Search

Background: The fractionation of the n-hexane phase of the EtOH extract from the leaves of Duguetia lanceolata (Annonaceae) led to the identification of the sesquiterpene (–)-cyclocolorenone. Objective: Chemical characterization, including determination of the absolute stereochemistry, and in vitro evaluation of antileishmanial activity of the sesquiterpene (–)-cyclocolorenone, isolated from D. lanceolata, were carried out. Methods: (–)-Cyclocolorenone was isolated from D. lanceolata leaves using different chromato-graphic steps and its structure was defined by analysis of NMR and ESI-HRMS data. Additionally, the absolute configuration of (–)-cyclocolorenone was ambiguously assigned by means of vibra-tional circular dichroism (VCD). Antileishmanial activity of (–)-cyclocolorenone was evaluated on promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. The integrity of the cell membrane of L. (L.) amazonensis was analyzed using the SYTOX green probe. Results: (–)-(1R,6S,7R,10R)-Cyclocolorenone displayed activity against promastigotes and amastigotes forms of L. (L.) amazonensis with IC50 of 4.54 and 28.44 , respectively. Further-more, this compound was non-toxic in J774 macrophage cells (CC50 > 458.71 ) with a selectivi-ty index > 100 (promastigotes) and > 32.2 (amastigotes). Additionally, (–)-cyclocolorenone was ob-served to target the parasite cell membrane. Conclusion: Obtained data suggested that (–)-cyclocolorenone, in which absolute configuration was determined, can be considered as a scaffold for the development of new drugs for the treatment of leishmaniasis.

The determination of the absolute configuration of chiral bioactive natural products is a crucial step in their structural characterization. Several well-established techniques, such as X-ray crystallography, stereo-controlled organic synthesis, NMR, and chiroptical spectroscopy, are commonly used to this end. However, even today, the configurational analysis of natural products remains a challenge, with a significant number of reassignments being reported every year. Among chiroptical methods, vibrational circular dichroism (VCD) has emerged as an excellent tool for the assignment of the absolute configuration of structurally diverse chiral natural products directly in solution. This review covers the use of VCD spectroscopy to elucidate the absolute stereochemistry of natural products in Brazil over the last 20 years. Although the number of VCD investigations on secondary metabolites has increased, VCD can still be considered under-explored in Brazil. Therefore, herein, we aim to demonstrate the unparalleled stereochemical discriminatory power of VCD to assign both conformation and absolute configuration of natural products in conditions not commonly accessible to other techniques.

Twigs of Nectandra barbellata were extracted using a solution of the ionic liquid 1-butyl-3-methylimidazolium bromide (BMImBr) in H2O, assisted by microwave (MAE). After successive chromatographic steps, one sesquiterpene, costic acid, and three new related lactones, (R)-3(7)-Z-3-hexadec-21-enylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (1), (R)-3(7)-Z-3-hexadecylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (2), and (R)-3(7)-Z-3-docosylidene-5-(hydroxymethyl)tetrahydrofuran-2-one (3), were isolated. After structural elucidation using IR, UV, HRESIMS, NMR, ECD, and VCD, compounds 1-3 were tested against trypomastigote forms of Trypanosoma cruzi. The mechanism of action of bioactive isolated compounds was studied using different fluorescent-based approaches to investigate alterations of the plasma membrane, permeability/electric potential (ΔΨp), reactive oxygen species levels, mitochondria (electric membrane potential, ΔΨm/ATP levels), Ca2+ levels, and pH of the acidocalcisomes. In addition, in silico studies predicted no resemblance to pan assay interference compounds (PAINS).

Five new neocassane-like diterpenes (1-5) were isolated from the roots of Eragrostis plana. Their structures were elucidated by spectroscopic data, and the absolute configurations of the representative compounds neocassa-12(17),15-dien-3-one (2) and neocassa-12(13),15-diene-3,14-dione (5) were assigned by vibrational circular dichroism. The phytotoxic activity of compounds 3, 4, and 5 was evaluated against the germination and growth of Ipomoea grandifolia and Euphorbia heterophylla. Compound 4 exhibited the most potent activity for growth variables, resulting in the smallest radicle length of I. grandifolia and in the smallest aerial part length of E. heterophylla. Compound 5 reduced the germination speed index more effectively than the herbicide glyphosate (Roundup).

The fractionation of the n-hexane phase of the EtOH extract from the leaves of Duguetia lanceolata (Annonaceae) led to the identification of the sesquiterpene (-)-cyclocolorenone.Chemical characterization, including determination of the absolute stereochemistry, and in vitro evaluation of antileishmanial activity of the sesquiterpene (-)-cyclocolorenone, isolated from D. lanceolata, were carried out.(-)-Cyclocolorenone was isolated from D. lanceolata leaves using different chromatographic steps and its structure was defined by analysis of NMR and ESI-HRMS data. Additionally, the absolute configuration of (-)-cyclocolorenone was ambiguously assigned by means of vibrational circular dichroism (VCD). Antileishmanial activity of (-)-cyclocolorenone was evaluated on promastigote and amastigote forms of Leishmania (Leishmania) amazonensis. The integrity of the cell membrane of L. (L.) amazonensis was analyzed using the SYTOX green probe.(-)-(1R,6S,7R,10R)-Cyclocolorenone displayed activity against promastigotes and amastigotes forms of L. (L.) amazonensis with ICObtained data suggested that (-)-cyclocolorenone, in which absolute configuration was determined, can be considered as a scaffold for the development of new drugs for the treatment of leishmaniasis.

Microbial strains isolated from extreme and understudied environments, such as caves, are still poorly investigated for the production of bioactive secondary metabolites. Investigation of the ethyl acetate extract from the growth medium produced by the soil-derived fungus Aspergillus sp. SDC28, isolated from a Brazilian cave, yielded two anthraquinones: versicolorin C (1) and versiconol (2). The complete assignment of nuclear magnetic resonance and mass spectroscopic data of 1 and 2 was performed for the first time. Moreover, the yet unreported absolute configuration of both compounds was unambiguously established by analysis of experimental and theoretical electronic circular dichroism data. Vibrational circular dichroism was also applied to confirm the absolute stereochemistry of 2. Compounds 1 and 2 showed cytotoxic activity against human ovarian cancer cells (OVCAR3).

Incorporation of the epigenetic modifier suberoylanilide hydroxamic acid (SAHA) into a potato dextrose broth culture of the endophytic fungus Aspergillus sp. AST0006 affected its polyketide biosynthetic pathway providing two new 3-(4-oxopyrano)-chromen-2-ones, aspyranochromenones A (1) and B (2), and the isocoumarin, (−)-6,7-dihydroxymellein (3). Eight additional metabolites (4–11) and two biotransformation products of SAHA (12–13) were also encountered. The planar structures and relative configurations of the new metabolites 1–2 were elucidated with the help of high-resolution mass, 1D and 2D NMR spectroscopic data and the absolute configurations of 1–3 were determined by comparison of experimental and calculated ECD data. Possible biosynthetic pathways to 1 and 2 are presented.

Three undescribed germacranolide sesquiterpene lactones, named macrocephalides A-C, along with known steroids, triterpenes and flavonoids were isolated from the aerial parts of Campuloclinium macrocephalum. The structures of the undescribed compounds were elucidated with basis on their 1D and 2D-NMR, and HR-ESI-MS data. Their absolute configurations were assigned by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Additionally, macrocephalides A-C were evaluated for their in vitro cytotoxic activities against nine human cancer cell lines. Macrocephalides A and B exhibited moderate to potent cytotoxic activity, inhibiting 50% of cell growth (GI50) at concentrations ranging from 0.576 to 6.37 μM.

Five new neocassane-like diterpenes (

Stereochemical determinations based solely on the comparison of optical rotation (OR) measured at a single wavelength may commonly result in misassignments. Herein, we use vibrational and electronic CD, NMR, OR, and DFT calculations, to confirm the absolute configuration (AC) of the cytotoxic marine polyketides spongosoritin A (1) and 9,10-dihydrospongosoritin A (2) as (-)-(6R,8R) and (-)-(6R,8S), respectively. The AC of natural 1 and 2 has so far relied upon comparisons of OR values only. Besides showing the dependence of OR on achiral structural features, such as E/Z double bond geometries, an IR spectral marker is provided to help distinguish the geometric isomers of related molecules.

This work describes the chromatographic fractionation of the aerial parts of Calea pinnatifida and the structural characterization and determination of the absolute configuration of the isolated compounds as well as their antitumor potential. The HPLC fractionation of the CH2Cl2 phase of the MeOH extract from the leaves of C. pinnatifida led to the isolation of two related sesquiterpene lactones (STLs): calein C (1) and calealactone B (2). Additionally, during the purification process, a derivative of calein C (3) was formed as a product of the Michael addition of MeOH. The structures of Compounds 1–3 were established based on spectroscopic and spectrometric data, while the absolute stereochemistry was established by vibrational circular dichroism. In order to evaluate the effect of the conjugated double bonds on the cytotoxic activity of STLs, Compounds 1–3 were tested against anaplastic (KTC-2) and papillary (TPC-1) thyroid carcinoma cells. Calein C was the most active of the STLs, and displayed activity against both KTC-2 and TPC-1. On the other hand, the calein C derivative (3) was the least cytotoxic of all the compounds tested. These results are promising and suggest the importance of studying sesquiterpene lactones isolated from C. pinnatifida in terms of antitumor activity, especially considering the effects of α,β-unsaturated carbonyl systems.

The phytochemical study of Hippeastrum goianum led to the identification of 13 compounds by means of gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR). Compounds 7-demethoxy-9-O-methylhostasine (1) and 7-deoxi-trans-dihydronarciclasine (2) had their absolute configurations determined by vibrational circular dichroism (VCD). This is the first time that compound 1 is described in the Amaryllidaceae family. The cytotoxicity of all isolated compounds was tested against colorectal carcinoma (HCT 116), breast carcinoma (MCF-7), and non-tumor human retinal pigment epithelium (RPE) cell lines. The half-maximum inhibitory concentration (IC50) of compound 2 against each cell line was equivalent to the positive control (doxorubicin), indicating a considerable cytotoxic activity. Keywords: narciclasine; galasine; cytotoxic activity; absolute configuration; vibrational circular dichroism

Made available in DSpace on 2020-12-11T10:26:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-03-01 INCT Program [INCT-BioNat] Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Centre for Scientific Computing (NCC/GridUNESP) of Sao Paulo State University (UNESP) Ethnopharmacological relevance: Croton floribundus Spreng. (Euphorbiaceae), popularly known as Capixingui, stands out due to its widespread use in traditional medicine to treat wounds, syphilis, hemorrhoids, eye diseases and as a purgative. Aim of the study: To characterize clerodanes diterpenes from C. floribundus and to evaluate the effects of the fraction and diterpenes (1-5) on inhibition of nitrite production. Materials and methods: The hydroethanolic root extract of C. floribundus was fractionated on a solid phase extraction column to obtain the fraction named Fr80%. From this, five compounds were obtained and characterized. The absolute configuration of compound 1 was determined by a combination of electronic and vibrational circular dichroism spectroscopies. Additionally, compounds 1-5 were evaluated for their inhibitory effects on nitrite production induced by lipopolysaccharide (LPS) in RAW 264 macrophage cell. Results: Five clerodane diterpenoids were characterized, and the absolute stereochemistry of 1 was established as 3R,4R,5R,8R,9R,10S,12S. The IC50 values obtained through inhibition of nitrite production were 28.52 +/- 2.21 mu M (1), 40.26 +/- 2.79 mu M (2), 25.47 +/- 2.16 mu M (3), 35.78 +/- 2.93 mu M (4) and 40.58 +/- 4.78 mu M (5). In the tested concentrations, the samples presented low toxicity in macrophages. Conclusions: Four new diterpenes were characterized from C. floribundus, these being croflorins A-D (1-4) and a known halimane (5). These compounds exhibited inhibitory effect on nitrite production. Sao Paulo State Univ, Inst Chem, BR-14800060 Araraquara, SP, Brazil Fluminense Fed Univ, Inst Chem, BR-24020141 Niteroi, RJ, Brazil Univ Fed Sao Paulo, Inst Sci & Technol, BR-12231280 Sao Jose Dos Campos, SP, Brazil Sao Paulo State Univ, Sch Pharmaceut Sci, BR-01049010 Araraquara, SP, Brazil Sao Paulo State Univ, Inst Chem, BR-14800060 Araraquara, SP, Brazil Sao Paulo State Univ, Sch Pharmaceut Sci, BR-01049010 Araraquara, SP, Brazil INCT Program [INCT-BioNat]: 465637/2014-0 INCT Program [INCT-BioNat]: 2014/50926-0 FAPESP: 2013/07600-3 FAPESP: 2014/25222-9 FAPESP: 2017/19870-6 CAPES: 001 CAPES: 88887.313278/2019-00 CNPq: 142286/2016-8 CNPq: 142014/2018-4 FAPESP: 2017/17098-4 FAPESP: 2019/04381-5 FAPESP: 2017/18807-9

Made available in DSpace on 2021-06-25T11:23:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-10-23 National Institutes of Health Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) College of Agriculture & Life Sciences of the University of Arizona Center for Scientific Computing (NCC/GridUNESP) of Sa eo Paulo State University (UNESP) Incorporation of the epigenetic modifier suberoylanilide hydroxamic acid (SAHA) into a potato dextrose broth culture of the endophytic fungus Aspergillus sp. AST0006 affected its polyketide biosynthetic pathway providing two new 3-(4-oxopyrano)-chromen-2-ones, aspyranochromenones A (1) and B (2), and the isocoumarin, (-)-6,7-dihydroxymellein (3). Eight additional metabolites (4-11) and two biotransformation products of SAHA (12-13) were also encountered. The planar structures and relative configurations of the new metabolites 1-2 were elucidated with the help of high-resolution mass, 1D and 2D NMR spectroscopic data and the absolute configurations of 1-3 were determined by comparison of experimental and calculated ECD data. Possible biosynthetic pathways to 1 and 2 are presented. (C) 2020 Elsevier Ltd. All rights reserved. Univ Arizona, Coll Agr & Life Sci, Southwest Ctr Nat Prod Res, Sch Nat Resources & Environm, 250 E Valencia Rd, Tucson, AZ 85706 USA Sao Paulo State Univ, Inst Chem, BR-14800900 Araraquara, SP, Brazil Jiangsu Normal Univ, Key Lab Biotechnol Med Plants Jiangsu Prov, 101 Shanghai Rd, Xuzhou 221116, Jiangsu, Peoples R China Univ Arizona, Coll Agr & Life Sci, Sch Plant Sci, Tucson, AZ 85721 USA Fluminense Fed Univ, Chem Inst, Dept Organ Chem, BR-24020141 Niteroi, RJ, Brazil Univ Fed Sao Paulo, Inst Sci & Technol, BR-12231280 Sao Jose Dos Campos, SP, Brazil Sao Paulo State Univ, Inst Chem, BR-14800900 Araraquara, SP, Brazil National Institutes of Health: R01 CA90265 National Institutes of Health: P41 GM094060 FAPESP: 2018/05905-5 FAPESP: 2014/25222-9

Peperomia obtusifolia, an ornamental plant from the Piperaceae family, accumulates a series of secondary metabolites with interesting biological properties. From a biosynthesis standpoint, this species produces several benzopyrans derived from orsellinic acid, which is a polyketide typically found in fungi. Additionally, the chiral benzopyrans were reported as racemic and/or as diastereomeric mixtures, which raises questions about the level of enzymatic control in the cyclization step for the formation of the 3,4-dihydro-2H-pyran moiety. Therefore, this article describes the use of shotgun proteomic and transcriptome studies as well as phytochemical profiling for the characterization of the main biosynthesis pathways active in P. obtusifolia. This combined approach resulted in the identification of a series of proteins involved in its secondary metabolism, including tocopherol cyclase and prenyltransferases. The activity of these enzymes was supported by the phytochemical profiling performed in different organs of P. obtusifolia. However, the polyketide synthases possibly involved in the production of orsellinic acid could not be identified, suggesting that orsellinic acid may be produced by endophytes intimately associated with the plant. Fil: Batista, Andrea N. L.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Dos Santos Pinto, José Roberto A.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Batista, Joao M.. Universidade Federal do São Carlos; Brasil Fil: Souza Moreira, Tatiana M.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Santoni, Mariana M.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Zanelli, Cleslei F.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Kato, Massuo J.. Universidade de Sao Paulo; Brasil Fil: López, Silvia Noelí. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Departamento de Química Orgánica. Área Farmacognosia; Argentina Fil: Palma, Mario S.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Furlan, Maysa. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil

Recent Raman and Raman optical activity (ROA) results have demonstrated that dimethyl sulfoxide (DMSO) induces the selective conversion of α-helix motifs into the poly(L-proline) II (PPII) helix conformation in an array of proteins, while β-sheets remain mostly unaffected. Human serum albumin (HSA), a highly α-helical protein, underwent the most dramatic changes and, therefore, was selected as a model for further investigations into the mechanism of this conformational change. Herein we report the use of two-dimensional ROA correlation analysis applying synchronous, autocorrelation, and moving windows approaches in order to understand the conformational transitions in HSA as a function of DMSO concentration. Our results indicate that the destabilization of native α-helix starts at DMSO concentrations as little as 20% in water (v/v), with the transition to PPII helix being complete at ~80% DMSO. These results clearly indicate that any protein preparation containing relatively low concentrations of DMSO should consider possible disruptions in α-helical domains.

A reinvestigation of the monoterpene chromane ester enriched fraction from Peperomia obtusifolia usingchiral chromatography led to the identification of a minor peak, which was elucidated by NMR and HRMSas fenchyl-3,4-dihydro-5-hydroxy-2,7-dimethyl-8-(3 00 -methyl-2 00 -butenyl)-2-(4 0 -methyl-1 0 ,3 0 -pentadie-nyl)-2H-1-benzopyran-6-carboxylate, the same structure assigned to two other fenchyl esters describedpreviously, pointing out a stereoisomeric relationship among them. Further NMR analysis revealed that itwas actually a mixture of two compounds, whose absolute configurations were determined by VCD mea-surements. Although, almost no vibrational transitions could be assigned to the chiral chromane, theexperimental VCD spectrum was largely opposite to that obtained for the average experimental VCD[(2S,1 000 R,2 000 R,4 000 S +2R,1 000 R,2 000 R,4 000 S)/2] for fenchol derivatives. These results allowed us to assign theputa-tive compounds as a racemic mixture of the chiral chromane esterified with the monoterpene (1S,2S,4R)-fenchol, which had not been identified in our early work. 2012 Elsevier Ltd. All rights reserved.

Gaudichaudianic acid, a prenylated chromene isolated from Piper gaudichaudianum, has been described as a potent trypanocidal compound against the Y-strain of Trypanosoma cruzi. We herein describe its isolation as a racemic mixture followed by enantiomeric resolution using chiral HPLC and determination of the absolute configuration of the enantiomers as (+)-S and (-)-R by means of a combination of electronic and vibrational circular dichroism using density functional theory calculations. Investigation of the EtOAc extract of the roots, stems, and leaves from both adult specimens and seedlings of P. gaudichaudianum revealed that gaudichaudianic acid is biosynthesized as a racemic mixture from the seedling stage onward. Moreover, gaudichaudianic acid was found exclusively in the roots of seedlings, while it is present in all organs of the adult plant. Trypanocidal assays indicated that the (+)-enantiomer was more active than its antipode. Interestingly, mixtures of enantiomers showed a synergistic effect, with the racemic mixture being the most active.

Six novel monoterpene chromane esters were isolated from the aerial parts of Peperomia obtusifolia (Piperaceae) using chiral chromatography. This is the first time that chiral chromane esters of this kind, ones with a tethered chiral terpene, have been isolated in nature. Due to their structural features, it is not currently possible to assess directly their absolute stereochemistry using any of the standard classical approaches, such as X-ray crystallography, NMR, optical rotation, or electronic circular dichroism (ECD). Herein we report the absolute configuration of these molecules, involving four chiral centers, using vibrational circular dichroism (VCD) and density functional theory (DFT) (B3LYP/6-31G*) calculations. This work further reinforces the capability of VCD to determine unambiguously the absolute configuration of structurally complex molecules in solution, without crystallization or derivatization, and demonstrates the sensitivity of VCD to specify the absolute configuration for just one among a number of chiral centers. We also demonstrate the sufficiency of using the so-called inexpensive basis set 6-31G* compared to the triple-ζ basis set TZVP for absolute configuration analysis of larger molecules using VCD. Overall, this work extends our knowledge of secondary metabolites in plants and provides a straightforward way to determine the absolute configuration of complex natural products involving a chiral parent moiety combined with a chiral terpene adduct.

Previous analysis of the ECD spectra of two prenylated benzopyrans isolated from Peperomia obtusifolia, by means of the helicity rule for the chromane chromophore, resulted in the incorrect assignment of their absolute configuration, (S) instead of (R) for a deduced P-helicity of the chromane ring for the (+)-enantiomers. This was discovered by the application of DFT calculations and VCD spectroscopy. Experimental and calculated (B3LYP/6-31G(d)) VCD and IR spectra were compared, and a definitive absolute configuration of (+)-1 and (+)-2 is reassigned directly in solution as (R). The assumption of equatorial positioning of bulky groups, shown here to be invalid for the title molecules, is the underlying cause of the previous incorrect assignment of absolute configuration. Moreover, TDDFT (B3LYP/6-311++G(2d,2p)//B3LYP/6-31G(d)) calculations of ECD spectra have shown that both P- and M-helicity of the heterocyclic ring, for a given absolute configuration, lead to the same sign for the 1Lb ECD band, thus bringing into question the validity of the empirical ECD helicity rule for chromane molecules.

Phyllanthus niruri L., commonly known in Brazil as 'quebra-pedra', has long been used in the treatment of diverse diseases and especially urolithiasis. The therapeutic effects of P. niruri are attributed to various compounds present in the plant, including the hydrolysable tannin corilagin. In the present study, high-performance liquid chromatography (HPLC-/PAD) profiles of leaves and commercial extracts of P. niruri were examined and three compounds, found to be present in all of the samples studied, were isolated by open column chromatography over C18)silica gel followed by preparative HPLC. These compounds were identified by nuclear magnetic resonance as corilagin, rutin and ethyl 3,4,5-trihydroxybenzoate. Corilagin, which has been proposed as a phytochemical marker for P. niruri, was employed as an external standard in the development and validation of a rapid and efficient qualitative and quantitative HPLC assay for the analyte. The method may be applied in the standardization of herbs and phytomedicines commercialized in Brazil as quebra-pedra.

Chronic inflammation presented in rheumatoid arthritis (RA) is associated with systemic manifestations, that include micronutrient deficiency, changes in body composition and cardiac morphofunctional alterations. The aim of this study is to evaluate the association of serum vitramin D and body composition with cardiac geometric pattern in patients with RA. Methods: 30 patients with RA were submitted to clinical, nutritional and biochemical evaluation. Bioimpedance analysis and dual-energy X-ray absorptiometry (DEXA) was performed to evaluate body composition. Transthoracic dopller- echocardiography was performed to evaluate left ventricle mass and relative wall thickness (RWT) in order to find cardiac geometry patterns. Patients were divided in Normal or abnormal pattern (concentric remodeling or concentric hypertrophy.) Results: The mean age was 53±9 years; 70% were woman, 43% presented with hypertension. All patients have been treated with methotrexate and a biological agent and presented with Disease a...

Recent Raman and Raman optical activity (ROA) results have demonstrated that dimethyl sulfoxide (DMSO) induces the selective conversion of α-helix motifs into the poly(L-proline) II (PPII) helix conformation in an array of proteins, while β-sheets remain mostly unaffected. Human serum albumin (HSA), a highly α-helical protein, underwent the most dramatic changes and, therefore, was selected as a model for further investigations into the mechanism of this conformational change. Herein we report the use of two-dimensional ROA correlation analysis applying synchronous, autocorrelation, and moving windows approaches in order to understand the conformational transitions in HSA as a function of DMSO concentration. Our results indicate that the destabilization of native α-helix starts at DMSO concentrations as little as 20% in water (v/v), with the transition to PPII helix being complete at ~80% DMSO. These results clearly indicate that any protein preparation containing relatively low concentrations of DMSO should consider possible disruptions in α-helical domains.

The function of a protein is determined by its structure, which is intrinsically related to its solvent environment. Based on this paradigm, there has been a great deal of interest in the role that non-aqueous solvents play in regulating protein structure, with some debate in the literature regarding dimethyl sulfoxide (DMSO). Thus, in this work we have used Raman and Raman optical activity (ROA) spectroscopies to investigate conclusively the changes induced by DMSO in the secondary structure of an array of proteins including human serum albumin (highly α-helical), bovine α-lactalbumin (mainly α-helical), bovine ribonuclease A (containing both α-helix and β-sheet), bovine β-lactoglobulin (mainly β-sheet), and bovine α-casein (disordered). Our results clearly demonstrate that 100% DMSO solutions destabilize α-helices completely, converting them into the poly(L-proline) II (PPII) helix conformation. However, low concentrations of DMSO (10% v/v) were found to have little effect on the structure of even the most helical protein, human serum albumin. In the case of α-casein, the natively unfolded protein rich in PPII helix was converted into a further disordered structure when dissolved in pure DMSO. By contrast, β-sheets remained mostly unaffected regardless of DMSO concentration. While providing new insights into protein structure in organic solvents, this work reinforces the capability of vibrational optical activity to assess conformations of biomolecules in conditions not accessible to other techniques, such as X-ray crystallography and NMR.