Synthesis of GDGT lipids. In earlier work led by the Burns group, an efficient synthetic route to the core structure of parallel GDGT-0 (iso-caldarchaeol) was described. In the same work, the synthesis of P2 and P1Glc were reported. In this work, along with P2 and P1Glc, the synthesis of two additional GDGT lipids -PG2 and PG1Glc was achieved (Figure , Supplementary Schemes S1-7). It should be noted that the glucosyl groups in P1Glc and PG1Glc are present as a mixture of anomers.