Pyrazolopyrimidines

With well-established animal models to evaluate vasodilation and FFA reduction, several compounds were profiled in vivo and they indeed displayed improved TIs relative to niacin. Furthermore, these models appeared to correlate to humans as two candidates including both 

MK-0354 and INCB-19062 showed excellent FFA reduction accompanied by minimal flushing in humans. 

At least four clinical candidates including GSK-256073 [112], MK-0354 [102], MK-1903 [113], and INCB-19062 [91], and one preclinical candidate MK-6892 [77] have been reported. Neither the structure of GSK-256073, nor the clinical data, has been reported. In Phase II clinical trials, neither GPR109A partial agonist MK-0354, nor the full agonist MK-1903 showed substantial lipoprotein effects, and both candidates were discontinued. INCB-19062 is targeted to a type II diabetes indication based upon the related role of FFA to insulin sensitization in type II diabetes, and the robust FFA lowering effect observed in a Phase I clinical trial devoid of FFA rebound. 

Carballo-Jane, and J. G. Richman, Bioorg. Med. Chem. Lett., 2010, 20, 2797. 

Annual Reports in Medicinal Chemistry, Volume 45 ISSN 0065-7743, DOI 10.1016/S0065-7743(10)45006-X 

---

From Multiring Systems Containing Pyrazoles. The pyrazolopyrimidine (65) on treatment with diazomethane forms the cyclopropane (66), which undergoes a ring-opening reaction with potassium hydroxide to yield the pyrazole (67) (eq. 16) (44). 

Pyrazoles can be prepared by ring opening reactions of fused systems already containing the pyrazole nucleus. Thus several [5.5], [5.6] and [5.7] fused heterocycles have been opened to substituted pyrazoles, usually in basic medium. In general, the method has little preparative interest since another pyrazole derivative has usually been used to build the ring-fused system. However, due to the unexpected structures obtained, two publications are worthy of notice. 6//-Cyclopropa[5a,6a]pyrazolo[l,5-a]pyrimidine (638) was readily obtained from the corresponding pyrazolopyrimidine by the action of diazomethane at room temperature (Scheme 59) (81H(15)265). When (638) was treated with potassium hydroxide, the pyrazole (640) was formed, probably via the diazepine (639). 

Pyrazolo[3,4-d]pyrimidine, 4-amino-tautomerism, 5, 310 Pyrazolopyrimidinediones synthesis, 5, 324 Pyrazolopyrimidines acidity, 5, 309 anions... 

Pyrazolopyrimidines, amino-acidity, 5, 309 alkylation, 5, 310 N-oxide synthesis, 5, 324 synthesis, 4, 525 5, 328 Pyrazolopyrimidines, dimethyl-synthesis, 5, 316 Pyrazolo[ 1,5-a]pyrimidines electrophilic attack, 5,311 synthesis, 5, 271, 320, 331 Pyrazolo[ 1,5-c]pyrimidines electrophilic attack, 5, 312 Pyrazolo[3,4- d]pyrimidines nucleophilic attack, 5, 313 synthesis, 5, 161, 272, 323, 334 tautomerism, 5, 309 Pyrazolo[4,3-d]pyrimidines alkylation, 5, 310 synthesis, 5, 272... 

A synthesis of pyrazolopyrimidines from methoxybutenone has been patented (99W054333). 

The two selective GABA j receptor agonists currently marketed in the United States, zaleplon and Zolpidem, are a pyrazolopyrimidine and a imidaz-opyridine, respectively. Both of these drugs are approved only for the shortterm treatment of insomnia. 

The pyrazoles 51 react with triethyl orthoformate and hydrazine to give the pyrazolopyrimidines 52 which react further with acetic anhydride and benzoyl chloride to give pyrazolotriazolopyrimidines 53 and with a-ketohydrazonoyl halides to give pyrazolopyrimidotriazines 54 <95MI01 96CA(124)86924>. 

The pyrimidines 62 undergo cyclisation on refluxing in dioxane to yield not only the pyrazolopyrimidines 63, but the novel pyrazolo[3, 4 4,5]pyrido[2,3-rflpyrimidines 64 by an intramolecular 1,3-dipolar cycloaddition reaction (Scheme 9)<96JCS(P1)1999>. 

PCI-32765 1 is the only Btk inhibitor which has been reported to have advanced to clinical trials [40]. Modeling of pyrazolopyrimidine 2 suggested that replacement of the cyclopentyl moiety could position an electrophilic group in proximity to Cys481, and subsequent optimization led to 1 [41]. Compound 1 inhibits Btk with an IC50 of 0.8 nM, and covalent binding to Btk was confirmed by mass spectrometry and washout experiments. In the Ramos B-cell line, 1 inhibits BCR-induced calcium... 

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... 

Grouped in this Section are the C-D-pentofuranosyl-imidazoles, -pyrazolopyrimidines, and -adenines. The last two analogs are positional isomers of formycin in which the heterocyclic moiety is attached to the sugar at an unnatural position. A rationale103 for the synthesis of this type of analog is of interest it was based on the possibility of a close structural similarity between a natural adenine nucleoside and synthetic analog with respect to available hydrogenbonding sites. 

N-(Pyrazolopyrimidin-7-yl)aminomethylenemalonates (640) were thermally cyclized when heated in diphenyl ether at 240°C for 7 min to give pyrazolopyridopyrimidinecarboxylates (641) in 73-75% yields (77GEP26 50780). 

In previous work (85MI1 87AHC319), the synthesis and chemistry of pyrazolopyridines and pyrazolopyrimidines was surveyed. This chapter reports synthetic approaches to other aromatic 10 tt electron systems containing a pyrazole moiety, as well as the systems main chemical and physicochemical properties. 

Three-component treatment of ketosulfones and related CH-acids with aldehydes and 5-aminopyrazoles was also patented by Han and Hu [74]. They used stirring of the starting materials in THF at 70°C and HPLC purification to synthesize biologically active pyrazolopyrimidines containing sulfonic group. 

Smith CJ, Iglesias-Siguenza FJ, Baxendale IR et al (2007) Flow and batch mode focused microwave synthesis of 5-amino-4-cyanopyrazoles and their further conversion to 4-amino-pyrazolopyrimidines. Org Biomol Chem 5(17) 2758-2761... 

In addition to the preceding chemotypes, a limited number of patent specifications include PDKI as a target for the inhibitors exemplified in the cases. Thus, 5-aminocarbonylindazoles, pyrazolopyrimidines, triazolo[l,5-a]-pyrimidines, pyrazolopyrroles and phthalimides have been claimed to be active against PDKI [1], but further biological data are awaited. 

PPl (8) and its pyrazolopyrimidine analog PP2 (9) [99-108] were first described as potent inhibitors of SFKs with marked selectivity versus ZAP-70, JAK2, EGF-R, and PKA kinases. PPl provided an early key inhibitor of Src kinase to enable determination of its roles in VEGF-mediated angiogenesis and vascular permeability, Src-driven human breast cancer cell lines with respect to both heregulin-dependent or independent growth, and Src-related,... 

Zaleplon (Sonata) [C IV] [Sedotive/Hypnotic] Uses Insomnia Action A nonbenzodiazepine sedative/hypnotic, a pyrazolopyrimidine Dose 5-20 mg hs PRN -1- w/ renal/hepatic insuff, elderly Caution [C, /-] w/ mental/ psychological conditions Contra Component allergy Disp Caps SE HA, edema, amnesia, somnolence, photosens Interactions t CNS depression W/ CNS d es-sants, imipramine, thioridazine, EtOH X effects W/ carbamazepine, phenobarbital, phenytoin, rifampin EMS Concurrent EtOH can t adverse CNS effects OD May cause profound CNS depression symptomatic and supportive Zanamivir (Relenza) [Antiviral/Neuramidase Inhibitor] Uses Influenza A (including HlNl swine flu) B Action X Viral neuraminidase Dose Adults Feds > 7 y.2 inhal (10 mg) bid for 5 d initiate w/in 48 h of Sxs Caution [C, M] Contra Pulm Dz Disp Powder for inhal SE Bron-chospasm, HA, GI upset EMS Does not reduce risk of transmitting virus monitor for bronchospasm or other severe resp events OD May cause resp problems s5rmptomatic and supportive... 

Related hypnotics that also act at benzodiazepine receptors are the newer agents zolpidem, a imida-zopyridine, zaleplon a pyrazolopyrimidine and the cyclopyrrolone zopiclone. Zopiclone might have a role for the treatment of benzodiazepine addiction. In patients in whom zopiclone was substituted for a benzodiazepine for 1 month and then itself abmptly terminated, improved sleep was reported during the zopiclone treatment, and withdrawal effects were absent on discontinuation of zopiclone. A series of non-sedating anxiolytic drugs derived from the same structural families as the above mentioned nonbenzodiazepines, have been developed, such as alpi-dem and pagoclone. 

PCls-induced dehydrative cyclization of the amino and amide functionalities of the thiadiazole moiety of the pyrazolopyrimidine 172 led to the formation of the imidazo[4,5-f][l,2,5]thiadiazole suhstmcture (Equation 13) <2001W0040231>. 

X-Ray data for ALP 61, formycine A 62, as well as the pyrazolopyrimidine derivatives 63 and oxazinopyrimidine 64 have been discussed in CHEC-II. 

Pyrazolopyrimidine 148 reacted with magnesium to yield the corresponding Grignard reagent 149 that reacted with pivaldehyde to yield the corresponding C-alkylated derivative 150 (Scheme 5) <2003JOC2054>. 

---