bluuebunny/crossref_metadata_2025_split huggingface dataset:
Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres? An analysis of diurnal courses of CO2 uptake under free‐air concentration enrichment (FACE)
Authors: Leakey A. D. B. , Bernacchi C. J. , Dohleman F. G. , Ort D. R. , Long S. P. 
Published: December 2004

AbstractThe C4 grass Zea mays (maize or corn) is the third most important food crop globally in terms of production and demand is predicted to increase 45% from 1997 to 2020. However, the effects of rising [CO2] upon C4 plants, and Z. mays specifically, are not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment utilizing free‐air concentration enrichment (FACE) technology in the primary area of global corn production (US Corn Belt) was undertaken to determine the effects of elevated [CO2] on corn. FACE technology allows experimental treatments to be imposed upon a complete soil–plant–atmosphere continuum with none of the effects of experimental enclosures on plant microclimate. Crop performance was compared at ambient [CO2] (354 μ mol mol−1) and the elevated [CO2] (549 μmol mol−1) predicted for 2050. Previous laboratory studies suggest that under favorable growing conditions C4 photosynthesis is not typically enhanced by elevated [CO2]. However, stomatal conductance and transpiration are decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and relatively high rainfall of the US Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO2]. The diurnal course of gas exchange of upper canopy leaves was measured in situ across the growing season of 2002. Contrary to the prediction, growth at elevated [CO2] significantly increased leaf photosynthetic CO2 uptake rate (A) by up to 41%, and 10% on average. Greater A was associated with greater intercellular [CO2], lower stomatal conductance and lower transpiration. Summer rainfall during 2002 was very close to the 50‐year average for this site, indicating that the year was not atypical or a drought year. The results call for a reassessment of the established view that C4 photosynthesis is insensitive to elevated [CO2] under favorable growing conditions and that the production potential of corn in the US Corn Belt will not be affected by the global rise in [CO2].
Tritrophic interactions in the context of climate change: a model of grasses, cereal Aphids and their parasitoids
Authors: Hoover Julia K. , Newman Jonathan A. 
Published: December 2004

AbstractBiologists have been challenged to envisage the likely consequences of increases in atmospheric carbon dioxide concentrations, and the suite of accompanying environmental changes (e.g. rising temperature, changing rainfall patterns, etc.) on our biotic systems. Research to date on plant responses has been extensive, but work on herbivore responses has been less complete, and work on higher trophic levels nearly nonexistent. One group of herbivores that has been reasonably well studied is aphids, and at least for this group, researchers have even begun to investigate responses at higher trophic levels, to include parasitoids. In this paper, we develop a mechanistic mathematical model of the general interaction between grasses, cereal aphids and their parasitoids. We used this model to investigate the interacting effects of rising CO2and temperature. The model suggests that, while parasitoids do have an impact on the aphid colony population dynamics, they do not fundamentally alter the aphid response to climate change. The model predicts that for both aphids and their parasitoids, the population responses to combined effects of elevated CO2and temperature will be more similar to current ambient conditions than we might expect from the individual effects of CO2or temperature increases. This interaction has important consequences for the interpretation of results from experiments that study only the effect of rising CO2.
Inhibition of pathogenic SHIV replication in macaques treated with antisense DNA of interleukin-4
Authors: Dhillon Navneet Kaur , Sui Yongjun , Potula Raghava , Dhillon Sukhbir , Adany Istvan , Li Zhuang , Villinger Francois , Pinson David , Narayan Opendra , Buch Shilpa 
Published: December 2004

AbstractInterleukin-4 is implicated in the pathogenesis of HIV-induced AIDS and causes enhancement of replication of virus strains that use the CXCR4 (X4) coreceptor. In this study, we explored the effects of interleukin-4 (IL-4) antisense (AS) DNA on replication of X4, simian human immunodeficiency viruses, SHIVKU-2 and SHIV89.6P. AS IL-4 oligomer caused inhibition of virus replication in cultures of CD4+ T cells and macrophages derived from macaques. Plasmid expressing AS IL-4 DNA was also effective in abrogating virus replication in macrophage cultures. Relevance of these cell culture studies was confirmed in vivo by treating SHIV89.6P-infected macaques with AS IL-4 DNA. Six macaques were inoculated with the virus, and 4 were treated with AS IL-4 DNA. This resulted in a significant decrease in viral RNA concentrations in the liver, lungs, and spleen tissues that are all sites of virus replication in macrophages. This is the first demonstration of effective inhibition of an HIV-like virus in tissues by AS DNA of a cytokine. In the present era of increasing resistance of HIV to antiviral compounds, exploration of adjunct therapies directed at host responses in combination with antiretroviral drugs may be of value for the treatment of AIDS.
CD38 is expressed selectively during the activation of a subset of mature T cells with reduced proliferation but improved potential to produce cytokines
Authors: Sandoval-Montes Claudia , Santos-Argumedo Leopoldo 
Published: December 2004

AbstractCD38 is an ∼45-kDa type II transmembrane glycoprotein expressed by hematopoietic and nonhematopoietic cells. Its surface expression is under complex control and varies during lymphocyte development, activation, and differentiation, suggesting an important role in these processes. Murine CD38 has been mainly characterized on B lymphocytes, and in humans, the molecule has been studied in T cells. This paper provides evidences that murine CD38 is regulated tightly during T cell activation and differentiation. On the periphery, a subset of mature T lymphocytes was identified by the expression of CD38. These cells showed an activated phenotype; they were larger and more granular than their negative counterparts. In accord with this observation, in vitro-activated T cells up-regulated CD38. Memory T lymphocytes also were CD38-positive. It is interesting that T cells expressing high levels of CD38 had a reduced, proliferative capacity but displayed an improved potential to produce interleukin-2 and interferon-γ, suggesting a role of this molecule during T cell activation and differentiation.
Defensin deficiency, intestinal microbes, and the clinical phenotypes of Crohn's disease
Authors: Wehkamp Jan , Schmid Michael , Fellermann Klaus , Stange Eduard F 
Published: December 2004

AbstractCrohn's disease is a chronic, inflammatory disease of the intestinal mucosa. Although intestinal bacteria are implicated in disease pathogenesis, the etiology is still unclear. The main location of disease is the small intestine (ileum) and the colon. Ileal disease has been linked to a mutation in the NOD2 gene. Defensins are antimicrobial peptides and in the ileum, are mainly expressed in Paneth cells, epithelial cells that also express NOD2. In the colon, defensins are expressed by enterocytes or metaplastic Paneth cells. Crohn's disease patients with ileal involvement, compared with controls or Crohn's patients without ileal involvement, have diminished expression of ileal Paneth cell defensins. This decrease is even more pronounced in Crohn's patients displaying a NOD2 mutation. In contrast, Crohn's disease of the colon is characterized by an impaired induction of β-defensins in enterocytes. The colonic expression of the constitutive β-defensin 1 is also decreased in the inflamed colonic mucosa, but this decrease is less specific to Crohn's disease, as it can also be found in ulcerative colitis patients. In conclusion, the regional localizations of Crohn's disease, ileal or colonic disease, can be linked to different defensin profiles. Crohn's disease of the ileum is associated with diminished defensin expression in Paneth cells. Crohn's disease of the colon is associated with diminished β-defensin expression in enterocytes. Thus, it can be speculated that decreased defensin levels lead to a weakened intestinal barrier function to intestinal microbes and might be crucial in the pathophysiology of Crohn's disease.
[18O]‐Studien zur Carboxylbeteiligung bei der sauren Hydrolyse von γ‐substituierten Carbonsäuren. 1. Mitteilung: Zum Sauerstoffaustausch von γ‐Lactonen in saurer Lösung
Authors: Moll H. 
Published: December 2004

AbstractSpecifically [18O]‐labelled γ‐valerolactone and 4‐methyl‐γ‐valerolactone were submitted to tracer equilibration in dilute mineral acid at reflux temperature. Though under these conditions the two lactones are known to be hydrolyzed to the extent of about 25% to the corresponding γ‐hydroxy acids only the «tertiary» 4‐methyl derivative lost its alkoxyl label whereas the unsubstituted «secondary» one retained it. – This may be understood on the base of two alternative mecanisms possible for lactone reformation.The results permit a quantitative evaluation of the amount of carboxyl‐participation during acid hydrolysis of 4‐substituted carboxylic acids to 4‐monoalkylated γ‐butyrolactones.
Die Deprotonierung von Metall‐Aquoionen I.: Be · aq2+ Solvatations‐Isomerie
Authors: Schwarzenbach G. , Wenger H. 
Published: December 2004

AbstractThe reaction of Be · aq2+ with OH− leeds not only to loss of protons by the metalaquo ion but also to structural changes in the solvation sphere. These can be studied by following the pH variations during the first decisecond after mixing the solutions of metal salt and alkali hydroxide. The equilibrium Be2+ ⇌ BeOH+ is reached within 5 milliseconds if acid free Beryllium solutions are used. If the metal solution is strongly acidic, however, the establishment of the equilibrium needs more time because of the slowness of the process H+ + BeOH+ → Be2+ (k ∼ 105 M−1, s−1). The extraction of two protons produces in the first instance an unstable Be(OH) species which transforms into the stable isomer Be(OH)2 (solvatation isomerism) in a first‐order reaction of half‐life of 7 ms. This isomerisation causes almost complete disappearance of BeOH+ from the equilibrium Be2+ ⇌ BeOH+ ⇌ Be(OH)2. (KAKIHANA & SILLEN state that the relaxed solutions contain only Be2+, Be(OH)2, Be3(OH) and some Be2OH3+.) The formation of the polynuclear species Be3(OH) needs about 30 seconds to go to completion.
Organische Phosphorverbindungen XXXVI. Darstellung und Eigenschaften von Bis‐(dialkoxyphosphonyl‐methyl)‐, Bis‐(alkoxyphosphinyl‐methyl)‐und Bis‐(oxophosphoranyl‐methyl)‐phosphinsäureestern sowie der entsprechenden Säuren [1]
Authors: Maier Ludwig 
Published: December 2004

AbstractHigh yields of bis‐(dialkoxyphosphonyl‐methyl)‐ phosphinic esters, (RO)2 (O)‐PCH2P(O)OR, bis‐(aloxyphosphinyl‐methyl)‐phosphinic esters, [R(RO)(O)PCH2]2P(O)OR, are obtained by heating bis‐chloromethyl‐phosphinic esters, (CICH2)2P(O)OR, with alkylphoshites, phosphonites and phosphinites, repectively, at 170 to 180°C for several hours. Hydrolysis of these esters in achieved by refluxing with conc. HCl for extended periods.Bis‐(dihydroxyphosphonyl‐methyl)‐phosphinic acid, HO(O)P[CH2P(O) (OH)2]2, obtained by hydrolysis of the all‐ethyl ester, titrates in aqueous solution as a tetrabasic acid with breaks at pH = 5,2 (three equivalents) and at pH = 8,8 (one equivalent). The fifth proton can be titrated only after addition of NaCl. This acid is an excellent chelating agent for metal ions.The 1H‐ and 31P‐NMR. spectra of all the compounds prepared are discussed.
Organische Phosphorverbindungen XXXVII. Darstellung und Eigenschaften von Bis‐(dialkoxyphosphonyl‐methyl)‐, Bis‐(alkoxyphosphinyl‐methyl)‐und Bis‐(oxophosphoranyl‐methyl)‐phosphinsäureestern sowie der entsprechenden Säuren [1]
Authors: Maier Ludwig 
Published: December 2004

AbstractBis‐chloromethyl‐alkyl‐and ‐ aryl‐phosphine oxides, (CICH2)2P(O)R, which are obtained by reaction of (CICH2)2P(O)Cl with GRIGNARD reagents, undergo a MICHAELIS‐ARBUSOV reaction when heated for several hours with trivalent phosphorus esters (phosphites, phosphonites, or phosphinites) at 170–180°C. The reaction affords bis‐(dialkyloxyphosphonyl‐methyl)‐, bis (alkyloxyphosphinyl‐methyl)‐, and bis‐(oxophosphoranyl‐methyl)‐, ‐alkyl‐ or ‐aryl‐phosphine oxides, R(O)P[CH2P(O)R′R″]2 R = CH3, C2H5, n‐C8H17, n‐C12H25, C6H5; R′ and R″ = C2H5O, C4H9O, C6H5, CH3 in good yields.Conversion of the compounds containing alkyloxy groups to the free acids is achieved by refluxing with conc. HCl. Bis‐(dihydroxyphosphonyl‐methyl)‐dodecylphosphine oxide, n‐C12H25(O)P[CH2P(O) (OH)2]2, obtained by hydrolysis of the all‐ethyl ester, titrates in aqueous solution as a tetrabasic acid with breaks at pH = 4 (two equivalents), pH = 6,9 (one equivalent) and pH = 9,6 (one equivalent). This acid, its disodium salt (m. p. 405–410°) and its tetrasodium salt (m.p. > 460°) are surface active and are excellent chelating agents.The 1H‐ and 31P‐NMR. spectra of all the compounds prepared are discussed.
Welkstoffe und Antibiotika. 38. Mitteilung [1]
Authors: Hardegger E. , Rostetter Ch. , Seres J. , Andreatta R. 
Published: December 2004

AbstractDie Synthese von Anhydro‐lycomarasminsäure (VII) führte zur endgültigen Bestätigung der früher für Lycomarasmin analytisch abgeleiteten Konstitution. Die Ermittlung der absoluten Konfiguration im Diaminopropionsäureteil am C‐5 (vgl. Formel VII) des Lycomarasmins scheiterte an der Herstellung der bereits bekannten S‐(−)‐Piperaz‐2‐on‐5‐carbonsäure, bzw. ihres Antipoden, an deren Stelle das Diketopiperazon XVI, die Aminosäure XV und als Nebenprodukt der α,β‐Diacetamido‐acrylsäure‐methylester (X, bzw. XII, bzw. XIII) erhalten wurden.
Synthese von (±)‐Dictyopteren A
Authors: Ohloff G. , Pickenhagen W. 
Published: December 2004

AbstractEs wird ein Weg zur Synthese des (±)‐Dictyopterens A (6), sowie seiner Stereoisomeren 7 und 9 angegeben. Der thermische Übergang der Dictyopterene 6–9 in das gemeinsame valenzisomere 6‐n‐Butyl‐cyclohepta‐1,4‐dien (10) wird beschrieben.
Kinetische Untersuchungen über Substitutionsreaktionen an Metallkomplexen. 9. Mitteilung [1]. Kinetik und Mechanismus der Reaktion von Hexamethylborazolchrom‐tricarbonyl mit tertiären Phosphinen und Phosphiten [2]
Authors: Deckelmann E. , Werner H. 
Published: December 2004

AbstractHexamethylborazolechromium tricarbonyl B3N3(CH3)6 Cr(CO)3 reacts with tertiary phosphines and phosphites under surprisingly mild conditions by cleavage of the ring‐to‐metal bond. For L = trialkylphosphines and trialkyl‐ or triaryl‐phosphites, compounds of the general composition cis‐Cr(CO)3L3 are formed, whereas for L = triphenyl‐ and tricyclohexyl‐phosphine the complexes trans‐Cr(CO)4L2 are obtained.The kinetics of the reaction of B3N3(CH3)6 Cr(CO)3 with phosphites P(OR)3 (R = CH3, C2H5, C6H5) have been studied by means of spectrophotometric methods. The second‐order rate law indicates a primary, rate‐determining attack of the phosphite to either the metal atom or the ring ligand of the borazole complex. This attack is favoured by an extremely low activation energy. The mechanism of the substitution process is discussed in detail, and the reactivity of the hexamethylborazole compound is compared with that of other half‐sandwich type complexes.
Synthèses dans la série des constituants odorants caractéristiques de l'essence absolue de cassie (Acacia farnesiana WILLD.): Les acides méthyl‐3‐décène‐3‐oïques cis et trans, méthyl‐3‐décène‐4‐oïques cis et trans, et les quatre méthyl‐3‐décénols‐1 correspondants
Authors: Demole Edouard , Enggist Paul 
Published: December 2004

AbstractThree new fragrant compounds formerly isolated from the absolute oil of cassie (Acacia farnesiana WILLD.) have been synthesized through stereospecific reactions, and their respective structures thus confirmed. These unusual C11 constituents are cis‐3‐methyl‐dec‐3‐enoic acid (Ia), trans‐3‐methyl‐dec‐4‐enoic acid (IIa) and cis‐3‐methyl‐dec‐3‐en‐1‐ol (Ib). The related ‘non natural’ stereomers, namely, trans‐3‐methyl‐dec‐3‐enoic acid (X) and cis‐3‐methyl‐dec‐4‐enoic acid (XIX), have also been synthesized, as well as the 3‐methyl‐decen‐1‐ols IIb, XVII and XX.
Photochemische Reaktionen. 51. Mitteilung [1]. Zur Photochemie von gesättigten β‐Ketosulfiden III. Strukturaufklärung eines weiteren Photoproduktes Zusammenfassende Beurteilung des photochemischen Reaktionsbildes
Authors: Ganter C. , Moser J.‐F. 
Published: December 2004

AbstractUltraviolet irradiation of the saturated β‐ketosulfide 2 [(charge‐transfer)‐ or (n → π*)‐excitation] in methanol or benzene solutions resulted in the formation of the products 4, 5a, 6 (due to α‐cleavage) and 7 [due to (Cα–S)‐fission].Compounds 4, 6 and 7 have been described earlier [1] [2]. The structure elucidation of 5a is reported in this paper.The photochemistry of the β‐ketosulfide 2 is summarized.
Photochemische Reaktionen. 53. Mitteilung [1]. Photochemische Addition von Alkylaromaten an Aryl‐Carbonylverbindungen
Authors: Belluš D. , Schaffner K. 
Published: December 2004

AbstractIn the preceding paper [1] a novel primary photochemical process of triplet excited α,β‐conjugated cycloalkenones in toluene solution has been reported: the abstraction of a benzylic hydrogen from the solvent by the β‐carbon (cf. 1 → 2 + 3 + 4). The reaction has been attributed to the π,π* triplet.Aromatic aldehydes and ketones (5–11a), the triplet state reactivity of which is known to be mostly π,π* in nature, have now been examined under the same irradiation conditions. However, a reaction similar to that of cycloalkenones — expected to result in the addition of hydrogen to the ortho and para positions of the aryl moiety and the formation of benzylcyclohexa‐1,3‐and 1,4‐diene derivatives — could not been found. Compounds 5–10 remained essentially unchanged. 4‐Methoxyacetophenone (11a) reacted slowly to form the same type of products [tert‐carbinol 12a, pinacol 13a and dibenzyl (4)] as the aromatic carbonyl compounds 11b‐d, benzophenone and cyclopropylphenylketone, which exhibit typical n,π* triplet reactivity (hydrogen abstraction by the carbonyl oxygen).
CLAISEN'sche Umlagerungen bei Allyl‐ und Benzylalkoholen mit 1‐Dimethylamino‐1‐methoxy‐äthen
Authors: Felix Dorothee , Gschwend‐Steen Katharina , Wick A. E. , Eschenmoser A. 
Published: December 2004

AbstractOf experiments on the CLAISEN rearrangement of allylic‐ and benzylic‐alcohols with 1‐dimethylamino‐1‐methoxy‐ethylene, communicated earlier in preliminary form, we still owe the description of the experimental details. Here they are.
Thyrocalcitonin V.. Synthese und Charakterisierung des geschützten Aufbaufragments α‐Thyrocalcitonin‐(1–9)‐nonapeptid
Authors: Kamber B. , Rittel W. 
Published: December 2004

AbstractIn the recently [1] [4] described synthesis of the hypocalcaemic hormone α‐thyrocalcitonin (I) isolated from porcine thyroid glands, the protected nonapeptide sequence 1–9, represented an important intermediate. The present report describes in detail the synthesis of III in which the disulfide ring present in I is already formed. Fragment coupling of the sequences 1–4 and 5–9 led to the protected open chain intermediate Boc‐Cys(Trt)‐Ser(But)‐Asn‐Leu‐Ser(But)‐Thr(But)‐Cys(Trt)‐Val‐Leu‐OH which was obtained in cristalline form. After removal of the protecting S‐trityl groups by mercury acetate as described by ZERVAS, et al. [5], ring closure leading to III was effected by means of diiodoethane according to WEYGAND & ZUMACH [6]. Purification of III was achieved by counter current distribution. Removal of protecting groups by trifluoroacetic acid gave the free α‐thyrocalcitonin‐(1–9)‐nonapeptide IV, which was devoid of biological activity.
Synthese von 3‐(2,4,5‐Trihydroxyphenyl)‐DL‐alanin
Authors: Langemann A. , Scheer M. 
Published: December 2004

AbstractCondensation of 2.4.5‐trimethoxybenzaldehyde with hydantoin followed by catalytic hydrogenation gave 5‐(2.4.5‐trimethoxybenzyl)‐hydantoin, which was converted to 3‐amino‐3.4‐dihydro‐6.7‐dihydroxycoumarin by treatment with hydrobromic acid. Hydrolysis of the lactone led to 3‐(2.4.5‐trihydroxyphenyl)‐DL‐alanine.
Synthese von Haschisch‐Inhaltsstoffen. 4. Mitteilung
Authors: Petrzilka T. , Haefliger W. , Sikemeier C. 
Published: December 2004

Abstract(−)‐Cannabidiol has been synthesized from (+)‐cis‐ and (+)‐trans‐p‐menthadien‐(2, 8)‐ol‐(1) and olivetol, using N, N‐dimethylformamide dineopentyl acetal or weak acids, such as oxalic, picric, or maleic acid, as catalysts.Since the chirality of (+)‐trans‐p‐menthadien‐(2, 8)‐ol‐(1) is known, the above synthesis constitutes an unambiguous prove for the absolute configuration of (−)‐cannabidiol and the two isomeric (−)‐6a, 10a‐trans‐tetrahydrocannabinols.If stronger acids, such as p‐toluenesulfonic, trifluoroacetic, or hydrochloric acid, are used as mediators for the reaction, (−)‐Δ8‐6a, 10a‐trans‐tetrahydrocannabinol is obtained as the main product.Transformation of the thermodynamically more stable Δ8‐tetrahydrocannabinol into the less stable Δ9‐isomer was achieved in a practically quantitative yield by addition of hydrochloric acid and elimination of the elements of hydrochloric acid by means of potassium t‐amylate. If resorcinols I were used instead of olivetol in the condensation reaction with strong acids, the corresponding homologues of Δ8‐tetrahydrocannabinol were obtained in varying yields.
Über 9β,10α‐Steroide. 4. Mitteilung [1]. Strukturaufklärung von mikrobiologischen Umsetzungsprodukten
Authors: Els H. , Englert G. , Fürst A. , Reusser P. , Schocher A. J. 
Published: December 2004

AbstractThe structure and the stereochemistry of some 8‐ and 9‐hydroxy‐9β, 10° (retro)‐steroids of the androstane and pregnane series, obtained microbiologically, have been elucidated.
α‐Santonin: Photochemie in protischen Lösungsmitteln und Pyrolyse
Authors: Schaffner‐Sabba K. 
Published: December 2004

AbstractIn protic media of the type ROH and RCOOH irradiation of α‐santonin yields addition products of the isophotosantonic‐lactone type 3 apart from lumisantonin (2) and in some cases its photoproducts. The amount of 3 depends on the acidity of the solvent up to a limiting value, above which exoanhydro‐isophotosantonic‐lactone (5) is also formed.Under pyrolytic conditions α‐santonin is in equilibrium with pyrosantonin (14), the structure of which is discussed.
Die Pyrolyse von (+)‐Verbenen
Authors: Thomas Alan F. , Willhalm B. , Ohloff G. 
Published: December 2004

AbstractThe pyrolysis of verbenene has been found to give rise to 39% of isobutenylcyclohexa‐1,3‐diene (3), 29% of o‐mentha‐1 (7),5,8‐triene (2) together with two double bond‐isomers (4 and 5) of the cyclohexadiene (3). The structures were proved by catalytic reduction to the saturated hydrocarbons, and isobutenylcyclohexa‐1,3‐diene was synthesized from 2,3‐dihydrobenzaldehyde.
Die absolute Konfiguration von Carquejol und verwandten o‐Menthan‐Derivaten
Authors: Snatzke G. , Thomas A. F. , Ohloff G. 
Published: December 2004

AbstractThe structure of carquejol is amended to that of cis‐3‐hydroxy‐o‐mentha‐1(7),4,8‐triene; the chirality has been confirmed as 2 R, 3 S by correlation with the (−)‐cis‐o‐menthane obtained from carquejol and that from (+)‐verbenene of known absolute configuration.The two double bonds of the dihydrocarquejol system (15 and 16) constitute a helical system, that especially in the case of the acetate (16) fixes the isopropenyl group in such a way that a very high Δϵ value in the CD. curve is observed. The conformational significance of this phenomenon is discussed.