Piperlotines are natural products characterized by an α,β-unsaturated amide moiety. These compounds found wide applications in Medicinal Chemistry like antibacterials, cytotoxic agents, anticoagulants, among others. To date, diverse methods of synthesis have been reported for piperlotines, but involving the use of catalysts, hazard reagents, anhydrous media or coupling reagents. Thus, in this work, we developed a greener method of synthesis of piperlotines A, C, and derivatives, through mechanochemical activation under solvent-free conditions. The reaction of a β-amidophosphonate, K₂CO₃, and an aromatic aldehyde afforded target compounds in moderate to good yields (46–77%), in an open atmosphere by grinding. It is worth to mention that this mechanochemical process was under thermodynamic control because just E isomer was isolated for every reaction. Moreover, synthesized piperlotines have been predicted by means of chemoinformatic analysis as potential therapeutic agents for the treatment of arthritis or cancer.

Herein we report the mild synthesis of 15 phosphonocinnamic esters by means of a solvent-free mechanically activated Horner-Wadsworth-Emmons (HWE) olefination, in regular to excellent yields (13–99%), from tetraethyl methylenediphosphonate, an aromatic or aliphatic aldehyde and potassium tert-butoxide, using 5 min of mortar and pestle grinding. Potassium tert-butoxide acts as a base and liquid-assisting grinding agent. All isolated products were fully characterized as (E)-isomers through NMR spectroscopy. Furthermore, among the synthesized compounds diethyl (E)-2-(4-methoxyphenyl)vinylphosphonate 1 was discovered as an interesting cytotoxic agent inhibiting growth of two breast cancer cell lines (MDA-MB-453, IC₅₀ = 79 µg/mL and MCF-7 IC₅₀ = 64 µg/mL). To the best of our knowledge, this is the first report of mechanically activated HWE reaction for the synthesis of α, β-unsaturated phosphonates and the first time some of them have been assessed as cytotoxic agents on breast cancer cell lines. In conclusion, the fast and operationally simple synthesis of (E)-phosphonocinnamic esters afforded new promising cytotoxic agents in regular to excellent yields in very short reaction times. Graphical Abstract

Bisphosphonic acids (or bisphosphonates) have been successfully used in the clinic treatment of bone diseases for over decades. Additionally, the antiinflammatory activity of these compounds has been gaining attention. In our previous work, we synthesized and in vivo evaluated the bisphosphonic esters 1 and 2, finding a moderate edema inhibition upon oral and topical administration on BALB/c mice. Thus, in this work, the bioisosteric replacement of an amide functional group for an ester afforded the new bisphosphonates 3–6, which had a moderate oral edema inhibition (25 mg/kg dose) and a significant topical antiinflammatory activity (2 mg/ear) on BALB/c mice, with 6 being the most active hit (55.9% edema inhibition), comparable to the positive control (55.5% edema inhibition) on a TPA topical model. Next, to assess the acute toxicity of the synthesized derivatives, test animals were administered with 50–100 mg/kg of 3–6, respectively, by an oral route, and after 14 days, neither lethality nor a significative weight loss were observed. Finally, a structure–activity relationship (SAR) and a molecular docking analysis of 3–6 helped us to explain the trend observed in biological tests. Considering all these aspects, we propose the inhibition of MMP-8 and MMP-9 as a possible action mechanism of the synthesized derivatives.