Chemical Transformations of Phyllocladane (=13β‐Kaurane) Diterpenoids

Abstract

Earlier phytochemical work on Plectranthus ambiguus (Lamiaceae) afforded a series of tetracyclic phyllocladane-type ( 13b-kaurane) diterpenoids (see 1a ± f). In the course of investigations concerning the reaction behavior of this rare natural-products, a new constituent of P. ambiguus was isolated, (2S,3R,16R)-phyllocladane-2,3,16,17-tetrol 2,3-diacetate (1g), and another eighteen new phyllocladanes were prepared by chemical transformations and characterized. The main constituent 1b of P. ambiguus was chemically transformed to the known natural diterpenoid calliterpenone ( (16R)-16,17-dihydroxyphyllocladan-3-one; 2) thus unambiguously establishing its structure (Scheme 1). Epimerization at C(16) via the epoxy derivative 20 yielded 16-epicalliterpenone (21), 17-hydroxyphylloclad-15-ene-3-one (22), and (16R)-3-oxophyllocladan-17-al (23) (Scheme 6). Comparing this reaction sequence with the corresponding one starting from diastereoisomeric (16R)-16,17-dihydroxy-ent-kauran-3-one ( abbeokutone; 27) showed basically the same outcome (Scheme 7). Furthermore, three new C(16)-substituted ent-kauran-3-ones were characterized.Reliable spectroscopic arguments for the determination of the configuration at C(16) in phyllocladanes and kauranes as well as for the differentiation of the diastereoisomeric skeletons are presented.

Eight <i>ent</i>-Kaurane Diterpenoid Glycosides Named Diosmariosides A–H from the Leaves of <i>Diospyros maritima</i> and Their Cytotoxic Activity

“…6 Hz) and that of D-aiofuranoside was also to be β by comparison of the 13 C-NMR data of authentic samples prepared in our laboratory [methyl β-D-apiofuranoside: δ C 111.6 (C-1), 77.9 (C-2), 80.5 (C-3), 74.9 (C-4), 65.5 (C-5) and methyl α-D-apiofuranoside: δ C 104.6 (C-1), 73.4 C-2), 77.9 (C-3), 75.1 (C-4), 65.6 (C-5)] .9,10) Diosmarioside A (1) was found to be in the enantio series from the negative Cotton effect at 289 nm (∆ε −2.87) in the circular dichroism (CD) spectrum. 11,12) Therefore, the structure of diosmarioside A (1) was elucidated, as shown in Fig. 1.…”

“…2). Diosmarioside E (5) was found to be in the enantio series from the negative Cotton effect at 294 nm (∆ε −0.71) in the CD spectrum 11,12) and the geometry at the 16-position was explored by the PS-ROESY experiment. Significant ROESY correlations between H-17b (δ H 3.47) and H-14b (δ H 1.06), and H-16 (δ H 2.18) and both of H-11a (δ H 1.53) and H-12b (δ H 1.32) suggested that the C-17 primary alcohol was in the α-face, namely, the absolute configuration of the 16-position to be R (Fig.…”

Chemistry of South African Lamiaceae: Structures and Biological Activity of Terpenoids

“…The plant afforded a series of tetracyclic phyllocladane-type (= 13β-kaurane) diter-penoids: (101). The authors discriminated between phyllocladane and ent-kaurane tetracyclic skeletons after extensive spectroscopic investigation as well as chemical transformations [48,49].…”

Chemical Constituents from the Stems of Manihot esculenta

“…Therefore, searching for novel structural and bioactive natural products from its stems led to the isolation of two new compounds 1 and 6 (Fig. 1), and four known diterpenoids, yucalexin P – 21 ( 2 ) [10, 11], cleistanthene – type sonderianol ( 3 ) [12], calliterpenone ( 4 ) [13], ent -kauran-3 α ,16 α , 17-triol ( 5 ) [14]. Herein, this paper describes the isolation, structure elucidation and antimicrobial activities of these compounds.

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