Efficient synthesis of pentasubstituted pyrroles via intramolecular C-arylation.

Immobilized L-aspartic acid beta-methyl ester (Fmoc-Asp(OMe)-OH) was reacted with 4-nitrobenzenesulfonyl chloride, followed by alkylation with various α-haloketones. The resulting intermediates were treated with potassium trimethylsilanolate, which yielded tetrasubstituted pyrroles after a one-step transformation consisting of sequential C-arylation, aldol condensation and spontaneous aromatization. The discovered synthetic strategy enables fast and simple access to pentasubstituted and functionalized pyrroles from a number of readily available starting materials.

Rearrangement of Threonine- and Serine-Based N-(3-Phenylprop-2-yn-1-yl) Sulfonamides Yields Chiral Pyrrolidin-3-ones.

N-(3-Phenylprop-2-yn-1-yl)-sulfonamides derived from serine and threonine were synthesized using solid-phase synthesis and subjected to reaction with trimethylsilyl trifluoromethanesulfonate (TMSOTf). In contrast to the previously reported formation of 1,4-oxazepanes, this reaction afforded pyrrolidin-3-ones. A mechanistic explanation for this unexpected outcome is proposed, and the limitations and scope of the rearrangement are outlined.

Steroid Degradation in Comamonas testosteroni TA441: Identification of the Entire ß-Oxidation Cycle of the Cleaved B Ring.

Comamonas testosteroni TA441 degrades steroids via aromatization of the A ring, followed by degradation of 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid, mainly by ß-oxidation. In this study, we revealed that 7ß,9α-dihydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostanoic acid-coenzyme A (CoA) ester is dehydrogenated by (3S)-3-hydroxylacyl CoA-dehydrogenase, encoded by scdE (ORF27), and then the resultant 9α-hydroxy-7,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid-CoA ester is converted by 3-ketoacyl-CoA transferase, encoded by scdF (ORF23). With these results, the whole cycle of ß-oxidation on the side chain at C-8 of 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid is clarified; 9-hydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid-CoA ester is dehydrogenated at C-6 by ScdC1C2, followed by hydration by ScdD. 7ß,9α-Dihydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostanoic acid-CoA ester then is dehydrogenated by ScdE to be converted to 9α-hydroxy-17-oxo-1,2,3,4,5,6,10,19-octanorandrostan-7-oic acid-CoA ester and acetyl-CoA by ScdF. ScdF is an ortholog of FadA6 in Mycobacterium tuberculosis H37Rv, which was reported as a 3-ketoacyl-CoA transferase involved in C ring cleavage. We also obtained results suggesting that ScdF is also involved in C ring cleavage, but further investigation is required for confirmation. ORF25 and ORF26, located between scdF and scdE, encode enzymes belonging to the amidase superfamily. Disrupting either ORF25 or ORF26 did not affect steroid degradation. Among the bacteria having gene clusters similar to those of tesB to tesR, some have both ORF25- and ORF26-like proteins or only an ORF26-like protein, but others do not have either ORF25- or ORF26-like proteins. ORF25 and ORF26 are not crucial for steroid degradation, yet they might provide clues to elucidate the evolution of bacterial steroid degradation clusters.IMPORTANCE Studies on bacterial steroid degradation were initiated more than 50 years ago primarily to obtain materials for steroid drugs. Steroid-degrading bacteria are globally distributed, and the role of bacterial steroid degradation in the environment as well as in relation to human health is attracting attention. The overall aerobic degradation of the four basic steroidal rings has been proposed; however, there is still much to be revealed to understand the complete degradation pathway. This study aims to uncover the whole steroid degradation process in Comamonas testosteroni TA441 as a model of steroid-degrading bacteria. C. testosteroni is one of the most studied representative steroid-degrading bacteria and is suitable for exploring the degradation pathway, because the involvement of degradation-related genes can be determined by gene disruption. Here, we elucidated the entire ß-oxidation cycle of the cleaved B ring. This cycle is essential for the following C and D ring cleavage.

Steroid Degradation in Comamonas testosteroni TA441: Identification of Metabolites and the Genes Involved in the Reactions Necessary before D-Ring Cleavage.

Bacterial steroid degradation has been studied mainly with Rhodococcus equi (Nocardia restrictus) and Comamonas testosteroni as representative steroid degradation bacteria for more than 50 years. The primary purpose was to obtain materials for steroid drugs, but recent studies showed that many genera of bacteria (Mycobacterium, Rhodococcus, Pseudomonas, etc.) degrade steroids and that steroid-degrading bacteria are globally distributed and found particularly in wastewater treatment plants, the soil, plant rhizospheres, and the marine environment. The role of bacterial steroid degradation in the environment is, however, yet to be revealed. To uncover the whole steroid degradation process in a representative steroid-degrading bacterium, C. testosteroni, to provide basic information for further studies on the role of bacterial steroid degradation, we elucidated the two indispensable oxidative reactions and hydration before D-ring cleavage in C. testosteroni TA441. In bacterial oxidative steroid degradation, A- and B-rings of steroids are cleaved to produce 2-hydroxyhexa-2,4-dienoic acid and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid. The latter compound was revealed to be degraded to the coenzyme A (CoA) ester of 9α-hydroxy-17-oxo-1,2,3,4,5,6,10,19-octanorandrostan-7-oic acid, which is converted to the CoA ester of 9,17-dioxo-1,2,3,4,5,6,10,19-octanorandrostan-7-oic acid by ORF31-encoded hydroxylacyl dehydrogenase (ScdG), followed by conversion to the CoA ester of 9,17-dioxo-1,2,3,4,5,6,10,19-octanorandrost-8(14)-en-7-oic acid by ORF4-encoded acyl-CoA dehydrogenase (ScdK). Then, a water molecule is added by the ORF5-encoded enoyl-CoA hydratase (ScdY), which leads to the cleavage of the D-ring. The conversion by ScdG is presumed to be a reversible reaction. The elucidated pathway in C. testosteroni TA441 is different from the corresponding pathways in Mycobacterium tuberculosis H37Rv.IMPORTANCE Studies on representative steroid degradation bacteria Rhodococcus equi (Nocardia restrictus) and Comamonas testosteroni were initiated more than 50 years ago primarily to obtain materials for steroid drugs. A recent study showed that steroid-degrading bacteria are globally distributed and found particularly in wastewater treatment plants, the soil, plant rhizospheres, and the marine environment, but the role of bacterial steroid degradation in the environment is yet to be revealed. This study aimed to uncover the whole steroid degradation process in C. testosteroni TA441, in which major enzymes for steroidal A- and B-ring cleavage were elucidated, to provide basic information for further studies on bacterial steroid degradation. C. testosteroni is suitable for exploring the degradation pathway because the involvement of degradation-related genes can be determined by gene disruption. We elucidated the two indispensable oxidative reactions and hydration before D-ring cleavage, which appeared to differ from those present in Mycobacterium tuberculosis H37Rv.

Convenient Synthesis of Thiohydantoins, Imidazole-2-thiones and Imidazo[2,1-b]thiazol-4-iums from Polymer-Supported α-Acylamino Ketones.

The preparation of 5-methylene-thiohydantoins using solid-phase synthesis is reported in this paper. After sulfonylation of immobilized Ser (t-Bu)-OH with 4-nitrobenzenesulfonyl chloride followed by alkylation with various bromoketones, the 4-Nos group was removed and the resulting polymer-supported α-acylamino ketones reacted with Fmoc-isothiocyanate. Cleavage of the Fmoc protecting group was followed by the spontaneous cyclative cleavage releasing the 5-methylene-thiohydantoin derivatives from the polymer support. Reduction with triethylsilane (TES) yielded the corresponding 5-methyl-thiohydantoins. When Fmoc-isothiocyanate was replaced with alkyl isothiocyanates, the trifluoroacetic acid (TFA) mediated cleavage from the polymer support, which was followed by the cyclization reaction and the imidazo[2,1-b]thiazol-4-iums were obtained. Their conversion in deuterated dimethylsulfoxide led to imidazole-2-thiones.

Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application.

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4(-), and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.

Fast Magic-Angle Spinning Three-Dimensional NMR Experiment for Simultaneously Probing H-H and N-H Proximities in Solids.

A fast magic-angle spinning (MAS, 70 kHz) solid-state NMR experiment is presented that combines 1H Double-Quantum (DQ) and 14N-1H HMQC (Heteronuclear Multiple-Quantum Coherence) pulse-sequence elements, so as to simultaneously probe H-H and N-H proximities in molecular solids. The proposed experiment can be employed in both two-dimensional (2D) and three-dimensional (3D) versions: first, a 2D 14N HMQC-filtered 1H-DQ experiment provides specific DQ-SQ correlation peaks for proton pairs that are in close proximities to the nitrogen sites, thereby achieving spectral filtration. Second, a proton-detected three-dimensional (3D) 1H(DQ)-14N(SQ)-1H(SQ) experiment correlates 1H(DQ)-1H(SQ) chemical shifts with 14N shifts such that longer range N···H-H correlations are observed between protons and nitrogen atoms with internuclear NH distances exceeding 3 Å. Both 2D and 3D versions of the proposed experiment are demonstrated for an amino acid hydrochloride salt, l-histidine·HCl·H2O, and a DNA nucleoside, guanosine·2H2O. In the latter case, the achieved spectral filtration ensures that DQ cross peaks are only observed for guanine NH and CH8 1H resonances and not ribose and water 1H resonances, thus providing insight into the changes in the solid-state structure of this hydrate that occur over time; significant changes are observed in the NH and NH21H chemical shifts as compared to the freshly recrystallized sample previously studied by Reddy et al., Cryst. Growth Des. 2015, 15, 5945.

Ultrafast Magic-Angle Spinning: Benefits for the Acquisition of Ultrawide-Line NMR Spectra of Heavy Spin-1/2 Nuclei.

The benefits of the ultrafast magic-angle spinning (MAS) approach for the acquisition of ultrawide-line NMR spectra-spectral simplification, increased mass sensitivity allowing the fast study of small amounts of material, efficient excitation, and application to multiple heavy nuclei-are demonstrated for tin(II) oxide (SnO) and the tin complex [(LB)Sn(II) Cl](+) [Sn(II) Cl3 ](-) [LB=2,6-diacetylpyridinebis(2,6-diisopropylanil)] containing two distinct tin environments. The ultrafast MAS experiments provide optimal conditions for the extraction of the chemical-shift anisotropy tensor parameters, anisotropy, and asymmetry for heavy spin-1/2 nuclei.

Identification of 9α-hydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid in steroid degradation by Comamonas testosteroni TA441 and its conversion to the corresponding 6-en-5-oyl coenzyme A (CoA) involving open reading frame 28 (ORF28)- and ORF30-encoded acyl-CoA dehydrogenases.

Comamonas testosteroni TA441 degrades steroids via aromatization and meta-cleavage of the A ring, followed by hydrolysis, and produces 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid as an intermediate compound. Herein, we identify a new intermediate compound, 9α-hydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid. Open reading frame 28 (ORF28)- and ORF30-encoded acyl coenzyme A (acyl-CoA) dehydrogenase was shown to convert the CoA ester of 9α-hydroxy-17-oxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid to the CoA ester of 9α-hydroxy-17-oxo-1,2,3,4,10,19-hexanorandrost-6-en-5-oic acid. A homology search of the deduced amino acid sequences suggested that the ORF30-encoded protein is a member of the acyl-CoA dehydrogenase_fadE6_17_26 family, whereas the deduced amino acid sequence of ORF28 showed no significant similarity to specific acyl-CoA dehydrogenase family proteins. Possible steroid degradation gene clusters similar to the cluster of TA441 appear in bacterial genome analysis data. In these clusters, ORFs similar to ORFs 28 and 30 are often found side by side and ordered in the same manner as ORFs 28 and 30.

Azoxystrobin amine: A novel azoxystrobin degradation product from Bacillus licheniformis strain TAB7.

Azoxystrobin (AZ) is a broad-spectrum synthetic fungicide widely used in agriculture globally. However, there are concerns about its fate and effects in the environment. It is reportedly transformed into azoxystrobin acid as a major metabolite by environmental microorganisms. Bacillus licheniformis strain TAB7 is used as a compost deodorant in commercial compost and has been found to degrade some phenolic and agrochemicals compounds. In this article, we report its ability to degrade azoxystrobin by novel degradation pathway. Biotransformation analysis followed by identification by electrospray ionization-mass spectrometry (MS), high-resolution MS, and nuclear magnetic resonance spectroscopy identified methyl (E)-3-amino-2-(2-((6-(2-cyanophenoxy)pyrimidin-4-yl)oxy)phenyl)acrylate, or (E)-azoxystrobin amine in short, and (Z) isomers of AZ and azoxystrobin amine as the metabolites of (E)-AZ by TAB7. Bioassay testing using Magnaporthe oryzae showed that although 40 µg/mL of (E)-AZ inhibited 59.5 ± 3.5% of the electron transfer activity between mitochondrial Complexes I and III in M. oryzae, the same concentration of (E)-azoxystrobin amine inhibited only 36.7 ± 15.1% of the activity, and a concentration of 80 µg/mL was needed for an inhibition rate of 56.8 ± 7.4%, suggesting that (E)-azoxystrobin amine is less toxic than the parent compound. To our knowledge, this is the first study identifying azoxystrobin amine as a less-toxic metabolite from bacterial AZ degradation and reporting on the enzymatic isomerization of (E)-AZ to (Z)-AZ, to some extent, by TAB7. Although the fate of AZ in the soil microcosm supplemented with TAB7 will be needed, our findings broaden our knowledge of possible AZ biotransformation products.

1H-, 13C-, and 15N-NMR chemical shifts for selected glucosides and ribosides of aromatic cytokinins.

The (1)H and (13)C NMR resonances of 16 purine glucosides were assigned by a combination of one- and two-dimensional NMR experiments, including gs-COSY, gs-HSQC, and gs-HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, (15)N NMR chemical shifts for selected derivatives were investigated by using (1)H-(15)N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N(9)-glucosides and their ribose analogs were compared. Characteristic long-range (1)H-(15)N coupling constants, measured by using (1)H-(15)N gradient-selected single-quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones.

Synthesis of chiral 1,4-oxazepane-5-carboxylic acids from polymer-supported homoserine.

The preparation of novel 1,4-oxazepane-5-carboxylic acids bearing two stereocenters is reported in this article. Fmoc-HSe(TBDMS)-OH immobilized on Wang resin was reacted with different nitrobenzenesulfonyl chlorides and alkylated with 2-bromoacetophenones to yield N-phenacyl nitrobenzenesulfonamides. Their cleavage from the polymer support using trifluoroacetic acid (TFA) led to the removal of the silyl protective group followed by spontaneous lactonization. In contrast, TFA/triethylsilane (Et3SiH)-mediated cleavage yielded 1,4-oxazepane derivatives as a mixture of inseparable diastereomers. The regioselectivity/stereoselectivity depended on the substitution of the starting 2-bromoacetophenones and was studied in detail. Catalytic hydrogenation of the nitro group improved the separability of the resulting diastereomeric anilines, which allowed us to isolate and fully characterize the major isomers.

Identification of 9-oxo-1,2,3,4,5,6,10,19-octanor-13,17-secoandrost-8(14)-ene-7,17-dioic acid as a metabolite of steroid degradation in Comamonas testosteroni TA441 and the genes involved in the conversion.

Comamonas testosteroni TA441 degrades steroid compounds via aromatization of the A-ring to produce 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid (a metabolite with C- and D-rings), which is presumed to be further degraded via ß-oxidation. In elucidating the complete steroid degradation process in C. testosteroni, we isolated 9-oxo-1,2,3,4,5,6,10,19-octanor-13,17-secoandrost-8(14)-ene-7,17-dioic acid and several other metabolites containing only C-ring. For conversion of the CoA-ester of this compound, a two-subunit ß -ketoacyl-CoA-transferase encoded by ORF1 and ORF2 was shown to be indispensable. ORF1 and ORF2 are located just after tesB, the meta-cleavage enzyme gene in one of the two major steroid degradation gene clusters of strain TA441. Conversion by the CoA-transferase leads to cleavage of the remaining C-ring, and the product was suggested to be further degraded by ß-oxidation involving other genes in the cluster. ORF1 and ORF2 are considered orthologues of ipdAB gene in Mycobacterium tuberculosis H37Rv, which is recently reported as the CoA-transferase of 9-oxo-1,2,3,4,5,6,10,19-octanor-13,17-secoandrost-8(14)-ene-7,17-dioic acid (Crowe AM, Casabon I, Brown KL, Liu J, Lian J, Rogalski JC, Hurst TE, Snieckus V, Foster LJ, Eltis LD. 2017. MBio 8).

Identification of 4-methyl-5-oxo-octane-1,8-dioic acid and the derivatives as metabolites of steroidal C,D-ring degradation in Comamonas testosteroni TA441.

Comamonas testosteroni TA441 degrades steroids via 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid, which is presumed to be further degraded by ß-oxidation. In the ß-oxidation process, Coenzyme A (CoA)-ester of 9-oxo-1,2,3,4,5,6,10,19-octanor-13,17-secoandrost-8(14)-ene-7,17-dioic acid is produced and converted by ß-ketoacyl-CoA-transferase encoded by ORF1 and ORF2 (scdL1L2) to cleave the remaining C-ring. In this study, we isolated and identified 4-methyl-5-oxo-octane-1,8-dioic acid and 4-methyl-5-oxo-3-octene-1,8-dioic acid from the culture of the ORF3 (scdN)-null mutant as metabolites of steroid degradation (ADD and cholic acid analogues; cholic acid, chenodeoxycholic acid, deoxycholic acid, and lithocholic acid). In addition of these compounds, UHPLC/MS analysis of the culture of the scdN-null mutant revealed significant accumulation of another compound, which was detected as a dominant peak of m/z 155 ([M-CO2]-) accompanied by a small peak of parental ion (m/z 199 [M-]). On the bases of experimental data, this compound was presumed to be 4-methyl-5-oxo-2-octene-1,8-dioic acid, whose CoA-ester was indicated to be converted by scdN-encoded CoA-hydratase into the CoA-ester of 3-hydroxy-4-methyl-5-oxooctan-1,7-carboxylic acid.

Identification of genes involved in inversion of stereochemistry of a C-12 hydroxyl group in the catabolism of cholic acid by Comamonas testosteroni TA441.

Comamonas testosteroni TA441 degrades steroids such as testosterone via aromatization of the A ring, followed by meta-cleavage of the ring. In the DNA region upstream of the meta-cleavage enzyme gene tesB, two genes required during cholic acid degradation for the inversion of an alpha-oriented hydroxyl group on C-12 were identified. A dehydrogenase, SteA, converts 7 alpha,12 alpha-dihydroxyandrosta-1,4-diene-3,17-dione to 7 alpha-hydroxyandrosta-1,4-diene-3,12,17-trione, and a hydrogenase, SteB, converts the latter to 7 alpha,12 beta-dihydroxyandrosta-1,4-diene-3,17-dione. Both enzymes are members of the short-chain dehydrogenase/reductase superfamily. The transformation of 7 alpha,12 alpha-dihydroxyandrosta-1,4-diene-3,17-dione to 7 alpha,12 beta-dihydroxyandrosta-1,4-diene-3,17-dione is carried out far more effectively when both SteA and SteB are involved together. These two enzymes are encoded by two adjacent genes and are presumed to be expressed together. Inversion of the hydroxyl group at C-12 is indispensable for the subsequent effective B-ring cleavage of the androstane compound. In addition to the compounds already mentioned, 12 alpha-hydroxyandrosta-1,4,6-triene-3,17-dione and 12 beta-hydroxyandrosta-1,4,6-triene-3,17-dione were identified as minor intermediate compounds in cholic acid degradation by C. testosteroni TA441.

1H, 13C and 77Se NMR study of tetraselenafulvalene derivatives supported by novel H(Se)C and H(C)Se triple-resonance experiments at natural abundance.

A series of substituted tetraselenafulvalenes (TSeFs) was studied in solution using 1H, 13C and 77Se NMR spectroscopy. Chemical shifts and heteronuclear coupling constant values were determined and assigned. Novel two-dimensional H(Se)C and H(C)Se triple-resonance correlation experiments were applied at natural abundance in order to accomplish 13C and 77Se signal assignments. Using this approach, all the signals were unambiguously assigned and atom connectivity was established in the studied TSeF derivatives. These experiments, allowing signal assignments of quaternary carbons, may find wide application in the study of substituted TSeF and other organoselenium compounds. To the best of our knowledge, triple-resonance experiments with proton detection have been applied to organoselenium compounds for the first time.

Revealing the Local Proton Network through Three-Dimensional 13C/1H Double-Quantum/1H Single-Quantum and 1H Double-Quantum/13C/1H Single-Quantum Correlation Fast Magic-Angle Spinning Solid-State NMR Spectroscopy at Natural Abundance.

1H double quantum (DQ)/1H single quantum (SQ) correlation solid-state NMR spectroscopy is widely used to obtain internuclear 1H-1H proximities, especially at fast magic-angle spinning (MAS) rate (>60 kHz). However, to date, 1H signals are not well-resolved because of intense 1H-1H homonuclear dipolar interactions even at the attainable maximum MAS frequencies of ∼100 kHz and/or under 1H-1H homonuclear dipolar decoupling irradiations. Here we introduce novel three-dimensional (3D) experiments to resolve the 1H DQ/1H SQ correlation peaks using the additional 13C dimension. Although the low natural abundance of 13C (1.1%) significantly reduces the sensitivities, the 1H indirect measurements alleviate this issue and make this experiment possible even in naturally abundant samples. The two different implementations of 13C/1H DQ/1H SQ correlations and 1H DQ/13C/1H SQ correlations are discussed and demonstrated using l-histidine·HCl·H2O at natural abundance to reveal the local 1H-1H networks near each 13C. In addition, the complete 1H resonance assignments are achieved from a single 3D 13C/1H DQ/1H SQ experiment. We have also demonstrated the applicability of our proposed method on a biologically relevant molecule, capsaicin.

Stereoselective Synthesis of Benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12-diones with Two Diversity Positions.

Herein, we report a stereoselective formation of tetrahydro-6H-benzo[e][1,4]oxazino[4,3-a][1,4]diazepine-6,12(11H)-diones. Their preparation consisted in solid-phase synthesis of linear intermediates starting from polymer-supported Ser(tBu)-OH. Using various 2-nitrobenzoic acids and bromoketones, the key intermediates were obtained in five steps and subjected to trifluoroacetic acid-mediated cleavage from the resin, followed by stereoselective reduction with triethylsilane. Subsequent catalytic hydrogenation of the nitro group and cyclization yielded the target compounds with full retention of the C12a stereocenter configuration.

Polymer-Supported Stereoselective Synthesis of Benzoxazino[4,3-b][1,2,5]thiadiazepinone 6,6-dioxides.

Herein, we report the stereoselective synthesis of trisubstituted benzoxazino[4,3-b][1,2,5]thiadiazepinone 6,6-dioxides from polymer-supported Fmoc-Ser(tBu)-OH and Fmoc-Thr(tBu)-OH. After the solid-phase synthesis of N-alkylated-N-sulfonylated intermediates using various 2-nitrobenzenesulfonyl chlorides and bromoketones, the target compounds were obtained via trifluoroacetic acid (TFA)-mediated cleavage from the resin, followed by cyclization of the diazepinone scaffold. Except for the threonine-based intermediates, the inclusion of triethylsilane (TES) in the cleavage cocktail yielded a specific configuration of the newly formed C3 chiral center. The final cyclization resulted in minor or no inversion of the C12a stereocenter configuration.