(S)-2-Carb-oxy-ethyl l-cysteinyl sulfone.

The title compound {systematic name: (2S)-2-aza-niumyl-3-[(2-carb-oxy-ethane)-sulfon-yl]propano-ate}, C6H11NO6S, forms enanti-opure crystals in the monoclinic space group P21 and exists as a zwitterion, with a protonated α-amino group and a deprotonated α-carboxyl group. Both the carboxyl groups and the amino group are involved in an extensive multicentered inter-molecular hydrogen-bonding scheme. In the crystal, the diperiodic network of hydrogen bonds propagates parallel to (101) and involves inter-connected heterodromic R 4 3(10) rings. Electrostatic forces are major contributors to the structure energy, which was estimated by DFT calculations as E total = -333.5 kJ mol-1.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives: An update.

1-Amino-1-deoxy-d-fructose (fructosamine, FN) derivatives are omnipresent in all living organisms, as a result of non-enzymatic condensation and Amadori rearrangement reactions between free glucose and biogenic amines such as amino acids, polypeptides, or aminophospholipids. Over decades, steady interest in fructosamine was largely sustained by its role as a key intermediate structure in the Maillard reaction that is responsible for the organoleptic and nutritional value of thermally processed foods, and for pathophysiological effects of hyperglycemia in diabetes. New trends in fructosamine research include the discovery and engineering of FN-processing enzymes, development of advanced tools for hyperglycemia monitoring, and evaluation of the therapeutic potential of both fructosamines and FN-recognizing proteins. This article covers developments in the field of fructosamine and its derivatives since 2010 and attempts to ascertain challenges in future research.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives.

Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.

Microglia Signaling Pathway Reporters Unveiled Manganese Activation of the Interferon/STAT1 Pathway and Its Mitigation by Flavonoids.

Neuroinflammatory responses to neurotoxic manganese (Mn) in CNS have been associated with the Mn-induced Parkinson-like syndromes. However, the framework of molecular mechanisms contributing to manganism is still unclear. Using an in vitro neuroinflammation model based on the insulated signaling pathway reporter transposon constructs stably transfected into a murine BV-2 microglia line, we tested effects of manganese (II) together with a set of 12 metal salts on the transcriptional activities of the NF-κB, activator protein-1 (AP-1), signal transducer and activator of transcription 1 (STAT1), STAT1/STAT2, STAT3, Nrf2, and metal-responsive transcription factor-1 (MTF-1) via luciferase assay, while concatenated destabilized green fluorescent protein expression provided for simultaneous evaluation of cellular viability. This experiment revealed specific and strong responses to manganese (II) in reporters of the type I and type II interferon-induced signaling pathways, while weaker activation of the NF-κB in the microglia was detected upon treatment of cells with Mn(II) and Ba(II). There was a similarity between Mn(II) and interferon-γ in the temporal STAT1 activation profile and in their antagonism to bacterial LPS. Sixty-four natural and synthetic flavonoids differentially affected both cytotoxicity and the pro-inflammatory activity of Mn (II) in the microglia. Whereas flavan-3-ols, flavanones, flavones, and flavonols were cytoprotective, isoflavones enhanced the cytotoxicity of Mn(II). Furthermore, about half of the tested flavonoids at 10-50 µM could attenuate both basal and 100-200 µM Mn(II)-induced activity at the gamma-interferon activated DNA sequence (GAS) in the cells, suggesting no critical roles for the metal chelation or antioxidant activity in the protective potential of flavonoids against manganese in microglia. In summary, results of the study identified Mn as a specific elicitor of the interferon-dependent pathways that can be mitigated by dietary polyphenols.

2-Bromo-6-hydrazinyl-pyridine.

The title compound, C5H6BrN3, crystallizes in the ortho-rhom-bic space group P212121 with two mol-ecules with different conformations in the asymmetric unit. In the crystal, N-H⋯N and bifurcated N-H⋯(N,N) hydrogen bonds link the mol-ecules into [100] chains; a short Br⋯Br halogen bond and π-π stacking inter-actions are also observed.

ß-d-Galacto-pyranosyl-(1→4)-2-amino-2-de-oxy-α-d-gluco-pyran-ose hydro-chloride monohydrate (lactosamine).

The title compound, C12H24NO10 +·Cl-·H2O, (I), crystallizes in the monoclinic space group P21 and exists as a monohydrate of a monosubstituted ammonium chloride salt, with the reducing carbohydrate portion existing exclusively as the α-pyran-ose tautomer. The glycosidic bond geometry in (I) is stabilized by an intra-molecular hydrogen bond and is close to that found in crystalline α-lactose. All heteroatoms except gluco-pyran-ose ring O4 participate in an extensive hydrogen-bonding network, which propagates in all directions in the crystal structure of (I).

Structural and Functional Studies of S-(2-Carboxyethyl)-L-Cysteine and S-(2-Carboxyethyl)-l-Cysteine Sulfoxide.

Insecticidal non-proteinogenic amino acid S-(2-carboxyethyl)-L-cysteine (ß-CEC) and its assumed metabolite, S-(2-carboxyethyl)-l-cysteine sulfoxide (ß-CECO), are present abundantly in a number of plants of the legume family. In humans, these amino acids may occur as a result of exposure to environmental acrylonitrile or acrylamide, and due to consumption of the legumes. The ß-CEC molecule is a homolog of S-carboxymethyl-l-cysteine (carbocisteine, CMC), a clinically employed antioxidant and mucolytic drug. We report here detailed structural data for ß-CEC and ß-CECO, as well as results of in vitro studies evaluating cytotoxicity and the protective potential of the amino acids in renal tubular epithelial cells (RTECs) equipped with reporters for activity of seven stress-responsive transcription factors. In RTECs, ß-CEC and the sulfoxide were not acutely cytotoxic, but activated the antioxidant Nrf2 pathway. ß-CEC, but not the sulfoxide, induced the amino acid stress signaling, which could be moderated by cysteine, methionine, histidine, and tryptophan. ß-CEC enhanced the cytotoxic effects of arsenic, cadmium, lead, and mercury, but inhibited the cytotoxic stress induced by cisplatin, oxaliplatin, and CuO nanoparticles and acted as an antioxidant in a copper-dependent oxidative DNA degradation assay. In these experiments, the structure and activities of ß-CEC closely resembled those of CMC. Our data suggest that ß-CEC may act as a mild activator of the cytoprotective pathways and as a protector from platinum drugs and environmental copper cytotoxicity.

Mechanochemical generation of N,N-diglycated glycine and MS/MS characterization of its isomeric composition.

The formation of Schiff bases and Amadori rearrangement products (ARP) during the Maillard reaction in solutions is well documented, but their studies in solid-state are limited. Here we report mass-spectrometric characterization of N,N-diglycated Schiff bases and Amadori products obtained during ball milling of amino acids and glucose. Signal intensities of the diglycated adducts in mass-spectra depended on type of the amino acid and the MS ionization mode. Glycine provided for the highest yields of N,N-diglycation, followed by lysine, when the reaction was analyzed under negative ionization mode. Using diagnostic MS/MS fragmentation, we were able to distinguish between Schiff-Schiff, Schiff-Amadori, or Amadori-Amadori isomers. Milling glucose/glycine model for 30 min at ambient temperature produced diglycated glycine as a mixture of the three possible isomers in approximately equal molar proportions. Milling of synthetic Schiff base or ARP of glycine with [U-13C]-glucose generated the same but partially labelled isomers, with respective predominance of N,N-diglucosyl-glycine or N,N-difructosyl-glycine.

Bidirectional Responses of Eight Neuroinflammation-Related Transcriptional Factors to 64 Flavonoids in Astrocytes with Transposable Insulated Signaling Pathway Reporters.

Neuroinflammation is implicated in a variety of pathologies and is mechanistically linked to hyperactivation of glial cells in the central nervous system (CNS), predominantly in response to external stimuli. Multiple dietary factors were reported to alter neuroinflammation, but their actions on the relevant transcription factors in glia are not sufficiently understood. Here, an in vitro protocol employing cultured astroglial cells, which carry reporters of multiple signaling pathways associated with inflammation, was developed for screening environmental factors and synthetic drugs. Immortalized rat astrocyte line DI TNC1 was stably transfected with piggyBac transposon vectors containing a series of insulated reporters for the transcriptional activity of NF-κB, AP-1, signal transducer and activator of transcription 1 (STAT1), signal transducer and activator of transcription 3 (STAT3), aromatic hydrocarbon receptor (AhR), Nrf2, peroxisome proliferator-activated receptor γ (PPARγ), and HIF-1α, which is quantified via luciferase assay. Concatenated green fluorescent protein (GFP) expression was employed for simultaneous evaluation of cellular viability. Responses to a set of 64 natural and synthetic monomeric flavonoids representing six main structural classes (flavan-3-ols, flavanones, flavones, flavonols, isoflavones, and anthocyan(id)ins) were obtained at 10 and 50 µM concentrations. Except for HIF-1α, the activity of NF-κB and other transcription factors (TFs) in astrocytes was predominantly inhibited by flavan-3-ols and anthocyan(id)ins, while flavones and isoflavones generally activated these TFs. In addition, we obtained dose-response profiles for 11 flavonoids (apigenin, baicalein, catechin, cyanidin, epigallocatechin gallate, genistein, hesperetin, kaempferol, luteolin, naringenin, and quercetin) within the 1-100 µM range and in the presence of immune-stimulants and immune-suppressors. The flavonoid concentration profiles for TF-activation reveal biphasic response curves from the astrocytes. Apart from epigallocatechin gallate (EGCG), flavonoids failed to inhibit the NF-κB activation by proinflammatory agents [lipopolysaccharide (LPS), cytokines], but most of the tested polyphenols synergized with STAT3 inhibitors (stattic, ruxolitinib) against the activation of this TF in the astrocytes. We conclude that transposable insulated reporters of transcriptional activation represent a convenient neurochemistry tool in screening for activators/inhibitors of signaling pathways.

Structure, Antioxidant and Anti-inflammatory Activities of the (4R)- and (4S)-epimers of S-Carboxymethyl-L-cysteine Sulfoxide.

S-Carboxymethyl-L-cysteine (CMC) is an antioxidant and mucolytic commonly prescribed to patients with chronic obstructive pulmonary disease. In humans, CMC is rapidly metabolized to S-carboxymethyl-L-cysteine sulfoxide (CMCO). In this study, we assessed structural and functional similarities between CMC and CMCO. X-Ray diffraction analysis provided detailed structural information about CMCO, which exists as a 1:1 mixture of epimers, due to the emergence of a new chiral center at the sulfur atom. Both CMC and CMCO epimers protected model DNA from copper-mediated hydroxyl free radical damage. Using an insulated transposable construct for reporting activity of the cellular stress-responsive transcription factors Nrf2, p53, NF-κB, and AP-1, we demonstrate that CMCO, especially its (4R)-epimer, is comparable to CMC in their ability to mitigate the effects of oxidative stress and pro-inflammatory stimuli in human alveolar (A549) and bronchial epithelial (BEAS-2B) cells. The results of these in vitro studies suggest that CMCO retains, at least partially, the antioxidant potential of CMC and may inform pharmacodynamics considerations of CMC use in clinics.

Intra-molecular 1,5-S⋯N σ-hole inter-action in (E)-N'-(pyridin-4-yl-methyl-idene)thio-phene-2-carbohydrazide.

The title compound, C11H9N3OS, (I), crystallizes in the monoclinic space group P21/n. The mol-ecular conformation is nearly planar and features an intra-molecular chalcogen bond between the thio-phene S and the imine N atoms. Within the crystal, the strongest inter-actions between mol-ecules are the N-H⋯O hydrogen bonds, which organize them into inversion dimers. The dimers are linked through short C-H⋯N contacts and are stacked into layers propagating in the (001) plane. The crystal structure features π-π stacking between the pyridine aromatic ring and the azomethine double bond. The calculated energies of pairwise inter-molecular inter-actions within the stacks are considerably larger than those found for the inter-actions between the layers.

Crystal structure of (R,S)-2-hy-droxy-4-(methyl-sulfan-yl)butanoic acid.

The title compound, a major animal feed supplement, abbreviated as HMTBA and alternatively called dl-me-thio-nine hy-droxy analogue, C5H10O3S, (I), was isolated in pure anhydrous monomeric form. The melting point is 302.5 K and the compound crystallizes in the monoclinic space group P21/c, with two conformationally non-equivalent mol-ecules [(I A ) and (I B )] in the asymmetric unit. The crystal structure is formed by alternating polar and non-polar layers running along the bc plane and features an extensive hydrogen-bonding network within the polar layers. The Hirshfeld surface analysis revealed a significant contribution of non-polar H⋯H and H⋯S inter-actions to the packing forces for both mol-ecules.

Diagnostic MS/MS fragmentation patterns for the discrimination between Schiff bases and their Amadori or Heyns rearrangement products.

Schiff bases, the Amadori and Heyns rearrangement products are the most important isomeric intermediates involved in the early Maillard reaction; distinguishing between them by analytical mass spectroscopic techniques remains a challenge. Here we demonstrate that MS/MS fragmentation patterns can be used for the discrimination between glucose derived Schiff bases, Amadori, and Heyns compounds with glycine. An ESI-qTOF-MS system operated in the positive mode under both acidic and neutral conditions was employed to generate unique MS/MS fragmentation patterns of the molecules. Analysis of the MS data has indicated that acidic medium is suitable for generating characteristic and diagnostic ions. At high collision energy (20 eV), the spectrum of Schiff base was largely uninformative, whereas both Amadori and Heyns compounds undergo characteristic fragmentations with high diagnostic value. At low collision energy values (10eV), we observed formation of prominent diagnostic ions from the Schiff base precursor, as well as extensive dehydration reactions of all three molecules. Under acidic conditions, the diagnostic fragmentation pattern of the Amadori compound featured consecutive dehydration reactions. At higher values (20 eV) it underwent the α-fission at the carbonyl group and produced a prominent diagnostic ion [AA + H + CH2]+ at m/z 88. The Schiff base was found to preferentially undergo the retro-aldol degradation and produce diagnostic ions at m/z 118 [AA + H + diose]+ and m/z 140 [AA + Na + diose]+, together with their sugar complements at m/z 85 [tetrose + H-2H2O]+ and m/z 143 [tetrose + Na]+. In the case of Heyns compound, several diagnostic ions were also detected, including the ions at m/z 154 [M + H-2H2O-C2H4O2]+, m/z 170 [AA + Na + triose]+ and m/z 142 [AA + H + Furan]+.

Bioactive components from garlic on brain resiliency against neuroinflammation and neurodegeneration.

Garlic (Allium sativum) has been widely used for culinary and medicinal purposes. Aged garlic extract (AGE) and sulfur-containing compounds, including S-allylcysteine (SAC) are well documented botanical active components of garlic. AGE is prepared by the prolonged extraction of fresh garlic with aqueous ethanol and is considered a nutritional supplement with potential to promote human health. SAC is a water-soluble organosulfur compound and the most abundant component of AGE. Studies have demonstrated that both AGE and SAC can exert neuroprotective effects against neuroinflammation and neurodegeneration. Another bioactive component in AGE is N-α-(1-deoxy-D-fructos-1-yl)-L-arginine (FruArg) although less is known about the metabolic activity of this compound. The main aim of this review was to provide an undated overview of the neuroprotective perspectives of these active garlic components (AGE, SAC and FruArg). Of interest, our studies and those of others indicate that both AGE and FruArg are involved in the regulation of gene transcription and protein expression. AGE has been shown to reverse 67% of the transcriptome alteration induced by endotoxins-lipopolysaccharide (LPS), and FruArg has been shown to account for the protective effects by reversing 55% of genes altered in a cell-based neuroinflammation paradigm stimulated by LPS in murine BV-2 microglial cells. AGE and FruArg can alleviate neuroinflammatory responses through a variety of signaling pathways, such as Toll-like receptor and interleukin (IL)-6 signaling, as well as by upregulating the nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated oxidative stress pathways known to promote microglial resiliency against neuroinflammation and neurodegeneration. The capability of FruArg to pass through the blood-brain barrier further supports its potential as a therapeutic compound. In summary, these experimental results provide new insight into the understanding of the neuroprotective effects of garlic components in promoting brain resiliency for health benefits.

4-(Di-methyl-amino)-benzohydrazide.

The title compound, C9H13N3O, crystallizes in the monoclinic space group C2/c and all non-hydrogen atoms are within 0.1 Šof the mol-ecular mean plane. In the crystal, the hydrogen-bonding pattern results in [001] chains built up from fused R 2 2(6) and R 2 2(10) rings; the former consists of N-H⋯N bonds and the latter N-H⋯O bonds. Electrostatic and dispersion forces are major contributors to the lattice energy, which was estimated by DFT calculations to be -215.7 kJ mol-1.

Dried Fruit Intake and Cancer: A Systematic Review of Observational Studies.

Insufficient intake of total fruits and vegetables is linked to an increased cancer risk, but the relation is not understood for dried fruits. Dried fruits are generally perceived, by both consumers and researchers, as a less attractive but shelf-stable equivalent to fresh fruits and constitute a small but significant proportion of modern diets. Chemical compositions of raw and dried fruits, however, may differ substantially. Several clinical and laboratory intervention studies have reported the protective effects of dehydrated fruits against the progression of some cancers and the modulating effects of dried fruits on common cancer risk factors. In this systematic review, we identified, summarized, and critically evaluated 9 prospective cohort and 7 case-control studies that examined the relations between traditional dried fruit (raisins, prunes, dates) consumption and cancer risk in humans. Prospective cohort studies determined that significant reductions in relative risk of precancerous colorectal polyps, incidence of prostate cancer, or mortality from pancreatic cancer, by, respectively, 24%, 49%, and 65%, were associated with 3-5 or more servings of dried fruits per week. Selected case-control studies revealed inverse associations between dried fruit intake and risk of cancer as well. The reported associations were comparable to or stronger than those observed for total or raw fruits. Although the small number and high heterogeneity impede meta-analysis of these studies, we conclude that currently available data provide some initial evidence that consumption of dried fruits may be associated with a lower cancer incidence or mortality in populations. The data suggest that higher intake of raisins and other dried fruits may be important in the prevention of cancers of the digestive system. Because only a limited number of health outcome and dried fruit intake relations have been evaluated in prospective studies to date, reanalyzing existing high-quality epidemiological data may expand the knowledge base.

Multicentered hydrogen bonding in 1-[(1-de-oxy-ß-d-fructo-pyranos-1-yl)aza-nium-yl]cyclo-pentane-carboxyl-ate ('d-fructose-cyclo-leucine').

The title compound, C12H21NO7, (I), is conformationally unstable; the predominant form present in its solution is the ß-pyran-ose form (74.3%), followed by the ß- and α-furan-oses (12.1 and 10.2%, respectively), α-pyran-ose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the 2 C 5 ß-pyran-ose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclo-pentane ring assuming the E 9 envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of anti-parallel infinite chains of fused R 3 3(6) and R 3 3(8) rings. The mol-ecule features extensive intra-molecular hydrogen bonding, which is uniquely multicentered and involves the carboxyl-ate, ammonium and carbohydrate hy-droxy groups. In contrast, the contribution of inter-molecular O⋯H/H⋯O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other d-fructose-amino acids. The 1H NMR data suggest a slow rotation around the C1-C2 bond in (I), indicating that the intra-molecular heteroatom contacts survive in aqueous solution of the mol-ecule as well.

Crystal structure of the acyclic form of 1-de-oxy-1-[(4-methoxyphenyl)(methyl)amino]-d-fructose.

The title compound, C14H21NO6, (I), crystallizes exclusively in the acyclic keto form. In solution of (I), the acyclic tautomer represents only 10% of the population in equilibrium, with the other 90% consisting of ß-pyran-ose, ß-furan-ose, α-pyran-ose, and α-furan-ose cyclic forms. The carbohydrate chain in (I) has a zigzag conformation and the aromatic amine group has a transitional sp2/sp3 geometry. Bond lengths and valence angles in the carbohydrate portion compare well with the average values for related acyclic polyol structures. All of the hydroxyl groups are involved in inter-molecular hydrogen bonding and form a two-dimensional network of infinite chains, which are inter-linked by intra-molecular hydrogen bonds and organized into R88(16) homodromic ring patterns. A comparative Hirshfeld surfaces analysis of (I) and four other 1-amino-1-de-oxy-d-fructose derivatives suggests the balance of hydro-philic/hydro-phobic inter-actions plays a role in the crystal packing, favoring the acyclic isomer.

Interaction of Bacterial Phenazines with Colistimethate in Bronchial Epithelial Cells.

Multidrug-resistant bacterial infections are being increasingly treated in clinics with polymyxins, a class of antibiotics associated with adverse effects on the kidney, nervous system, or airways of a significant proportion of human and animal patients. Although many of the resistant pathogens display enhanced virulence, the hazard of cytotoxic interactions between polymyxin antibiotics and bacterial virulence factors (VFs) has not been assessed, to date. We report here the testing of paired combinations of four Pseudomonas aeruginosa VF phenazine toxins, pyocyanin (PYO), 1-hydroxyphenazine (1-HP), phenazine-1-carboxylic acid (PCA), and phenazine-1-carboxamide (PCN), and two commonly prescribed polymyxin drugs, colistin-colistimethate sodium (CMS) and polymyxin B, in three human airway cell lines, BEAS-2B, HBE-1, and CFT-1. Cytotoxicities of individual antibiotics, individual toxins, and their combinations were evaluated by the simultaneous measurement of mitochondrial metabolic, total transcriptional/translational, and Nrf2 stress response regulator activities in treated cells. Two phenazines, PYO and 1-HP, were cytotoxic at clinically relevant concentrations (100 to 150 µM) and prompted a significant increase in oxidative stress-induced transcriptional activity in surviving cells. The polymyxin antibiotics arrested cell proliferation at clinically achievable (<1 mM) concentrations as well, with CMS displaying surprisingly high cytotoxicity (50% effective dose [ED50] = 180 µM) in BEAS-2B cells. The dose-response curves were probed by a median-effect analysis, which established a synergistically enhanced cytotoxicity of the PYO-CMS combination in all three airway cell lines; a particularly strong effect on BEAS-2B cells was observed, with a combination index (CI) of 0.27 at the ED50 PCA, PCN, and 1-HP potentiated CMS cytotoxicity to a smaller extent. The cytotoxicity of CMS could be reduced with 10 mM N-acetyl-cysteine. Iron chelators, while ineffective against the polymyxins, could rescue all three bronchial epithelial cell lines treated with lethal PYO or CMS-PYO doses. These findings suggest that further evaluations of CMS safety are needed, along with a search for means to moderate potentially cytotoxic interactions.

Crystal structure and hydrogen bonding in N-(1-de-oxy-ß-d-fructo-pyranos-1-yl)-2-amino-isobutyric acid.

The title compound, alternatively called d-fructose-2-amino-isobutyric acid (FruAib), C10H19NO7, (I), crystallizes exclusively in the ß-pyran-ose form, with two conformationally non-equivalent mol-ecules [(IA) and (IB)] in the asymmetric unit. In solution, FruAib establishes an equilibrium, with 75.6% of the population consisting of ß-pyran-ose, 10.4% ß-furan-ose, 10.1% α-furan-ose, 3.0% α-pyran-ose and <0.7% the acyclic forms. The carbohydrate ring in (I) has the normal 2C5 chair conformation and the amino acid portion is in the zwitterion form. Bond lengths and valence angles compare well with the average values from related pyran-ose structures. All carboxyl, hy-droxy and ammonium groups are involved in hydrogen bonding and form a three-dimensional network of infinite chains that are connected through homodromic rings and short chains. Intra-molecular hydrogen bonds bridge the amino acid and sugar portions in both mol-ecules. A comparative Hirshfeld surfaces analysis of FruAib and four other sugar-amino acids suggests an increasing role of intra-molecular heteroatom inter-actions in crystal structures with an increasing proportion of C-H bonds.