetranuclear silver cluster fully occupy the one bonding molecular orbital, with the assumption that this Ag₄ cluster is Ag₄²⁺, leading to extensive electron delocalization over the planar square and significant stabilization. This bonding pattern of the tetranuclear silver cluster represents an aromatic all-metal structure that follows a 4n + 2 electron counting rule (n = 0). This is the first time an all-metal aromatic silver cluster was observed in a protein.

Metal clusters, such as iron–sulfur clusters, play key roles in sustaining life and are intimately involved in the functions of metalloproteins.     

Synthetic scope, computational chemistry and mechanism of a base induced 5-endo cyclization of benzyl alkynyl sulfides

We present an experimental and computational study of the reaction of aryl substituted benzyl 1-alkynyl sulfides with potassium alkoxide in acetonitrile, which produces 2-aryl 2,3-dihydrothiophenes in poor to good yields. The cyclization is most efficient with electron withdrawing groups on the aromatic ring. Evidence indicates there is rapid exchange of protons and tautomerism of the alkynyl unit prior to cyclization. Theoretical calculations were also conducted to help rationalize the base induced 5-endo cyclization of benzyl 1-propynyl sulfide (1a). The potential energy surface was calculated for the formation of 2,3-dihydrothiophene in a reaction of benzyl 1-propynyl sulfide (1a) with potassium methoxide. Geometries were optimized with CAM-B3LYP/6-311+G(d,p) in acetonitrile with the CPCM solvent model. It is significant that the benzyl propa-1,2-dien-1-yl sulfane (6) possessed a lower benzylic proton affinity than the benzyl prop-2-yn-1-yl sulfane (8) thus favoring the base induced reaction of the former. From benzyl(propa-1,2-dien-1-yl sulfane (6), 2,3-dihydrothiophene can be formed via a conjugate base that undergoes 5-endo-trig cyclization followed by a protonation step.     

Peroxynitrite-Promoted Persulfide Prodrugs with Protective Potential against Paracetamol Poisoning

The newly emerging persulfide prodrugs provide additional options for the profound study of persulfide, a fascinating molecule expected to intervene in biological functions and even diseases. Peroxynitrite is often the culprit in pathological processes characterized by oxidative stress, while the persulfide prodrug responsive to it is still pending. To enrich the family of redox-activated prodrugs, we designed prodrugs with a 2-oxo-2-phenylacetamide trigger, which achieved the release of persulfide via 1, 6-N, S-relay. The degradation of prodrugs and the formation of persulfides were confirmed to be peroxynitrite-responsible by the qualitative and quantitative studies based on LC-MS/MS methods and a spectrophotometry-based tag-switch strategy. Furthermore, these prodrugs showed potent peroxynitrite scavenging activity, cellular therapeutic potential against paracetamol poisoning in HepG2 and oxidative stress in H9c2, as well as desirable in vitro metabolic properties.     

The first rubidium rare-earth(III) thiophosphates: Rb3M3[PS4]4 (M=Pr, Er)

The two non-isotypical rubidium rare-earth(III) thiophosphates Rb₃M₃[PS₄]₄ of praseodymium and erbium can easily be obtained by the stoichiometric reaction of the respective rare-earth metal, red phosphorus and sulfur with an excess of rubidium bromide (RbBr) as flux and rubidium source at 950°C for 14 days in evacuated silica tubes. The pale green platelet-shaped single crystals of Rb₃Pr₃[PS₄]₄ as well as the pink rods of Rb₃Er₃[PS₄]₄ are moisture sensitive. Rb₃Pr₃[PS₄]₄ crystallizes triclinically in the space group (, , , α=84.329(4)°, β=88.008(4)°, γ=80.704(4)°; Z=2), Rb₃Er₃[PS₄]₄ monoclinically in the space group P2₁/n (, , , β=95.601(6)°; Z=4). In both structures, there are three crystallographically different rare-earth cations present. (M1)³⁺ is eightfold coordinated in the shape of a square antiprism, (M2)³⁺ and (M3)³⁺ are both surrounded by eight sulfur atoms as bicapped trigonal prisms each with a coordination number of eight as well as for the praseodymium, but better described as CN=7+1 in the case of the erbium compound. These [MS₈]¹³⁻ polyhedra form a layer according to by sharing edges with the isolated [PS₄]³⁻ tetrahedra (d(P-S)=200-209 pm, ?(S-P-S)=102-116°). These layers are stacked with a repetition period of three in the case of the praseodymium compound, but of only two for the erbium analog. The rubidium cation (Rb1)⁺ is located in cavities of these layers and tenfold coordinated in the shape of a tetracapped trigonal antiprism. The also tenfold but more irregularly coordinated rubidium cations (Rb2)⁺ and (Rb3)⁺ reside between the layers.     

Regulating sulfur removal efficiency of fuels by Lewis acidity of ionic liquids

It is urgent to develop a new deep desulfurization process of fuels as the environmental pollution increases seriously. In this work, a series of Lewis acidic ionic liquids (ILs) [C₄³MPy]Cl/nZnCl₂ (n=1, 1.5, 2, 3) were synthesized and used in extraction and catalytic oxidative desulfurization (ECOD) of the fuels. The effects of the Lewis acidity of ILs, the molar ratio of H₂O₂/sulfur, temperatures, and different substrates including dibenzothiophene (DBT), benzothiophene (BT) and thiophene (TS), on sulfur removal were investigated. The results indicated that [C₄³MPy]Cl/₃ZnCl₂ presented near 100% DBT removal of model oil under conditions of 323 K, H₂O₂/DBT molar ratio 6:1. Kinetics for the removal of DBT, BT and TS by the [C₄³MPy]Cl/₃ZnCl₂-H₂O₂ system at 323 K is first-order with the apparent rate constants of 1.1348, 0.2226 and 0.0609 h^-1, and the calculated apparent activation energies for DBT, BT and TS were 61.13, 60.66, and 68.14 kJ/mol from 298 to 308 K, respectively. After six cycles of the regenerated [CC₄³MPy]Cl/₃ZnCl₂, the sulfur removal had a slight decrease. [CC₄³MPy]Cl/₃ZnCl₂ showed a good desulfurization performance under optimal conditions.     

OvoAMtht from Methyloversatilis thermotolerans ovothiol biosynthesis is a bifunction enzyme: thiol oxygenase and sulfoxide synthase activities

Mononuclear non-heme iron enzymes are a large class of enzymes catalyzing a wide-range of reactions. In this work, we report that a non-heme iron enzyme in Methyloversatilis thermotolerans, OvoA_Mtht, has two different activities, as a thiol oxygenase and a sulfoxide synthase. When cysteine is presented as the only substrate, OvoA_Mtht is a thiol oxygenase. In the presence of both histidine and cysteine as substrates, OvoA_Mtht catalyzes the oxidative coupling between histidine and cysteine (a sulfoxide synthase). Additionally, we demonstrate that both substrates and the active site iron''s secondary coordination shell residues exert exquisite control over the dual activities of OvoA_Mtht (sulfoxide synthase vs. thiol oxygenase activities). OvoA_Mtht is an excellent system for future detailed mechanistic investigation on how metal ligands and secondary coordination shell residues fine-tune the iron-center electronic properties to achieve different reactivities.

Modulation of OvoA_Mtht''s dual activities: sulfoxide synthase and thiol oxygenase.     

Synthesis and crystal structure of the isotypic rare earth thioborates Ce[BS3], Pr[BS3], and Nd[BS3]

The orthothioborates Ce[BS₃], Pr[BS₃] and Nd[BS₃] were prepared from mixtures of the rare earth (RE) metals together with amorphous boron and sulfur summing up to the compositions CeB₃S₆, PrB₅S₉ and NdB₃S₆. The following preparation routes were used: solid state reactions with maximum temperatures of 1323 K and high-pressure high-temperature syntheses at 1173 K and 3 GPa. Pr[BS₃] and Nd[BS₃] were also obtained from rare earth chlorides RECl₃ and sodium thioborate Na₂B₂S₅ by metathesis type reactions at maximum temperatures of 1073 K. The crystal structure of the title compounds was determined from X-ray powder diffraction data. The thioborates are isotypic and crystallize in the orthorhombic spacegroup Pna2₁ (No. 33; Z=4; Ce: , , ; Pr: , , ; Nd: , , ) . The crystal structures contain isolated [BS₃]^3‐ groups with boron in trigonal-planar coordination. The sulfur atoms form the vertices of undulated kagome nets, which are stacked along [100] according to the sequence ABAB. Within these nets every second triangle is occupied by boron and the large hexagons are centered by rare earth ions, which are surrounded by overall nine sulfur species.