Developing 13C NMR quantitative spectrometric data-activity relationship (QSDAR) models of steroid binding to the corticosteroid binding globulin

We have developed four quantitative spectrometric data-activity relationship (QSDAR) models for 30 steroids binding to corticosteroid binding globulin, based on comparative spectral analysis (CoSA) of simulated ¹³C nuclear magnetic resonance (NMR) data. A QSDAR model based on 3 spectral bins had an explained variance (r ²) of 0.80 and a cross-validated variance (q ²) of 0.78. Another QSDAR model using the 3 atoms from the comparative structurally assigned spectral analysis (CoSASA) of simulated ¹³C NMR on a steroid backbone template gave an explained variance (r ²) of 0.80 and a cross-validated variance (q ²) of 0.73. Positions 3 and 14 from the steroid backbone template have correlations with the relative binding activity to corticosteroid binding globulin that are greater than 0.52. The explained correlation and cross-validated correlation of these QSDAR models are as good as previously published quantitative structure-activity relationship (QSAR), self-organizing map (SOM) and electrotopological state (E-state) models. One reason that the cross-validated variance of QSDAR models were as good as the other models is that simulated ¹³C NMR spectral data are more accurate than the errors introduced by the assumptions and approximations used in calculated electrostatic potentials, E-states, HE-states, and the molecular alignment process of QSAR modeling. The QSDAR models developed provide a rapid, simple way to predict the binding activity of a steroid to corticosteroid binding globulin.     

Glycosides of marine invertebrates. VIII. Steroid glycosides of the holothurianIsostichopus badionotus

The steroid glycoside fraction ofIsostichopus badionotus, consisting of a mixture of D-xylosides of steroid alcohols, has been isolated by column chromatography on silica gel. The mixture of aglycones obtained after acid hydrolysis was separated with the aid of argentation chromatography into several fractions. GLC-MS analysis, and also the use of IR and¹³C NMR spectroscopy has shown that the steroid glycosides ofI. badionotus are xylosides of Δ⁰-, Δ⁷-, Δ²²-, and Δ^7.22-, C₂₇-, C₂₈-, and C₂₉-steroids of the cholestane series.     

Synthesis and Study of Equilenin Derivatives and Modified Analogs

Modified equilenin analogs were synthesized with a view to examine the relation between the structure and biological properties of steroid estrogens. The ¹H and ¹³C NMR signals of six estra-1,3,5,7,9-pentaenes were completely assigned using homo- and heteronuclear correlation NMR spectroscopy. The structure of equilenin methyl ester was determined by X-ray analysis. Among the synthesized steroids, compounds were found which exhibit hypocholesterinemic activity with no uterotropic and hypertriglyceridemic effects.     

Chemical constituents from the roots of <Emphasis Type="Italic">Polygonum bistorta</Emphasis>

Investigation of the roots of Polygonum bistorta L. afforded seven compounds including five triterpenoids, a coumarin, and a steroid, the structures of which were identified by EIMS, ¹H NMR, ¹³C NMR, DEPT, and HMBC experiments. All the compounds have been isolated from Polygonum genus for the first time. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 463–465, September–October, 2007.     

An NMR study of cyclodextrin complexes of the steroidal neuromuscular blocker drug Rocuronium Bromide

The interaction of Rocuronium Bromide, and a model steroid Org 7402, with three cyclodextrins (β‐cyclodextrin, γ‐cyclodextrin and Org 25969) was studied by solution state NMR experiments. Stoichiometries and binding constants were determined from ¹H chemical shift titrations. All of the systems formed 1 : 1 complexes. Most of the complexes were in fast exchange with unbound species on the NMR time scale, but the most tightly bound complex (Rocuronium Bromide–Org 25969) was in the slow exchange regime. The geometry of the complexes was inferred from ¹H and ¹³C NMR shift changes upon complexation and from intramolecular NOE correlations. Rocuronium Bromide forms a weak complex with β‐cyclodextrin (K_a = 3.3 ± 0.5 × 10³ M ^?1) and no clear picture of the structure of the complex emerges. The complexes with γ‐cyclodextrin (K_a = 1.8 ± 0.2 × 10⁴ M ^?1) and Org 25969 (K_a > 10⁵ M ^?1) are true inclusion complexes with the steroid located inside the central void of the cyclodextrin. Copyright © 2002 John Wiley & Sons, Ltd.     

New steroid‐group‐containing borazine compounds and their 13C NMR spectra

New borazine compounds containing steroid units (cholesteryl and stigmasteryl) were prepared by the reactions of B,B′,B″‐trichloro‐N,N′,N″‐trimethylborazine with the 3‐chloro derivatives of the corresponding steroids under Grignard conditions. The products were characterized by ¹³C–¹H correlation NMR measurements to give fully assigned ¹³C NMR data. Copyright © 2001 John Wiley & Sons, Ltd.     

Pregnane‐Based Steroids from a Formosan Gorgonian Subergorgia Mollis

A new steroid, 11α, 15α‐diacetoxy‐17α‐pregna‐4,20‐dien‐3‐one ( 1 ), and a known one, 17α‐pregna‐4,20‐dien‐3‐one ( 2 ), have been isolated from a Formosan gorgonian Subergorgia mollis. The structures of both compounds were determined on the basis of extensive NMR experiments, including HMQC, HMBC, ¹H‐¹H COSY and NOESY. Metabolite 2 has not been isolated from a natural source before. The detailed ¹H and ¹³C NMR spectral data of 2 are reported for the first time.     

The Role of Temperature in Enantioseparation of Norgestrel with Native Cyclodextrins: A Combined LC and NMR Study

Temperature dependence (10–50 °C) of the chiral LC separation of norgestrel was studied using native CDs added to a methanol–water 1:1 eluent. α- or β-CDs gave no enantiodiscrimination, while baseline LC separation was achieved with γ-CD. ¹H NMR titrations of the racemate with α-CD showed only weak complexation, while β- or γ-CDs caused enantiomeric splitting of the steroid signals. Both the chiral selectivity values and their insignificant temperature dependence measured in the γ-CD-modified LC system were successfully reproduced by NMR titrations. This agreement corroborates the intuitive view for a wider temperature range that the stability difference of the diastereomeric γ-CD/steroid complexes governs this LC enantioseparation.     

Structure of a new steroid 24<Emphasis Type="Italic">S</Emphasis>-ergost-4-en-3,6-dione from <Emphasis Type="Italic">Aconitum septentrionale</Emphasis>

β-Sitosterol and the new phytosteroid 24S-ergost-4-en-3,6-dione were isolated from the industrial extraction waste of the alkaloid-bearing plant Aconitum septentrionale Koelle. The structure of the isolated compound was determined by x-ray structure analysis and PMR, ¹³C NMR, and IR spectroscopy. The crystal structure of the steroid contains a disordered terminal 24-methyl,24-isopropyl group that occupies two positions in a 0.55:0.45 ratio.     

Steroid template associated peptides: design, synthesis and 2D NMR characterization of a novel protected 18-Phe,19-Gly-containing steroidal compound

We report herein the synthesis of a novel modified steroid with two rigidly positioned amino acids in C- and N-protected forms (Gly-O^tBu and N-Fmoc-l-Phe) at the angular positions (C-18 methylamino group and C-19 carboxylic function) of the steroid nucleus via amide bonds, starting from 18-cyanopregnenolone acetate over 10 steps. In an attempt to gain more insight into the structural and conformational features of this novel 18-Phe,19-Gly-containing steroidal compound, we describe the detailed 2D NMR spectral analysis. Despite the large size and the conformational flexibility of the amino acid units in this molecule, conformational analysis by NOESY connectivities showed the existence of mainly one conformation (∼95%) in CDCl₃ solution with approximately parallel orientation of the phenylalanine and glycine moieties.     

Design and Synthesis of New Bile AcidSterol Conjugates Linked via 1,2,3‐Triazole Ring

A new steroid conjugates have been obtained from bile acids and sterol derivatives using ‘click chemistry’. Intermolecular 1,3‐dipolar cycloaddition of the propargyl ester of bile acids (lithocholic, deoxycholic, and cholic acid) and azide derivatives of sterols (ergosterol and cholesterol) gave a new bile acid? sterol conjugates linked with a 1,2,3‐triazole ring. The structures of all products were confirmed by spectroscopic (¹H‐ and ¹³C‐NMR, and FT‐IR) analyses, mass spectrometry (ESI‐MS), and in silico biological activity evaluation methods (PASS), as well as PM5 semiempirical methods.     

A Study of b-Cyclodextrin Inclusion Complexes with Progesterone and Hydrocortisone Using Rotating Frame Overhauser Spectroscopy

Summary.  Inclusion complexes of β-cyclodextrin with two steroid derivatives, progesterone (pregn-4-ene-3,20-dione) and hydrocortisone (11,17,21-trihydroxy-pregn-4-ene-3,20-dione), were studied in the liquid state by NMR spectroscopy. The complex formation process was monitored by intermolecular dipolar interactions between ¹H signals in the hydrophobic β-cyclodextrin cavity (H-3 and H-5 of the α-glucose units) and the steroid moiety in ROESY spectra. The data revealed that progesterone is fully immersed in the β-cyclodextrin cavity; however, complete inclusion of the hydrocortisone molecule was prevented by the polar hydroxyl groups on its surface. Received April 26, 2001. Accepted (revised) May 18, 2001     

Thermodynamics of the interaction of γ-cyclodextrin and tauro- and glyco-conjugated bile salts

The structural differences in the interaction between natural γ-cyclodextrin and bile salts common in rat, dog and man was were investigated by ¹H-ROESY and ¹³C NMR and molecular modeling and the thermodynamic parameters of the reaction by isothermal titration calorimetry. The γ-cyclodextrin was selected based upon its frequent use in drug formulation as excipients to facilitate the solubilisation of drug substances with low aqueous solubility upon oral administration. The NMR studies and the molecular modeling demonstrated an interaction with inclusion of the C-ring of the steroid body of the bile salt and partly inclusion of the B and D ring. A large variation was observed in the stability constants among the investigated bile salt. The variations in the enthalpic and entropic contributions to the overall Gibbs free energy and consequently the stability constants revealed structural differences between the bile salts, where bile salts with a hydroxyl group on C12 has a weaker interaction than the bile salts without the hydroxyl group. Based upon the theoretical calculations of the available surface area the differences observed in the entropic contribution seems to be mainly driven by dehydration effects.     

Glycosides of marine invertebrates. VIII. Steroid glycosides of the holothurianIsostichopus badionotus

The steroid glycoside fraction ofIsostichopus badionotus, consisting of a mixture of D-xylosides of steroid alcohols, has been isolated by column chromatography on silica gel. The mixture of aglycones obtained after acid hydrolysis was separated with the aid of argentation chromatography into several fractions. GLC-MS analysis, and also the use of IR and¹³C NMR spectroscopy has shown that the steroid glycosides ofI. badionotus are xylosides of ⁰-, ⁷-, ²²-, and ^7.22-, C₂₇-, C₂₈-, and C₂₉-steroids of the cholestane series.Pacific Ocean Institute of Bioorganic Chemistry of the Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. National Institute of Oncology and Radiobiology of the Ministry of Public Health of the Republic of Cuba, Havana. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 799–802, November–December, 1979.     

Mass Spectrometry Combinations for Structural Characterization of Sulfated-Steroid Metabolites

Steroid conjugates, which often occur as metabolites, are challenging to characterize. One application is female-mouse urine, where steroid conjugates serve as important ligands for the pheromone-sensing neurons. Although the two with the highest abundance in mouse urine were previously characterized with mass spectrometry (MS) and NMR to be sulfated steroids, many more exist but remain structurally unresolved. Given that their physical and chemical properties are similar, they are likely to have a sulfated steroid ring structure. Because these compounds occur in trace amounts in mouse urine and elsewhere, their characterization by NMR will be difficult. Thus, MS methods become the primary approach for determining structure. Here, we show that a combination of MS tools is effective for determining the structures of sulfated steroids. Using 4-pregnene analogs, we explored high-resolving power MS (HR-MS) to determine chemical formulae; HD exchange MS (HDX-MS) to determine number of active, exchangeable hydrogens (e.g., OH groups); methoxyamine hydrochloride (MOX) derivatization MS, or reactive desorption electrospray ionization with hydroxylamine to determine the number of carbonyl groups; and tandem MS (MSⁿ), high-resolution tandem MS (HRMS/MS), and GC-MS to obtain structural details of the steroid ring. From the fragmentation studies, we deduced three major fragmentation rules for this class of sulfated steroids. We also show that a combined MS approach is effective for determining structure of steroid metabolites, with important implications for targeted metabolomics in general and for the study of mouse social communication in particular.

Nanodimer cyclodextrin ligands with high affinity to steroids

Molecular-imprinting by cross-linking of ligands of ??-cyclodextrin (CD) complex with steroids has been developed for the synthesis of tailor-made CD dimer. Steroids of androstane (9??-hydroxy-androst-4-en-3,17-dione, androst-4-en-3,17-dione, androsta-1,4-dien-3,17-dione (ADD)) and pregnane (hydrocortisone, 6-methyl-hydrocortisone, 20-hydroxymethylpregna-1,4-diene-3-one (HMPD)) series were used as template molecules. For imprinting procedure, crystalline ??-CD complexes of exact stoichiometry (??-CD:steroid template = 2:1) were synthesized following by toluene 2,4-diisocyanate (TDI) cross-linking. The attempts to produce CD dimer for steroid without hydrophobic side chain failed, while tailor-made CD dimer has been obtained using HMPD as a template. The dimer was characterized by ¹H NMR and mass-spectrometry. The complex stability constant (K_S) towards HMPD template exceeded 10⁷ M^?1. The K_S of CD dimer with ADD exceeded the corresponded value of TDI-modified CD monomer by more than an order of magnitude. The dimer was applied for quantitative extraction of ADD from aqueous solution using dialysis membranes impermeable for CD. The value of K_S for ADD estimated from balanced concentrations of dialysis data corresponded to that calculated by nonlinear spectrometric method.     

Synthesis of novel steroidal oxazolo quinoxaline as antibacterial agents

Steroidal[oxazolo(4,5-b)quinoxaline-2-yl-hydrazone] derivative (7a–9a) (7b–9b) were prepared by the multi-step reactions of steroid. It is prepared via the reaction of steroidal semicarbazones with 2,3-dichloroquinoxaline at 80 °C in ethanol. The structures of the compounds were evident by IR, ¹H NMR and mass spectrometry and their purities were confirmed by elemental analyses. The antibacterial activity of these compounds was evaluated by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria and then the minimum inhibitory concentration (MIC) of compounds was determined. The results showed that compounds (7a, 7b, 8a, 8b) are better antibacterial agent as compared with the standard drug amoxicillin.     

Thermodynamics of complexation of tauro- and glyco-conjugated bile salts with two modified ��-cyclodextrins

The interaction between two modified ??-cyclodextrins and bile salts, common for rat, dog and man, was studied using isothermal titration calorimetry. The structural differences in the interaction were investigated by ¹³C NMR. The two modified ??-cyclodextrins were chosen because of their frequent use as oral excipients in drug formulation and in marketed products. All the investigated bile salts had an affinity for the ??-cyclodextrins, although there were large variations in the stability constants. The variations in the enthalpic and entropic contributions to the overall Gibbs free energy revealed differences in the binding mode to the investigated bile salts, i.e. the bile salts with a hydroxyl group at C12 interacted differently than bile salts without this hydroxyl group. These observations were supported by ¹³C NMR, which suggested binding to the D-ring of the steroid structure for bile salts with a hydroxyl group at C12 and to the C-ring for the bile salts without this hydroxyl group. The type of substitution of ??-cyclodextrin had significant effects on the thermodynamics of the interaction where especially the entropic changed were affected.     

Synthesis and Spectroscopic Characterization of Silver(I) Complexes of Selenones

Silver(I) complexes of selenones, [LAgNO₃] and [AgL₂]NO₃ (where L is imidazolidine-2-selenone or diazinane-2-selenone and their derivatives) have been prepared and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ¹⁰⁷Ag) spectroscopy. An upfield shift in the C=Se resonance of selenones in ¹³C NMR and a downfield shift in N-H resonance in ¹H NMR are consistent with selenium coordination to silver(I). In ¹⁰⁷Ag NMR, the AgNO₃signal is deshielded by 450-650 ppm on coordination to selenones. Greater upfield shifts in ¹³C NMR were observed for [LAgNO₃] compared to [AgL₂]NO₃complexes, whereas the opposite trend was observed for ¹H and¹⁰⁷Ag NMR chemical shifts.     

Phosphorus Derivatives of Natural Lactones. Synthesis of New Grosshemin Dialkylphosphonates

New phosphorus-containing derivatives of grosshemin were synthesized in 68-70% yield by reacting this guaianolide with dialkylphosphites. Their structures were established by IR, PMR, ¹³C NMR, and ³¹P NMR spectroscopies and two-dimensional ¹H-¹H NMR spectroscopy (COSY). The reaction of grosshemin with dialkylphosphites was found to be highly stereoselective.