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Search for "stereochemistry" in Full Text gives 575 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Regio- and stereochemical stability induced by anomeric and gauche effects in difluorinated pyrrolidines
Beilstein J. Org. Chem. 2024, 20, 1572–1579, doi:10.3762/bjoc.20.140
- Lewis interactions from a natural bond orbital perspective. Keywords: anomeric effect; fluoropyrrolidine; gauche effect; stereochemistry; Introduction The pyrrolidine ring structure is prevalent in numerous natural alkaloids and is an important feature of the proline and hydroxyproline residues that
- pervade biochemistry in peptides and proteins. The chemical and biological properties of substituted pyrrolidine derivatives, along with many other compounds, hinge on the relative stereochemistry. It is well established that the presence of fluorine in an organic molecule can significantly influence the
- , substituted 3-fluoropyrrolidines, particularly in the form of 2-carboxy derivatives (fluoroprolines), have been extensively explored. These compounds represent valuable nonnatural amino acids, and depending on the regio- and stereochemistry of fluorine substitution, fluoroproline substututions can enhance the
Mining raw plant transcriptomic data for new cyclopeptide alkaloids
Beilstein J. Org. Chem. 2024, 20, 1548–1559, doi:10.3762/bjoc.20.138
- , Figures S16–S26, Table S1). Indeed, our results support the proposed structure of ceanothine B while also assigning absolute stereochemistry consistent with all ʟ-amino acids (Figure 5). We next explored the GNPS network for new cyclopeptide alkaloids from C. americanus. We previously noted the presence
- and Leu-β is supported by HMBC correlation between Tyr-C3 (δ 156.3 ppm) and Tyr-C4 (δ120.5 ppm) and NOESY correlation between Tyr4-H (δ 7.01 ppm, 1H) and Leuβ-H (δ 4.80 ppm, 1H). Similar to other characterized cyclopeptide alkaloids, J-coupling constant (Jα-β = 8.0 Hz) supports S-stereochemistry at
- mass spectra were used to generate a GNPS network using the following parameters: 0.2 Da precursor ion mass tolerance, 0.5 Da fragment ion tolerance, and a minimum of 8 matched fragment ions. Marfey’s analysis To determine the stereochemistry of the new molecules, Marfey’s analysis was used. Standards
Benzylic C(sp3)–H fluorination
Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137
- bond formation to afford the acyloxylation product was observed, and favoured when using directing groups with less steric bulk. This product had the opposite stereochemistry to the fluorination product suggesting it occurred via a competitive SN2 pathway. This is supported by the selectivity for C–O
Primary amine-catalyzed enantioselective 1,4-Michael addition reaction of pyrazolin-5-ones to α,β-unsaturated ketones
Beilstein J. Org. Chem. 2024, 20, 1518–1526, doi:10.3762/bjoc.20.136
- center. Under the disclosed optimized conditions, the product ent-3ba was isolated as white solid with 85% ee and the enantiopurity of the product could be enriched to 98% ee by single recrystallization. The absolute stereochemistry was determined to be “R” on the basis of single-crystal X-ray
- crystallography data of ent-3ba (Figure 2) [37]. The stereochemistry of the products in this series was assigned by analogy. Based on the observed absolute configuration of product ent-3ba and preceding literature reports [38][40], a plausible mechanistic pathway is outlined in Scheme 5. Initially, in the
Bioinformatic prediction of the stereoselectivity of modular polyketide synthase: an update of the sequence motifs in ketoreductase domain
Beilstein J. Org. Chem. 2024, 20, 1476–1485, doi:10.3762/bjoc.20.131
- stereochemistry. However, the reliability and applicability of these prediction methods have not been thoroughly assessed. In this study, we conducted a comprehensive bioinformatic analysis of 1,762 KR sequences from cis-AT PKSs to reevaluate the residues involved in conferring stereoselectivity. Our findings
- elongated growing chain may undergo further processing by KR, DH, and ER domains, generating β-hydroxy, α,β-alkene, and saturated β-methylene groups, respectively (Figure 1a). KR domains have garnered significant attention from researchers due to their ability to control the stereochemistry at the α- and β
- . There are also instances where KRs contain or lack both of the LDD and W motifs, making it difficult to predict stereochemistry (Figure 1c). With the increasing availability of whole genome sequencing, a growing number of PKS gene clusters and their products have been characterized [19]. To assess and
Rapid construction of tricyclic tetrahydrocyclopenta[4,5]pyrrolo[2,3-b]pyridine via isocyanide-based multicomponent reaction
Beilstein J. Org. Chem. 2024, 20, 1436–1443, doi:10.3762/bjoc.20.126
- clearly showed that this reaction has a wide scope of substrates. The obtained compounds 4a–t have four chiral carbon atoms. The multicomponent reaction might result in several diastereomers. On the basis of TLC analysis and 1H NMR spectra of the crude products, only one relative stereochemistry was
Sustainable tandem acylation/Diels–Alder reaction toward versatile tricyclic epoxyisoindole-7-carboxylic acids in renewable green solvents
Beilstein J. Org. Chem. 2024, 20, 1308–1319, doi:10.3762/bjoc.20.114
- and in good yields. The ring stereochemistry (exo- or endo-geometry) of the product, epoxyisoindole-7-carboxylic acid, is easily determined by 1H NMR by evaluating the coupling constants of the protons Ha, Hb and Hc (Figure 2) [119][127][128]. The values of the coupling constants shown in Figure 2 are
The Ugi4CR as effective tool to access promising anticancer isatin-based α-acetamide carboxamide oxindole hybrids
Beilstein J. Org. Chem. 2024, 20, 1213–1220, doi:10.3762/bjoc.20.104
- adducts, with stereochemistry control [4][5]. Unquestionable potential of application in the pharmaceutical industry is recognizable by the number of APIs obtained by this reaction approach [6][7]. The oxindole framework is a privileged unit, recognized massively by its extensive biological applications
Stability trends in carbocation intermediates stemming from germacrene A and hedycaryol
Beilstein J. Org. Chem. 2024, 20, 1189–1197, doi:10.3762/bjoc.20.101
- stereochemistry. Theory is an important tool in understanding the complex chemistry in terpene synthesis. Gas-phase and in-enzyme tools have been employed extensively to understand terpene chemistry in general and terpene synthases in particular [21][22][23][24][25][26][27][28][29]. In the current work, we
Synthesis of 1,4-azaphosphinine nucleosides and evaluation as inhibitors of human cytidine deaminase and APOBEC3A
Beilstein J. Org. Chem. 2024, 20, 1088–1098, doi:10.3762/bjoc.20.96
- ) and FdZ (IId) form tetrahedral intermediates after hydrolysis of the N3–C4 double bond in the active sites of A3Gctd and A3A [59][60]. The intermediates formed had the same R-stereochemistry at the C4 atom of the nucleobase as previously observed for CDA, and thus confirming the general mechanism of
Structure–property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives
Beilstein J. Org. Chem. 2024, 20, 1037–1052, doi:10.3762/bjoc.20.92
- to access 7a as depicted in Scheme 3. The synthetic strategy first involved the access of dihydropyrazine precursor 10 which then underwent oxidation in the final step. Next, 7e was easily converted to (Z,E)-bis-oxime derivative 7d in satisfactory yield. The oxime stereochemistry shown is presumably
Enhancing structural diversity of terpenoids by multisubstrate terpene synthases
Beilstein J. Org. Chem. 2024, 20, 959–972, doi:10.3762/bjoc.20.86
- analogues 80 and 81 with shifted double bonds were synthesized to study the stereochemistry and cyclization mechanism of casbene synthase (CS) from the castor bean (Ricinus communis), which indicated a stereochemical course in accordance with the reported absolute configuration of casbene [41] (Figure 6b
Enantioselective synthesis of β-aryl-γ-lactam derivatives via Heck–Matsuda desymmetrization of N-protected 2,5-dihydro-1H-pyrroles
Beilstein J. Org. Chem. 2024, 20, 940–949, doi:10.3762/bjoc.20.84
- ). The total yields were determined to be 49% for (R)-baclofen hydrochloride (6) and 61% (R)-rolipram (5b) from starting pyrrolidine 1d. Determination of the absolute stereochemistry of the Heck adducts/lactams and rationalization of the enantioselectivity The absolute stereochemistry of the products was
- determined by the correlation of their optical rotations with that of the previously reported aryl-lactam 4bb [23], and its deprotected analog [24], as well as with the intermediates 5b, 5a, and 6 in the (R)-rolipram (5b) and (R)-baclofen hydrochloride (6) [25] syntheses. Assignment of the stereochemistry of
- all other lactams as R was done by analogy. The assignment of the absolute stereochemistry allowed us to propose a rationale for the Heck–Matsuda reaction (Scheme 7). Upon activation of the catalyst (I), oxidative addition of aryldiazonium salt and subsequent nitrogen release generates the cationic
Three-component N-alkenylation of azoles with alkynes and iodine(III) electrophile: synthesis of multisubstituted N-vinylazoles
Beilstein J. Org. Chem. 2024, 20, 891–897, doi:10.3762/bjoc.20.79
- iodonium salts [9], which usually occurs with the retention of the stereochemistry of the vinylating agents (Scheme 1a). Nonetheless, this approach is not necessarily suited for the stereoselective preparation of densely substituted N-vinylazoles because preparing the requisite multisubstituted vinylating
- agents, preferably with well-defined stereochemistry, is a nontrivial task. The addition of azoles to alkynes represents an alternative approach to N-vinylazoles. For example, Nolan and co-workers recently reported a gold-catalyzed addition of azoles to alkynes (hydroazolation; Scheme 1b) [10]. The gold
Confirmation of the stereochemistry of spiroviolene
Beilstein J. Org. Chem. 2024, 20, 852–858, doi:10.3762/bjoc.20.77
- Abstract We confirm the previously revised stereochemistry of spiroviolene by X-ray crystallographically characterizing a hydrazone derivative of 9-oxospiroviolane, which is synthesized by hydroboration/oxidation of spiroviolene followed by oxidation of the resultant hydroxy group. An unexpected thermal
- cyclization mechanism of spiroviolene. Keywords: boron migration; diterpene; spiroviolene; stereochemistry; Introduction Terpenes represent one of the most fascinating families of natural products due to their structural complexity and diversity, as well as their indispensable biological functions that
- stereoselective process to form complex terpene skeletons, normally with multiple stereocenters. In this context, the 3D-defined cyclization products retain the rich information of the complex cyclization process. Thus, assignment of the stereochemistry of the terpene skeleton with high confidence is crucial for
Advancements in hydrochlorination of alkenes
Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72
- investigations into the kinetics and stereochemistry of hydrochlorination reactions. However, both aspects are highly dependent on the reaction conditions and substrates, and no general conclusions could be drawn [3][4][5][6][7][8][9]. Research activity in this field remained relatively dormant until the early
- by the British Oxygen Cooperation in 1956 [47]. In 2012, Carreira reported the hydrochlorination of alkene 27, yielding racemic (±)- gomerone C (28) [48]. Grob observed that the stereochemistry of hydrochlorination reactions can be significantly influenced by the solvent or temperature (Table 1) [9
Methodology for awakening the potential secondary metabolic capacity in actinomycetes
Beilstein J. Org. Chem. 2024, 20, 753–766, doi:10.3762/bjoc.20.69
- Streptomyces sp. JA74 [86]. Maniwamycin E (43) [87] was also discovered from this strain as a metabolite for which production is enhanced by high-temperature culture. These substances have an azoxy structure, which is relatively rare in the natural environment [88]. The stereochemistry of dihydromaniwamycin E
Genome mining of labdane-related diterpenoids: Discovery of the two-enzyme pathway leading to (−)-sandaracopimaradiene in the fungus Arthrinium sacchari
Beilstein J. Org. Chem. 2024, 20, 714–720, doi:10.3762/bjoc.20.65
- GGPP, followed by hydrolysis by acid phosphatase. GC–MS analysis revealed that AsCPS synthesizes the same product to ObCPS_11g (see Supporting Information File 1, Figure S4A and B). It should be noted that the stereochemistry of CPP needs further verification due to the lack of chiral resolution of our
New variochelins from soil-isolated Variovorax sp. H002
Beilstein J. Org. Chem. 2024, 20, 692–700, doi:10.3762/bjoc.20.63
- )-ʟ-alaninamide) derivatives [5]. In addition, a combination of NOESY and bioinformatics analyses proposed all three stereocenters of 4-amino-7-guanidino-3-hydroxy-2-methylheptanoic acid as S configured [5]. The stereochemistry of these moieties in 3–5 are discussed in the next section, regarding the
Evaluation of the enantioselectivity of new chiral ligands based on imidazolidin-4-one derivatives
Beilstein J. Org. Chem. 2024, 20, 684–691, doi:10.3762/bjoc.20.62
- underscore the paramount importance of the stereochemistry at position 2 in chiral ligands dictating enantioselectivity. This study provides essential insights for the design of asymmetric catalysts, especially for Henry and aldol reactions. The structure of newly designed ligands I–IV. Plausible transition
Chemical and biosynthetic potential of Penicillium shentong XL-F41
Beilstein J. Org. Chem. 2024, 20, 597–606, doi:10.3762/bjoc.20.52
- from the known brocaeloid D by the addition of a methyl group, and there is a change in the relative stereochemistry at C2 and C3. In addition, the conversion of the five-membered pyrrole ring in compound 2 to the six-membered piperidine ring in compound 1 is intriguing. Although there have been many
- 1 and those previously reported. This suggests that the formation of the quinoline ring in compound 1 may represent a new and unreported biosynthetic pathway. Moreover, to address the low yields that hindered the determination of absolute stereochemistry, we attempted to boost the production of
Switchable molecular tweezers: design and applications
Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45
- an achiral diamine (1,12-diaminododecane or DAD) that binds to both Zn–porphyrins and sets them further apart, a higher CD signal intensity is obtained making it a sensitive probe for determining the absolute stereochemistry of chiral carboxylates directly, without the need for derivatization. More
A new analog of dihydroxybenzoic acid from Saccharopolyspora sp. KR21-0001
Beilstein J. Org. Chem. 2024, 20, 497–503, doi:10.3762/bjoc.20.44
- the presence of a new compound designated KR21-0001A (1). The structure was elucidated by NMR, and the absolute stereochemistry was determined by advanced Marfey’s method. The results indicated that 1 is a new analog of dihydroxybenzoic acid. 1 has no antimicrobial activity against bacteria and fungi
Discovery of unguisin J, a new cyclic peptide from Aspergillus heteromorphus CBS 117.55, and phylogeny-based bioinformatic analysis of UngA NRPS domains
Beilstein J. Org. Chem. 2024, 20, 321–330, doi:10.3762/bjoc.20.32
- – unguisin J (1) – along with known unguisin B (2) were isolated from a solid culture of Aspergillus heteromorphus CBS 117.55. The structure of compound 1 was elucidated by extensive 1D and 2D NMR spectroscopic analysis including HSQC, HMBC, COSY, and 2D NOESY as well as HRESIMS. The stereochemistry of 1 and
Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3H-indoles
Beilstein J. Org. Chem. 2024, 20, 205–211, doi:10.3762/bjoc.20.20
- obtained in 98% yield with 20% ee after 12 h (Table 1, entry 1). Then, the effect of steric hindrance of the CPA catalyst and solvents on the stereochemistry of this transfer hydrogenation were investigated in detail. Among various 3,3’-disubstituted CPA catalysts (Table 1, entries 2–6), chiral phosphoric
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