Total Syntheses and Synthetic Studies of Spongiane Diterpenes

Total Syntheses and Synthetic Studies of Spongiane Diterpenes

Available online at www.sciencedirect.com Tetrahedron 64 (2008) 445e467 www.elsevier.com/locate/tet Tetrahedron report number 821 Total syntheses and synthetic studies of spongiane diterpenes Miguel A. Gonza´lez* Departamento de Quı´mica Orga´nica, Universidad de Valencia, E-46100 Burjassot, Valencia, Spain Received 2 October 2007 Available online 22 October 2007 Keywords: Diterpenes; Spongiane; Marine natural products; Synthesis Contents 1. Introduction ................................................................................................................. 445 2. Structure, occurrence, and biological activity ................................................................................ 446 3. Syntheses of spongiane diterpenes ........................................................................................... 446 3.1. Syntheses from other natural products ............................................................................... 446 3.2. Syntheses by biomimetic approaches ................................................................................. 456 3.3. Other approaches and total syntheses ................................................................................ 459 4. Conclusions .................................................................................................................. 465 Acknowledgements .......................................................................................................... 465 References and notes ........................................................................................................ 465 Biographical sketch .......................................................................................................... 467 1. Introduction sequestering the spongian-derived metabolites from the sponges, soft corals, hydroids, and other sessile marine inver- Spongiane diterpenoids are bioactive natural products iso- tebrates on which they feed. Most of these compounds play lated exclusively from sponges and marine shell-less mollusks a key role as eco-physiological mediators and are of interest (nudibranchs), which are believed to be capable of for potential applications as therapeutic agents. Spongianes having the characteristic carbon skeleton I (Fig. 1) have been reviewed up to 1990 and listed in the Dictio- Abbreviations: AcCl, acetyl chloride; Ac2O, acetic anhydride; AIBN, azo- 1 bisisobutyronitrile; BuLi, buthyllithium; DIBAL-H, diisobutylaluminum hy- nary of Terpenoids. During the last two decades, many new dride; DHP, dihydropyrane; DMAD, dimethyl acetylenedicarboxylate; members of this family of natural products have been isolated DMAP, 4-(N,N-dimethylamino)pyridine; DMF, dimethylformamide; DMSO, and described in specific reviews on naturally occurring diter- 2 dimethylsulfoxide; Et3N, triethylamine; EVK, ethyl vinyl ketone; HMPA, hexa- penoids by Hanson, and the excellent reviewing work on ma- methyl phosphorotriamide; IBX, 2-iodoxybenzoic acid; LDA, lithium diisopro- rine natural products by Faulkner,3,4 now continued by the team pylamide; LiHMDS, lithium hexamethyldisilylamide; MsCl, mesyl chloride; 5e7 MCPBA, m-chloroperbenzoic acid; NaHMDS, sodium hexamethyldisilyl- of Blunt, all of which have covered mainly the isolation and amide; NMO, 4-methylmorpholine N-oxide; PCC, pyridinium chlorochromate; structural aspects of spongianes. A recent review on the chem- PPTS, pyridinium p-toluenesulfonate; p-TSA, p-toluenesulfonic acid; PhH, istry of diterpenes isolated from marine opisthobranchs has also benzene; PhMe, toluene; Py, pyridine; TBDMSOTf, tert-butyl dimethylsilyl tri- included articles on isolation and structure determination of fluoromethanosulfonate; TBDPSCl, tert-butyldiphenylsilyl chloride; TBAF, spongianes up to 1999.8 The latter survey also covered some tetra-n-butylammonium fluoride; TFA, trifluoroacetic acid; TMSCl, trimethyl- silyl chloride; TPAP, tetrapropylammonium perruthenate. synthetic studies of this class of substances. To the best of our * Tel.: þ34 96 354 3880; fax: þ34 96 354 4328. knowledge, there is only one more report dealing with the initial 9 E-mail address: [email protected] studies toward the synthesis of spongianes. 0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2007.10.057 446 M.A. Gonza´lez / Tetrahedron 64 (2008) 445e467 O 3. Syntheses of spongiane diterpenes 12 16 11 13 20 1 9 C D O O 2 14 Several syntheses have appeared within the last 25 years and A 10H 8 15 H H 5 17 3 B 7 we will classify them in three main groups. We will also include 4 H 6 H the synthetic studies developed so far and, thus, we will 19 18 I, spongiane skeleton 1, isoagatholactone describe the syntheses from other natural products, syntheses using biomimetic approaches and, finally, other approaches in- CO2H cluding the total synthesis of rearranged spongianes. O CO H Generally, despite the interesting molecular architectures H 2 and biological properties of the spongianes, there have been H H HO2C relatively few synthetic studies toward their synthesis. In the 2, isoagathic acid 3, grindelic acid 1980s, most of the synthetic studies toward spongiane-type di- Figure 1. terpenes addressed mainly the synthesis of isoagatholactone and the preparation of simple furanospongianes. In the next decade, the syntheses of several pentacyclic spongianes were accomplished together with the development We now provide full coverage of recent advances in the of biomimetic-like strategies for the synthesis of more com- field including a comprehensive description of the synthetic plex furanospongianes and isoagatholactone derivatives. approaches and syntheses reported in the literature on spon- Over the last three or four years, some structureeactivity stud- gianes up to September 2007. ies have emerged together with several approaches toward the more complex oxygenated spongianes. 2. Structure, occurrence, and biological activity 3.1. Syntheses from other natural products The semisystematic naming of this family of diterpenoids Manool (4), copalic acid (5), sclareol (6), labdanolic acid was introduced in 1979 after the isolation of the first members (7), abietic acid (8), and carvones (9)(Fig. 2) have been used of the family from sponges of the genus Spongia. Thus, in for the preparation of optically active spongianes. Naturally oc- accordance with the IUPAC recommendations the saturated curring racemic labda-8(20),13,dien-15-oic acid (copalic acid) hydrocarbon I, named ‘spongian’, was chosen as the funda- has also been used for preparing racemic compounds. mental parent structure with the numbering pattern as depicted 10 These starting materials were converted into versatile tricy- in Figure 1. clic intermediates having the characteristic ABC-ring system of The first known member of the spongiane family, isoaga- spongianes (Scheme 1) such as ent-methyl isocopalate (10), po- tholactone (1), was discovered by Minale et al. from the docarp-8(14)-en-13-one (11), and phenanthrenones (12,13). sponge Spongia officinalis about 30 years ago, being the first Several strategies have been reported to build up the necessary natural compound with the carbon framework of isoagathic ring D from these key intermediates, preferably as a furan or acid (2). Structure (1) was assigned based on spectroscopic 11 g-lactone ring. The choice of podocarpenone 11 as starting data and chemical correlation with natural grindelic acid (3). material assures the absolute stereochemistry at C5, C9, and To date, there are nearly 200 known compounds belonging to this family of marine natural products, including those with a spongiane-derived skeleton.12 Most of them present a high OH CO H degree of oxidation in their carbon skeleton, particularly at po- H H 2 sitions C17 and C19, as well as on all the rings AeD. Given H H the variety of chemical structures found in the spongiane fam- 4, manool 5, copalic acid ily, we could group them according to the degree of oxidation as well as the degree of carbocyclic rearrangement of the par- OH ent 6,6,6,5-tetracyclic ring system. CO2H Sponges are exposed to a variety of dangers in their envi- H OH H OH ronment and this has led to the development of chemical de- H H fense mechanisms against predation. Nudibranchs feed on 6, sclareol 7, labdanolic acid a variety of sponges and are capable of storing selected meta- bolites, even transforming them, for their own self-defense. Thus, sponges and nudibranchs are a rich source of biologi- cally active metabolites, and the spongianes, in particular, H O have displayed a wide spectrum of interesting biological prop- H erties including antifeedant, antifungal, antimicrobial, ichthyo- CO2H 9, (+)- and (-)-carvone 8 toxic, antiviral, antitumor, antihypertensive, fragmentation of , abietic acid 12,13 Golgi complex, as well as anti-inflammatory activity. Figure 2. M.A. Gonza´lez / Tetrahedron 64 (2008) 445e467 447 C10. Moreover, the selection of methyl isocopalate 10 and lactonization to give lactone 16, followed by reductive open- phenanthrenones 12,13 also assures the stereochemistry of ing of the lactone ring, gave the known degradation product the additional methyl group at C8 of the ring system. of isoagatholactone, diol 17.11 Finally, allylic oxidation with MnO2 gave (þ)-isoagatho- lactone (1) in 3.9% yield from 10. manool Contemporaneous studies by Nakano et al. described, soon CO Me copalic acid H 2 after, the synthesis of racemic isoagatholactone using a similar sclareol labdanolic acid H strategy in which the reaction conditions were

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    23 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us