Automation and Microfluidics for the Efficient, Fast, and Focused Reaction Development of Asymmetric Hydrogenation Catalysis

Automation and microfluidic tools potentially enable efficient, fast, and focused reaction development of complex chemistries, while minimizing resource- and material consumption. The introduction of automation-assisted workflows will contribute to the more sustainable development and scale-up of new and improved catalytic technologies. Herein, the application of automation and microfluidics to the development of a complex asymmetric hydrogenation reaction is described. Screening and optimization experiments were performed using an automated microfluidic platform, which enabled a drastic reduction in the material consumption compared to conventional laboratory practices. A suitable catalytic system was identified from a library of Ru^II -diamino precatalysts. In situ precatalyst activation was studied with ¹ H/³¹ P nuclear magnetic resonance (NMR), and the reaction was scaled up to multigram quantities in a batch autoclave. These reactions were monitored using an automated liquid-phase sampling system. Ultimately, in less than a week of total experimental time, multigram quantities of the target enantiopure alcohol product were provided by this automation-assisted approach.

Synthesis of 4-Azido-N-acetylhexosamine Uridine Diphosphate Donors: Clickable Glycosaminoglycans

Unnatural chemically modified nucleotide sugars UDP-4-N3-GlcNAc and UDP-4-N3-GalNAc were chemically synthesized for the first time. These unnatural UDP sugar products were then tested for incorporation into hyaluronan, heparosan, or chondroitin using polysaccharide synthases. UDP-4-N3-GlcNAc served as a chain termination substrate for hyaluronan or heparosan synthases; the resulting 4-N3-GlcNAc-terminated hyaluronan and heparosan were then successfully conjugated with Alexa Fluor 488 DIBO alkyne, demonstrating that this approach is generally applicable for labeling and detection of suitable glycosaminoglycans.

Chemoenzymatic Synthesis of 4-Fluoro-N-Acetylhexosamine Uridine Diphosphate Donors: Chain Terminators in Glycosaminoglycan Synthesis

Unnatural uridine diphosphate (UDP)-sugar donors, UDP-4-deoxy-4-fluoro-N-acetylglucosamine (4FGlcNAc) and UDP-4-deoxy-4-fluoro-N-acetylgalactosamine (4FGalNAc), were prepared using both chemical and chemoenzymatic syntheses relying on N-acetylglucosamine-1-phosphate uridylyltransferase (GlmU). The resulting unnatural UDP-sugar donors were then tested as substrates in glycosaminoglycan synthesis catalyzed by various synthases. UDP-4FGlcNAc was transferred onto an acceptor by Pastuerella multocida heparosan synthase 1 and subsequently served as a chain terminator.

Regulation of serum calcitriol by serum ionized calcium in rats during pregnancy and lactation

Serum calcitriol concentrations in rats follow a biphasic pattern during reproduction, with elevated levels during late pregnancy, a decline after parturition, and a rise to even higher levels during peak lactation. We have previously shown that serum calcitriol in rats at peak lactation correlates significantly with, and appears to be regulated by, serum ionized Ca (Ca2+), with parathyroid hormone (PTH) serving a permissive role. We have extended this study by determining if serum calcitriol also correlates with serum Ca2+ during late pregnancy, when calcitriol levels are clearly elevated, and during early lactation, when only modest increases in serum calcitriol are observed. Analyses of data combined from nonmated, 21-day pregnant (P), and 1-day lactating rats (L) revealed a significant regression (p < 0.001) of calcitriol on Ca2+, but a nonsignificant regression (p = 0.34) of calcitriol on serum PTH. An even stronger correlation (p < 0.001) between calcitriol and Ca2+ was found for the combined data for 5-, 8-, and 14-day L rats. The partial correlation coefficient for calcitriol versus Ca2+, with PTH as the independent variable, was highly significant (p < 0.01) for the data from both combined groups. However, the coefficient for calcitriol versus PTH, with Ca2+ as the independent variable, was not significant (p > 0.05). Fetal weights (uterus and contents) correlated significantly with both maternal calcitriol and Ca2+ concentrations (p < 0.01), but not with maternal PTH levels. Litter weights for 14-day-old pups likewise correlated significantly with maternal calcitriol and Ca2+ (p < 0.001). We conclude that hypocalcemia, induced by the demands for Ca for fetal calcification and milk production, appears to be a controlling factor in serum calcitriol elevation in late pregnancy and throughout lactation, whereas PTH may be important for calcitriol synthesis without playing a direct regulatory role.

Altered regulation of parathyroid hormone secretion by calcium in pregnant and lactating rats

We have previously shown that the serum parathyroid hormone (PTH) concentration in lactating (L) rats is not suppressed by high serum Ca2+ to the same extent as in nonmated (NM) rats. To investigate further Ca2+ regulation of PTH secretion, parathyroid cells from NM rats and rats in late pregnancy and at peak lactation were dispersed and incubated for 2 h in medium containing 0.52-2.05 mM Ca2+. Medium PTH was assayed with a homologous immunoradiometric assay (IRMA). At the two highest Ca2+ levels (1.81 and 2.05 mM), medium PTH was significantly higher (p = 0.031) for cells from L rats than for cells from NM rats. In contrast, significantly less (p < 0.001) PTH was secreted for the L group versus the NM group at medium Ca2+ values of 1.27 and 1.46 mM. Estimated set points for L and NM groups were 1.17 mM and 1.35 mM, respectively, corresponding closely to the prevailing serum Ca2+ for these two groups. Consistent with the present in vitro data, high serum PTH (> 40 pg/ml) in L rats occurred only at serum Ca2+ values below 1.27 mM. Elevated serum PTH at lower serum Ca2+ levels was also seen in pregnant rats. Dispersed parathyroid cells from 20- to 21-day pregnant rats secreted significantly more PTH (p = 0.028) than cells from NM rats at all Ca2+ levels tested (1.1-1.6 mM). In conclusion, the relationship between extracellular Ca2+ and PTH secretion is altered in rats during late pregnancy and at peak lactation, perhaps as part of the adaptation to the demands for calcium for pre- and postnatal growth.

Several anesthetics, but not diethyl ether, cause marked elevation of serum parathyroid hormone concentration in rats

The effects of anesthetics on serum parathyroid hormone (PTH) concentrations were determined by a new homologous two-site immunoradiometric assay for rat PTH. Serum PTH concentrations (mean +/- SE) from ether-anesthetized rats (14.7 +/- 1.5 pg/ml, n = 22) were not significantly different from those of decapitated unanesthetized female rats (13.0 +/- 1.8 pg/ml, n = 21). Serum PTH concentrations in pg/ml (n = 4-14) for other anesthetics tested were: ketamine, 12.5 +/- 1.1; Na pentobarbital, 23.3 +/- 2.4; methoxyflurane (inhalation), 42.2 +/- 6.8; and xylazine combined with ketamine, 51.4 +/- 11.3 pg/ml. The latter two concentrations were significantly (p < 0.001) higher than the values for all other anesthetics and decapitation. Elevation of serum PTH induced by pentobarbital or ketamine + xylazine increased with time under anesthesia. Neither serum Ca2+ concentrations nor pH differed among any of the groups. We conclude that anesthesia induced by pentobarbital, methoxyflurane, or ketamine + xylazine in rats leads to a marked elevation of serum PTH levels that appears to be related to the duration of anesthesia and not due to any measurable fall in serum Ca2+.

Determination of bioactive rat parathyroid hormone (PTH) concentrations in vivo and in vitro by a 2-site homologous immunoradiometric assay

A new homologous 2-site assay for rat parathyroid hormone (IRMA), developed by Immutopics, Inc., has been evaluated and compared with a bone cell cAMP bioassay. Circulating PTH for adult rats assayed with this IRMA are in the range 10-15 pg/ml, and of the same order of magnitude as published values for biologically active PTH. The standard curve for the IRMA was linear over the range 3.4-240 pg/ml of rPTH 1-34, and serum samples diluted in parallel with the standard curve. The within-assay and between-assay coefficients of variation ranged from 5.2% (n = 18) to 7.6% (n = 24) and 8.3% (n = 16) to 26.4% (n = 10), respectively. Serum PTH values (mean +/- S.E.) for parathyroidectomized rats were 3.5 +/- 0.6 pg/ml (n = 18) versus 10.3 +/- 1.4 pg/ml (n = 16) for intact non-mated rats. Calcium injections suppressed circulating PTH by 50%. Lactating rats had serum PTH levels 5-fold higher and vitamin D deficient rats 60-fold higher than non-mated controls. PTH secreted from parathyroid cells in vitro was in the range 60-490 pg/ml as determined by the IRMA. These values represented 86.0 +/- 9.0% of the comparable bioassay values, indicating that the IRMA detects only bioactive PTH.