Synthesis of diterpene glycosides

Summary Mono-, di-, and linear triglycosides of a diterpene alcohol, derived from abietic acid and glucose have been synthesized employing peracetylbromo--D-glucose (4) and maltose derivatives5 and8 as glycosyl donors. The triglycoside14 exhibits slight haemolytic activity.

---

Synthese von Diterpenglycosiden

Zusammenfassung Es wird die Synthese von Mono-, Di-, und linearen Triglycosiden aus einem von Abietinsäure abgeleiteten Diterpenalkohol beschrieben. Als Glycosyldonoren wurden neben Peracetobrom--D-glucose (4) die Maltosederivate5 und8 verwendet. Das Triglycosid14 zeigt schwache hämolytische Aktivität.

     

A New ent‐Kaurane Diterpene from Stems of Alibertia macrophylla K. Schum. (Rubiaceae)

Phytochemical investigations of the stems of a specimen of Alibertia macrophylla led to the isolation and characterization of the new diterpene ent‐kaurane‐2β,3α,16α‐triol ( 1 ), along with triterpenes 2 – 8 , iridoids 9 – 12 , and phenolic acids 13 – 15 . The structure of 1 was established based on spectroscopic studies (¹H‐ and ¹³C‐NMR, IR, and HR‐ESI‐MS). This is the first report of the isolation of a diterpene from the Alibertia genus in Rubiaceae.     

Biotransformation of 7-oxo-ent-kaur-16-ene derivatives by Gibberella fujikuroi

The microbiological transformation of 7-oxo-ent-kaur-16-ene by the fungus Gibberella fujikuroi gave fujenoic acid as the main compound, whilst the incubation of 18-hydroxy-7-oxo-ent-kaur-16-ene and 3α,18-dihydroxy-7-oxo-ent-kaur-16-ene afforded the corresponding 6β-hydroxy-derivatives. These facts indicate that the formation of fujenoic acid in this biotransformation should occur via a 7-oxo-6β-hydroxy derivative. In the three biotransformations, an 11β-hydroxylation was also produced, in low yield, indicating that a 7-oxo-group also directs hydroxylation at C-11.     

Biotransformation of two stemodane diterpenes by Mucor plumbeus

The microbiological transformation of 13α,17-dihydroxy-stemodane (2) by the fungus Mucor plumbeus afforded 13α,17,19-trihydroxy-stemodane (3), 3β,13α,17-trihydroxy-stemodane (5), 3-oxo-13α,17-dihydroxy-stemodane (7), 7α,13α,17,19-tetrahydroxy-stemodane (8), 3β,11α,13α,17-tetrahydroxy-stemodane (10), 3β,7α,13α,17-tetrahydroxy-stemodane (12), 3β,8β,13α,17-tetrahydroxy-stemodane (14), 2α,13α,17-trihydroxy-stemodane (16), 2α,13α,17,19-tetrahydroxy-stemodane (17), 2α,3β,13α,17-tetrahydroxy-stemodane (20) and 3β,11β,13α,17-tetrahydroxy-stemodane (22), whilst the incubation of 13α,14-dihydroxy-stemodane (25) gave 3β,13α,14-trihydroxy-stemodane (28), 2α,13α,14-trihydroxy-stemodane (29) and 13α,14,19-trihydroxy-stemodane (30). Preference for hydroxylations of ring A at C-2(α), C-3(β) and C-19 were observed in both incubations. An interesting rearrangement of 13α,14α-dihydroxy-stemodanes to 14-oxo derivatives with an unusual carbon framework has been observed under acetylation conditions. We have named this skeleton prestemodane, which, as a hydrocarbon ion, had been postulated as a biogenetic precursor of stemodane.     

Sesquiterpenes and Other Metabolites from the Marine Red Alga Laurencia composita (Rhodomelaceae)

Two new halogenated sesquiterpenes, (8β)‐10‐bromo‐3‐chloro‐2,7‐epoxychamigr‐9‐en‐8‐ol ( 1 ) and 2‐bromo‐3‐chlorobisabola‐7(14),11‐diene‐6,10‐diol ( 3 ), and one new phytol‐derived diterpene, 2,3‐epoxyphytyl acetate ( 4 ), along with cis‐ and trans‐1‐methylcyclohexane‐1,4‐diol ( 5 and 6 ) which were isolated from a natural source for the first time but have been previously synthesized, were isolated from the marine red alga Laurencia composita and characterized. In addition, a known sesquiterpene, pacifenediol ( 2 ), and the known furanone derivative 7 were also identified. Their structures were established by NMR and mass spectroscopic methods.     

ToF-SIMS characterisation of diterpenoic acids after chromatographic separation

Microcolumn liquid chromatography (μHPLC) coupled on-line with time of flight secondary ion mass spectrometry (ToF-SIMS) was applied for mixture of diterpenoic acids (abietic, gibberellic and kaurenoic) analysis. Chromatographic effluent, with analytes separated, was carried out directly onto different, ToF-SIMS compatible surface substrates, for further ToF-SIMS analysis. Silica gel Si₆₀, aluminium backplate modified Si₆₀, monolithic silica gel and Raman spectroscopy chromatographic thin layers were used as the deposition substrates in this experiment. By ToF-SIMS surface imaging the deposition trace picture has been obtained. Effluent deposition surface area was scanned for diterpenoic acid fragment mass values based on mass spectrometric library. Measured ToF-SIMS dataset of fragment abundance and intensities were used for preliminary fragmentation schemes construction. The lowest substrate background activity has been established for monolithic silica gel thin layer and aluminium backplate modified Si₆₀ thin layer. In the case of Raman spectroscopy pre-treated thin layer or conventional chromatographic thin layer Si₆₀, the both, high background signal intensity and impossibility to construct negative ions surface image, were observed. Diterpenoic acids studied serve the similar mass spectrum but ToF-SIMS coupled with liquid chromatographic separation brings new impact to the positive identification of analytes studied.     

ent‐Kaurane Diterpenes and Further Constituents from Wedelia trilobata

Two new ent‐kaurane diterpenes, wedelidins A ( 8 ) and B ( 9 ), together with eighteen other constituents, including the sesquiterpenoids 1 and 2 , ent‐kaurane diterpenes 3 – 7 , triterpenoids 10 and 11 , steroids 12 – 14 , and flavonoids 15 – 17 as well as benzene derivatives 18 – 20 , were isolated from the aerial parts of Wedelia trilobata. The structures of wedelidins A ( 8 ) and B ( 9 ) were elucidated by extensive spectroscopic analyses (including UV, IR, NMR, and MS). Furthermore, the structures of compounds 2 and 3 were confirmed by X‐ray single‐crystal diffraction analyses.     

Clerodane and ent‐Kaurane Diterpene Glycosyl and Glycoside Derivatives from the Leaves of Casearia sylvestris

Five new clerodane diterpene glycosyl derivatives, caseariasides A–E ( 1 – 5 , resp.) and three new ent‐kaurane diterpene glucosides, sylvestrisides C–E ( 6 – 8 , resp.) were isolated from the leaves of Casearia sylvestris. Their structures were determined on the basis of chemical and spectroscopic analyses.     

Isolation and structure determination of new 4,12-dideoxyphorbol esters from Euphorbia pannonica Host.

Phytochemical study of the aerial parts of Euphorbia pannonica led to the isolation of two new tigliane diterpenes, 4,12-dideoxy(4β)phorbol-20-benzoate-13-isobutyrate (1) and 4,12-dideoxy(4β)phorbol-20-benzoate-13-isovalerianate (2). The structures and relative stereochemistry were elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR experiments (¹H NMR, JMOD, COSY, NOESY, HSQC and HMBC).     

Synthesis of (+)-lagerstronolide from (+)-sclareol

The γ-acetoxybutenolide (+)-lagerstronolide was synthesized from (+)-sclareol, with an overall yield of 10%. The absolute stereochemistry for the natural compound (−)-lagerstronolide has been correctly established.