Total synthesis of proposed structure of xylogiblactone B by chiron approach

Total synthesis of the proposed structure of xylogiblactone B is described using d-(+)-mannitol, regioselective epoxide ring-opening, Yamaguchi esterification, and ring-closing metathesis as key steps.     

Total synthesis of compounds related to triterpenoids

Conclusions It was shown that it is theoretically possible to synthesize polycyclic structures, related to triterpenoids of the dammarane series, via diene condensation using 2-acetyl-4-methyl-4-cyclopentene-1,3-dione as the dienophile.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1390–1393, June, 1980.     

利用天然手性源合成复杂手性化合物的方法

利用天然手性源来合成一些复杂的手性化合物,其合成策略往往具有很高的艺术性.本文主要对糖类和甘露糖以及一些氨基酸类天然产物作为合成子来合成手性分子的一些新方法作了报道.     

Total synthesis of an antitumor agent,mucocin, based on the "chiron approach"

The total synthesis of a powerful antitumor acetogenin, mucocin (1), was achieved through a palladium-catalyzed cross-coupling reaction of the THP-THF fragment 2 and a terminal butenolide 3. The key process for construction of the fragment 2 was chelation-controlled addition of ethynylmagnesium chloride to disilyl aldehyde 23a and condensation of the alkyllithium prepared therefrom with THP aldehyde 4 in the presence of CeCl(3). Synthesis of the lactone 3 relied on a novel approach by taking advantage of a radical cyclization of acyclic selenocarbonate 6. The three building blocks 4, 5a, and 6 were prepared stereoselectivly from D-galactose (7), 2,5-anhydro-D-mannitol (8), and L-rhamnose (9), respectively. A new and efficient method for desymmetrization of the C(2)-symmetrical compound 8 is also described.     

An approach for disaccharide chiron synthesis using a Ferrier-type rearrangement

We report a new approach for the synthesis of new chiral synthons in which two unsaturated sugars are linked via a glycosidic bond. The di-unsaturated disaccharide can be further functionalized using effective, highly selective methods and used in convergent syntheses of relatively complex glycoconjugates. Our approach utilizes in situ generation of active glycosyl donors via Ferrier-type rearrangement under phase-transfer conditions and subsequent reaction with a nucleophile.     

Total synthesis of 8-oxypseudopalmatine and 8-oxypseudoberberine via ring-closing metathesis

Concise synthesis of 8-oxypseudopalmatine and 8-oxypseudoberberine has been achieved using ruthenium-catalyzed ring-closing metathesis (RCM) as the key step, in which the RCM substrates, 3-arylisoquinolinones, were prepared by lithiated cycloaddition reaction with o-toluamides and benzonitriles.     

Total synthesis of cryptophycin analogues via a scaffold approach

[reaction: see text] Allylation of in situ generated beta,gamma-unsaturated aldehydes affords rapid access to vinyl halide analogues of fragment A of the cryptophycins. Three scaffolds are prepared in gram quantities by a ring-closing metathesis approach. Derivatization via a variety of cross-coupling protocols is possible, which affords novel analogues of these potent antimitotic agents.     

A chiron approach to the total synthesis of (+)-aculeatin D

A synthesis of natural aculeatin D has been achieved, with the key stereogenic centers taken from inexpensive and readily available D-xylose. In elaboration of D-xylose into a desired form readily applicable in synthesis a previously misinterpreted and overlooked abnormal selectivity in hydroxyl protection was noticed and exploited. Protocols were developed for monotosylation of a triol insoluble in CH2Cl2 and "freezing" the less stable isomer (aculeatin D) at the PIFA-mediated oxidative spirocyclization, respectively. An unexplained deprotonation at a benzyl protecting group by a thermodynamically more stable dithiane carbanion in the literature was also addressed.     

Total synthesis of naturally occurring chiral cyclopropane fatty acids and related compounds

Cyclopropane fatty acids (CFAs) and related compounds containing CFAs commonly occur in various natural sources, including plants or microorganisms. Some CFAs exhibit intriguing biological activities such as antifungal or immunosuppressive activities. Due to their biological importance and structural features, a number of synthetic studies have been conducted to date. These total syntheses have helped to elucidate their structural determinants or biological activities. Herein the total syntheses of naturally occurring CFAs and related compounds are summarized.     

Total synthesis of microcin B17 via a fragment condensation approach

The total synthesis of the 43 amino acid antibacterial peptide Microcin B17 (MccB17) is described. The natural product was synthesized via a convergent approach from a heterocycle-derived peptide and peptide thioester fragments prepared via Fmoc-strategy solid phase peptide synthesis (SPPS). Final assembly was achieved in an efficient manner using two Ag(I)-assisted peptide ligation reactions to afford MccB17 in excellent overall yield.     

High pressure approach to the synthesis of cryptands and related compounds

Some fundamentals concerning the high-pressure technique in organic chemistry and recent progress in high-pressure synthesis of cryptands and related compounds are described. A brief discussion is given of several examples illustrating various approaches to high-pressure syntheses of simple and chiral cryptands. Emphasis is placed on double-quaternization reactions carried out under high pressure.This review is based on a lecture presented at the Fourth International Symposium on Inclusion Phenomena/Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Total synthesis of a natural antioxidant and structure-activity relationships of related compounds.

A total synthesis of benzodioxole derivative 1 was achieved via a palladium(0)-catalyzed cross-coupling reaction in a 68% overall yield (4 steps). A novel series of benzodioxoles bearing a variety of aromatic and heterocyclic rings was also prepared and the antioxidative activity evaluated using in vitro model systems. Structure-activity studies revealed that i) intramolecular hydrogen-bonding in the phenol moiety reduced activity, ii) introduction of disubstituents at the ortho location relative to the phenol increased activity, and iii) the methylenedioxy function contributed to stabilization of the phenoxy radical. Among of these compounds, 5,7-di-(4-methoxyphenyl)-4-methoxy-6-hydroxy-1,3-benzodioxole (7p) was the most favorable agent and more potent than n-propyl gallate.     

First synthesis of (+)-8-methoxygoniodiol and its analogue, 8-deoxygoniodiol, using a three component strategy

We have described the first total synthesis of the natural product, (+)-8-methoxygoniodiol, and its analogue, 8-deoxygoniodiol using a catalytic asymmetric hetero-Diels-Alder/allylboration sequence involving three partners. The cytotoxic activity of these final compounds and of two synthetic intermediates has been evaluated against human cancer cell lines (A375P and A375M), showing the importance of the lactone moiety.     

Total synthesis of aculeatins A and B via a tethered oxa-Michael approach

A stereocontrolled total synthesis of aculeatins A and B has been achieved in eight steps and in 15% overall yield. The key feature of this synthetic approach is the application of a Marouka allylation and tethered intramolecular oxa-Michael reaction to install the required stereocentres on the tetrahydropyran ring.     

Total synthesis of (+)-blastmycinone, (-)-litsenolide C1, and related natural trisubstituted lactones via alkynyltungsten compounds

A general method for total synthesis of natural trisubstituted gamma-lactones is developed on the basis of the chemistry of alkynyltungsten compounds. The key step in this approach involves the cycloalkenation of tungsten-eta1-(3R,4S)-pent-1-yne-3,4-diol with aldehydes to give tungsten-oxacarbenium salts, further leading to 3-alkylidene-4-hydroxy-5-methyl-gamma-lactones upon demetalation. This synthetic sequence proceeds well for alkynylaldehydes and the MOM derivative of tungsten-eta1-(3R,4S)-pent-1-yne-3,4-diol. The resulting butyrolactone products are transformed into natural trisubstituted butyrolactones including (+)-blastmycinone, (+)-blastmycinolactol, (+)-antimycinone, NFX-2, and (+)-isodihydromahubanolide A. By using the same approach based on (R)-ethyl lactate, the natural (-)-litsenolide C1 can be prepared in a few steps.     

青蒿素及其一类物的结构和合成 XXI: 青蒿酸的全合成

青蒿酸与抗疟新药青蒿素共存于植物青蒿中, 具有显著的抗菌活性, 它的结构和立体化学已经确定, 并被用作合成青蒿素及其一类物的原料, 本文报导以R-(+)-香草醛为原料合成青蒿酸。     

One-pot synthesis of isoquinoline and related compounds via Cu-mediated tandem cross-coupling and cyclization

One-pot synthetic strategy has been developed to access isoquinolines and its analogs via Cu-mediated tandem cross-coupling and cyclization in good yields under mild reaction conditions. A mixture of suitably substituted α-bromoaldehyde, terminal alkyne, and aq NH₃ in CuI/1,10-phenanathroline catalytic system afforded the 3-substituted isoquinoline regio-selectively in good to excellent yields.     

Total synthesis of 8-deshydroxyajudazol B

The total synthesis of a stereoisomer of 8-deshydroxyajudazol B (4), the putative biosynthetic intermediate of the ajudazols A (1) and B (2), is described. The key steps in the synthesis included an intramolecular Diels-Alder (IMDA) reaction to secure the isochromanone fragment, a novel selective acylation/O,N-shift to give a hydroxyamide which was cyclized to the oxazole and a high yielding Sonogashira coupling to form the C18-C19 bond. Partial alkyne reduction then afforded the target 4.