CARMENES is a spectrograph for radial velocity surveys of M dwarfs with the aim of detecting Earth-mass planets orbiting in the habitable zones of their host stars. To ensure an optimal use of the CARMENES Guaranteed Time Observations, in this paper we investigate the correlation of activity and rotation for approximately 2200 M dwarfs, ranging in spectral type from M0.0 V to M9.0 V. We present new high-resolution spectroscopic observations with FEROS, CAFE, and HRS of approximately 500 M dwarfs. For each new observation, we determined its radial velocity and measured its Hα activity index and its rotation velocity. Additionally, we have multiple observations of many stars to investigate if there are any radial velocity variations due to multiplicity. The results of our survey confirm that early-M dwarfs are Hα inactive with low rotational velocities and that late-M dwarfs are Hα active with very high rotational velocities. The results of this high-resolution analysis comprise the most extensive catalogue of rotation and activity in M dwarfs currently available.

Aims. The main goal of this work is to measure rotation periods of the M-type dwarf stars being observed by the CARMENES exoplanet survey to help distinguish radial-velocity signals produced by magnetic activity from those produced by exoplanets. Rotation periods are also fundamental for a detailed study of the relation between activity and rotation in late-type stars. Methods. We look for significant periodic signals in 622 photometric time series of 337 bright, nearby M dwarfs obtained by long-time baseline, automated surveys (MEarth, ASAS, SuperWASP, NSVS, Catalina, ASAS-SN, K2, and HATNet) and for 20 stars which we obtained with four 0.2–0.8 m telescopes at high geographical latitudes. Results. We present 142 rotation periods (73 new) from 0.12 d to 133 d and ten long-term activity cycles (six new) from 3.0 a to 11.5 a. We compare our determinations with those in the existing literature; we investigate the distribution of Prot in the CARMENES input catalogue, the amplitude of photometric variability, and their relation to v sini and pEW(Hα); and we identify three very active stars with new rotation periods between 0.34 d and 23.6 d.

Molecular modeling calculations using high-level ab initio methods (MP2/6-31+G) of a new type of spiro beta-lactams predict that these systems could adopt a beta-turn secondary structure in solution. Strong intramolecular hydrogen bonds stabilize the beta-turn conformation with a geometry that is very close to the ideal type II beta-turns. The synthesis of the spiro beta-lactams is achieved by Staudinger reaction of a cyclic ketene derived from N-bencyloxycarbonyl-L-proline acid chloride with an imine. This reaction allows the formation of the spiranic backbone in a single-step with high diastereoselectivity and good yields. The new spiro beta-lactams obtained are the core for the preparation of different types of peptidomimetics using well-established peptide chemistry. The NMR conformational analysis shows that these compounds adopt beta-turn conformation as predicted by the theoretical studies.

The synthesis of a,a-disubstituted b-amino esters and peptide derivatives from readily available 4-spiro-b-lactams 1 is described. The geminally disubstituted b-amino esters are obtained from the N-Boc spiro b-lactams 2 by treatment with potassium cyanide in methanol. Alternatively, the use of spiro b-lactams 2 as acylating agents of the amino group of C-protected amino acids, allowed its direct incorporation into a peptidic chain.b-Amino acids have attracted a great deal of interest during the last few years due to their presence in a wide number of natural products (e.g., the side chain of the anticancer agent, taxol). On the other hand, and perhaps even more interesting, recent results show that synthetic b-peptides (b-amino acids oligomers) present some interesting features. They form much more stable secondary structures than do their parents a-peptides, 1 and some of them exhibit biological activity acting as inhibitors of cholesterol and fat absorption 2 or as antibiotics. 3Among the available methods for the synthesis of b-amino acids (a-or b-monosubstituted), just a few are suitable for the preparation of a,a-and b,b-disubstituted ones. 4 Seebach et al. 5 have recently shown that a,a-disubstitution in b-peptides leads to the formation of very stable peptide secondary structures. In this context, especially remarkable folding properties were observed in b-peptides bearing a cyclic a,a-disubstitution pattern ( Figure 1). These cyclic a,a-disubstituted b-peptides adopt unprecedented peptide secondary structures not only in the a-amino acid field, but also in realm of b-peptides. 6 Figure 1In this paper we describe the synthesis of cyclic a,a-disubstituted b-amino esters and peptide derivatives employing 4-spiro b-lactams 1 as starting materials (Scheme 1). 7 b-Lactams can be viewed as cyclic b-amino acids, in which both the amino and the acid moieties are simultaneously protected, and therefore they are usually employed as precursors of b-amino acids. 8 It is interesting to point out that a few synthetic methodologies to prepare spiro b-lactams have been described so far, 9 and only in one case they were employed as precursors of cyclic a,adisubstituted b-amino acid derivatives (Figure 2). 10 Figure 2At this point, we thought that 4-spiro b-lactams 1, could be useful intermediates for the preparation of b-amino acids with a,a-cyclic disubstitution. These a,a-disubstituted cyclic b-amino acids present some new interesting structural features: a) their unsymmetrical (tetrahydrofuran ring) a,a-disubstitution (almost all previously described cyclic a,a-or b,b-disubstituted b-amino acids bear a cycloalkane ring); 6,11 b) the presence of an oxygen atom in the tetrahydrofuran ring, since oxygen could act as a hydrogen bond acceptor increasing the conformational bpeptide possibilities and their hydrogen bond interactions with peptide receptors.Although b-amino acids could be directly obtained from N-alkyl or N-aryl b-lactams by treatment with HCl (6 N) at 100 ºC, we previously transformed the b-lactams 1 to the N-B...

We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d⋆ ≈ 22 pc), bright (J ≈ 9 mag) M3.5 dwarf LTT 3780 (TOI–732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of Teff = 3360 ± 51 K, a surface gravity of log g⋆ = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M⋆ = 0.379 ± 0.016M⊙ and a radius of R⋆ = 0.382 ± 0.012R⊙. The ultra-short-period planet LTT 3780 b (Pb = 0.77 d) with a radius of 1.35−0.06+0.06 R⊕, a mass of 2.34−0.23+0.24 M⊕, and a bulk density of 5.24−0.81+0.94 g cm−3 joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42−0.10+0.10 R⊕, mass of 6.29−0.61+0.63 M⊕, and mean density of 2.45−0.37+0.44 g cm−3 belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST).

The synthesis of enantiomerically pure modified proline derivatives was achieved by using spiro beta-lactams as starting material that were prepared in turn by the [2+2]-cycloaddition of unsymmetrical cyclic ketenes with optically active imines. A theoretical study of the [2+2]-cycloaddition reaction, using density-functional methods, gave insights on the origin of the observed stereoselectivity of the Staudinger reaction. The spiro beta-lactams were transformed in the N-Boc derivatives and subjected to nucleophilic ring opening, affording the corresponding enantiomerically pure modified proline derivatives, isolated as orthogonally protected compounds.

We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384–1735–1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of Mp = 5.9 ± 0.6 M⊕ and a radius of Rp = 1.69 ± 0.08 R⊕, which together result in a density of ρp = 6.7− 1.1+ 1.3 g cm−3. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R⊕ or larger at the insolation levels received by TOI-1235 b (~60 S⊕). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.

No abstract