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Montmorillonite K-10 mediated MCR of anilines, arylaldehydes and ethyl-3,3-diethoxypropionate in water afforded 2,6-unsubstituted dihydropyridines depending on the nature of anilines employed. A variety of dihydropyridines were prepared by using this green methodology in good yields and montmorillonite K-10 was found to be an inexpensive and reusable catalyst. The structure elaboration of a representative compound was carried out under Heck conditions. Some of the compounds synthesized showed significant inhibition of PDE4B when tested in vitro. Docking studies indicated that one of the ester moieties of these compounds played a key role in their interactions with the PDE4B protein.

The design and synthesis of 4-alkynyl pyrazole derivatives has led to the identification of new class of PDE4 inhibitors. All these compounds were accessed for the first time via a facile Pd/C-CuI-PPh(3) mediated C-C bond forming reaction between an appropriate pyrazole iodide and various terminal alkynes. In vitro PDE4B inhibitory properties and molecular modeling studies of some of the compounds synthesized indicated that 4-alkynyl pyrazole could be a promising template for the discovery of novel PDE4 inhibitors.

An efficient and green synthesis of functionalized cyano pyridines has been achieved via montmorillonite K-10 mediated multi-component reaction in a chemo- and regioselective manner. The four-component reaction of β-keto ester, arylaldehyde, malononitrile and an alcohol provided a variety of pyridine derivatives and montmorillonite K-10 was found to be a reusable catalyst. The potential of this operationally simple methodology has been demonstrated in further structure elaboration of a compound synthesized via C–C bond forming reactions under Suzuki, Sonogashira and Heck conditions. Some of the cyano pyridines synthesized showed PDE4B inhibitory properties in vitro and good interactions with PDE4B protein in silico suggesting cyano pyridine scaffold as a potential template for the discovery of novel PDE4 inhibitors.

A number of novel 1-(3-arylprop-2-ynyl) substituted 1,2-dihydroquinoline derivatives related to nimesulide and their 2-oxo analogues have been designed as potential inhibitors of PDE4. All these compounds were synthesized by using Sonogashira coupling as a key step. In vitro PDE4B inhibitory properties and molecular modeling studies of some of the compounds synthesized are presented.

A new strategy for converting antipsychotic drug olanzapine into PDE4 inhibitors is described via the design and Pd/C mediated synthesis of novel N-indolylmethyl olanzapine derivatives. One compound showed good inhibition (IC50 1.1 μM) and >10 fold selectivity towards PDE4B over D that was supported by docking studies. This compound also showed significant inhibition of TNF-α and no major toxicities in cell lines and a zebrafish embryo model except the teratogenic effects to be re-assessed in rodents.

A number of novel imidazophenoxazine-4-sulfonamides have been designed as potential inhibitors of PDE4. All these compounds were readily prepared via an elegant multi-step method involving the initial construction of 1-nitro-10H-phenoxazine ring and then fused imidazole ring as key steps. Some of these compounds showed promising PDE4B and D inhibition when tested in vitro and good interactions with these proteins in silico. Three of these compounds showed dose dependent inhibition of PDE4B with IC50 value of 3.31 ± 0.62, 1.23 ± 0.18 and 0.53 ± 0.18 μM.

Substituted 1,4-dihydropyridines were discovered as a novel and potent series of phosphodiesterase 4 (PDE4) inhibitors. Structure–activity relationships within this series have been carried out and studies revealed that the dihydropyridine core, with indole moiety and 3,4-dimethoxybenzyl group, is a potent analogue for PDE4 inhibition. These novel series of compounds were prepared via a 3-component reaction in a single pot. In vitro biological activity, modeling studies and crystallography data are also reported.

Novel thieno[2,3-d]pyrimidines containing a cyclohexane ring fused with a six- or five-membered heterocyclic moiety along with a benzylic nitrile were designed as potential inhibitors of PDE4. Expeditious synthesis of these compounds was carried out via a multi-step sequence consisting of a few key steps such as Gewald reaction, Dieckmann type cyclisation and Krapcho decarboxylation. This newly developed strategy involved construction of the thienopyrimidine ring followed by the cyclohexanone moiety and subsequently the fused heterocyclic ring. A number of thieno[2,3-d]pyrimidine based derivatives were synthesized using this method some of which showed promising PDE4B inhibitory properties. One of them was tested for PDE4D inhibition in vitro and dose dependent inhibition of TNF-α. A few selected molecules were docked into the PE4B protein the results of which showed good overall correlations to their observed PDE4B inhibitory properties in vitro. The crystal structure analysis of representative compounds along with hydrogen bonding patterns and molecular arrangement present within the molecule is described.

Novel polysubstituted pyrroles have been designed and accessed via a one-pot multicomponent reaction followed by Pd-mediated C-C bond forming reactions. All the compounds synthesized were tested for their PDE4B inhibitory properties in vitro and two of them obtained via Heck reaction showed significant inhibition. The docking results suggested that these alkenyl derivatives containing ester moiety interact well with the PDE4B protein in silico where the ester carbonyl oxygen played a key role. The pyrrole framework presented here could be a new template for the identification of small molecule based novel inhibitors of PDE4. The single crystal X-ray data of a representative compound is presented.

A number of novel 1,8-disubstituted 5,5-dimethyl-4,5-dihydro-1H-benzo[g]indazoles based on a conformationally restricted pyrazole framework have been designed as potential inhibitors of PDE4. All these compounds were readily prepared by using simple chemistry strategy. The in vitro PDE4B inhibitory properties and molecular modeling studies of some of the compounds synthesized along with the X-ray single crystal data of a representative compound is presented.

A conceptually new and general strategy has been developed for the construction of a benzimidazole or a benzoxazole ring fused with isoquinolinone affording a diverse and unique class of small molecules as potential and novel inhibitors of PDE4.

A one-pot cascade reaction has been developed leading to the concurrent construction of six and five membered fused N-heterocyclic rings of indazolo[3,2-b]quinazolinones. The methodology involved the reaction of isatoic anhydride, a hydrazine and o-iodo benzaldehyde in the presence of Pd(PPh(3))(4) and BINAP in MeCN. The mechanism of this cascade reaction is discussed. A variety of indazolo[3,2-b]quinazolinone derivatives were prepared by using this methodology in good yields, some of which were tested for their PDE4 inhibitory properties in vitro. The dose response and docking study performed using a representative compound is presented.