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The reactions between 5-substituted pyrazolidine-3-ones, aldehydes, and methyl methacrylate provided tetrahydropyrazolo[1,2-a]pyrazole-1-carboxylates as mixtures of syn- and anti-diastereomers. Testing for inhibition of dihydroorotate dehydrogenase of Plasmodium falciparum (PfDHODH) revealed high activity of some anti-isomers of the methyl esters, while the corresponding carboxylic acids and carboxamides were not active. The most active representative, methyl (1S*,3S*,5R*)-1,5-dimethyl-7-oxo-3-phenyltetrahydro-1H,5H-pyrazolo[1,2-a]pyrazole-1-carboxylate (IC50 = 2.9 ± 0.3 μM), also exhibited very high selectivity of the parasite enzyme vs. the human enzyme, PfDHODH/HsDHODH > 350. According to the molecular docking score, this high activity is explainable by synergic interactions of the methyl, phenyl and the CO2Me substituent with the hydrophobic pockets in the active site of the enzyme. The carboxylic acid and carboxamides derived from this compound did not inhibit PfDHODH.

A constrained tricyclic analogue of α-L-LNA (2), which contains dual modes of conformational restriction about the ribose sugar moiety, has been synthesized and characterized by X-ray crystallography. Thermal denaturation experiments of oligonucleotide sequences containing this tricyclic α-L-LNA analogue (α-L-TriNA 2, 5) indicate that this modification is moderately stabilizing when paired with complementary DNA and RNA, but less stabilizing than both α-L-LNA (2) and α-L-TriNA 1 (4).

Treatment of β-keto ester 8 with hydrazines 9a-g gave 1'-substituted tert-butyl 2-(5-hydroxy-1H- pyrazol-3-yl)ethylcarbamates 10a-e and 2-(5-oxo-2,5-dihydro-1H-pyrazol-3-yl)ethylcarbamates 11f,g. Acidolytic deprotection of 10b,c afforded the corresponding 3-(2-aminoethyl)-5-hydroxy- 1H-pyrazoles 6b,c in good yields. Acylation of 6 gave either the N-acyl compounds 12b,c and 13c, or the N,O-diacyl derivative 14. Next, three N,N-dialkyl analogues 15a,b and 26c were prepared from dimethyl acetone-1,3-dicarboxylate 21 via condensation with hydrazines 9a and 9h followed by hydrolysis of the esters 22a,b, amidation of the carboxylic acids 23a,b, and reduction of the tertiary carboxamides 24a and 25b,c.

For the use of analytics, European pharmacopoeial impurities A, B, C, and D of cabergoline were synthesized. Ergocryptine was chosen as a starting material and synthesis was accomplished via two approaches, different in length and stereochemical outcome. A longer, indirect approach was realized through otherwise problematic oxidations of the 9,10-dihidrolysergol derivative, to the corresponding aldehyde and carboxylic acid. This was achieved by the use of activated DMSO and a Pinnick oxidation sequence. All four synthesized impurities are used as analytical standards in cabergoline manufacturing processes.