Aggregation of hyperphosphorylated tau is a major hallmark of many neurodegenerative diseases, including Alzheimer disease (AD). In vivo imaging with PET may offer important insights into pathophysiologic mechanisms, diagnosis, and disease progression. We describe different strategies for quantification of F-AV-1451 (T807) tau binding, including models with blood sampling and noninvasive alternatives. Fifteen subjects (4 controls, 6 AD, 3 progressive supranuclear palsy, 2 cortico basal syndrome) underwent 180-min PET with F-AV-1451 and arterial blood sampling. Modeling with arterial input functions included 1-, 2-, and 3-tissue-compartment models and the Logan plot. Using the cerebellum as reference region, we applied the simplified reference tissue model 2 and Logan reference plot. Finally, simplified outcome measures were calculated as ratio, with reference to cerebellar concentrations (SUV ratio [SUVR]) and SUVs. Tissue compartment models were not able to describe the kinetics of F-AV-1451, with poor fits in 33%-53% of cortical regions and 80% in subcortical areas. In contrast, the Logan plot showed excellent fits and parameter variance (total volume of distribution SE< 5%). Compared with the 180-min arterial-based Logan model, strong agreement was obtained for the Logan reference plot also for a reduced scan time of 100 min ( = 0.91) and SUVR 100-120 min ( = 0.94), with 80-100 min already representing a reasonable compromise between duration and accuracy ( = 0.93). Time-activity curves and kinetic parameters were equal for cortical regions and the cerebellum in control subjects but different in the putamen. Cerebellar total volumes of distribution were higher in controls than patients. For these methods, increased cortical binding was observed for AD patients and to some extent for cortico basal syndrome, but not progressive supranuclear palsy. The Logan plot provided the best estimate of tau binding using arterial input functions. Assuming that the cerebellum is a valid reference region, simplified methods seem to provide robust alternatives for quantification, such as the Logan reference plot with 100-min scan time. Furthermore, SUVRs between target and cerebellar activities obtained from an 80- to 100-min static scan offer promising potential for clinical routine application.

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Epimerization of glycopeptide stereocenters and beta-elimination have been considered as important potential side reactions on deacylation of glycopeptides which have the carbohydrate moieties protected with O-acyl groups. Since no systematic investigation of these side reactions has been reported, a model acetylated, O-linked glycotripeptide and its three epimers at the alpha-carbon stereocenters were prepared. The model glycopeptide did not undergo any epimerization (<1%) or beta-elimination, as determined by (1)H NMR spectroscopy, under various conditions which are in common use for deacetylation of glycopeptides. Under more severe conditions, which are required for removal of O-benzoyl groups, beta-elimination occurred slowly and was accompanied by slight (<5%) epimerization. The surprisingly low tendency of glycopeptides to undergo base catalyzed epimerization and beta-elimination is most likely due to protection of the alpha-carbon stereocenters by deprotonation of the adjacent amide groups.

Fluorobenzoyl groups have been investigated as alternatives to acetyl and benzoyl protective groups in carbohydrate and glycopeptide synthesis. D-Glucose and lactose were protected with different fluorobenzoyl groups and then converted into glycosyl bromides in high yields (>80% over two steps). Glycosylation of protected derivatives of serine with these donors gave 1,2-trans glycosides in good yields (approximately 60--70%) and excellent stereoselectivity without formation of ortho esters. The resulting glycosylated amino acid building blocks were then used in solid-phase synthesis of two model O-linked glycopeptides known to be unusually sensitive to beta-elimination on base-catalyzed deacylation. When either a 3-fluoro- or a 2,5-difluorobenzoyl group was used for protection of each of the two model glycopeptides the extent of beta-elimination decreased from 80% to 10% and from 50% to 0%, respectively, as compared to when using the ordinary benzoyl group. Fluorobenzoyl groups thus combine the advantages of the benzoyl group in formation of glycosidic bonds (i.e., high stereoselectivity and low levels of ortho ester formation) with the ease of removal characteristic of the acetyl group.

ABSTRACT:The airway retention of inhaled glucocorticosteroids (GCs) depends largely on their lipophilicity. Inhaled budesonide (BUD) becomes highly lipophilic reversibly by the formation of esters acting as a reservoir of active BUD. Ciclesonide (CIC) was also reported to form esters after hydrolysis to active metabolite (CIC-AM). We have investigated lipophilicity and airway retention of BUD, CIC/ CIC-AM, fluticasone propionate (FP), and mometasone furoate (MF), and compared esterification of BUD and CIC-AM and its contribution to GC airway retention. Rat tracheas were preincubated with the esterification inhibitor cyclandelate or vehicle. A 3 H-GC (ϳ10 ؊7 M: BUD, CIC, CIC-AM, FP, MF) was added for 20 min.After incubation, one half of the trachea was used for analysis of GC uptake and the other to analyze GC release during 3 h in drug-free medium. GC species in trachea halves were analyzed by radiochromatography. At 20 min, the uptake of BUD was similar to that of CIC/CIC-AM; however, the BUD-ester pool was 9-fold greater (p < 0.01). BUD overall retention in trachea at 3 h was greater than that of other GCs (p < 0.01), and the BUD-ester pool was 3-fold greater than the CIC-AM-ester pool (p < 0.01). Cyclandelate decreased the initial BUD-and CIC-AM-ester pools (p < 0.01), and reduced the overall retention of BUD at 3 h (p < 0.01) but not of CIC-AM. Thus, BUD becomes esterified in the airways more promptly and to a greater extent than CIC-AM, and BUD esterification prolongs BUD airway retention. In contrast, airway retention of CIC-AM and CIC seems to be determined mainly by their lipophilicity, similar to FP and MF, which are not esterified.