The Antiproliferative Activity and NO Inhibition of Neo-Clerodane Diterpenoids from Salvia guevarae in RAW 264.7 Macrophages

In this study, nine <i>neo</i>-clerodane-type diterpenoids (<b>1</b>-<b>9</b>) were isolated from the dichloromethane extract of <i>Salvia guevarae</i> Bedolla & Zamudio leaves. Compounds <b>1</b>-<b>6</b> were new natural products, and <b>7</b>-<b>9</b> were acetone artifacts. In addition, four <i>neo</i>-clerodanes diterpenoids (<b>10</b>-<b>13</b>) previously described from different sources and six triterpenoids-identified as 3β,20,25-trihydroxylupane, oleanolic acid, 3β-<i>O</i>-acetyl-oleanolic acid, ursolic acid, 3β-<i>O</i>-acetyl-betulinic acid, and 3β,28-<i>O</i>-diacetyl-betulin-were isolated. Additionally, five flavonoids were also isolated from the methanol extract: quercetin-3-<i>O</i>-β-xylopyranosyl-(1 → 2)-β-galactopyranoside, taxifolin-7-<i>O</i>-β-glucopyranoside, naringenin-7-<i>O</i>-β-glucopyranoside, a mixture of 2<i>R</i> and 2<i>S</i> eriodictyol-7-<i>O</i>-β-glucopyranoside, caffeic acid, the methyl ester of rosmarinic acid, and rosmarinic acid. The structure of the isolated compounds was established by spectroscopic means, mainly ¹H and ¹³C NMR, including 1D and 2D homo- and heteronuclear experiments. The absolute configuration of <b>1</b> and <b>10</b> was ascertained via an X-ray analysis, and that of the other compounds via ECD. The antiproliferative activity of some diterpenoids was determined using the sulforhodamine B method, where guevarain B (<b>2</b>) and 6α-hydroxy-patagonol acetonide (<b>7</b>) showed moderate activity against the K562 line, with IC₅₀ (μM) = 33.1 ± 1.3 and 39.8 ± 1.5, respectively. The NO inhibition in RAW 264.7 macrophage activity was also determined for some compounds, where 2-oxo-patagonal (<b>6</b>), 6α-hydroxy-patagonol acetonide (<b>7</b>), and 7α-acetoxy-<i>ent</i>-clerodan-3,13-dien-18,19:16,15-diolide (<b>10</b>) were proven to be active, with IC₅₀ (μM) of 26.4 ± 0.4, 17.3 ± 0.5, and 13.7 ± 2.0, respectively. The chemotaxonomy of <i>Salvia guevarae</i> is also discussed.