Mountain forest islands and Holocene environmental changes in Central Asia: A case study from the southern Gobi Altay, Mongolia

A multi-proxy case study conducted on Central Asia's most isolated mountain forest sheds light on the apparent decline of forest in the Subboreal time period and the incisive environmental changes from dark taiga to steppe in the Gobi Altay of Southern Mongolia over the last 5000 yr.

New vegetation records from the ‘Gobi Gurvan Saykhan’ (43°30′ N/103°10′ E) reveal long distance disjunctions of birch–willow forests as well as a number of herbaceous forest plants. Thus the question arises as to whether long-distance dispersal or fragmentation, following climatic changes and human interference, are more plausible explanations for such a pattern. Analysis of current plant distribution patterns lead to conclusions which are corroborated by zoological surveys of the Gobi Altay: During the Holocene, dark taiga forests apparently existed approximately 600 km to the southeast of their present range, and pollen analysis and charcoal remains provide evidence of a forest decline during the Subboreal time period. The presence of humans during these environmental changes is highly probable as pollen indicating human presence was found. Thus, it is assumed that humans at least contributed to the subboreal forest decline and the spreading of sagebrush and pastures. Moreover we cannot rule out with certainty that disjunctions of forest flora between the Gobi Altay and the forests of north-eastern Tibet are indicative of migration through the present North China desert, as forests may have partly replaced deserts during the moister periods of the Holocene. This multidisciplinary approach implies a mid-Holocene and subboreal scenario, which is new for Central Asia and more in accordance with the environmental history of the Holocene in the western desert belt of the Old World.     

Sources and accumulation rates of organic carbon in an equatorial peat bog (Burundi, East Africa) during the Holocene: carbon isotope constraints

The relationship between organic carbon accumulation rates and ¹³C/¹²C ratios of total organic carbon (TOC) was investigated in an highland peat bog core (Ru-3) from Equatorial Africa. This core yielded a sequence spanning the last 14 kyr and was analysed with a 100–300 yr resolution for TOC-δ¹³C values. The Holocene section shows contrasted TOC accumulation regimes and TOC δ¹³C varying between −28.5 and −19.5‰ with a few very short ‘isotopic excursions' (dated at ca. 9.3, 7.5, 4.2 ka B.P.). The organic carbon accumulation rates range from 2 to 20 mg C cm⁻² yr⁻¹. They increase when TOC becomes more depleted in ¹³C, notably between 12 and 9.8 ka B.P., 8.5 and 7.8 ka B.P. and after 1.6 ka B.P. Periods of restricted carbon storage correspond to heavier TOC accumulation at 9.3, and between 7.5 and 1.6 ka B.P. At the study site, the δ-variations can be related to variable C4-plant inputs, and possibly, to changes in the fractionation between CO₂ and the organic carbon in C3 vascular plants. The Ru-3 record indicates restricted carbon storage during the periods of increased contribution from C4 plants and/or of decreased fractionation between CO₂ and organic carbon in C3 plants. Changes in TOC-δ¹³C values in core Ru-3 seem to match fluctuations of East Equatorial African lakes. High lake stands correspond to low δ¹³C intervals and vice versa. This points to indirect climatic forcing of δ¹³C changes in intertropical peats.     

Thermal biology of the fossorial rodent Ctenomys fulvus from the Atacama desert, northern Chile

The Andean tuco-tuco, Ctenomys fulvus (Rodentia: Ctenomyidae) inhabits one of the most arid regions of the world, the Salar de Atacama, Northeast of Antofagasta, Chile (23°17′06″S, 68°05′43″W; 2.240 m.a.s.l). We found that a stable microclimate in burrows, a low evaporative water loss (EWL), and a diet of roots (59% water content) are the main factors that permit the survival of this fossorial species in harsh desert conditions. Large circadian variation in T_a was observed above ground. Daily ΔT_a (T_a max − T_a min) = 37.9±0.2°C in summer and in winter. In contrast, circadian variation of T_a inside the burrows was only 5.8±0.5°C in the same seasons. Relative humidity (RH) was 1.9–3.1% during the day, increasing to maximum values of 27% at night and early morning. Inside the burrows RH was higher and quite stable, ranging between 53.1 and 65%, independent of the time of day and season. EWL, measured between 10 and 25°C, was low (1.26 mg/g h), and a moderate increase of 13–20% was observed at higher temperatures. The low EWL may prevent dehydration. However, because of the low heat loss capability, animals became hyperthermic (0.8–1.6°C) in dry air at T_a=30–35°C. As T_a during afternoon normally exceeded 35°C, the microclimate of burrows provided the only way to avoid the lethal effects of hyperthermia.     

Synthesis, NMR study, and X-ray structure of 2-(N-methyl-N′-cyano-N″-ethylguanidino) thiotriophenylphosphinegold(I)

The reaction between cimetidine in a methanolic solution of KOH and a dichloromethane solution of PPh₃AuCl affords a new compound with formula [L-Au-PPh₃] (I) (L = 2-(N-methyl-N′-cyano-N″-ethylguanidino)thiolate), the thiolato ligand resulting from cleavage of one of the thioether bonds of cimetidine. (I) has been characterized by elemental analysis, infrared, and ¹H and ¹³C NMR spectroscopy. Single crystal x-ray structure determination shows that the gold atom is linearly coordinated by a phosphine ligand (Au-P 2.258(1) Å) and by an S atom (Au-S 2.282(1) Å) of the thiolato ligand. Crystal data: triclinic, space group P with a = 8.848(1), b = 11.343(3), c = 12.107(3)Å, = 87.63(1), β = 85.24(1), γ = 79.89(1)°, R = 0.024 for 3673 reflections with I > 3 δ (I).     

The Quaternary eolian sequence of Madeira: stratigraphy, chronology, and paleoenvironmental interpretation

A thick (ca. 40 m) sequence of coastal eolian sediments occurs on a narrow peninsula on the eastern end of the island of Madeira, located in the Eastern Atlantic at 33°N latitude. The sediments consist of black volcanic sands (with or without bioclasts) as well as clay units up to 2 m thick. A series of inceptisols (Eutrochrepts) and one alfisol (a Hapludalf) are developed in these sediments. Land snail shells and secondary carbonates, in the form of well-developed rhizoliths, calcretes, fissure-fills, and soil nodules, are present in abundance. The chronology of the sequence was determined by ¹⁴C and U---Th analyses of land snail shells and secondary carbonates and amino acid epimerization analysis of land snail shells. All sediments, including the clay units, are originally of eolian origin, derived from the beach to the south of the deposit, but some have been redeposited by colluviation. Temporal variation in the lithology of the sediments relates to variations in sea-level, with black sands being deposited during lower sea level stands and clays at the lowest. It is suggested that fine marine sediments, exposed during low sea-level stands, may also be the dominant source of silty or clayey units in other coastal eolian deposits in the subtropical Atlantic and Mediterranean.

The sequence spans from 200,000–300,000 years ago up to the 20th century. Sedimentation was discontinuous and often rapid; erosional hiatuses are present. During the Holocene, eolian sands started accumulating at 8200 yr B.P. during a transgressive phase and stopped at 4500 yr B.P. as sea level approached its present height. Colluviation increased dramatically following the first human settlement of the island in the 15th century and continued up to the 20th century, as dated by amino acid epimerization analysis of land snails. Earlier periods of colluviation were identified from the age distribution of land snail shells redeposited in younger colluvium.

Paleoenvironmental reconstruction was based mainly on soil and sediment features (including rhizolith morphology) and land snail faunas but also on stable isotope variations (¹³C, ¹⁸O) in land snails and secondary carbonates, pollen (generally not well preserved), and phytoliths. Most of the portion of the Middle Pleistocene represented in the sequence was characterized by moderately dry conditions, in comparison to the late Pleistocene and Holocene. During the last interglacial, relatively wet conditions occurred, wetter than during the Holocene interglacial. Moderately moist conditions were present during the accumulation of the thick unit dating to ca. 80,000 yr B.P. As sea level fell subsequent to this period, conditions appear to have become drier. Starting ca. 50,000–55,000 yr B.P., conditions were especially wet, but prior to the last glacial maximum, markedly arid conditions ensued. Toward the end of the last glacial, wet conditions returned and produced the best-developed soil preserved in the sequence. Moderately moist conditions occurred during the early to middle Holocene but apparently become slightly drier after 4500 yr B.P. The impact of human settlement can be seen in the loss of woody vegetation and enhanced gullying and colluviation during the last ca. 500 years.     

Activation of [C]chlorobiphenyls to protein-binding metabolites by rat liver microsomes

The irreversible binding of [¹⁴C]2,2′-di- and [¹⁴C]2,4,5,2′,4′,5′-hexachlorobiphenyl ([¹⁴C]DCB and [¹⁴C]HCB) to protein was studied in the presence of rat liver microsomes and a NADPH-generating system. Protein-bound radioactivity was found with [¹⁴C]DCB but not with [¹⁴C]HCB. The binding of ¹⁴C-metabolites was increased by pretreatment of the rats with phenobarbital or polychlorinated biphenyls. Protein binding was linear for 80 min. In contrast, monohydroxy-metabolites of DCB were formed and degraded within 40 min. Inhibition of secondary oxidation of DCB by scavening superoxide anions or by glucuronidation of the monophenols markedly decreased the protein binding. Addition of trichloropropene oxide or styrene oxide, both inhibitors of epoxide hydrase, did not significantly stimulate the binding. The results suggest that the majority of reactive metabolites of DCB arise from secondary metabolism, i.e., the subsequent oxidation of the phenolic metabolites. Arene oxides, the primary products, appear to play a minor role in the protein binding of DCB.     

Holocene climatic changes in the Western Mediterranean, from south-east France to south-east Spain

Holocene climatic changes along coastal regions from south-east France to south-east Spain were studied using pollen ratios. Comparing modern pollen rain, vegetation and climate along selected transects from the Atlantic Ocean to the Mediterranean, we obtained threshold values of two different ratios corresponding to the different climatic conditions along the transects. These pollen ratios and threshold values were employed to characterize the Holocene climatic changes from nine Mediterranean coastal sites. The results were compared with data from marine and continental pollen sequences distributed in the western Mediterranean basin, and with additional regional data independent of human activity: lake-level fluctuations, alpine glacier advance and retreat chronology, ¹⁴C anomaly and cooling phases in Eastern France and Central Europe. The role of anthropogenic activities and climate on the changes in vegetation is discussed. Six major changes in vegetation cover were identified. They correspond to aridification phases that occurred around 9500–9000 yr BP (10 900–9700 cal BP), 7500–7000 yr BP (8400–7600 cal BP), 4500–4000 yr BP (5300–4200 cal BP), 3700–3300 yr BP (4300–3400 cal BP), 2600–1900 yr BP (2850–1730 cal BP) and 1300–1000 yr BP (1300–750 cal BP). These arid episodes were regional responses to more global climatic changes and determined the changes in the vegetation cover. Humans undoubtedly enhanced the vegetation changes, but none the less had to adapt to these new climatic conditions.     

Variation in δC values for the seagrass Thalassia testudinum and its relations to mangrove carbon

Carbon isotope ratios (¹³C/¹²C) were measured for the leaves of the seagrass Thalassia testudinum Banks ex König and carbonates of shells collected at the seagrass beds from seven sites along the coast of southern Florida, U.S.A. The δ¹³C values of seagrass leaves ranged from −7.3 to −16.3‰ among different study sites, with a significantly lower mean value for seagrass leaves from those sites near mangrove forests (−12.8 ± 1.1‰) than those far from mangrove forests (−8.3 ± 0.9‰; P < 0.05). Furthermore, seagrass leaves from a shallow water area had significantly lower δ¹³C values than those found in a deep water area (P < 0.01). There was no significant variation in δ¹³C values between young and mature leaves (P = 0.59) or between the tip and base of a leaf blade (P = 0.46). Carbonates of shells also showed a significantly lower mean δ¹³C value in the mangrove areas (−2.3 ± 0.6‰) than in the non-mangrove areas (0.6 ± 0.3‰; P <0.025). In addition, the δ¹³C values of seagrass leaves were significantly correlated with those of shell carbonates (δ¹³C seagrass leaf = −9.1 + 1.3δ¹³C shell carbonate (R² = 0.83, P < 0.01)). These results indicated that the input of carbon dioxide from the mineralization of mangrove detritus caused the variation in carbon isotope ratios of seagrass leaves among different sites in this study.     

Changes in C NMR chemical shifts of DNA as a tool for monitoring drug interactions

The antibiotic drug, netropsin, was complexed with the DNA oligonucleotide duplex [d(GGTATACC)]₂ to explore the effects of ligand binding on the ¹³C NMR chemical shifts of the DNA base and sugar carbons. The binding mode of netrospin to TA-rich tracts of DNA has been well documented and served as an attractive model system. For the base carbons, four large changes in resonance chemical shifts were observed upon complex formation: −0.64 ppm for carbon 4 of either Ado4 or Ado6, 1.36 ppm for carbon 2 of Thd5, 1.33 ppm for carbon 5 of Thd5 and 0.94 for carbon 6 of Thd5. AdoC4 is covalently bonded to a heteroatom that is hydrogen bonded to netropsin; this relatively large deshielding is consistent with the known hydrogen bond formed at AdoN3. The three large shielding increases are consistent with hydrogen bonds to water in the minor groove being disrupted upon netropsin binding. For the DNA sugar resonances, large changes in chemical shifts were observed upon netropsin complexation. The 2′, 3′ and 5′ ¹³C resonances of Thd3 and Thd5 were shielded whereas those of Ado4 and Ado6 were deshielded; the ¹³C resonances of 1′ and 4′ could not be assigned. These changes are consistent with alteration of the dynamic pseudorotational states occupied by the DNA sugars. A significant alteration in the pseudorotational states of Ado4 or Ado6 must occur as suggested by the large change in chemical shift of −1.65 ppm of the C3′ carbon. In conclusion, ¹³C NMR may serve as a practical tool for analyzing structural changes in DNA-ligand complexes.     

Piezoelectric properties of poly-β-hydroxybutyrate and copolymers of β-hydroxybutyrate and β-hydroxyvalerate

The shear piezoelectricity was observed in oriented films of poly-β-hydroxybutyrate (PHB) and copolymers of β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV). The piezoelectric stress constant 3₁₄ = e′₁₄ − ie″₁₄ (polarization/strain), the piezoelectric strain constant d₁₄ = d′₁₄ − id″₁₄ (polarization/stress), the elastic constant c = c′ + ic″ and the dielectric constant = ′ − i″ were determined at a frequency of 10 Hz over a temperature range from −150° to +150°C. Piezoelectric relaxations as well as elastic and dielectric relaxations were clearly observed at the glass transition temperature of about 15°C. In order to evaluate the piezoelectric constants (e₂ and d₂) for the piezoelectric phase which consists of the crystalline region and the oriented non-crystalline region, a spherical dispersion two phase model was utilized. Assuming the appropriate fixed values for the elastic and dielectric constants in the piezoelectric phase, d₂ and d₂ were calculated as a function of temperature. For a PHB and a copolymer (17 HV/83 HB), e₂ and d₂ showed relaxations, leading to a conclusion that the instantaneous piezoelectric constant in the crystalline phase is constant independent of temperature but the piezoelectric constant in the oriented non-crystalline phase is relaxational and has the opposite sign. For a copolymer (25 HV/75 HB) and a chloroform treated copolymer (17 HV/83 HB), e₂ and d₂ were constant independent of temperature, indicating that the oriented non-crystalline phase has disappeared owing to the increased molecular flexibility due to copolymerization or annealing in chloroform vapour.     

Pollen-based quantitative reconstructions of Holocene climate variability in NW Romania

A modern analogue technique is applied to two high-resolution pollen sequences from NW Romania to provide the first quantitative evidence for winter, summer and annual temperatures and for precipitation across the Holocene in this region.

The pollen-based climate reconstructions allow the identification of four main intervals: i) an early, less stable period between 11,700 and 11,200 cal. yr BP; (ii) generally stable conditions between 11,200 and 8300 cal. yr BP with winter and annual temperatures and precipitation higher than at present, and summer temperatures about the same; (iii) lower winter and annual temperatures, and higher summer temperatures and precipitation between 8000 and 2400 cal. yr BP; (iv) warmer winter and annual temperatures and lower precipitation for the last 2400 years, whereas summer temperatures became cooler at Steregoiu and remained stable at Preluca Tiganului.

The pollen-based climate reconstructions at the two sites show similar patterns in annual and winter temperatures and precipitation changes during the Holocene, but the trends appear to be less consistent for summer temperatures.

Our pollen-based reconstructions revealed several short-term climatic oscillations during the Holocene, the strongest of which occur between 10,300–10,100, 8300–8000, 6800–6400, 5100–4900, 4000–3600 and 3200–3000 cal. yr BP.     

C NMR relaxation studies of 1:2 LiCl-ethylaluminum dichloride solutions

A new room-temperature molten salt, 1:2 LiCl-ethylaluminum dichloride (LiCl-EtAlCl₂, f.p. about 178 K), is examined using ¹³C relaxation methods at 7.05 T (−25 to + 80 °C). The methylene carbon undergoes scalar relaxation of the ‘second kind’ as it is coupled to a faster relaxing (quadrupolar) nucleus. LiCl-EtAlCl₂ undergoes a significant liquid-state phase change between 5 and 15 °C as evidenced by observed changes in the relaxation properties of the methylene and methyl carbons and J(¹³C−²⁷Al). The J(¹³C−²⁷Al) coupling constants are 75 (− 10 to + 5 °C) and 11 Hz (15–65 °C), indicating a change in structure between 5 and 15 °C. Chemical shift anisotropies of 56 and 48 ppm are obtained for the methylene and methyl carbons in the EtAlCl₂ dimer part of the 1:2 LiCl-EtAlCl₂ solution.     

Prenylated flavonoids of Erythrina lysistemon grown in Egypt

Three prenylated flavonoid derivatives; 5,7,4′-trihydroxy-8-(3-methylbut-2-enyl)-6-(2″-hydroxy-3″-methylbut-3″enyl) isoflavone (isoerysenegalensein E), 5,7,2′-trihydroxy-4′-methoxy-5′-(3″-methylbut-2″-enyl) isoflavanone (lysisteisoflavanone), 5, 4′-dihydroxy-6-(3-methylbut-2-enyl)-2″-hydroxyisopropyl dihydrofurano [4″,5″:8,7] isoflavone (isosenegalensin), together with the four known flavonoids abyssinone V-4′-methylether, alpinumisoflavone, wighteone and burttinone were isolated from the stem bark of Erythrina lysistemon Hutch. (Leguminosae). Structures were elucidated by spectroscopic methods.     

Methylenedioxy- and methoxyflavones from Melicope coodeana syn. Euodia simplex

Three new natural products, 3,8-dimethoxy-5,7-dihydroxy-3′,4′-methylenedioxyflavone, 3,6,8-trimethoxy-5,7-dihydroxy-3′,4′-methylenedioxyflavone and 3,6,8,3′,4′-pentamethoxy-5,7-dihydroxyflavone were isolated from Melicope coodeana syn. Euodia simplex (Rutaceae) along with 3,6,3′-trimethoxy-5,7,4′-trihydroxyflavone and 3,3′-dimethoxy-5,7,4′-trihydroxyflavone. The structural assignments are based on ¹H and ¹³C NMR data, including discussion of the chemical shifts of C-2 in 3,5-dihydroxy- and 3-methoxy-5-hydroxyflavones. The presence of highly methoxylated and methylenedioxyflavones is characteristic of the genus Melicope, and the present findings support the recent transfer of Euodia simplex to Melicope.     

The synthesis of [26,27-11C]dihydroxyvitamin D(3), a tracer for positron emission tomography (PET).

1,25-Dihydroxyvitamin D₃, an endogenous ligand with the highest affinity for the vitamin D receptor (VDR), was labeled with ¹¹C for use in biological experiments. The radionuclide was incorporated via the reaction of [¹¹C]methyllithium on a methyl ketone precursor in tetrahydrofuran at −10 °C. Deprotection of the labeled intermediate yielded 2.5–3 GBq [26,27-¹¹C]1,25-dihydroxyvitamin D₃ [¹¹C-1,25(OH)₂ D₃] with specific radioactivity averaging 100 GBq/μmol at the end of synthesis and HPLC purification. The entire process took 48 min from the end of radionuclide production. In vitro binding experiments in rachitic chick purified VDR demonstrated the high affinity binding of this novel tracer. Thus; ¹¹C-1,25(OH)₂ D₃ is available for in vivo distribution studies and may be suitable for the positron emission tomography (PET) determination of VDR levels and occupancy in animals and humans.     

Isoflavonoids from the roots of Erythrina poeppigiana

Five isoflavonoids, 7,4′-dihydroxy-2′-methoxy-8-(γ,γ-dimethylallyl)isoflav-3-ene, 4′-hydroxy-2′-methoxy-6″,6″-dimethylpyran[2″,3″:7,8]isoflav-3-ene, 5,7,4′-trihydroxy-2′-methoxy-5′-(γ,γ-dimethylallyl)isoflavanone, 5,4′-dihydroxy-7,2′-dimethoxy-5′-(γ,γ-dimethylallyl)isoflavanone and 3,9-dihydroxy-4-(γ,γ-dimethylallyl)pterocarpene as well as six known compounds were isolated from the roots of Erythrina poeppigiana. Their structures were established on the basis of spectroscopic evidence.     

Pleistocene paleoenvironmental evolution at continental middle latitude inferred from carbon and oxygen stable isotope analysis of ostracodes from the Guadix-Baza Basin (Granada, SE Spain)

A representative paleoenvironmental reconstruction of continental middle latitude from ca. 2 my to the upper part of Middle Pleistocene (279 ± 77 ky) was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells (Cyprideis torosa) recovered in the Guadix-Baza Basin (SE Spain), an intramontaneous closed depression filled by alluvial and lacustrine sediments. This study was performed along a 356-m-thick composite section, dated previously by paleomagnetism and the amino acid racemization method. δ¹³C and δ¹⁸O profiles reflected changes in temperature, the evaporation/infill ratio in the water bodies and the amount of rain. δ¹³C is also affected by changes in plant biomass: periods with high δ¹³C and δ¹⁸O values are associated with warm and dry regimes, and with less vegetation, which, in some cases, coincide with the development of displacive gypsum crystals, whereas low δ¹³C and δ¹⁸O values correlate with cold and humid episodes, which cause more vegetation biomass and, therefore, increasing the input of isotopically light carbon. Intermediate δ¹⁸O values are linked to temperate dry or humid episodes when they coincide with high or low δ¹³C values, respectively. 86 paleoclimatic events were distinguished in the Pleistocene record from the δ¹³C and δ¹⁸O profiles. From both the statistical analysis of the geochemical data and the geological observations, four Cold and Humid Long Periods (low δ¹⁸O) and four Warm and Dry Long Periods (high δ¹⁸O) were defined. This differs with respect to the paleoclimatological behavior established for the Northern Hemisphere where during cold periods (glacial), no water was available while permafrost conditions persisted, whereas in warm episodes (interglacial), higher precipitation rates occurred. Good correspondences between the Guadix-Baza Basin paleoclimatic record and a marine oxygen-isotope sequence, two continental cores and other long Mediterranean paleoenvironmental records (pollen sequences from Israel) were found, which suggested that climate changes in the Guadix-Baza Basin were in tune with global climatic changes.     

The effect of temperature on the primary reaction of chloroplast Photosystem II Evidence for a temperature-dependent back reaction

The primary reaction of Photosystem II has been studied over the temperature range from −196 to −20 °C. The photooxidation of the reaction-center chlorophyll (P680) was followed by the free-radical electron paramagnetic resonance signal of P680⁺, and the photoreduction of the Photosystem II primary electron acceptor was monitored by the C-550 absorbance change.

At temperatures below −100 °C, the primary reaction of Photosystem II is irreversible. However, at temperatures between −100 and −20 °C a back reaction that is insensitive to 3-(3′,4′-dichlorophenyl)-1,1′-dimethylurea (DCMU) occurs between P680⁺ and the reduced acceptor.

The amount of reduced acceptor and P680⁺ present under steady-state illumination at temperatures between −100 and −20 °C is small unless high light intensity is used to overcome the competing back reaction. The amount of reduced acceptor present at low light intensity can be increased by adjusting the oxidation-reduction potential so that P680⁺ is reduced by a secondary electron donor (cytochrome b₅₅₉) before P680⁺ can reoxidize the reduced primary acceptor. The photooxidation of cytochrome b₅₅₉ and the accompanying photoreduction of C-550 are inhibited by DCMU. The inhibition of C-550 photoreduction by DCMU, the dependence of P680 photooxidation and C-550 photoreduction on light intensity, and the effect of the availability of reduced cytochrome b₅₅₉ on C-550 photoreduction are unique to the temperature range where the Photosystem II primary reaction is reversible and are not observed at lower temperatures.     

Synthesis and pharmacology of the isomeric methylheptyl-Δ-tetrahydrocannabinols

The synthesis of the 3-heptyl, and the eleven isomeric 3-methylheptyl-Δ⁸-tetrahydrocannabinols (3–7, R and S methyl epimers, and 8) has been carried out. The synthetic approach entailed the synthesis of substituted resorcinols, which were subjected to acid catalyzed condensation with trans-para-menthadienol to provide the Δ⁸-THC analogue. The 1′-, 2′- and 3′-methylheptyl analogues (3–5) are considerably more potent than Δ⁸-THC. The 4′-, 5′- and 6′-methylheptyl isomers (6–8) are approximately equal in potency to Δ⁸-THC.     

Isolation, structural elucidation, and partial synthesis of lutein dehydration products in extracts from human plasma

All-E-(3R,6′R)-3-hydroxy-3′,4′-didehydro-β,γ-carotene (anhydrolutein I) and all-E-(3R,6′R)-3-hydroxy-2′,3′-didehydro-β,ε-carotene (2′,3′-anhydrolutein II) have been isolated and characterized from extracts of human plasma using semipreparative high-performance liquid chromatography (HPLC) on a C₁₈ reversed-phase column. The identification of anhydroluteins was accomplished by comparison of the UV-Vis absorption and mass spectral data as well as HPLC-UV-Vis-mass spectrometry (MS) spiking experiments using fully characterized synthetic compounds. Partial synthesis of anhydroluteins from the reaction of lutein with 2% H₂SO₄ in acetone, in addition to anhydrolutein I (54%) and 2′,3′-anhydrolutein II (19%), also gave (3′R)-3′-hydroxy-3,4-dehydro-β-carotene (3′,4′-anhydrolutein III, 19%). While anhydrolutein I has been shown to be usually accompanied by minute quantities of 2′,3′-anhydrolutein II (ca. 7–10%) in human plasma, 3′,4′-anhydrolutein III has not been detected. The presence of anhydrolutein I and II in human plasma is postulated to be due to acid catalyzed dehydration of the dietary lutein as it passes through the stomach. These anhydroluteins have also been prepared by conversion of lutein diacetate to the corresponding anhydrolutein acetates followed by alkaline hydrolysis. However, under identical acidic conditions, loss of acetic acid from lutein diacetate proceeded at a much slower rate than dehydration of lutein. The structures of the synthetic anhydroluteins, including their absolute configuration at C(3) and C(6′) have been unambiguously established by ¹H NMR and in part by ¹³C NMR, and circular dichroism.