Growth inhibitory effects of gossypol and related compounds on fungal cotton root pathogens.

UNLABELLED: The effect of the terpenoids gossypol, 6-methoxygossypol, 6,6'-dimethoxygossypol, gossypolone and apogossypolone on growth of fungal soil pathogens was investigated. The compounds were tested at a concentration of 100 µg ml(-1) in a Czapek Dox agar medium at 25°C. Gossypol, gossypolone and apogossypolone demonstrated strong growth inhibitory activity (≥90%) against Pythium irregulare, Pythium ultimum and Fusarium oxysporum. These same terpenoids provided good growth inhibition against most Rhizoctonia solani isolates. Methylated gossypol derivatives generally yielded reduced growth inhibition against the tested fungi compared with gossypol. Dose-response effects of gossypol, gossypolone and apogossypolone were determined over a concentration range of 5-100 µg ml(-1) against P. irregulare CR1, P. ultimum ATCC 56081 and R. solani CR15. At lower concentrations, gossypol proved to be a more potent growth inhibitor of P. irregulare (ED50  = 4 µg ml(-1) ) and P. ultimum (ED50  = 13·2 µg ml(-1) ) than the other tested compounds. Rhizoctonia solani CR15 was more resistant to growth inhibitory effects of all tested terpenoids (ED50  = 35-43 µg ml(-1) ). SIGNIFICANCE AND IMPACT OF THE STUDY: This work demonstrates that gossypol is an effective natural antimicrobial agent against a wide range of potential fungal pathogens of cotton. Relative to gossypol, methylated gossypol derivatives that are also found naturally in root tissue were less effective at inhibiting the growth of soil fungal pathogens. However, by virtue of their significant concentration in root tissue, they still may contribute to cotton defence.

Effects of temperature and medium composition on inhibitory activities of gossypol-related compounds against aflatoxigenic fungi.

AIMS: To investigate the effects of temperature and medium composition on growth/aflatoxin inhibitory activities of terpenoids gossypol, gossypolone and apogossypolone against Aspergillus flavus and A. parasiticus. METHODS AND RESULTS: The compounds were tested at a concentration of 100 µg ml(-1) in a Czapek Dox (Czapek) agar medium at 25, 31 and 37°C. Increased incubation temperature marginally increased growth inhibition caused by these compounds, but reduced the aflatoxin inhibition effected by gossypol. Gossypolone and apogossypolone retained good aflatoxin inhibitory activity against A. flavus and A. parasiticus at higher incubation temperatures. However, increased temperature also significantly reduced aflatoxin production in control cultures. The effects of the terpenoids on fungal growth and aflatoxin production against the same fungi were also determined in Czapek, Czapek with a protein/amino acid addendum and yeast extract sucrose (YES) media. Growth of these fungi in the protein-supplemented Czapek medium or in the YES medium greatly reduced the growth inhibition effects of the terpenoids. Apogossypolone displayed strong anti-aflatoxigenic activity in the Czapek medium, but this activity was significantly reduced in the protein-amended Czapek and YES media. Gossypol, which displayed little to no aflatoxin inhibitory activity in the Czapek medium, did yield significant anti-aflatoxigenic activity in the YES medium. CONCLUSIONS: Incubation temperature and media composition are important parameters involved in the regulation of aflatoxin production in A. flavus and A. parasiticus. These parameters also affect the potency of growth and aflatoxin inhibitory activities of these gossypol-related compounds against aflatoxigenic fungi. SIGNIFICANCE AND IMPACT OF THE STUDY: Studies utilizing gossypol-related compounds as inhibitory agents of biological activities should be interpreted with caution due to compound interaction with multiple components of the test system, especially serum proteins.

Effect of replacing soybean meal protein with protein from upland cottonseed, Pima cottonseed, or extruded Pima cottonseed on production of lactating dairy cows.

Pima cotton production is increasing in the United States, but Pima cottonseed generally contains higher concentrations of the antinutritive pigment gossypol than conventional upland cottonseed. Heating promotes the reaction of gossypol with protein, reducing gossypol absorption and toxicity. The objective of this study was to assess the nutritional value for dairy cattle of Pima cottonseed cake (PCSC) that was heated and oil largely removed by an experimental extrusion process, compared with upland cottonseed (UCS) and Pima cottonseed (PCS). The PCS had greater crude protein (CP) and ether extract, less neutral detergent fiber (NDF) and acid detergent fiber (ADF), similar total gossypol, but higher (-)-gossypol isomer compared with UCS. Extrusion reduced lipid content by 73%, increased concentrations of CP, NDF, and ADF, and reduced total gossypol, (+)-gossypol, and (-)-gossypol in PCSC versus PCS. Forty lactating Holsteins (8 with ruminal cannulas) were blocked by days in milk into 5 squares in a replicated, incomplete 8 × 8 Latin square, and were fed diets containing, on a dry matter (DM) basis, 30% alfalfa silage, 31% corn silage, 21 to 25% high-moisture corn, and about 15% CP. Diets were fed as total mixed rations for ad libitum intake. Supplemental CP was from (1) solvent soybean meal (SSBM) only or 50% from SSBM plus 50% from (2) UCS, (3) PCS, (4) PCSC, (5) UCS plus PCS, and (6) UCS plus PCSC, or (7) 50% from expeller soybean meal (ESBM) plus 50% from PCS, and (8) 50% from ESBM plus 50% from PCSC. Periods were 4 wk long (total of 16 wk); production data were collected over the last 2 wk and blood and ruminal samples were taken on d 28 of each period. Data were analyzed using Proc Mixed of SAS (SAS Institute Inc., Cary, NC). Diet affected dry matter intake, with greatest intake on diet 6 and lowest intake on diets 1 and 3. The highest milk fat content was observed on diet 5 and the greatest fat yield on diet 7; fat content and yield were lowest on diet 1 (soybean meal control). Milk fat secretion was proportional to dietary fat content, indicating that cottonseed oil was used effectively for milk fat synthesis. We observed a trend for an effect on milk protein yield with the greatest protein secretion occurring on diet 7. Milk urea was lowest on diets 3, 7, and 8. Ruminal concentrations of branched-chain volatile fatty acids were lower, or tended to be lower, when PCSC replaced either UCS or PCS in the diet, suggesting reduced degradation and increased escape of PCSC protein. Among cottonseed-containing diets, total gossypol intake was lowest on PCSC, intermediate on PCS, and highest on UCS. Total gossypol and both (+)- and (-)-isomers of gossypol were higher in blood plasma on PCS and lower on PCSC than on the corresponding diets containing UCS, indicating that the extrusion process reduced gossypol absorption. In this trial, production on diets supplemented with UCS, PCS, or PCSC was comparable to that on diets containing soybean meal.

Inhibitory effects of gossypol-related compounds on growth of Aspergillus flavus.

AIMS: The objective of this study was to test a series of gossypol-related compounds for growth inhibition against Aspergillus flavus. METHODS AND RESULTS: A series of chiral and achiral gossypol derivatives, some natural products of the cotton plant and others prepared by synthesis from gossypol, were incorporated into agar plates to follow the rate of A. flavus isolate AF13 colony growth. All tested compounds exhibited some growth inhibition against this organism. The synthetic compounds, gossypolone and apogossypolone, exhibited greater activity than either racemic or chiral gossypol. Methylated derivatives (i.e. 6-methoxy and 6,6'-dimethoxy derivatives) generally exhibited less activity than the nonmethylated parent compounds. The (-)-optical form of gossypol was found to be slightly more active than the (+)-optical form, and this trend was observed regardless of the presence of methoxy groups at the 6-position. Growth inhibition of gossypolone and apogossypolone was concentration dependent. For gossypolone, the 50% effective dose was 90 µg ml⁻¹ of medium (165 µmol l⁻¹). For apogossypolone, the most active compound in the study, the 50% effective dose was 19 µg ml⁻¹ (38·7 µmol l⁻¹). The presence of gossypol-related terpenoids appeared to stimulate production of A. flavus sclerotia, although replicate variability was so large that it was not possible to determine a significant correlation between the mass of sclerotia formed and compound growth inhibition. CONCLUSIONS: The quinone derivatives of gossypol, gossypolone and apogossypolone demonstrated significant fungal growth inhibitory activity against A. flavus. SIGNIFICANCE AND IMPACT OF THE STUDY: These gossypol derivatives may provide a new class of fungicide for use against the mycotoxigenic fungus A. flavus.

Relative toxicity of gossypol enantiomers in laying and broiler breeder hens.

Gossypol, a natural component of cottonseed meal, exists in positive (+) or negative (-) enantiomeric forms, and their levels and ratio could be altered by developing new genetic strains of cotton. Two experiments were conducted to determine the relative toxicity of the individual gossypol enantiomers in laying and broiler breeder hens. In the first experiment, 25 individually caged Hy-Line W-36 forty-three-week-old laying hens were fed a standard corn-soy diet supplemented with either no gossypol or the individual enantiomers at 200 and 400 mg/kg of diet for 20 d (5 hens/treatment). In the second experiment, 15 individually caged Cobb 500 fast-feathering 44-wk-old broiler breeder hens were fed a standard corn-soy-wheat middlings diet supplemented with either no gossypol or the individual enantiomers at 400 mg/kg of diet for 18 d (5 hens/treatment). In both experiments, feed intake, egg production, and egg weight were determined daily. All eggs were individually opened and scored for yolk discoloration. At the end of both experiments, several organ and tissue samples were collected for gossypol analyses. In both experiments, the addition of (+)-gossypol to the diet reduced egg production. Only laying and broiler breeder hens fed (+)-gossypol produced eggs with severe yolk discoloration (score > or = 4). Total feed intake was lower (P < 0.05) in laying hens fed the 400 mg/kg level of (+)-gossypol compared with laying hens fed the other dietary treatments. In contrast, broiler breeder hens consumed less of the diet supplemented with (-)-gossypol. In both experiments, tissue accumulation of (+)-gossypol was higher than (-)-gossypol, with the exception of bile and excreta. The results suggest that in hens the ingestion of (+)-gossypol has a greater effect on egg yolk discoloration than the consumption of (-)-gossypol.

Relative toxicity of gossypol enantiomers in broilers.

Use of cottonseed meal in poultry diets has been avoided in large part because of fear of gossypol toxicity. Gossypol exists naturally as a mixture of 2 enantiomers that exhibit different biological activities. Two experiments were conducted to determine the relative toxicity of gossypol enantiomers on broilers. In the first experiment, 3-d-old broilers were fed a standard diet containing 0, 100, 200, 300, or 400 mg of gossypol from gossypol acetic acid per kilogram of diet from 3 to 42 d of age. This form of gossypol contains both enantiomers in an equimolar ratio. Each dietary treatment consisted of 6 replicate pens of 4 birds. In the second experiment, 3-d-old broilers were divided into 15 pens of 4 birds each and fed a standard diet supplemented with either no gossypol or one of the gossypol enantiomers at 200 or 400 mg/kg of diet from 3 to 21 d of age. In both experiments, feed intake and BW gain were measured. In addition, several organ and tissue samples were collected at 21 d (experiments 1 and 2) and 42 d (experiment 1) of age and analyzed for gossypol. In experiment 1, feed consumption and BW gain were reduced (P < 0.05) at 21 and 42 d for the birds fed the highest level of gossypol. The concentration of gossypol in the heart, kidney, and plasma were equivalent at 21 and 42 d of age. In experiment 2, total feed consumption was reduced only in birds consuming (-)-gossypol, but BW gains were lower for birds fed either enantiomer. However, (-)-gossypol was more detrimental to growth than (+)-gossypol. The liver had the highest tissue concentration of both enantiomers, and accumulation of (+)-gossypol was higher than (-)-gossypol in all tissues examined. No racemization of the enantiomers was apparent in the tissues analyzed. Our results indicated that both gossypol enantiomers were toxic to broilers but that (-)-gossypol was more harmful to efficient broiler production than (+)-gossypol.

In vitro inhibitory effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri.

AIM: This study was conducted to evaluate the toxic effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri. METHODS AND RESULTS: Inhibitory effect of various concentrations of gossypol on the growth of E. ictaluri was determined. Bacterial recovery was performed by preincubation of bacteria in medium containing various concentrations of gossypol and subsequent activation of bacteria by inoculating on gossypol-free plates. Concentrations of racemic gossypol, (+)-gossypol and (-)-gossypol of 1.5 microg ml(-1) or higher significantly reduced the number of bacterial colonies compared with that of the control. The growth of E. ictaluri was completely inhibited on agar plates supplemented with 3 microg ml(-1), regardless of the forms of gossypol. The inhibitory effect of (+)-gossypol was higher than that of (-)-gossypol or gossypol-acetic acid. Recovery of E. ictaluri was <50% for all three forms of gossypol at concentrations of 5 microg ml(-1). Bacterial recovery remained relatively constant (6.5%) at gossypol concentrations from 10 to 100 microg ml(-1). Complete killing of E. ictaluri was not reached at gossypol levels up to 100 microg ml(-1). CONCLUSION: Gossypol-acetic acid, and (+)- and (-)-optical isomers have anti-bacterial effect against E. ictaluri. The results suggest the action is bacteriostatic rather than bactericidal. SIGNIFICANCE AND IMPACT OF THE STUDY: The therapeutic effect of gossypol against E. ictaluri may be useful in controlling enteric septicaemia of catfish.

Modeling of deoxy- and dideoxyaldohexopyranosyl ring puckering with MM3(92).

Extensive variations of the ring structures of three deoxyaldohexopyranoses, L-fucose, D-quinovose, and L-rhamnose, and four dideoxyaldohexopyranoses, D-digitoxose, abequose, paratose, and tyvelose, were studied by energy minimization with the molecular mechanics algorithm MM3(92). Chair conformers, 4C(1) in D-quinovose and the equivalent 1C(4) in L-fucose and L-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the D-dideoxyhexoses, 4C(1) is again dominant, but with increased amounts of 1C(4) forms in the alpha anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both alpha and beta anomers of the 2,6-dideoxyhexose D-digitoxose. In general, modeled proton-proton coupling constants agreed well with experimental values. Computed anomeric ratios strongly favor the beta configuration except for D-digitoxose, which is almost equally divided between alpha and beta configurations, and L-rhamnose, where the beta configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial beta anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.

Constructing and evaluating energy surfaces of crystalline disaccharides.

This paper focuses on the methods used to construct Ramachandran plots for disaccharides. Our recent work based on a hybrid of molecular mechanics and quantum mechanics energies pointed to the need to take extra care when making these maps. Care is also important in the quantitative validation of these energy surfaces with linkage conformations that were determined by crystallography. To successfully predict conformations that have been observed experimentally, the calculation of the energy should include stereoelectronic effects and correctly weight the hydrogen bonding. Technical concerns include the method used to scan the range of conformations, starting geometries, and finding the zero of relative potential energy on a surface where the values were collected at regular intervals. The distributions of observed conformations on energy maps of sucrose, maltose, and laminarabiose at dielectric constants of 1.5 and 7.5 illustrate the effects of an elevated dielectric constant for the MM3 component of the hybrid energy calculations. At dielectric constants of 3.5 and 7.5, the overall average energies of observed conformations of sucrose and seven disaccharides of glucose were less than 1.0 kcal mol-1. The distribution of corresponding energies of the various crystalline conformations conformed well to a Boltzmann-like equation.

Influence of lipids with and without other cottonseed reserve materials on aflatoxin B(1) production by Aspergillus flavus.

Cottonseed storage lipids (primarily triglycerides), in either crude or refined form, were found to support growth and aflatoxin B(1) production by Aspergillus flavus. When lipids were removed from ground whole cottonseed by petroleum ether extraction, aflatoxin production dropped by more than 800-fold. Reconstitution of the lipid-extracted ground whole seed with a crude preparation of cottonseed lipids restored aflatoxin production to the previous levels. Fungal utilization of the three major cottonseed reserve materials, raffinose, triglycerides (refined cottonseed oil), and cottonseed storage protein, was monitored in vitro over a 7 day fermentation period. The fermentation medium contained the reserve compounds in proportions approximating those found in mature cottonseed. A. flavus rapidly converted raffinose to fructose and melibiose, presumably by action of invertase, and then hydrolyzed the melibiose. These simple sugars apparently supported initial growth and aflatoxin B(1) production. Raffinose and the resulting melibiose were nearly exhausted by day 2. Fungal hydrolysis of triglycerides began as exhaustion of carbohydrate approached. After day 2, rapid catabolism of the released fatty acids began and coincided with glucose regeneration through gluconeogenesis, which peaked on day 6. The fungus did not preferentially utilize specific fatty acids. A. flavus also produced a number of storage metabolites, including arabitol, erythritol, mannitol, and trehalose. Mannitol was produced in much higher concentrations than the other storage metabolites. Selective use of simple carbohydrates by A. flavus to drive aflatoxin production may suggest strategies for reducing vulnerability of cottonseed to aflatoxin contamination.

A QM/MM analysis of the conformations of crystalline sucrose moieties.

Both ab initio quantum mechanics (QM) and molecular mechanics (MM) were used to produce a hybrid energy surface for sucrose that simultaneously provides low energies for conformations that are observed in crystal structures and high energies for most unobserved structures. HF/6-31G* QM energies were calculated for an analogue based on tetrahydropyran (THP) and tetrahydrofuran (THF). Remaining contributions to the potential energy of sucrose were calculated with MM. To do this, the MM surface for the analogue was subtracted from the MM surface for the disaccharide, and the QM surface for the analogue was added. Prediction of the distribution of observable geometries was enhanced by reducing the strength of the hydrogen bonding. Reduced hydrogen-bonding strength is probably useful because many crystalline sucrose moieties do not have intramolecular hydrogen bonds between the fructose and glucose residues. Therefore, hydrogen bonding does not play a large role in determining the molecular conformation. On the hybrid energy surface that was constructed with a dielectric constant of 3.5, the average potential energy of 23 sucrose moieties from crystal structures is 1.16 kcal/mol, and the population of observed structures drops off exponentially as the energy increases.

Influence of lactic acid on the solubilization of protein during corn steeping.

The role of lactic acid (LA) in corn wet-mill steeping is not well understood. Because LA is known to improve wet-milling starch yields and steepwater contains a large amount of proteinaceous material, one of the effects of LA in steeping may be to help break down the endosperm protein matrix. Protein solubilization was studied for four different steeping solutions containing LA, sulfur dioxide (SO(2)), a combination of LA and SO(2), or no added chemicals at temperatures between 44 and 60 degrees C with steep times of up to 48 h. The accumulation of proteinaceous material in steepwater with time was sigmoidal regardless of the steeping chemicals or temperature. The initial slow rate of solubilization appeared to be due to incomplete kernel hydration. Significantly greater amounts of protein were released in the presence of LA than in its absence, with the greatest amounts found when steeping was performed with both LA and SO(2). The increase of proteinaceous material in steepwater containing LA was not due to low pH, because steeping solutions containing other organic and inorganic acids did not increase steepwater protein. The effect of LA concentration was also studied. In the absence of SO(2), higher concentrations of LA resulted in higher steepwater protein concentrations. The opposite trend was observed in the presence of SO(2). Similar steepwater protein concentrations were obtained with DL-lactic acid and L-lactic acid, indicating that the additional protein release was not sensitive to isomeric effects.

Automated docking of maltose, 2-deoxymaltose, and maltotetraose into the soybean beta-amylase active site.

In this study, products and substrates were docked into the active site of beta-amylase using the simulated annealing algorithm AutoDock. Lowest-energy conformers reproduced known crystallographic atom positions within 0.4 to 0.8 A rmsd. Docking studies were carried out with both open and closed configurations of the beta-amylase mobile flap, a loop comprising residues 96 to 103. Ligands with two rings docked within the cleft near the active site when the flap was open, but those with four rings did not. The flap must be closed for alpha-maltotetraose to adopt a conformation allowing it to dock near the crystallographically determined subsites. The closed flap is necessary for productive but not for nonproductive binding, and therefore it plays a essential role in catalysis. The gain in total binding energy upon closing of the flap for alpha-maltose docked to subsites -2, -1 and +1, +2 is about 22 kcal/mol, indicating more favorable interactions are possible with the flap closed. Larger intermolecular interaction energies are observed for two alpha-maltose molecules docked to subsites -2, -1 and +1, +2 than for one alpha-maltotetraose molecule docked from subsites -2 to +2, suggesting that it is only upon cleavage of the alpha-1,4 linkage that optimal closed-flap binding can occur with the crytallographically determined enzyme structure.

Automated docking of glucosyl disaccharides in the glucoamylase active site.

To better understand the molecular basis of glucomylase selectivity, low-energy conformers of glucosyl disaccharides obtained from relaxed-residue conformational mapping were flexibly docked into the glucoamylase active site using AutoDock 2.2. This procedure ensures that significant conformational space is searched and can produce bound structures comparable to those obtained by protein crystallography. alpha-Linked glucosyl disaccharides except alpha,alpha-trehalose dock easily into the active site while exclusively beta-linked disaccharides do not, explaining why only the former are glucoamylase substrates. The optimized docking modes are similar at the nonreducing end of the different substrates. Individual atomic energies of intermolecular interaction allow the definite identification of key hydroxyl groups for each substrate. This approach confirmed the versatility of the second subsite of the glucoamylase active site in binding different substrates.

Automated docking of monosaccharide substrates and analogues and methyl alpha-acarviosinide in the glucoamylase active site.

Glucoamylase is an important industrial glucohydrolase with a large specificity range. To investigate its interaction with the monosaccharides D-glucose, D-mannose, and D-galactose and with the substrate analogues 1-deoxynojirimycin, D-glucono-1,5-lactone, and methyl alpha-acarviosinide, MM3(92)-optimized structures were docked into its active site using AutoDock 2.1. The results were compared to structures of glucoamylase complexes obtained by protein crystallography. Charged forms of some substrate analogues were also docked to assess the degree of protonation possessed by glucoamylase inhibitors. Many forms of methyl alpha-acarviosinide were conformationally mapped by using MM3(92), characterizing the conformational pH dependence found for the acarbose family of glucosidase inhibitors. Their significant conformers, representing the most common states of the inhibitor, were used as initial structures for docking. This constitutes a new approach for the exploration of binding modes of carbohydrate chains. Docking results differ slightly from x-ray crystallographic data, the difference being of the order of the crystallographic error. The estimated energetic interactions, even though agreeing in some cases with experimental binding kinetics, are only qualitative due to the large approximations made by AutoDock force field.

Relaxed-residue conformational mapping of the three linkage bonds of isomaltose and gentiobiose with MM3 (92).

Isoenergy surfaces were calculated for the alpha- and beta-anomers of isomaltose and gentiobiose, based on 46,656 conformers for each disaccharide. Low-energy regions exist for each of the three staggered positions about the C-5'-C-6' bonds, and known crystal structures lie in two of these regions. As expected, the molecular partition function showed greater flexibility for these three-bond-linked disaccharides than for comparable two-bond-linked structures. A model miniature crystal of gentiobiose accounts for most of the remaining structural differences between the modeled isolated molecule and the crystal structure. Based on models of isolated molecules of isomaltose and gentiobiose, the predicted Boltzmann-weighted nmr coupling constants were satisfactory, as were predicted optical rotations for gentiobiose.

Effects of dietary fat on cholesterol movement between tissues in CBA/J and C57BR/cdJ mice.

Differences in dietary fats cause differences in cholesterol metabolism in mice. CBA/J mice are resistant to diet-induced hypercholesterolemia and atherosclerosis; they adjust hepatic hydroxymethyl-glutaryl-CoA reductase activity (HMGR) to maintain homeostasis; C57BR/cdJ mice are susceptible, but young animals are thought to maintain homeostasis by changing fecal excretion of sterols. Compartmental modelling of movement of [4-14C]cholesterol was used to analyze movement of cholesterol between serum and liver, heart, and carcass in mice fed 40 en% fat, polyunsaturated to saturated fatty acid ratio (P/S) = 0.24 (US74) or 30 en% fat, P/S = 1 (MOD). Dietary effects were quite pronounced, while strain effects were more subdued. The C57/cdJ animals appear to regulate the overall cholesterol balance by reducing synthesis, as do the CBA/J animals, even though synthesis is not reduced to the same degree as in the CBA/J animals. Both diet and strain influence the whole-animal turnover rate, with slower turnover occurring for C57BR/cdJ animals and animals fed the US74 diet.

Conformational analysis of the anomeric forms of sophorose, laminarabiose, and cellobiose using MM3.

Relaxed-residue energy maps based on the MM3 force-field were computed for relative orientations of the pyranosyl rings of sophorose, laminarabiose, and cellobiose, respectively the (1----2)-beta-; (1----3)-beta-; and (1----4)-beta-linked D-glucosyl disaccharides. Sixteen starting conformations of the rotatable exocyclic side-groups were considered for each molecule. All of the energy surfaces have two intersecting low-energy troughs and illustrate the importance of exo-anomeric effects in determining disaccharide conformation. Local minima were found by relaxed minimization without restriction. The energy surfaces of these disaccharides are very similar to the energy surfaces of their corresponding 6-methyltetrahydropyran analogues. There is good agreement between disaccharide structures having minimal MM3 energy and those found by crystallography.